Cationic aluminum alkyl complexes incorporating aminotroponiminate ligands

Article abstract of DOI:10.1021/ja010242e

The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N'-diisopropylaminotroponiminate ligand (ⁱPr₂-ATI^-) are described. The reaction of (ⁱPr₂-ATI)A1R₂ (1a-e,g,h; R = H (a), Me (b), Et (c), Pr (d), ⁱBu (e), Cy (g), CH₂Ph (h)) with [Ph₃C][B(C₆F₅)₄] yields (ⁱPr₂-ATI)A1R⁺ species whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph₃C]-[B(C₆F₅)₄] to produce dinuclear monocationic complexes [{(ⁱPr₂-ATI)AIR}₂(μ-R)][ (C₆F₅)₄] (2a,b). The cation of 2b contains two (ⁱPr₂-ATI)AlMe⁺ units linked by an almost linear Al-Me-Al bridge; 2a is presumed to have an analogous structure. 2b does not react further with [Ph₃C][B(C₆F₅)₄]. However, 1a reacts with 1 equiv of [Ph₃C][B(C₆F₅)₄] to afford (ⁱPr₂-ATI)Al(C₆F₅) (μ-H)₂B(C₆F₅)₂ (3) and other products, presumably via C₆F₅^- transfer and ligand redistribution of a [(ⁱPr₂-ATI)AlH] [(C₆F₅)₄] intermediate. 1c-e react with 1 equiv of [Ph₃C]-[B(C₆F₅)₄] to yield stable base-free [(ⁱPr₂-ATI)AIR][B (C₆F₅)₄] complexes (4c-e). 4c crystallizes from chlorobenzene as 4c(ClPh)·0.5PhCl, which has been characterized by X-ray crystallography. In the solid state the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph π-stacking interaction. 1g,h react with [Ph₃C][B(C₆F₅)₄] to yield (ⁱPr₂-ATI)Al(R)(C₆F₅)(5g,h) via C₆F₅^- transfer of [(ⁱPr₂-ATI)A1R]-[ (BC₆F₅)₄] intermediates. 1c,h react with B(C₆F₅)₃ to yield [(ⁱPr₂-ATI)Al(R)](C₆F₅) (5c,h) via C₆F₅^- transfer of [ⁱPr₂-ATI)A1R][RB (C₆F₅)₃] intermediates. The reaction of 4c-e with MeCN or acetone yields [(ⁱPr₂-ATI)-Al(R)(L)][B (C₆F₅)₄] adducts (L = MeCN (8c-e), acetone (9 c-e)), which undergo associative intermolecular L exchange. 9c-e undergo slow β-H transfer to afford the dinuclear dicationic alkoxide complex [{(ⁱPr₂ -ATI)Al(μ-OⁱPr)}₂][B (C₆F₅)₄]₂ (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization of tert-butyl acetylene by an insertion/σ-bond metathesis mechanism involving [(ⁱPr₂-ATI)Al(C≡C^tBu)]- [B(C₆F₅)₄] (13) and [(ⁱPr₂-ATI)Al(CH =C(^tBu)C≡C^t(Bu)] [B(C₆F₅)₄] (14) intermediates. 13 crystallizes as the dinuclear dicationic complex [{(ⁱPr₂-ATI)Al (μ-C≡^tBu)}₂] [B(C₆F₅)₄]₂·5PhCl from chlorobenzene. 4e catalyzes the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react with ethylene-d₄ by β-H transfer to yield [(ⁱPr₂- ATI)AlCD₂CD₂H][B (C₆F₅)₄ initially. Polyethylene is also produced in these reactions by an unidentified active species.

Full text of DOI:10.1021/ja010242e

J. Am. Chem. Soc. 2001, 123, 8291-8309
8291
Cationic Aluminum Alkyl Complexes Incorporating
Aminotroponiminate Ligands
Andrey V. Korolev,† Eiji Ihara,† Ilia A. Guzei,‡ Victor G. Young, Jr.,§ and
Richard F. Jordan*,†
Contribution from the Department of Chemistry, The UniVersity of Chicago, 5735 South Ellis AVenue,
Chicago, Illinois 60637, Department of Chemistry, Iowa State UniVersity, Ames, Iowa 50011, and
Department of Chemistry, UniVersity of Minnesota, Minneapolis, Minnesota 55455
ReceiVed January 29, 2001. ReVised Manuscript ReceiVed May 17, 2001
Abstract: The synthesis, structures, and reactivity of cationic aluminum complexes containing the N,N′-
diisopropylaminotroponiminate ligand (iPr2-ATI-) are described. The reaction of (iPr2-ATI)AlR2 (1a-e,g,h;
i
R ) H (a), Me (b), Et (c), Pr (d), Bu (e), Cy (g), CH2Ph (h)) with [Ph3C][B(C6F5)4] yields (iPr2-ATI)AlR+
species whose fate depends on the properties of the R ligand. 1a and 1b react with 0.5 equiv of [Ph3C]-
[B(C6F5)4] to produce dinuclear monocationic complexes [{(iPr2-ATI)AlR}2(µ-R)][(C6F5)4] (2a,b). The cation
of 2b contains two (iPr2-ATI)AlMe+ units linked by an almost linear Al-Me-Al bridge; 2a is presumed to
have an analogous structure. 2b does not react further with [Ph3C][B(C6F5)4]. However, 1a reacts with 1 equiv
of [Ph3C][B(C6F5)4] to afford (iPr2-ATI)Al(C6F5)(µ-H)2B(C6F5)2 (3) and other products, presumably via C6F5
-
transfer and ligand redistribution of a [(iPr2-ATI)AlH][(C6F5)4] intermediate. 1c-e react with 1 equiv of [Ph3C]-
[B(C6F5)4] to yield stable base-free [(iPr2-ATI)AlR][B(C6F5)4] complexes (4c-e). 4c crystallizes from
chlorobenzene as 4c(ClPh)‚0.5PhCl, which has been characterized by X-ray crystallography. In the solid state
the PhCl ligand of 4c(ClPh) is coordinated by a dative PhCl-Al bond and an ATI/Ph π-stacking interaction.
1g,h react with [Ph3C][B(C6F5)4] to yield (iPr2-ATI)Al(R)(C6F5) (5g,h) via C6F5- transfer of [(iPr2-ATI)AlR]-
[(BC6F5)4] intermediates. 1c,h react with B(C6F5)3 to yield (iPr2-ATI)Al(R)(C6F5) (5c,h) via C6F5- transfer of
[(iPr2-ATI)AlR][RB(C6F5)3] intermediates. The reaction of 4c-e with MeCN or acetone yields [(iPr2-ATI)-
Al(R)(L)][B(C6F5)4] adducts (L ) MeCN (8c-e), acetone (9c-e)), which undergo associative intermolecular
L exchange. 9c-e undergo slow â-H transfer to afford the dinuclear dicationic alkoxide complex [{(iPr2-
ATI)Al(µ-OiPr)}2][B(C6F5)4]2 (10) and the corresponding olefin. 4c-e catalyze the head-to-tail dimerization
of tert-butyl acetylene by an insertion/σ-bond metathesis mechanism involving [(iPr2-ATI)Al(CtCtBu)]-
[B(C6F5)4] (13) and [(iPr2-ATI)Al(CHdC(tBu)CtCtBu)][B(C6F5)4] (14) intermediates. 13 crystallizes as the
dinuclear dicationic complex [{(iPr2-ATI)Al(µ-CtCtBu)}2][B(C6F5)4]2‚5PhCl from chlorobenzene. 4e catalyzes
the polymerization of propylene oxide and 2a catalyzes the polymerization of methyl methacrylate. 4c,e react
with ethylene-d4 by â-H transfer to yield [(iPr2-ATI)AlCD2CD2H][B(C6F5)4] initially. Polyethylene is also
produced in these reactions by an unidentified active species.
Introduction
the Lewis acidity of the Al center and influence the reactivity
of the Al-R group.3 Low-coordinate cationic Al species which
contain vacant coordination sites or labile ligands are particularly
attractive for applications in catalysis.
Neutral aluminum AlX3 complexes (X ) halide, alkyl,
alkoxide, etc.) are widely used as Lewis acid reagents and
catalysts (Friedel-Crafts, Diels-Alder, etc.), alkylating and
reducing agents, initiators for cationic polymerizations, catalysts
for the oligomerization of ethylene to R-olefins, and cocatalysts/
activators in transition-metal-catalyzed olefin polymerizations.1,2
Cationic aluminum alkyl complexes are potentially interesting
for these and other applications because the charge may enhance
Bochmann has reported that transient “R2Al+” (R ) Me,
iBu) species can be generated in toluene-d8, but abstract C6F5
-
from B(C6F5)4 to form neutral Al and B complexes.4 Alumi-
-
nocenium cations, (C5R5)2Al+, which can be considered to be
+
6-coordinate complexes, are more stable than AlR2 alkyl
species, and [(C5H5)2Al][MeB(C6F5)3] has been exploited as an
initiator for the cationic polymerization of isobutylene and the
synthesis of butyl rubber.5 No¨th has investigated [Al(NR2)2(L)]-
[AlX4] salts (NR2 ) 2,2,6,6-tetramethylpiperidide; L ) pyridine
bases; X ) Br, I) and concluded on the basis of 27Al NMR,
* Address correspondence to this author.
† The University of Chicago.
‡ Iowa State University.
§ University of Minnesota.
(1) (a) Starowieyski, K. B. In Chemistry of Aluminium, Gallium, Indium
and Thallium; Downs, A. J., Ed.; Chapman & Hall: London, UK, 1993;
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II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: Oxford,
UK, 1995; Vol. 11, Chapter 6. (c) Matyjaszewski, K., Ed. Cationic
Polymerizations: Mechanisms, Synthesis and Applications; Marcel Dek-
ker: New York, 1996. (d) Kennedy, J. P.; Marechal, E. Carbocationic
Polymerization; Wiley-Interscience: New York, 1982. (e) Eisch, J. J. In
ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; Elsevier: Oxford, UK, 1995; Vol. 1, Chapter 10.
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A.; Bishop, E.; Cambour, P.; Fuqua, S.; Lim, P. Ind. Eng. Chem. 1960, 52,
695. (c) Skup´ınska, J. Chem. ReV. 1991, 91, 613. (d) Al-Jarallah, A. M.;
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10.1021/ja010242e CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/02/2001

8292 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
conductivity, and computational results that the Al cations have
three-coordinate structures.6 Several classes of four-coordinate
Al cations have also been reported.7 Bertrand showed that
bisaminoamide complexes {η3-HRN(CH2)2N(R′)(CH2)2NR}-
AlCl+ adopt trigonal monopyramidal geometries with a vacant
axial coordination site and catalyze the polymerization of
propylene oxide, probably by an anionic-coordination mecha-
nism.8 Gibson reported that pyridylaminoamide complexes {η3-
2-(ArNCRMe),6-(ArNdCR)-C3H3N}AlMe+ and pendant arm
Schiff base complexes {3,5-tBu2-2-(O)C6H2CHdNL}AlMe+ (L
) CH2CH2NMe2, 8-quinolinyl) polymerize ethylene.9,10 Atwood
has prepared several 6-coordinate Shiff base complexes that
contain labile axial ligands, including (salen)Al(MeOH)2+ and
Chart 1
+
(acen)Al(MeOH)2 , and has shown that these species polymerize
propylene oxide, probably by a cationic mechanism.11
Our work in this area is focused on the chemistry of 3-coor-
dinate (L--X)AlR+ cations (A, Chart 1) or weakly solvated/
ion-paired versions thereof, which contain chelating monoan-
ionic L-X- ancillary ligands. These species are expected to be
more stable than AlR2+ species but may be highly reactive due
to the combination of the low coordination number and the
charge at Al. The use of chelating L-X- ligands minimizes
complications from ligand exchange/redistribution reactions. In
our initial approach to (L-X)AlR+ species we investigated the
synthesis of cationic amidinate complexes {RC(NR′)2}AlR+,
via alkyl abstraction from {RC(NR′)2}AlR2 precursors.10d,12 The
a thermally unstable mononuclear cation {tBuC(NtBu)2}AlMe+
that could not be isolated. The difficulty in generating stable
mononuclear {RC(NR′)2}AlR+ species is due to the small bite
angle of the amidinate ligand (N-Al-N angles ca. 70° in {RC-
(NR′)2}AlR2 complexes),13 which results in sterically open and
hence highly reactive Al centers. To circumvent this problem,
we investigated alkyl abstraction reactions of N,N-diaryldiketim-
inate complexes {HC(CMeNAr)2}AlMe2 (Ar ) 2,6-iPr2-C6H3),
in which the larger ligand bite angle (N-Al-N angle ca. 96°)
and bulky N-aryl substituents provide increased steric protection
at Al.14 These reactions yield stable 3-coordinate {HC-
(CMeNAr)2}AlR+ cations (D), several salts of which have been
characterized by X-ray crystallography. Cationic {HC-
(CMeNAr)2}AlR+ species readily coordinate Lewis bases to
form 4-coordinate {HC(CMeNAr)2}Al(R)(L)+ adducts, but react
with ethylene by reversible cycloaddition across the Al-
diketiminate ring to yield products of type E. Smith has also
investigated the synthesis of {diketiminate}AlR+ species.15
In our studies of cationic Al amidinate and diketiminate
complexes, three reagents were investigated for the conversion
of (L-X)AlR2 complexes to (L-X)AlR+ cations: [Ph3C]-
[B(C6F5)4],16 B(C6F5)3,17 and [NMe2Ph][B(C6F5)4].18 Each of
these “activators” has been used successfully to generate reactive
transition-metal LnMR+ cations from LnMR2 precursors.19
Our work shows that [Ph3C][B(C6F5)4] is the most useful of
these reagents for the generation of (L-X)AlR+ species because
t
i
reaction of {RC(NR′)2}AlMe2 (R ) Me or Bu, R′ ) Pr or
Cy) with [Ph3C][B(C6F5)4] or B(C6F5)3 yields amidinate-bridged
dinuclear species (B, C), the structures and stability of which
depend on the steric properties of the amidinate substituents
-
and the reactivity of the anion (B(C6F5)4 < RB(C6F5)3-).
Dinuclear species are formed in these reactions because the
initially generated {RC(NR′)2}AlR+ cation is trapped by the
starting {RC(NR′)2}AlMe2 complex. Alkyl abstraction from the
“super bulky” amidinate complex {tBuC(NtBu)2}AlMe2 yields
(5) (a) Dohmeier, C.; Schno¨ckel, H.; Robl, C.; Schneider, U.; Ahlrichs,
R. Angew. Chem., Int. Ed. Engl. 1993, 32, 1655. (b) Bochmann, M.;
Dawson, D. M. Angew. Chem., Int. Ed. Engl. 1996, 35, 2226. (c) Burns, C.
T.; Stelck, D. S.; Shapiro, P. J.; Vij, A.; Kunz, K.; Kehr, G.; Concolino,
T.; Rheingold, A. L. Organometallics 1999, 18, 5432.
(6) Krossing, I.; No¨th, H.; Schwenk-Kircher, H. Eur. J. Inorg. Chem.
1998, 927.
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Raston, C. L. J. Organomet. Chem. 1990, 384, C1. (g) Engelhardt, L. M.;
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(10) For other reports of ethylene polymerization by Al catalysts see:
(a) Kim, J. S.; Wojcinski, L. M., II; Liu, S.; Sworen, J. C.; Sen, A. J. Am.
Chem. Soc. 2000, 122, 5668. (b) Soga, K.; Shiono, T.; Doi, Y. J. Chem.
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-
the B(C6F5)4 anion is very stable and the organic byproducts
(Ph3CR or Ph3CH) do not react with (L-X)AlR+ cations.
(13) (a) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1997, 16, 5183. (b) Coles, M. P.; Swenson, D. C.; Jordan,
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Marks, T. J. J. Am. Chem. Soc. 1994, 116, 10015 and references therein.
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Abstr. 1991, 115, 136998g.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8293
B(C6F5)3 is also efficient at abstracting R- groups from (L-X)-
AlR2 compounds; however, the resulting RB(C6F5)3- anions are
(iPr2-ATI)Al(CH2Ph)2 (1h, eq 3), for which the corresponding
AlR3 compounds are not commercially available.
-
often incompatible with (L-X)AlR+ species due to R- or C6F5
transfer leading to neutral products.15,19a,20 Ammonium salts
[HNR3][B(C6F5)4] generally react with (L-X)AlR2 to produce
stable 4-coordinate (L-X)Al(R)(NR3)+ amine adducts.
The specific objective of the work described here is to prepare
and study the reactivity of cationic (iPr2-ATI)AlR+ complexes
(F) which contain the N,N′-diisopropylaminotroponiminate
ligand (iPr2-ATI-). This ligand was introduced in main group
chemistry by Dias and forms stable 5-membered chelate ring
i
complexes with aluminum.21 The bite angle of the Pr2-ATI-
ligand is intermediate between that of the amidinate and
diketiminate ligands discussed above (N-Al-N ) 83.3(1)° in
(iPr2-ATI)AlMe2),21a and thus (iPr2-ATI)AlR+ species are
expected to be moderately stable and reactive. Additionally, the
fused ring structure of (iPr2-ATI)AlR+ species may disfavor
cycloaddition reactions analogous to those observed in the
diketiminate systems. Here we describe the synthesis, structures,
and reactivity of several novel families of mononuclear and
Compounds 1a-g are isolated as red to yellow crystalline
solids while 1h is isolated as a red oil. The dialkyl derivatives
are stable in solution to well above 100 °C, do not react with
Lewis bases such as nitriles, amines, or ethers, but enflame when
i
dinuclear cationic Al alkyls which incorporate the Pr2-ATI-
1
exposed to air. The H and 13C NMR spectra of 1a-h are
ligand.22
consistent with C2V structures.
Results
Synthesis of Cationic Al Hydrides. The reaction of 1a with
0.5 equiv of [Ph3C][B(C6F5)4] yields a cationic Al hydride
species [{(iPr2-ATI)Al}2H3][B(C6F5)4] (2a, eq 4). Compound
Synthesis of (iPr2-ATI)AlR2 Complexes. The (iPr2-ATI)H
ligand precursor was synthesized from 2-tropolone using the
procedure described by Dias et al.21a Dialkyl complexes
(iPr2-ATI)AlR2 (1a-e, R ) H, Me, Et, Pr, Bu) are easily
i
prepared in moderate to high yield by the alkane elimination
procedure described by Dias for 1a,b (eq 1).21a Alternatively,
2a separates as an oil (liquid clathrate)23 from benzene solution
and can be isolated in high yield as a solid after extensive
washing of the oil with hexanes. 2a is stable at room temperature
in benzene and toluene clathrates and in chlorobenzene solution.
The 1H NMR spectrum of 2a in C6D6 contains a broad signal
i
at δ 4.54 (3H) and one Pr-methyl doublet at δ 0.92 (24H),
corresponding to three hydride ligands and two C2V-symmetric
(iPr2-ATI)Al units, respectively. The same pattern is observed
at -90 °C in CD2Cl2. These data are insufficient to establish
the structure of 2a; however, by analogy to the structurally
characterized Me analogue (2b, vide infra), we propose that
the cation of 2a has a dinuclear mono-H-bridged structure,
{(iPr2-ATI)AlH}2(µ-H)+, and undergoes fast bridge/terminal H
exchange resulting in time-averaged C2V symmetry.
the reaction of Li[iPr2-ATI] with AlCl3 yields (iPr2-ATI)AlCl2
(1f, eq 2), which can be cleanly alkylated by Grignard reagents.
This approach was used to prepare (iPr2-ATI)AlCy2 (1g) and
(18) Use of HNR3+ reagents for the generation of LnM(R)+ species: (a)
Bochmann, M.; Wilson, L. M. J. Chem. Soc., Chem. Commun. 1986, 1610.
(b) Lin, Z.; Le Marechal, J.; Sabat, M.; Marks, T. J. J. Am. Chem. Soc.
1987, 109, 4127. (c) Turner, H. W.; Hlatky, G. G. European Patent
Application 0,277,003, 1988. (d) Hlatky, G. G.; Turner, H. W.; Eckman,
R. R. J. Am. Chem. Soc. 1989, 111, 2728. (e) Turner, H. W. European
Patent Application 0,277,004, 1988. (f) Hlatky, G. G.; Eckman, R. R.;
Turner, H. W. Organometallics 1992, 11, 1413.
The reaction of 1a with 1 equiv of [Ph3C][B(C6F5)4] at 60
°C in benzene produces a mixture of Al species, one of which,
(iPr2-ATI)Al(C6F5)(µ-H)2B(C6F5)2 (3), crystallizes from solution
(eq 5). It is probable that the formation of 3 involves generation
(19) (a) Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391. (b)
Piers, W. E.; Chivers, T. Chem. Soc. ReV. 1997, 26, 345. (c) Guram, A. S.;
Jordan, R. F. In ComprehensiVe Organometallic Chemistry; Lappert, M.
F., Ed.; Pergamon: Oxford, UK, 1995; Vol. 4, pp 589-626.
-
of (iPr2-ATI)AlH+ which abstracts a C6F5 group from the
-
B(C6F5)4 anion.24 Subsequent ligand redistribution reactions
(20) For a recent example of C6F5- transfer from RB(C6F5)3- to a cationic
transition metal species see: Deckers, P. J. W.; van der Linden, A. J.;
Meetsma, A.; Hessen, B. Eur. J. Inorg. Chem. 2000, 929.
produce 3.
(21) (a) Dias, H. V. R.; Jin, W.; Ratcliff, R. E. Inorg. Chem. 1995, 34,
6100. (b) Dias, H. V. R.; Jin, W. Inorg. Chem. 1996, 35, 6546. (c) Dias, H.
V. R.; Jin, W.; Wang, Z. Inorg. Chem. 1996, 35, 6074. (d) Dias, H. V. R.;
Wang, Z.; Jin, W. Coord. Chem. ReV. 1998, 176, 67. (e) Roesky, P. W.
Chem. Soc. ReV. 2000, 29, 335. (f) Bailey, P. J.; Dick, C. M. E.; Fabre, S.;
Parsons, S. J. Chem. Soc., Dalton Trans. 2000, 1655.
(22) Aspects of this work were communicated previously: (a) Ihara, E.;
Young, V. G., Jr.; Jordan, R. F. J. Am. Chem. Soc. 1998, 120, 8277. (b)
Korolev, A. V.; Guzei, I. A.; Jordan, R. F. J. Am. Chem. Soc. 1999, 121,
11606.

8294 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
mixture is washed with hexanes. No further reaction occurs
when 2b is mixed with excess [Ph3C][B(C6F5)4] in benzene at
23 °C for several days. Compound 2b is stable at room
temperature as a benzene or toluene liquid clathrate and in C6H5-
Cl solution, but decomposes in CH2Cl2 to unidentified species.
The 1H NMR spectrum of 2b at -90 °C in CD2Cl2 contains
two singlets at δ 0.63 and -0.38, in a 1:2 intensity ratio, which
are assigned to the bridging and terminal methyl groups,
respectively. The -90 °C 13C NMR spectrum of 2b contains
separate resonances for the bridging (δ -0.8) and terminal (δ
-5.2) methyl carbons. A large 1JC-H (133 Hz) is observed for
the µ-Me group, which is consistent with a large Al-C-Al
angle and substantial sp2-C character in the C-H bonds.27 The
terminal Me 1JC-H value (118 Hz) is normal for an Al-Me group.
The bridge and terminal Me signals coalesce to a broad singlet
(δ 0.00) at -60 °C, indicating that bridge/terminal exchange is
rapid at this temperature. The free energy barrier for this process
is ∆Gq ) 9.5(3) kcal/mol.28
The 1H NMR spectrum of a C6D5Cl solution of 2b containing
2 equiv of 1b contains a single set of resonances at the weighted
average chemical shifts of the two components down to -40
°C, implying that intermolecular exchange between 2b and 1b
is rapid. It is unlikely that 2b reversibly dissociates to 1b and
(iPr2-ATI)AlMe+, because, as noted above, 2b does not react
further with [Ph3C][B(C6F5)4] even at 25 °C. Hence, the
exchange between 2b and 1b probably occurs by an associative
mechanism.
Figure 1. Molecular structure of (iPr2-ATI)Al(C6F5)(µ-H)2B(C6F5)2 (3).
Selected bond distances (Å) and angles (deg): Al(1)-N(1) 1.870(2),
Al(1)-N(2) 1.864(2), Al(1)-H(1A) 1.82(2), Al(1)-H(1B) 1.93(2), Al-
(1)-C(14) 1.976(3), Al(1)-B(1) 2.283(3), B(1)-C(20) 1.605(4),
B(1)-C(26) 1.620(4); N(1)-Al(1)-N(2) 86.28(9), N(1)-Al(1)-C(14)
122.4(1), N(2)-Al(1)-C(14) 117.7(1), N(1)-Al(1)-H(1A) 88.2(8),
N(1)-Al(1)-H(1B) 130.8(8), N(2)-Al(1)-H(1A) 131.8(8), N(2)-Al-
(1)-H(14B) 89.3(7), H(1A)-Al(1)-H(1B) 59.8(1), H(1A)-B(1)-
H(1B) 106(2), C(20)-B(1)-C(26) 117.3(2).
Crystals of 2b suitable for X-ray crystallographic analysis
were obtained by slow (months) crystallization from a C6D6
liquid clathrate. Compound 2b crystallizes as discrete ions
(Figure 2). Consistent with the NMR data, the cation contains
two (iPr2-ATI)AlMe units linked by a nearly linear Al-Me-
Al bridge (Al(1)-C(1)-Al(2) angle ) 167.8(2)°). The µ-CH3
hydrogens were located in the equatorial plane of the nearly
trigonal bipyramidal (tbp) carbon center (sum of H-C(1)-H
angles ) 357°). The µ-CH3 carbon is sp2-hybridized and the
remaining p orbital is used for 3-center, 2-electron bonding to
the two Al atoms. This bonding description is consistent with
the large 1JCH value observed in the 13C NMR spectrum.29 The
Al-Cbridge distances are ca. 0.2 Å longer than the Al-Cterm
distances as expected. The structure of the (iPr2-ATI)Al frame-
work of 2b is very similar to that in 1b.21a
The molecular structure of 3 was established by X-ray
crystallography (Figure 1). The Al and B atoms in 3 are linked
by two bridging hydride ligands. The Al-H distances (Al-
H(1A) 1.82(2) Å, Al-H(1B) 1.93(2) Å) are longer than those
in Al{(µ-H)2BH2}3 (gas phase, 1.801(6) Å)25a and (tmp)2Al(µ-
H)2(9-BBN) (tmp ) 2,2,6,6-tetramethylpiperidinyl, 9-BBN )
9-borabicyclononane; 1.738 Å).25b The B-H bond distances
(B-H(1A) 1.18(2) Å and B-H(1B) 1.17(2) Å) are shorter than
those in Al{(µ-H)2BH2}3 (B-(µ-H) 1.28(1) Å), but close to
those in (tmp)2Al(µ-H)2(9-BBN) (1.208 Å). The 5-coordinate
geometry at Al is made possible by the compactness of the η2-
H2B(C6F5)2- ligand; the H-Al-H angle (59.8(11)°) is smaller
than those in Al{(µ-H)2BH2}3 and (tmp)2Al(µ-H)2(9-BBN)
(73.4(8) and 65.4°, respectively)). The Al-C6F5 bond distance
(Al-C(14), 1.976(3) Å) is similar to that in {tBuC(NCy)2}-
AlMe(C6F5) (2.011(3) Å)12 and the terminal Al-Ph bond
distance in Al2Ph6 (1.95(8) Å average).26
In contrast to the behavior of 1b, complexes 1c-e, which
contain higher primary alkyl groups, react with 1 equiv of [Ph3C]-
[B(C6F5)4] in benzene, toluene, hexanes, or pentane at 25 °C
by net â-H abstraction to give base-free [(iPr2-ATI)AlR]-
Synthesis of Cationic Al Alkyls. The reaction of (iPr2-ATI)-
AlMe2 (1b) with 0.5 equiv of [Ph3C][B(C6F5)4] at ambient
temperature in benzene or chlorobenzene yields the dinuclear
Me-bridged species [{(iPr2-ATI)AlMe}2(µ-Me)][B(C6F5)4] (2b)
and Ph3CMe (eq 6). 2b separates as an oil from benzene and
can be isolated as a pale green precipitate when the reaction
(23) Leading references to liquid clathrate phenomena: (a) Atwood, J.
L. In Coordination Chemistry of Aluminum; Robinson, G. H., Ed.; VCH:
New York, 1993; pp 197-232. (b) Lambert, J. B.; Zhao, Y.; Wu, H.; Tse,
W. C.; Kuhlmann, B. J. Am. Chem. Soc. 1999, 121, 5001.
-
-
(24) For examples of C6F5 transfer from the B(C6F5)4 anion to the
metal center see ref 4 and: Go´mez, R.; Green, M. L. H.; Haggitt, J. L. J.
Chem. Soc., Dalton Trans. 1996, 939.
(25) (a) Almenningen, A.; Gundersen, G.; Haaland, A. Acta. Chem.
Scand. 1968, 22, 328. (b) Knabel, K; Krossing, I.; No¨th, H.; Schwenk-
Kircher, H.; Schmidt-Amelunxen, M.; Seifert, T. Eur. J. Inorg. Chem. 1998,
1095. (c) Holloway, C. E.; Melnik, M. J. Organomet. Chem. 1997, 543, 1.
(26) Malone, J. F.; McDonald, W. S. J. Chem. Soc., Dalton Trans. 1972,
2646.
(27) Waymouth, R. M.; Santarsiero, B. D.; Coots, R. J.; Bronikowski,
M. J.; Grubbs, R. H. J. Am. Chem. Soc. 1986, 108, 1427.
(28) The free energy barrier for bridge/terminal methyl exchange of 2b
was determined using the graphical method described in the following:
Shanan-Atidi, H.; Bar-Eli, K. H. J. Phys. Chem. 1970, 74, 961. TC ) 213
K; ∆ν ) 364 Hz at 360 MHz.
(29) Analogous dinuclear zirconocene cations have been reported. (a)
Bochmann, M.; Lancaster, S. Angew. Chem., Int. Ed. Engl. 1994, 33, 1634.
(b) Chen, Y.-X.; Stern, C. L.; Yang, S.; Marks, T. J. J. Am. Chem. Soc.
1996, 118, 12451.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8295
Figure 2. Structure of the {(iPr2-ATI)AlMe}2(µ-Me)+ cation in 2b.
Selected bond distances (Å) and angles (deg): Al(1)-N(1) 1.865(2),
Al(1)-N(2) 1.876(2), Al(2)-N(3) 1.881(2), Al(2)-N(4) 1.884(2), Al-
(1)-C(1) 2.177(3), Al(2)-C(1) 2.120(3), Al(1)-C(2) 1.949(3), Al-
(2)-C(16) 1.953(3), C(1)-H(1A) 0.92(3), C(1)-H(1B) 0.89(3), C(1)-
H(1C) 0.96(3); N(1)-Al(1)-N(2) 86.07(9), N(3)-Al(2)-N(4) 85.58(9),
Al(1)-C(1)-Al(2) 167.8(2), N(1)-Al(1)-C(1) 109.0(1), N(1)-Al-
(1)-C(2) 122.2(1), N(2)-Al(1)-C(1) 110.2(1), N(2)-Al(1)-C(2)
119.0(1), C(1)-Al(1)-C(2) 108.5(1), N(3)-Al(2)-C(1) 112.7(1),
N(3)-Al(2)-C(16) 120.4(1), N(4)-Al(2)-C(1) 110.3(1), N(4)-Al-
(2)-C(16) 118.0(1), C(1)-Al(2)-C(16) 108.3(1).
Figure 3. Structure of the [(iPr2-ATI)Al(Et)(ClPh)][B(C6F5)4] unit in
4c(ClPh)‚0.5PhCl. Selected bond distances (Å) and angles (deg):
Al-N(1) 1.827(6), Al-N(2) 1.850(5), Al-C(1) 1.919(7), Al-Cl 2.540-
(3), C(40)-Cl 1.774(7); N(1)-Al-N(2) 87.8(2), Al-Cl-C(40) 102.7-
(2), Al-C(1)-C(2) 119.4(6), N(1)-Al-C(1) 129.3(3), N(1)-Al-Cl
99.4 (2), N(2)-Al-C(1) 133.8(3), N(2)-Al-Cl 99.3(2), C(1)-Al-
Cl 99.9(2). Hydrogen atoms are omitted.
[B(C6F5)4] salts (4c-e) and the corresponding olefin (eq 7).
Pale yellow-green powders of 4c-e precipitate after extensive
(1.774(7) Å vs 1.737(5) Å in free PhCl in the gas phase)32 but
does induce a significant displacement (0.31 Å) of the Al atom
out of the N(1)-N(2)-C(1) plane (∑ of the angles at Al )
350.9°). Additionally, the PhCl phenyl ring is positioned
i
close to the Pr2-ATI ligand in an orientation that permits an
attractive π-stacking interaction.33 The distances between PhCl
carbon atoms and the plane of the iPr2-ATI ligand are between
3.3 and 4.0 Å, and the PhCl ring is shifted to one side of the
iPr2-ATI ligand such that the electron-deficient PhCl ipso car-
bon lies under the electron-rich N(2) atom (C(40)- - -N(2) 3.39
Å), and the centroid of the PhCl phenyl ring lies under one of
washing of the benzene (toluene) clathrates which form during
the reaction, or when the reaction is conducted in hexane or
pentane. Compounds 4c-e are stable at room temperature as
benzene or toluene clathrates and in C6H5Cl solution, but
decompose to unidentified species in CH2Cl2.
Recrystallization of 4c from chlorobenzene at -40 °C yields
yellow crystals of the PhCl complex [(iPr2-ATI)Al(Et)(ClPh)]-
[B(C6F5)4] (4c(ClPh)) which also contain 0.5 equiv of nonco-
ordinated PhCl of crystallization. This material readily loses
PhCl and is converted to base-free 4c upon exposure to vacuum.
The structure of the 4c(ClPh) unit (Figure 3) consists of a
distorted tetrahedral (iPr2-ATI)Al(Et)(ClPh)+ cation that is
weakly ion-paired to the B(C6F5)4- anion. The Al-Cl distance
(2.540(3) Å) is somewhat longer than the Al-(µ-Cl) distances
in Cl-bridged dialuminum complexes (2.2-2.5 Å)1a,30 or the
sum of the Al and Cl covalent radii (2.24 Å), but is far shorter
than the sum of Al and Cl van der Waals (vdW) radii (3.8 Å),31
consistent with a dative Al-ClPh bond. The Al-ClPh interac-
tion does not significantly perturb the C-Cl bond distance
i
the electron-deficient Pr2-ATI iminato carbon atoms (cen-
troid- - -C(12) ) 3.66 Å). The Al-Cl-Ph angle is 102.7(2)°
i
and the angle between the PhCl and Pr2-ATI planes is 17.1°.
The closest Al-F contact to the anion (Al- - -F(2); 3.23 Å) is
close to the sum of the Al and F vdW radii (3.52 Å),31 indicating
that the cation-anion interaction is extremely weak.34,35
Variable-temperature multinuclear NMR spectra of 4c in
C6D5Cl (to -40 °C) and CD2Cl2 (to -90 °C) establish that the
(iPr2-ATI)AlEt+ cation retains effective C2V symmetry and that
ion-pairing interactions are not significant enough to perturb
-
the spectra of the B(C6F5)4 anion in these chlorocarbon
(32) Penionzhkevich, N. P.; Sadova, N. I.; Vilkov, L. V. Zh. Struct. Khim.
1979, 20, 527.
(33) Hunter, C. A.; Sanders, K. M. J. Am. Chem. Soc. 1990, 112, 5525.
(34) The Re PhCl complexes [(C5R5)Re(NO)(PPh3)(ClPh)][BF4] (C5R5
) C5H5, C5Me5) have been characterized in C6H5Cl/C6D5Cl solution by
multinuclear NMR. These species exist predominantly as Cl-ligated isomers
at -45 °C, but other isomers are also observed at higher temperatures. (a)
Peng, T.-S.; Winter, C. H.; Gladysz, J. A. Inorg. Chem. 1994, 33, 2534.
(b) Kowalczyk, J. J.; Agbossou, S. K.; Gladysz, J. A. J. Organomet. Chem.
1990, 397, 333.
(30) Representative examples: (a) [(BHT)AlMe(µ-Cl)]2 (BHT ) 2,6-
bis-tert-butyl-4-methylphenoxide; Al-Cl 2.277(3) and 2.291(3) Å): Healy,
M. D.; Ziller, J. W.; Barron, A. R. Organometallics 1992, 11, 3041. (b)
[(ArO)AlMe(µ-Cl)]2 (Ar ) 2,6-bis-tert-butylphenyl; Al-Cl 2.298(2) Å):
Jegier, J. A.; Atwood, D. A. Bull. Soc. Chim. Fr. 1996, 133, 965.
(31) The covalent and van der Waals radii for Al (1.25 and 2.05 Å)
were taken from ref 1a, p 2, and those for F (0.64 and 1.47 Å) and Cl (0.99
and 1.75 Å) were taken from the following: Kulawiec, R. J.; Crabtree, R.
H. Coord. Chem. ReV. 1990, 99, 89.
(35) For a review of fluorocarbon coordination chemistry see: Plenio,
H. Chem. ReV. 1997, 97, 3363.

8296 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
solvents.36 On the basis of the X-ray and solution NMR data
we conclude that in chlorocarbon solution the (iPr2-ATI)AlR+
cations of 4c-e exist as RCl adducts which undergo fast RCl
exchange.
Scheme 1
The structures of “base-free” 4c-e in aromatic solvents or
in the solid state are uncertain.37 The most likely situation is
that these cations are monomeric and weakly solvated and/or
ion-paired in aromatic solvents and more strongly ion-paired
in the solid state. However, dinuclear dicationic structures with
i
bridging Pr2-ATI or R ligands are also possible. Two lines of
evidence suggest that 4c-e are monomeric in aromatic solvents.
First, the 1JCH values for the Al-CH2 carbons of 4c-e in C6D6
or toluene-d8 liquid clathrates are in the same range as those in
chlorinated solvents (115-120 Hz). In particular, the Al-CH2
1JCH value for 4c (119 Hz, C6D6 or toluene-d8, 25 °C) is close
to the 1JCH value of the Al-Etterm methylene carbon of (Et2Al)2-
(µ-Et)2 (114 Hz, CD2Cl2, -90 °C) rather than to that of the
Al-Etbridge (106 Hz).38 These data support the presence of
terminal alkyl ligands in 4c-e. Additional evidence against
dinuclear dicationic structures is provided by experiments in
which 1c, 1e, and [Ph3C][B(C6F5)4] were mixed in 1:1:2 ratio
in C6D5Cl and C6D6. In both cases, only signals of 4c and 4e
were observed by NMR; if these species were dimeric, new
resonances or shifts in resonances due to the presence of the
“mixed” species [(iPr2-ATI)2Al2(Et)(iBu)]2+ would be expected.
There is no evidence for agostic Al- - -HC interactions in these
cationic Al alkyls.
1
The H and 13C NMR spectra of CD2Cl2 solutions of 4c-e
containing 1 equiv of 1c-e, respectively, each contain only one
i
the mononuclear (iPr2-ATI)AlMe+ cation. Thus, [(iPr2-ATI)-
AlMe][B(C6F5)4] (4b) forms when 1b, 1c, and [CPh3][B(C6F5)4]
are mixed in 1:1:2 stoichiometry (eq 9). As summarized in
set of Pr2-ATI and Al-R signals which are very close to the
weighted average of the corresponding signals of the two
components down to -90 °C. Similar results are obtained for
solutions of 4c-e and 1c-e generated in situ by the reaction
of 1c-e with 0.5 equiv of [Ph3C][B(C6F5)4]. These results are
indicative of fast alkyl exchange between the (iPr2-ATI)AlR+
cations and (iPr2-ATI)AlR2 dialkyls, presumably via µ-R
intermediates (2c-e, eq 8). It is possible to separate 1c-e from
Scheme 1, this reaction probably proceeds by initial â-H
abstraction from 1c by Ph3C+ to produce (iPr2-ATI)AlEt+,
methyl transfer from 1b to produce (iPr2-ATI)AlMe+ and
(iPr2-ATI)Al(Me)(Et), and â-H abstraction from the latter species
by Ph3C+ to produce a second equivalent of (iPr2-ATI)AlMe+.39
4b separates as a clathrate from benzene solution and can be
isolated in high yield as a solid after extensive washing of the
clathrate with hexanes. The properties of 4b are very similar to
those of 4c-e.
1c-e/4c-e mixtures simply by washing the mixture with
hexanes to extract the neutral dialkyl complex. The poorer
bridging ability of the higher alkyls versus Me is respon-
sible for the lower stability of 2c-e versus the Me-bridged
analogue 2b.
Generation and Fate of Cationic Al Cyclohexyl and Benzyl
Species. Compound 1g reacts with [Ph3C][B(C6F5)4] in pentane
at 25 °C to give pentane-soluble (iPr2-ATI)Al(Cy)(C6F5) (5g,
eq 10). This reaction proceeds by initial formation of the
transient base-free complex [(iPr2-ATI)AlCy][B(C6F5)4],40 fol-
Synthesis of [(iPr2-ATI)AlMe][B(C6F5)4] (4b). It is possible
to exploit the poorer bridging ability of the Et group (vs Me)
and the â-H abstraction from Al-Et groups by Ph3C+ to prepare
(36) The 13C, 11B, and 19F NMR spectra for the B(C6F5)4- anion in 4c-e
are identical to those for [Ph3C][B(C6F5)4].
(37) Cryoscopic molecular weight and conductivity studies of 4c-e in
benzene are precluded by the formation of clathrates.
(38) Olah, G. A.; Prakash, G. K. S.; Liang, G.; Henold, K. L.; Haigh,
G. B. Proc. Natl. Acad. Sci. U.S.A. 1977, 74, 5217.
lowed by abstraction of a C6F5 group from the anion.24 No
-
(39) It is also possible that the Me-bridged intermediate (iPr2-ATI)Al-
(Me)(µ-Me)Al(Et)(iPr2-ATI)+ is stable and undergoes reaction with Ph3C+
without dissociation.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8297
-
Scheme 2
by C6F5 transfer to 5h and B(CH2Ph)(C6F5)2. In the 1:1
stoichiometric reaction, 0.5 equiv of [Ph3C][B(C6F5)4] remains
unreacted and can be separated from the pentane-soluble
products. In this case, B(C6F5)3 reacts more rapidly with 1h
than does [Ph3C][B(C6F5)4] because the latter reagent is
insoluble in the reaction solvent (pentane), resulting in the 2:1
stoichiometry of the reaction. Under the reaction conditions,
B(CH2Ph)(C6F5)2 undergoes ligand redistribution reactions
resulting in a mixture of all possible B(CH2Ph)x(C6F5)3-x (x )
0-3) boranes with B(CH2Ph)(C6F5)2 being the major species.41
No further reaction of 5h and [Ph3C][B(C6F5)4] or B(C6F5)3 is
1
observed at room temperature. The H and 13C NMR spec-
tra of 5h are consistent with Cs symmetry. The boranes
1
B(CH2Ph)x(C6F5)3-x (x ) 0-3) were identified by H and 19F
NMR spectra of the reaction mixture.
Observation of an Intermediate in Reaction of (iPr2-ATI)-
AlR2 Complexes with [Ph3C][B(C6F5)4]. Low-temperature
NMR experiments show that 1b and 1c react with [Ph3C]-
[B(C6F5)4] at ca. -90 °C in CH2Cl2 via electrophilic attack of
i
Ph3C+ at the Pr2-ATI C5 carbon to yield thermally unstable
diimine intermediates {1,2-(NiPr)2-5-CPh3-cyclohepta-3,6-
+
diene}AlR2 (R ) Me, 6b; R ) Et, 6c; eq 12). The structures
further reaction between 5g and B(C6F5)3 is observed at 25 °C
1
in benzene. The H and 13C NMR spectra of 5g are consistent
with Cs symmetry. The 19F NMR spectrum of the product
mixture contains two sets of C6F5 signals in 1:3 intensity ratio
which are assigned to 5g and B(C6F5)3, respectively. The
reaction of 1h and [Ph3C][B(C6F5)4] in 2:1 stoichiometry results
in the formation of pentane-soluble (iPr2-ATI)Al(CH2Ph)(C6F5)
(5h, eq 11). As summarized in Scheme 2, this reaction proceeds
of these species were assigned on the basis of the following
key observations: (i) The C5 13C NMR resonance of 6b appears
1
at δ 51.8 with JCH ) 138 Hz indicative of the loss of
unsaturation at C5. Similarly the C5 resonance of 6c appears at
δ 52.0. In contrast, the C5 resonances of 1b,c both appear at δ
119.2 with 1JCH ) 159 Hz. (ii) The NMR spectra of 6b,c each
contain two iPr Me resonances and one iPr methine resonance,
and resonances for two inequivalent Al-R groups, consistent
with Cs symmetry. (iii) Signals corresponding to Ph3CMe
(reaction of 1b) or Ph3CH and ethylene or Ph3CEt (reaction of
1c) are not observed. (iv) The NMR spectra of 6b,c are similar
to those of analogous Ga and In complexes {1,2-(NiPr)2-5-CPh3-
+
cyclohepta-3,6-diene}MMe2 (M ) Ga, In), which have been
characterized by X-ray crystallography.42
In the temperature range -40 to -30 °C, 6b,c decompose to
4b,c, most likely via dissociation of Ph3C+ followed by Me or
â-H abstraction. In the case of R ) Me, the ratio of 1b and
[Ph3C][B(C6F5)4] was set to 2:1, and a 1:1 mixture of 6b and
1b was formed at -90 °C; warming this mixture to -30 °C
produced dinuclear 2b rather than base-free 4b. It is likely that
by initial abstraction of a benzyl group from 1h by Ph3C+ to
form 1 equiv of the transient base-free complex [(iPr2-ATI)-
-
Al(CH2Ph)][B(C6F5)4], which undergoes rapid C6F5 transfer
to yield 5h and B(C6F5)3. The B(C6F5)3 coproduct reacts with
the second equivalent of 1h to give the unstable intermediate
[(iPr2-ATI)Al(CH2Ph)][B(CH2Ph)(C6F5)3], which decomposes
(41) The ligand redistribution reaction of B(CH2Ph)(C6F5)2 was observed
previously: Horton, A. D.; de With, J. Organometallics 1997, 16, 5424.
(42) Dagorne, S.; Delpech, F.; Guzei, I. A.; Jordan, R. F. Unpublished
results.
(40) The reaction of (iPr2-ATI)AlCy2 with [Ph3C][B(C6F5)4] in pentane
produces a transient yellow precipitate that dissolves after ca. 1 h. The yellow
compound may be [(iPr2-ATI)AlCy][B(C6F5)4].

8298 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
analogous intermediates are formed in the reactions of 1d,e,g,h
and Ph3C+.
symmetry. These cationic species do not react further with
excess HNMe2Ph+ at ambient temperature.
Reaction of (iPr2-ATI)AlR2 Complexes with B(C6F5)3. We
tested the utility of B(C6F5)3 as an alkyl abstraction reagent in
the (iPr2-ATI)AlR2 systems by investigating two representative
cases. The reaction of diethyl complex 1c with 1 equiv of
B(C6F5)3 in pentane yields a 1:1 mixture of (iPr2-ATI)Al(Et)-
(C6F5) (5c) and B(Et)(C6F5)2 (eq 13). Presumably, [(iPr2-ATI)-
Reaction of (iPr2-ATI)AlR+ Cations with Acetonitrile. The
reaction of 4c-e with acetonitrile yields simple [(iPr2-ATI)Al-
(R)(NCMe)][B(C6F5)4] adducts (8c-e, eq 16). Compound 8c
is isolated as a yellow crystalline solid. Unlike the base-free
precursor 4c, 8c is stable in CH2Cl2 solution at 25 °C.
Remarkably, chlorobenzene solutions of 8c show no sign of
reaction after 16 h at 180 °C (sealed tube). In contrast, neutral
alkylaluminum compounds generally react with nitriles by
insertion, C-H activation, or â-H transfer under similar
conditions.44,45 For example, AlEt3(NCtBu) undergoes â-H
transfer to produce {AlEt2(µ-NdCHtBu)}2 (80% yield) and
ethylene at 155 °C. The MeCN adduct, AlEt3(NCMe), reacts
at 110-130 °C predominantly by ethane elimination to produce
polymeric (Et2AlCH2CtN)n; the insertion product {AlEt2-
(µ-NdCMeEt)}2 is formed as a minor product (18%).44b
The 1H and 13C NMR spectra of 8c in C6D5Cl in the absence
AlEt][BEt(C6F5)3] forms in this reaction initially, but decom-
poses to the observed products by C6F5 transfer. No further
-
reaction of 5c and B(Et)(C6F5)2 is observed at 25 °C in benzene.
1
The H and 13C NMR spectra of 5c are consistent with Cs
symmetry. The 19F NMR spectrum of the product mixture
contains two sets of C6F5 signals in 1:2 intensity ratio which
are assigned to 5c and B(Et)(C6F5)2, respectively.43
Similarly, the reaction of dibenzyl compound 1h with 1 equiv
of B(C6F5)3 in pentane yields a mixture of 5h and B(CH2Ph)x-
(C6F5)3-x (x ) 0-3, eq 14). Compound 5h is much more soluble
i
i
of excess MeCN each exhibit two Pr Me resonances, one Pr
methine resonance and a resonance for coordinated MeCN
(1H: δ 1.77), consistent with Cs symmetry. However, in the
i
presence of even trace amounts of excess MeCN, the two Pr
Me resonances are collapsed to a single resonance, and only a
single MeCN resonance is observed, which is indicative of time-
averaged C2V symmetry due to fast exchange of free and
coordinated MeCN by an associative mechanism. For example,
8c exhibits time-averaged C2V symmetry in the presence of less
than 1 mol % excess MeCN even at -90 °C in CD2Cl2 solution.
The molecular structure of the (iPr2-ATI)Al(Et)(NCMe)+
cation of 8c is shown in Figure 4. The Al-NCMe bond in
8c (Al-N(3) 1.955(1) Å) is ca. 0.06 Å shorter and the
C(16)-Al-N(3) angle (103.82(7)°) is nearly identical with the
corresponding parameters in Me3Al(NCMe) (2.02(1) Å, 102.0-
(5)°).46 The Al-N(1) (1.856(1) Å) and Al-N(2) (1.854(1) Å)
bonds involving the iPr2-ATI ligand of 8c are ca. 0.06 Å shorter
than corresponding bonds in (iPr2-ATI)AlMe2 (1.915(1) Å),21a
but are very close to those in the dinuclear cation [{(iPr2-ATI)-
AlMe}2(µ-Me)]+ of 2b.22a The structure of the B(C6F5)4- anion
is normal.
than the borane coproducts in toluene/pentane solution at -37
°C, and was isolated in 70% yield. The Al and B species formed
in eq 14 are identical to those formed in eq 11. This result
facilitates assignment of the NMR signals of the mixture
obtained in reaction 11 and supports the mechanism proposed
in Scheme 2. These results show that RB(C6F5)3- anions (R )
Et, CH2Ph) are too reactive to be compatible with (iPr2-ATI)-
AlR+ cations.
Reaction of (iPr2-ATI)AlR2 Complexes with [HNMe2Ph]-
[B(C6F5)4]. The reaction of (iPr2-ATI)AlR2 complexes 1a-c,e,h
with [HNMe2Ph][B(C6F5)4] proceeds by clean Al-R bond
protonolysis to afford [(iPr2-ATI)AlR(NMe2Ph)][B(C6F5)4]
(7a-c,e,h, eq 15). These amine complexes are soluble and very
Reaction of (iPr2-ATI)AlR+ Cations with Acetone. Com-
pound 4c reacts with 1 equiv of acetone to yield the acetone
adduct 9c (Scheme 3). The solution behavior of 9c is similar to
that of MeCN adduct 8c. Thus, the 1H and 13C NMR spectra of
i
9c in the absence of excess acetone each exhibit two Pr Me
i
resonances, one Pr methine resonance, and a resonance for
coordinated acetone, while in the presence of even a slight (4%)
excess of acetone, the two iPr Me resonances collapse to a single
resonance, and only one acetone resonance is observed. This
results are consistent with associative intermolecular acetone
exchange. Compound 9c is slowly (3 days, 23 °C, CD2Cl2)
(44) (a) Lloyd, J. E.; Wade, K. J. Chem. Soc. 1965, 2662. (b) Jennings,
J. R.; Lloyd, J. E.; Wade, K. J. Chem. Soc. 1965, 5083. (c) Jensen, J. A. J.
Organomet. Chem. 1993, 456, 161.
(45) McDonald, W. S. Acta Crystallogr. 1969, B25, 1385.
(46) Atwood, J. L.; Seale, S. K.; Roberts, D. H. J. Organomet. Chem.
1973, 51, 105.
1
stable in C6D5Cl and CD2Cl2 at ambient temperature. The H
and 13C NMR spectra of 7a-c,e,h are consistent with Cs
(43) B(Et)(C6F5)2 was characterized previously: Parks, D. J.; Piers, W.
E.; Yap, G. P. A. Organometallics 1998, 17, 5492.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8299
2+
Figure 5. Structure of the {(iPr2-ATI)Al(µ-OiPr)}2 dication in 10‚
2CD2Cl2. Selected bond distances (Å) and angles (deg): Al(1)-N(1)
1.820(3), Al(1)-N(2) 1.832(3), Al(1)-O(1) 1.809(2), Al(1)-O(1A)
1.817(3), Al(1)-Al(1A) 2.774(2), O(1)-C(1) 1.508(5); N(1)-Al(1)-
N(2) 89.0(1), O(1)-Al(1)-O(1A) 80.2(1), N(1)-Al(1)-O(1) 123.3-
(1), N(1)-Al(1)-O(1A) 118.4(1), N(2)-Al(1)-O(1) 124.3(1), N(2)-
Al(1)-O(1A) 126.3(1), Al(1)-O(1)-Al(1A) 99.8(1), Al(1)-O(1)-
C(1) 131.0(2), Al(1A)-(1)-C(1) 127.6(2). Hydrogen atoms are
omitted.
Figure 4. Structure of the (iPr2-ATI)Al(Et)(NCMe)+ cation in 8c.
Selected bond distances (Å) and angles (deg): Al-N(1) 1.856(1), Al-
N(2) 1.854(1), Al-N(3) 1.955(1), Al-C(16) 1.942(2), N(3)-C(14)
1.135(2); N(1)-Al-N(2) 87.04(5), Al-N(3)-C(14) 169.9(1), Al-
C(16)-C(17) 116.0(1), N(1)-Al-C(16) 125.68(8), N(1)-Al-N(3)
106.50(6), N(2)-Al-C(16) 122.60(8), N(2)-Al-N(3) 109.88(6),
C(16)-Al-N(3) 103.82(7). Hydrogen atoms are omitted.
[{(iPr2-ATI)Al(µ-OiPr)}2][B(C6F5)4]2‚2CH2Cl2 (10‚2CH2Cl2).
The structure of the dinuclear cation of 10 is shown in Figure
5. The planar Al2O2 ring features an acute O(1)-Al(1)-O(1A)
angle (80.2(1)°) and an obtuse Al(1)-O(1)-Al(1A) angle (99.8-
(1)°), and is nearly perpendicular to the ATI rings (angle
between planes 93.2°). The Al-N bond distances (Al(1)-N(1)
1.820(3), Al(1)-N(2) 1.832(3) Å) are ca. 0.05 Å shorter than
those in {(iPr2-ATI)AlMe}2(µ-Me)+,22a and ca. 0.09 Å shorter
than those in (iPr2-ATI)AlMe2.21a The Al-O bond distances
(Al(1)-O(1) 1.809(2), Al(1)-O(1A) 1.817(3) Å) are similar
to those in neutral aluminum µ-OR compounds.25c,49 The
geometry at the oxygens is almost planar (sum of angles around
O(1) ) 358.4°) as normally observed in alkoxy-bridged
aluminum compounds.49,50 The dinuclear structure of the cation
explains the low solubility of 10.
Scheme 3
Reactions of (iPr2-ATI)AlR+ Cations with tert-Butyl
Acetylene. Compounds 4c-e catalytically dimerize tert-butyl
acetylene to the head-to-tail dimer 2-tert-butyl-5,5-dimethyl-1-
hexen-3-yne (11, C6D5Cl, 23 °C, ca. 4 t.o./h, >90% selectivity
for 11) as shown in Scheme 4.51 Support for the mechanism in
Scheme 4 is provided by the following observations from NMR
and GC-MS studies of stepwise reactions. (i) 4c reacts with 1
t
equiv of BuCtCH by â-H transfer to yield cationic vinyl
compound 12 and ethylene quantitatively. 12 is stable in C6D5-
converted to isopropoxide complex 10 in quantitative yield by
net â-H transfer with release of ethylene (Scheme 3). Complexes
4d and 4e react with acetone in a similar manner; however,
the corresponding intermediates 9d and 9e are less stable than
9c, and are completely converted to 10 within 5 h at 23 °C in
C6D5Cl.
For comparison, AlEt3 reacts with diethyl ketone by competi-
tive ketone insertion into the Al-Et bond, â-H transfer, and
enolization; the product ratio depends on the AlEt3/ketone
ratio.47 The monomeric Al alkyls (BHT)xAlEt3-x (BHT ) 2,6-
di-tert-butyl-4-methylphenoxide) react with enolizable ketones
by enolization and subsequent aldol condensation.48
t
Cl solution at 23 °C in the absence of BuCtCH. The trans
stereochemistry is established by a vinyl 3JHH value of 21 Hz.52
t
(ii) 12 reacts with additional BuCtCH by σ-bond metathesis
to yield alkynyl complex 13 and tert-butyl ethylene, followed
by tBuCtCH insertion to yield 14. When 12 is reacted with 1
t
equiv of BuCtCH, a 4:1:1 mixture of 13, 14, and unreacted
12 is formed, indicating that the two reactions occur at similar
rates. Removal of the volatiles from this reaction mixture
followed by addition of C6H5Cl affords yellow crystalline 13
(49) (a) Turova, N. Ya.; Kozunov, V. A.; Yanovskii, A. I.; Bokii, N.
G.; Struchkov, Yu. T.; Tarnopol’skii, B. L. J. Inorg. Nucl. Chem. 1979,
41, 5. (b) Wengrovius, J. H.; Garbauskas, M. F.; Williams, E. A.; Going,
R. C.; Donahue, P. E.; Smith, J. F. J. Am. Chem. Soc. 1986, 108, 982. (c)
Cayton, R. H.; Chisholm, M. H.; Davidson, E. R.; DiStasi, V. F.; Du, P.;
Huffman, J. C. Inorg. Chem. 1991, 30, 1020. (d) Kunicki, A.; Sadowski,
R.; Zachara, J. J. Organomet. Chem. 1996, 508, 249.
Unlike 9c,d, 10 is insoluble in C6H5Cl and only sparingly
soluble in CH2Cl2. An X-ray crystallographic analysis estab-
lished that 10 crystallizes from CH2Cl2 as the complex salt
(47) (a) Pasynkiewicz, S.; Dluzniewski, T.; Sonnek, G. J. Organomet.
Chem. 1987, 321, 1. (b) Pasynkiewicz, S.; Sliwa, E. J. Organomet. Chem.
1965, 3, 121.
(48) (a) Power, M. B.; Bott, S. G.; Clark, D. L.; Atwood, J. L.; Barron,
A. R. Organometallics 1990, 9, 3086. (b) Power, M. B.; Apblett, A. W.;
Bott, S. G.; Atwood, J. L.; Barron, A. R. Organometallics 1990, 9, 2529.
(50) The preliminary communication (ref 22b) reported erroneous data
on the sum of the angles around O(1).
(51) Small amounts of trimer and tetramer products were detected by
GC-MS.
(52) Silverstein, R. M.; Webster, F. X. Spectrometric Identification of
Organic Compounds, 6th ed.; Wiley: New York, 1998.

8300 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
Scheme 4
Figure 6. Structure of the {(iPr2-ATI)Al(µ-CtCtBu)}2 dication in
2+
13‚5C6D5Cl. Selected bond distances (Å) and angles (deg): Al(1)-
N(1) 1.834(2), Al(1)-N(2) 1.837(2), Al(1)-C(14) 1.971(2), Al(1)-
C(14A) 2.151(2), C(14)-C(15) 1.217(3); N(1)-Al(1)-N(2) 88.86(7),
N(1)-Al(1)-C(14) 125.98(7), N(1)-Al(1)-C(14A) 112.12(7), N(2)-
Al(1)-C(14) 125.01(7), N(2)-Al(1)-C(14A) 118.91(7), C(14)-Al-
(1)-C(14A) 88.49(7), Al(1)-C(14)-Al(1A) 91.51(7), Al(1)-C(14)-
C(15) 163.6(2), Al(1A)-C(14)-C(15) 103.9(1), C(14)-C(15)-C(16)
176.8(2). Hydrogen atoms are omitted.
It is not established if the cations of 12, 13, and 14 exist in
C6D5Cl solution as solvated mononuclear species (cf. 4c(ClPh))
or dinuclear dicationic species with bridging alkynyl or alkenyl
ligands (cf. solid-state structure of 13); however, the former
possibility is most probable given the catalytic activity ob-
served.59
Reactions of (iPr2-ATI)AlR+ Cations with Olefins. It was
observed that when 4c was generated in benzene or toluene in
closed vessels, the ethylene byproduct was completely polym-
erized after several hours at room temperature. These results
prompted further studies of the reactions of (iPr2-ATI)AlR+
cations with ethylene. Neither the base-stabilized complexes
(iPr2-ATI)Al(R)(NMe2Ph)+ (7a-c,e) and (iPr2-ATI)Al(R)-
(NCMe)+ (8c) nor the dinuclear cationic species [{(iPr2-ATI)-
Al}2H3]+ and [{(iPr2-ATI)AlMe}2(µ-Me)]+ react with ethylene
(1 atm) at 25-80 °C in toluene or C6H5Cl. However, the base-
free complexes 4c,e (generated in situ, toluene, 80-100 °C,
1-5 atm of ethylene) polymerize ethylene with low activity
(900-2600 g PE/mol‚h‚atm, Mn ) 106 500 and Mw/Mn ) 2.4).
The yield and Mn values imply that, at most, only a small
fraction (<1%) of Al centers produce polymer chains. The fate
of the (iPr2-ATI)AlR+ species and the identity of the active
catalyst species in bench scale polymerization experiments was
not established. To probe the mechanism of the ethylene
polymerization further, reactions were monitored by NMR.
1H NMR monitoring of the reaction of 4c with ethylene (1-8
equiv) in C6D5Cl at 25 °C shows that polyethylene is formed,
but the spectrum of 4c is not significantly changed and no
significant new Al species are observed. However, NMR
monitoring of the reaction of 4c with ethylene-d4 (ca. 8 equiv,
25 °C, 3 days) showed that the intensity of the Al-CH2 signal
of 4c was reduced by ca. 22% due to deuterium incorporation
at this site,60 and a small broad peak appeared at δ 5.26 that
was assigned to ethylene. Similarly, the reaction of 4e and
in 55% isolated yield (vide infra). (iii) The reaction of 12 with
excess BuCtCH results in catalytic formation of 11. (iv)
t
Isolated 13 is insoluble in C6D5Cl, but dissolves in the presence
of excess tBuCtCH yielding 14 with catalytic formation of 11.
(v) The only Al species detected by NMR under catalytic
conditions is 14, indicating that this species is the resting state
of the catalytic cycle.
The neutral bis-amidinate compound {PhC(NSiMe3)2}2AlH,53
MAO,54 and a variety of early transition metal species55
catalytically dimerize terminal alkynes by analogous mecha-
nisms. For comparison, AlEt3 reacts with RCtCH (R ) C4H9,
C5H11 and C6H13) at 20 °C predominantly by σ-bond metathesis
to give {AlEt2(µ-CtCR)}2 (>80% yield) and RH along with
minor amounts of insertion (both Markovnikov and anti-
Markovnikov) and â-H transfer products.56
13 crystallizes from C6H5Cl as [{(iPr2-ATI)Al(µ-CtCtBu)}2]-
[B(C6F5)4]2‚5PhCl (13‚5PhCl). The dinuclear dication of 13‚
5PhCl (Figure 6) consists of two (iPr2-ATI)Al units linked by
two unsymmetrical σ,π-alkynyl bridges. The short Al-C
σ-bonds (Al(1)-C(14) 1.971(2) Å) are associated with a slightly
bent Al-CtC unit (Al(1)-C(14)-C(15) ) 163.6(2)°). The
long Al-C bonds (Al(1)-C(14A) 2.151(2) Å) are formed by
donation of alkynyl π-electrons to an empty Al p orbital.57 The
C(14)-C(15) bond (1.217(3) Å) retains triple bond character.
The Al2C2 plane is almost perpendicular to the ATI rings (angle
between planes 93.6°). Similar structures have been observed
for neutral dinuclear aluminum alkynyl compounds.58,59
(58) (a) Almenningen, A.; Fernholt, L.; Haaland, A. J. Organomet. Chem.
1978, 155, 245. (b) Stucky, G. D.; McPherson, A. M.; Rhine, W. E.; Eisch,
J. J.; Considine, J. L. J. Am. Chem. Soc. 1974, 96, 1941.
(53) Duchateau, R.; Meetsma, A.; Teuben, J. H. J. Chem. Soc., Chem.
Commun. 1996, 223.
(54) Dash, A. K.; Eisen, M. S. Org. Lett. 2000, 2, 737.
(55) (a) Yoshida, M.; Jordan, R. F. Organometallics 1997, 16, 4508. (b)
Horton, A. D. J. Chem. Soc., Chem. Commun. 1992, 185 and references
therein.
(56) Riena¨cker, R.; Schwengers, D. Liebigs Ann. Chem. 1970, 737, 182.
(57) Erker, G.; Albrecht, M.; Kruger, C.; Nolte, M.; Werner, S.
Organometallics 1993, 12, 4979 and references therein.
(59) The neutral dinuclear Al alkenyl complex {Al(iBu)2(µ-CHdCHt-
Bu)}2 was characterized by X-ray crystallography. Albright, M. J.; Butler,
W. M.; Anderson, T. J.; Glick, M. D.; Oliver, J. P. J. Am. Chem. Soc.
1976, 98, 3995.
(60) The intensities of the ATI-ring 1H NMR resonances of 4c are
unchanged. Due to the presence of poly(ethylene-d4) gel in the NMR tube,
the AlCH2CH3, NCHMe2 (and probably polyethylene) signals were
overlapped in a broad peak, preventing accurate integration.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8301
Scheme 5
ethylene-d4 (3 equiv, 25 °C) yields [(iPr2-ATI)AlCD2CD2H]-
[B(C6F5)4] (4c-d4), poly(ethylene-d4), and polyisobutylene. The
1H NMR spectrum of this reaction after 8 h contains signals
for 4c-d4, but not for 4e, and the 13C NMR spectrum contains
Figure 7. Structure of the {AlEt(µ-iPr2-ATI)(µ-Et)AlEt2}+ cation in
15. Selected bond distances (Å) and angles (deg): Al(1)-N(1) 1.904-
(2), Al(1)-N(2) 1.937(2), Al(1)-C(14) 1.896(2), Al(1)-C(16) 2.095-
(2), Al(2)-C(16) 2.208(2), Al(2)-C(18) 1.963(2), Al(2)-C(20) 1.957-
(2), Al(2)-N(2) 2.050(2), Al(1)-Al(2) 2.6927(8); N(1)-Al(1)-N(2)
84.87(6), N(1)-Al(1)-C(14) 116.0(1), N(1)-Al(1)-C(16) 112.68(8),
N(2)-Al(1)-C(14) 129.61(9), N(2)-Al(1)-C(16) 100.65(8), Al(1)-
N(2)-Al(2) 84.92(6), Al(1)-C(16)-Al(2), 77.41(7), Al(1)-C(16)-
C(17) 112.3(2), Al(2)-C(16)-C(17) 119.3(2), N(2)-Al(2)-C(16)
93.57(7), C(18)-Al(2)-C(20) 119.1(1), C(18)-Al(2)-C(16) 106.2-
(1), C(18)-Al(2)-N(2) 112.22(8), C(20)-Al(2)-C(16) 110.18(9),
C(20)-Al(2)-N(2) 112.32(8). Hydrogen atoms are omitted.
1
an AlCD2CD2H resonance at δ 6.9 with a characteristic JCD
of 20 Hz for 4c-d4, which is isotopically shifted ca. 0.7 ppm
upfield versus the corresponding signal for 4c.52 Control
experiments show that 4c polymerizes isobutylene under these
conditions, presumably by a cationic mechanism, without
formation of 4e. These results show that the predominant
reaction of 4c and 4e with ethylene-d4 is â-H transfer to yield
4c-d4 and ethylene or isobutylene (Scheme 5). This observation
is consistent with recent ab initio calculations for a model
aluminum amidinate complex {HC(NH)2}AlCH2CH3+, which
showed that â-H transfer from the Al-Et group to ethylene has
a lower energy barrier than ethylene insertion, â-H transfer to
Al to produce {HC(NH)2}AlH+ and ethylene, or σ-bond
ing) mode, as seen in previous p-, d-, and f-block metal
aminotroponiminate complexes.21d-f However, given the ten-
dency of amidinate ligands to coordinate in a bridging mode in
i
cationic Al species,12 it is reasonable to expect that the Pr2-
ATI ligand might also function as a bridging ligand in suitably
electron deficient and sterically open systems. This is in fact
the case. The reaction of 4c and 1 equiv of AlEt3 in CD2Cl2 at
-78 °C yields a 2:1 mixture of [AlEt(µ-η2,η1-iPr2-ATI)(µ-Et)-
AlEt2][B(C6F5)4] (15) and an isomer tentatively identified as
[(iPr2-ATI)Al(µ-Et)2AlEt2][B(C6F5)4] (16, eq 17). The C1-
symmetric mixed-bridge isomer 15 was isolated from the
reaction of 4c and AlEt3 in toluene, which results in separation
of an oil from which 15 crystallizes. Compound 15 was
characterized by X-ray crystallography. The C2V-symmetric
isomer 16 was detected by NMR analysis of mixtures of 15
and 16.
metathesis to produce {HC(NH)2}AlCHdCH2 and ethane.61
+
Computational studies also predict a high barrier to ethylene
insertion in {MeC(NMe)2}AlMe+.62 We conclude that intact
(iPr2-ATI)AlR+ are not active ethylene polymerization catalysts,
and that the observed polymerization is due to a minor as yet
unidentified species in solution. Further work on this issue is
in progress.
Polymerization of Propylene Oxide by (iPr2-ATI)AlR+
Cations. Compound 4e polymerizes propylene oxide (PO). The
reaction of 4e with a ca. 500-fold excess of PO in toluene is
very exothermic and yields atactic poly(propylene oxide) with
activity of 240 t.o./h. The neutral diethyl complex 1c does not
polymerize PO under these conditions. This reaction was not
studied in further detail.
Polymerization of Methyl Methacrylate by {(iPr2-ATI)-
+
Al}2H3 (2a). The dinuclear cationic hydride complex 2a
completely polymerizes a ca. 450-fold excess of methyl meth-
acrylate (MMA) in 3 h in toluene at room temperature in an
exothermic reaction. The poly(MMA) is moderately syndiotactic
with mm:mr:rr ) 1:22:77. In contrast, the neutral dihydride
complex 1a and the cationic alkyl species 2b and 4c,e do not
polymerize MMA under these conditions. The polymerization
by 2a may occur by a group transfer mechanism, similar to
that established for MMA polymerization catalyzed by transition
metal complexes.63
Reaction of (iPr2-ATI)AlEt+ with AlEt3. In all of the neutral
and cationic Al aminotroponiminate complexes described to this
point, the iPr2-ATI ligand coordinates in a chelating (nonbridg-
Compound 15 crystallizes as discrete ions (Figure 7). The
two Al centers of the cation of 15 are bridged by one nitrogen
(61) Talarico, G.; Budzelaar, P. H. M.; Gal, A. W. J. Comput. Chem.
2000, 21, 398.
(62) Reinhold, M.; McGrady, J. E.; Meier, R. J. J. Chem. Soc., Dalton
Trans. 1999, 487.
(63) Leading references to polymerization of MMA by a group transfer
mechanism: (a) Collins, S.; Ward, D. G. J. Am. Chem. Soc. 1992, 114,
5460. (b) Coates, G. W. Chem. ReV. 2000, 100, 1223. (c) Cameron, P. A.;
Gibson, V. C.; Graham, A. J. Macromolecules 2000, 33, 4329.

8302 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
Table 1. 27Al NMR Data for Neutral (iPr2-ATI)Al(R1)(R2)
Complexes
corresponding (iPr2-ATI)AlR+ cations (4a-e,g,h). The prefer-
ence for â-H abstraction is ascribed to the greater steric
accessibility of the â-C-H unit versus the Al-R bond to the
bulky Ph3C+ electrophile. NMR monitoring studies of two cases
(R ) Et, Me) indicate that these reactions proceed by initial
compd
R1, R2
H, H
Me, Me
Et, Et
Pr, Pr
iBu, iBu
Cl, Cl
δ
∆ν1/2, Hz
solvent
1a
1b
1c
1d
1e
1f
1g
1h
5c
5g
5h
126
154
153
152
150
109
147
146
137
138
130
1900
3200
2700
5000
5900
490
4900
3500
4100
5100
3600
C6D6
C6D6
C6D5CD3
C6D5Cl
C6D5Cl
C6D6
C6D6
C6D6
C6D6
C6D6
i
addition of Ph3C+ to the Pr2-ATI C5 carbon to generate {1,2-
(NiPr)2-5-CPh3-cyclohepta-3,6-diene}AlR2+ diimine intermedi-
ates 6, which decompose at ca. -30 °C to (iPr2-ATI)AlR+
species by dissociation of Ph3C+ followed by R or â-H
abstraction. Base-free (iPr2-ATI)AlR+ cations are very reactive,
as expected for 6-electron cationic Al species, and their stability
depends on (i) the steric properties, electron donating ability,
and bridging tendency of the Al-R group, (ii) the reactivity of
the counterion, and (iii) the availability of Lewis bases which
coordinate to Al to produce stable 4-coordinate adducts.
Cy, Cy
CH2Ph, CH2Ph
Et, C6F5
Cy, C6F5
CH2Ph, C6F5
C6D5Cl
of the iPr2-ATI ligand and one Et group. The iPr2-ATI ligand is
thus coordinated in an “imine, µ-amide” mode and has a
localized π-system, which is manifested by a pronounced
alternation of bond lengths. The N(1)-C(4) (1.333(2) Å) and
C(5)-C(6), C(7)-C(8), and C(9)-C(10) (1.364 Å average)
bonds have significant double bond character while the N(2)-
C(10) (1.427(2) Å) and C(4)-C(5), C(6)-C(7), and C(8)-C(9)
(1.414 Å average) bonds have significant single bond character.
The Al(1)-Nimine distance (Al(1)-N(1) (1.904(2) Å) is shorter
than the Al-Nimine distance in {η2-(p-tolyl)NCH2CMedN(p-
tolyl)}AlMe2 (1.979(6) Å),64 and the Al-Nµ-amide distances (Al-
(1)-N(2) 1.937(2) Å; Al(2)-N(2) 2.050(2) Å) are comparable
to those in {Me2Al(µ-NH(adamantyl))}2 (1.97(2) Å average).65
The Al(1)-C distances to the bridging and terminal Et groups
(Al(1)-C(16) 2.095(2) Å; Al(1)-C(14) 1.896(2) Å) are sig-
nificantly shorter than the corresponding distances involving
Al(2) (Al(2)-C(16) 2.208(2) Å; Al(2)-C(20) 1.957(2) Å; Al-
(2)-C(18) 1.963(2) Å). These differences suggest that the
positive charge is more localized on Al(1) than on Al(2). The
Al(1)-N(2)-Al(2)-C(16) ring is puckered (torsion angles
C(16)-Al(2)-N(2)-Al(1) -13.95(7)° and N(2)-Al(1)-C(16)-
The primary alkyl complexes 4b-e are thermally stable and
have been isolated as base-free materials. The (iPr2-ATI)AlR+
cations in 4b-e are most likely monomeric in the solid state
and in benzene/toluene liquid clathrates, and form (iPr2-ATI)-
Al(R)(ClR)+ solvent adducts in chlorocarbon solution. An X-ray
crystallographic analysis of one such adduct, [(iPr2-ATI)Al(Et)-
(ClPh)][B(C6F5)4] (4c(ClPh)‚0.5PhCl), shows that the PhCl is
coordinated by a dative PhCl- -Al interaction and an attractive
Ph/ATI π-stacking interaction.
In contrast, the mononuclear hydride complex [(iPr2-ATI)-
AlH][B(C6F5)4] is thermally unstable and decomposes by
-
transfer of a C6F5 group from B to Al and subsequent ligand
redistribution reactions to produce (iPr2-ATI)Al(C6F5)(µ-H)2B-
(C6F5)2 (3) and other products. The Al center in (iPr2-ATI)-
AlH+ is more sterically accessible and perhaps more electro-
philic than those in 4c-e, due to the smaller size and poorer
-
electron donating ability of H versus R, which facilitates C6F5
abstraction from the anion. The benzyl complex [(iPr2-ATI)AlCH2-
Ph][B(C6F5)4] is also thermally unstable and decomposes by
C6F5 abstraction to (iPr2-ATI)Al(CH2Ph)(C6F5) (5h). The
-
-
(iPr2-ATI)AlCH2Ph+ cation is probably more electrophilic than
primary alkyl (iPr2-ATI)AlR+ species due to the poorer electron
donating ability of CH2Ph versus R. Similarly, the (iPr2-ATI)-
Al(2) -14.15(7)°). The structure of the B(C6F5)4 anion is
normal.
27Al NMR Spectra of (iPr2-ATI)AlR2 Complexes. The
27Al NMR spectra of neutral four-coordinate (iPr2-ATI)AlR1R2
complexes contain one broad peak in the δ 100-160 region
(Table 1). For the hydrocarbyl derivatives, the signal shifts
downfield as the electron-donating ability of the R groups
increases. The peak width for (iPr2-ATI)AlCl2 (1f, ∆ν1/2 ) 490
Hz) is much narrower than those for the (iPr2-ATI)AlR2
complexes (∆ν1/2 ) 1900-6000 Hz). This difference is ascribed
to the smaller differences in the ionic character of the Al-N
bonds versus the Al-Cl or Al-R bonds which results in a
smaller electric field gradient at Al in the former species.66 No
27Al NMR signals in the δ -200-900 region were observed
for the cationic species 2b or 4c-e in C6D6 clathrates or C6D5-
Cl solutions, so 27Al NMR is not a useful probe of the structures
of these species.
-
-
AlCy+ cation abstracts a C6F5 group from B(C6F5)4 to
produce (iPr2-ATI)Al(Cy)(C6F5) (5g). In this case, steric interac-
tions between the Cy ring and Pr groups of the (iPr2-ATI)-
i
ligand may weaken the Al-C bond and enhance the electro-
philic character of the Al center. The stability of [(iPr2-ATI)-
AlR][B(C6F5)4] compounds containing primary Al-R groups
is thus quite fortuitous, as the cations in these salt species must
-
be near the limit of compatibility with the B(C6F5)4 anion.
In cases where the Al-R group can form a strong 3-center,
2-electron bridge (i.e. R ) Me, H), stable dinuclear monoca-
tionic {(iPr2-ATI)AlR}2(µ-R)+ species are formed. The dinuclear
Me complex 2b forms unavoidably in the reaction of 1b with
Ph3C+ (regardless of the 1b/Ph3C+ ratio) because 1b is trapped
by (iPr2-ATI)AlMe+ faster than it reacts with Ph3C+, and
because 2b does not react with Ph3C+ due to steric crowding
and does not dissociate into 1b and 4b, the former of which
could react with Ph3C+. Similarly, the dinuclear hydride 2a is
formed in the reaction of 2 equiv of 1a with 1 equiv of Ph3C+,
but reacts further with excess Ph3C+ to produce the unstable
(iPr2-ATI)AlH+ cation. In contrast, dinuclear {(iPr2-ATI)AlR}2-
(µ-R)+ cations are not stable for the higher alkyls which are
poorer bridging ligands than Me or H, although these species
are probably intermediates in alkyl exchange reactions between
(iPr2-ATI)AlR2 and (iPr2-ATI)AlR+. In cases where the Al-R
group can form a strong 3-center, 4-electron bridge (R ) -OR,
Discussion
The reaction of (iPr2-ATI)AlR2 complexes with [Ph3C]-
[B(C6F5)4] proceeds by net R abstraction (R ) H, Me, CH2Ph)
or, if â-hydrogens are present on the alkyl group (R ) Et, Pr,
iBu, Cy), â-H abstraction/alkene elimination to produce the
(64) Kanters, J. A.; Van Mier, G. P. M.; Nijs, R. L. L. M.; Van Der
Steen, F.; Van Koten, G. Acta Crystallogr. C 1988, 44, 1391.
(65) Waggoner, K. M.; Power, P. P. J. Am. Chem. Soc. 1991, 113, 3385.
(66) (a) Delpuech, J. J. In NMR of Newly Accessible Nuclei; Laszlo, P.,
Ed.; Academic Press: New York, 1983; Vol. 2, p 153. (b) Mason, J.
Multinuclear NMR; Plenium Press: New York and London, 1987; pp 259-
278.
-CtCR), unique dinuclear dicationic {(iPr2-ATI)Al(µ-R)}2
2+

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8303
Table 2. Average Al-N Bond Distances in (iPr2-ATI)Al
Rather these reactions probably involve direct hydride transfer
to coordinated substrate via six-membered transition states
(Schemes 3-5). The (iPr2-ATI)AlR+ species do not exhibit high
insertion reactivity. Complexes 4c,e react with ethylene by â-H
transfer rather than insertion, and the acetonitrile adducts 8c-e
do not undergo MeCN insertion, even at very high temperature
for 8c. The preference for â-H transfer over insertion in the
reactions with unsaturated substrates is more pronounced for
cationic Al alkyls than for neutral AlR3 compounds which
may reflect, at least in part, increased Al-R bond strengths
due to the charge at Al. However, the alkynyl complex
[(iPr2-ATI)Al(CtCtBu)][B(C6F5)4] (13) does insert tBuCtCH
to produce vinyl complex 14. This reaction is a key step in
catalytic dimerization of tBuCtCH, which occurs by an
insertion/σ-bond metathesis cycle.
Complexes
compd
dAl-N, Å
(iPr2-ATI)AlMe2 (1b)a
1.915
1.890
1.867
1.876
1.855
1.838
1.836
1.826
(iPr2-ATI)AlH2 (1a)a
(iPr2-ATI)Al(C6F5)(µ-H)2B(C6F5)2 (3)
[{(iPr2-ATI)AlMe}2(µ-Me)][B(C6F5)4] (2b)
[(iPr2-ATI)Al(Et)(NCMe)][B(C6F5)4] (8c)
[(iPr2-ATI)AlEt][B(C6F5)4] (4c)
[{(iPr2-ATI)Al(µ-CtCtBu)}2][B(C6F5)4] (13)
[{(iPr2-ATI)Al(µ-OiPr)}2][B(C6F5)4] (10)
a Taken from ref 21a.
species are formed.67 The driving force to achieve an 8-electron
configuration at Al overcomes the Coulombic repulsion between
the two cationic centers in the formation of these dications.68
i
The steric and electronic properties of the Pr2-ATI ligand
Conclusions
both contribute to the stability of the (iPr2-ATI)AlR+ cations.
As pointed out by Dias, steric interactions between the ATI
ring and the isopropyl groups favor a conformation in which
the iPr methyl groups point toward the Al center in (iPr2-ATI)-
Al complexes.21a Also, the N-Al-N bite angle in cationic
(iPr2-ATI)Al complexes (83-89°) is larger than those in
amidinate complexes (ca. 70°).12,13 These factors provide a
moderate degree of steric protection to the unsaturated Al center
in (iPr2-ATI)AlR+ cations. The strong electron donor ability and
i
The Pr2-ATI ligand, which was originally used for neutral
Al alkyls by Dias,21a permits the synthesis of several novel
classes of cationic Al species, including mononuclear (iPr2-ATI)-
AlR+ and (iPr2-ATI)Al(R)(L)+ complexes and dinuclear {(iPr2-
ATI)AlR}2(µ-R)+ and {(iPr2-ATI)Al(µ-R)}22+ complexes. The
(iPr2-ATI)AlR+ cations are potent Lewis acids and undergo
facile â-H transfer to unsaturated substrates. These reactivity
properties are important in the polymerization of isobutylene
and propylene oxide by (iPr2-ATI)AlR+, the dimerization of
tBuCtCH catalyzed by (iPr2-ATI)AlR+, and the polymerization
of methyl methacrylate by {(iPr2-ATI)AlH}2(µ-H)+. However,
the present systems exhibit several complications which must
be addressed before this catalytic chemistry can be fully
developed. Neutral (iPr2-ATI)AlR2 complexes are susceptible
to electrophilic attack by Ph3C+ at the ATI C5 position, which
suggests that similar reactions may provide a decomposition
pathway for (iPr2-ATI)AlR+ cations. Additionally, the Al-N
bonds in (iPr2-ATI)AlR+ species are susceptible to attack by
AlR3 (and presumably other reactive alkyls), which can lead to
dinuclear species and complicate the chemistry. Finally, and
perhaps most importantly, (iPr2-ATI)AlR+ species are clearly
near the limit of compatibility with B(C6F5)4-, which is one of
the most stable anions known. Our future work in this area will
address these issues by modification of the iPr2-ATI ligand and
utilization of other anions.69,70
i
polarizability of the Pr2-ATI ligand stabilizes the electron
deficient Al center in (iPr2-ATI)AlR+ species. As summarized
in Table 2, the Al-N bond distances are significantly shorter
in (iPr2-ATI)Al(R)(L)+ than in (iPr2-ATI)AlR2 complexes, which
reflects stronger N-Al bonding in the former systems.
The reactivity of (iPr2-ATI)AlR+ species is dominated by their
Lewis acidity. These cations form robust adducts with Lewis
bases such as NMe2Ph, Me2CdO, MeCN, and even PhCl, which
undergo associative rather than dissociative ligand exchange.
For R ) H, Cy, and CH2Ph, the base-free cations are so
electrophilic that they abstract a C6F5- group from the B(C6F5)4
-
anion. The formation of dinuclear monocations {(iPr2-ATI)-
AlR}2(µ-R)+ (R ) H, Me) and dinuclear dications {(iPr2-ATI)-
Al(µ-R)}2 (R ) -OR, -CtCR) by coordination of (iPr2-
2+
ATI)AlR2 or (iPr2-ATI)AlR+ to (iPr2-ATI)AlR+ also reflects the
Lewis acidity at aluminum. Cationic (iPr2-ATI)AlR+ species
initiate the polymerization of isobutylene and propylene oxide,
and the dinuclear hydride complex {(iPr2-ATI)AlH}2(µ-H)+
catalyzes the polymerization of MMA. While the mechanisms
of these polymerizations have not yet been studied, the Lewis
acid character of the cationic Al species is probably important.
The predominant reaction of the higher alkyl (iPr2-ATI)Al-
(CH2CHRR′)+ species (RR′ ) H2, HMe, Me2) with unsatu-
rated substrates is â-H transfer to the substrate. Thus, (iPr2-
ATI)Al(CH2CHRR′)+ species react with Me2CdO, tBuCtCH,
and ethylene to yield (iPr2-ATI)Al(OiPr)+, (iPr2-ATI)Al-
(CHdCHtBu)+, and (iPr2-ATI)AlEt+, respectively, with extru-
sion of the corresponding CH2dCRR′ olefin. These reactions
proceed in high yield and therefore probably do not involve
â-H transfer to Al to produce a (iPr2-ATI)AlH+ intermediate,
since this species (at least in base-free form) decomposes to 3.
Experimental Section
General Procedures. All manipulations were performed in a
glovebox filled with purified nitrogen or on a high-vacuum line.
Pentane, hexane, toluene, benzene (Fisher), toluene-d8, and benzene-
d6 (Cambridge) were distilled under nitrogen from sodium/benzophe-
none ketyl and stored in flasks sealed with Teflon valves. Acetone
(Fisher) and tert-butyl acetylene (Aldrich) were distilled under nitrogen
from P2O5. Acetonitrile, methylene chloride (Fisher), chlorobenzene
(Aldrich), and acetonitrile-d3, methylene chloride-d2, and chlorobenzene-
d5 (Cambridge) were dried over CaH2 for 24 h, degassed by freeze-
pump-thaw cycles, and vacuum transferred to a storage vessel.
[CPh3][B(C6F5)4] (Boulder Scientific) was recrystallized from toluene/
pentane. B(C6F5)3 (Boulder Scientific) was purified by sublimation and
the purity was confirmed by 19F and 11B NMR. [HNMe2Ph][B(C6F5)4]
(67) Several dinuclear dicationic Al compounds incorporating 5-coor-
dinate Al centers have been reported: (a) [(EtAl)2‚diaza-18-crown-6]-
[EtAlCl3]2: Self, M. F.; Pennington, W. T.; Laske, J. A.; Robinson, G. H.
Organometallics 1991, 10, 36. (b) [{Salpen(tBu)4Al}2][GaCl4]2 and
[{Salomphen(tBu)3Al}2][GaCl4]2: ref 11c.
(68) Dinuclear dicationic Zr compounds have been proposed or charac-
terized. See ref 41 and the following: (a) Martin, A.; Uhrhammer, R.;
Gardner, T. G.; Jordan, R. F.; Rogers, R. D. Organometallics 1998, 17,
382. (b) Cuenca, T.; Royo, P. J. Organomet. Chem. 1985, 293, 61.
(69) We have prepared N-tert-butyl-2-(tert-butylamino)troponimine
(tBu2-ATI)H and the Al complexes (tBu2-ATI)AlEt2 and [(tBu2-ATI)AlEt]-
[B(C6F5)4]. Korolev, A. V.; Jordan, R. F. Unpublished results.
(70) (a) Lancaster, S. J.; Walker, D. A.; Thornton-Pett, M.; Bochmann,
M. Chem. Commun. 1999, 1533. (b) Metz, M. V.; Schwartz, D. J.; Stern,
C. L.; Nickias, P. N.; Marks, T. J. Angew. Chem. Int. Ed. 2000, 39, 1312.
(c) Li, L.; Stern, C. L.; Marks, T. J. Organometallics, 2000, 19, 3332. (d)
Reed, C. A. Acc. Chem. Res. 1998, 31, 133. (e) Lupinetti, A. J.; Strauss, S.
H. Chemtracts-Inorg. Chem. 1972, 11, 565.

8304 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
n
(Boulder Scientific) were used as received. BuLi (1.6 M solution in
(iPr2-ATI)AlPr2 (1d). A pentane solution (ca. 20 mL) of (iPr2-ATI)H
(1.08 g, 5.29 mmol) was added to a solution of AlPr3 (827 mg, 5.29
mmol) in pentane at -37 °C. The mixture was allowed to warm to 25
°C and stirred for 3 h. The volatiles were removed under vacuum
leaving a yellow solid. Recrystallization of this solid from pentane
hexanes), PhCH2MgCl (1.0 M solution in Et2O), CyMgCl (2.0 M
solution in Et2O), and AlCl3 were purchased from Aldrich and used as
received. Mg(CH2Ph)2‚2THF was synthesized by a literature proce-
dure,71 and the purity was checked by 1H and 13C NMR. N-Isopropyl-
2-(isopropylamino)troponimine ((iPr2-ATI)H), 1a, and 1b were prepared
using procedures described by Dias,21a and 1c-e were prepared by
analogous procedures.
1
afforded (iPr2-ATI)AlPr2 as a yellow powder (1.58 g, 95%). H NMR
3
(C6D6) δ 6.77 (m, 2H, H4 and H6), 6.35 (d, JHH ) 8, 2H, H3 and
H7), 6.22 (t, 3JHH ) 9, 1H, H5), 3.56 (sept, 3JHH ) 6.5, 2H, Me2CHN),
1H, 13C, 19F, and 11B NMR spectra were recorded in sealed tubes at
ambient probe temperature unless otherwise indicated. 1H and 13C
chemical shifts are reported versus SiMe4 and were determined by
1.63 (m, 4H, AlCH2CH2CH3), 1.23 (d, JHH ) 6.5, and t, JHH ) 7,
3
3
18H, Me2CHN and AlCH2CH2CH3), 0.37 (m, 4H, AlCH2CH2CH3). 1H
3
NMR (C6D5Cl) δ 6.90 (m, 2H, H4 and H6), 6.45 (d, JHH ) 12, 2H,
reference to the residual H and 13C solvent peaks. The residual H
NMR resonances for C6D5Cl appear at δ 7.14, 7.00, and 6.97, and the
13C NMR resonances for C6D5Cl appear at δ 134.2, 129.3(t), 128.3(t),
and 126.0(t). 11B chemical shifts are reported versus BF3‚Et2O in C6D5-
Cl. 19F chemical shifts are reported versus neat CFCl3. Coupling
constants are reported in Hz. Elemental analyses were performed by
Desert Analytics Laboratory (Tucson, AZ) or Midwest Microlabs
(Indianapolis, IN).
H3 and H7), 6.30 (t, JHH ) 9, 1H, H5), 3.70 (sept, JHH ) 6.5, 2H,
1
1
3
3
3
Me2CHN), 1.48 (m, 4H, AlCH2CH2CH3), 1.27 (d, JHH ) 6.5, 12H,
Me2CHN), 1.07 (t, 3JHH ) 7, 6H, AlCH2CH2CH3), 0.20 (m, 4H, AlCH2-
CH2CH3). 13C NMR (C6D6) δ 161.6 (s, C1 and C2), 136.4 (d, JCH
)
1
151, C4 and C6), 119.1 (d, 1JCH ) 161, C5), 113.7 (d, 1JCH ) 150, C3
1
1
and C7), 47.5 (d, JCH ) 135, Me2CHN), 22.3 (q, JCH ) 127, Me2-
1
1
CHN), 21.4 (q, JCH ) 122, AlCH2CH2CH3), 20.1 (t, JCH ) 127,
AlCH2CH2CH3), 17.0 (t, 1JCH ) 113, AlCH2CH2CH3). 13C NMR (C6D5-
-
1
The B(C6F5)4 salts studied in this work separate from C6D5CD3
Cl) δ 161.4 (s, C1 and C2), 136.5 (d, JCH ) 153, C4 and C6), 119.1
1
1
1
and C6D6 as oily phases (liquid clathrates) which contain the salt and
sufficient solvent to allow NMR locking. In these cases, NMR spectra
were recorded for the liquid clathrate directly.
(d, JCH ) 160, C5), 113.5 (d, JCH ) 151, C3 and C7), 47.5 (d, JCH
1 1
) 134, Me2CHN), 22.2 (q, JCH ) 126, Me2CHN), 21.2 (q, JCH
)
1
126, AlCH2CH2CH3), 19.9 (t, JCH ) 124, AlCH2CH2CH3), 17.1 (t,
The NMR spectra of cationic Al compounds contained signals of
the free B(C6F5)4- anion. 13C NMR (C6D5Cl) δ 148.9 (d, 1JCF ) 238),
138.7 (d, 1JCF ) 246), 136.9 (d, 1JCF ) 245), 126.5 (br, Cipso). 13C NMR
(liquid clathrate, C6D6) δ 149.0 (d, 1JCF ) 243), 138.8 (d, 1JCF ) 233),
137.0 (d, 1JCF ) 245), 124.8 (br, Cipso). 13C NMR (CD2Cl2) δ 148.7 (d,
1JCH ) 109, AlCH2CH2CH3).
(iPr2-ATI)AliBu2 (1e). A hexanes solution (ca. 20 mL) of (iPr2-
ATI)H (1.17 g, 5.73 mmol) was added to a hexanes solution (10 mL)
of AliBu3 (1.27 g, 6.40 mmol) at 0 °C. The mixture was allowed to
warm to 23 °C and was stirred overnight. A small amount of insoluble
solid was removed by filtration. The volatiles were removed under
vacuum leaving a yellow solid. Recrystallization of this solid from
pentane afforded (iPr2-ATI)AliBu2 as yellow crystals (0.95 g, 48%).
1JCF ) 237), 138.8 (d, JCF ) 244), 136.8 (d, JCF ) 241). 13C NMR
(CD2Cl2, -90 °C) δ 147.0 (d, 1JCF ) 241), 137.3 (d, 1JCF ) 246), 135.4
(d, 1JCF ) 244), 122.5 (br, Cipso). 11B NMR (C6D5Cl) δ -16.4 (s). 19F
1
1
3
3
1H NMR (C6D6) δ 6.76 (dd, JHH ) 11.5, 9.0, 2H, H4 and H6), 6.36
3
NMR (C6D5Cl) δ -132.2 (d, JFF ) 10.5, 8F, Fo), -162.7 (t, JFF
)
21, 4F, Fp), -166.7 (t, 3JFF ) 18.5, 8F, Fm). 19F NMR (liquid clathrate,
C6D6) δ -131.9 (8F, Fo), -162.6 (4F, Fp), -166.7 (8F, Fm). In cases
where cationic Al compounds were analyzed by NMR spectroscopy
without isolation, the spectra contain signals for Ph3CMe or Ph3CH
coproducts (see Supporting Information).
3
3
(d, JHH ) 11.5, 2H, H3 and H7), 6.20 (t, JHH ) 9.0, 1H, H5), 3.58
3
3
(sept, JHH ) 6.5, 2H, Me2CHN), 2.01 (nonet, JHH ) 6.5, 2H,
3
3
AlCH2CHMe2), 1.27 (d, JHH ) 6.5, 12H, Me2CHN), 1.12 (d, JHH
)
6.5, 12H, AlCH2CHMe2), 0.38 (d, 3JHH ) 6.5, 4H, AlCH2CHMe2). 1H
NMR (C6D5Cl) δ 6.90 (t, 3JHH ) 10.5, 2H, H4 and H6), 6.46 (d, JHH
3
(iPr2-ATI)AlMe2 (1b). The preparation and H and 13C NMR data
1
) 11, 2H, H3 and H7), 6.29 (t, 3JHH ) 9, 1H, H5), 3.70 (sept, 3JHH
)
in C6D6 have been reported by Dias.21a 1H NMR (C6D5Cl) δ 6.91 (t,
6.5, 2H, Me2CHN), 1.89 (nonet, 3JHH ) 6.5, 2H, AlCH2CHMe2), 1.31
3JHH ) 10.5, 2H, H4 and H6), 6.41 (d, JHH ) 12, 2H, H3 and H7),
3
3
3
(d, JHH ) 6.5, 12H, Me2CHN), 0.99 (d, JHH ) 6.5, 12H, AlCH2-
CHMe2), 0.23 (d, 3JHH ) 6.5, 4H, AlCH2CHMe2). 13C NMR (C6D6) δ
161.6 (s, C1 and C2), 136.4 (d, 1JCH ) 151, C4 and C6), 119.2 (d, 1JCH
3
3
6.32 (t, JHH ) 9.0, 1H, H5), 3.64 (sept, JHH ) 6.5, 2H, Me2CHN),
1.24 (d, JHH ) 6.5, 12H, Me2CHN), -0.41 (s, 6H, AlMe). 13C NMR
3
1
1
1
(C6D5Cl) δ 160.9 (s, C1 and C2), 136.5 (d, JCH ) 153, C4 and C6),
) 158, C5), 114.2 (d, JCH ) 151, C3 and C7), 47.5 (d, JCH ) 135,
119.2 (d, 1JCH ) 159, C5), 113.4 (d, 1JCH ) 151, C3 and C7), 47.5 (d,
1JCH ) 135, Me2CHN), 22.5 (q, 1JCH ) 126, Me2CHN), -4.3 (q, 1JCH
) 112, AlCH3).
1
1
Me2CHN), 28.7 (q, JCH ) 124, AlCH2CHMe2), 27.3 (d, JCH ) 124,
1
1
AlCH2CHMe2), 26.5 (t, JCH ) 107, AlCH2CHMe2), 22.3 (q, JCH
)
126, NCHMe2). 13C{H} NMR (C6D5Cl) δ 161.4 (s, C1 and C2), 136.5
(C4 and C6), 119.3 (C5), 114.1 (C3 and C7), 47.5 (Me2CHN), 28.6
(AlCH2CHMe2), 27.2 (AlCH2CHMe2), 26.3 (AlCH2CHMe2), 22.3 (Me2-
CHN). Anal. Calcd for C21H37AlN2: C, 73.21; H, 10.82; N, 8.13.
Found: C, 73.07; H, 11.04; N, 8.01.
(iPr2-ATI)AlEt2 (1c). A hexanes solution (ca. 20 mL) of (iPr2-ATI)H
(2.04 g, 9.98 mmol) was added to a hexanes solution of AlEt3 (1.52 g,
13.3 mmol) at 0 °C. The mixture was allowed to warm to 23 °C and
stirred overnight. A small amount of insoluble solid was removed by
filtration. The volatiles were removed under vacuum leaving a yellow
solid, which was recrystallized from pentane to afford (iPr2-ATI)AlEt2
Li[iPr2-ATI]. A solution of (iPr2-ATI)H (1.25 g, 6.12 mmol) in
hexanes (10 mL) was cooled to -37 °C, and BuLi (5 mL of 1.6 M
solution in hexanes, 8 mmol) was added dropwise by syringe. A yellow
precipitate formed. The mixture was stirred for 2 h, and the precipitate
was collected by filtration, washed with hexanes (3 × 5 mL) and dried
1
3
as a yellow powder (1.20 g, 42%). H NMR (C6D6) δ 6.76 (t, JHH
)
10.5, 2H, H4 and H6), 6.35 (d, 3JHH ) 11.5, 2H, H3 and H7), 6.22 (t,
3JHH ) 9.5, 1H, H5), 3.55 (sept, JHH ) 6.5, 2H, Me2CHN), 1.34 (t,
3
3JHH ) 8, 6H, AlCH2CH3), 1.23 (d, JHH ) 6.5, 12H, Me2CHN), 0.38
3
1
under vacuum to give 1.27 g (98%) of Li[iPr2-ATI]. H NMR (CD3-
(q, 3JHH ) 8, 4H, AlCH2CH3). 1H NMR (C6D5Cl) δ 6.90 (t, 3JHH ) 10,
CN) δ 6.48 (m, 2H, H4 and H6), 5.96 (d, 3JHH ) 12, 2H, H3 and H7),
2H, H4 and H6), 6.45 (d, 3JHH ) 11, 2H, H3 and H7), 6.30 (t, 3JHH
)
3
3
5.49 (t, JHH ) 9, 1H, H5), 3.69 (sept, JHH ) 6, 2H, Me2CHN), 1.14
9, 1H, H5), 3.70 (sept, 3JHH ) 6.5, 2H, Me2CHN), 1.27 (d, 3JHH ) 6.5,
12H, Me2CHN), 1.14 (t, 3JHH ) 8, 6H, AlCH2CH3), 0.17 (q, 3JHH ) 8,
4H, AlCH2CH3). 13C NMR (C6D6) δ 161.6 (s, C1 and C2), 136.5 (d,
3
(d, JHH ) 6, 12H, Me2CHN).
(iPr2-ATI)AlCl2 (1f). AlCl3 (116 mg, 870 µmol) was suspended in
toluene (4 mL) and solid Li[iPr2-ATI] (183 mg, 870 µmol) was slowly
added. The mixture was stirred for 36 h at room temperature, filtered
through Celite, and evaporated under vacuum leaving a yellow-green
solid. Recrystallization of this material from hexanes at -37 °C afforded
257 mg (98%) of a yellow crystalline product. 1H NMR (C6D6) δ 6.74
(m, 2H, H4 and H6), 6.38 (d, 3JHH ) 12, 2H, H3 and H7), 6.33 (t, 3JHH
) 9, 1H, H5), 3.45 (sept, 3JHH ) 6, 2H, Me2CHN), 1.37 (d, 3JHH ) 6,
12H, Me2CHN). 13C NMR (C6D6) δ 159.8 (s, C1 and C2), 137.2 (d,
1JCH ) 153, C4 and C6), 119.1 (d, JCH ) 160, C5), 113.6 (d, JCH
)
1
1
151, C3 and C7), 47.5 (d, 1JCH ) 135, Me2CHN), 22.2 (q, 1JCH ) 125,
Me2CHN), 9.9 (q, 1JCH ) 124, AlCH2CH3), 4.2 (t, 1JCH ) 114, AlCH2-
CH3). 13C NMR (C6D5Cl) δ 161.5 (s, C1 and C2), 136.5 (d, JCH
)
1
153, C4 and C6), 119.2 (d, 1JCH ) 158, C5), 113.5 (d, 1JCH ) 151, C3
1
1
and C7), 47.5 (d, JCH ) 134, Me2CHN), 22.2 (q, JCH ) 126, Me2-
1
1
CHN), 9.7 (q, JCH ) 124, AlCH2CH3), 4.1 (t, JCH ) 109, AlCH2-
CH3). Anal. Calcd for C17H29AlN2: C, 70.80; H, 10.13; N, 9.71.
Found: C, 70.69; H, 9.95; N, 9.53.
1
1
1JCH ) 154, C4 and C6), 123.0 (d, JCH ) 159, C5), 116.2 (d, JCH
)
153, C3 and C7), 47.7 (d, 1JCH ) 135, Me2CHN), 22.4 (q, 1JCH ) 126,
Me2CHN).
(71) Schrock, R. R. J. Organomet. Chem. 1976, 122, 209.

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8305
3
3
(iPr2-ATI)AlCy2 (1g). A solution of (iPr2-ATI)AlCl2 (350 mg, 1.16
mmol) in hexanes (5 mL) was cooled to -37 °C, and CyMgCl (1.2
mL of 2 M solution in Et2O, 2.4 mmol) was added by syringe. The
solution was stirred for 16 h, filtered through Celite, and evaporated
under vacuum to give a dark red oily residue. The residue was dissolved
in pentane, ca. 0.2 mL of dioxane was added, and the solution was
cooled to -37 °C for 16 h. A white precipitate formed. The mixture
was filtered and the filtrate was evaporated under vacuum leaving a
dark red oily residue. The residue was dissolved in a minimum amount
of pentane and kept at -37 °C for 16 h. Red crystals formed and were
isolated by filtration (yield 317 mg, 74%). 1H NMR (C6D6) δ 6.77 (m,
4H, H3 and H7), 6.87 (t, JHH ) 9, 2H, H5), 4.02 (sept, JHH ) 6.5,
4H, Me2CHN), 1.30 (d, 3JHH ) 6.5, 24H, Me2CHN), 0.00 (s, 9H, AlMe).
13C NMR (C6D5Cl) δ 160.5 (s, C1 and C2), 138.1 (d, JCH ) 157, C4
1
and C6), 124.6 (d, 1JCH ) 153, C5), 116.9 (d, 1JCH ) 154, C3 and C7),
47.3 (d, 1JCH ) 137, NCHMe2), 22.7 (q, 1JCH ) 126, Me2CHN), -3.0
(q, JCH ) 122, AlMe). 13C NMR (CD2Cl2, -90 °C, slow bridge/
1
terminal Me exchange) δ 159.7 (s, C1 and C2), 137.4 (d, 1JCH ) 153,
1
1
C4 and C6), 123.2 (d, JCH ) 164, C5), 115.9 (d, JCH ) 153, C3
1
1
and C7), 46.5 (d, JCH ) 135, Me2CHN), 22.4 (q, JCH ) 127,
MeAMeBCHN), 22.1 (q, JCH ) 127, MeAMeBCHN), -0.8 (q, JCH
)
1
1
1
133, AlMebridge), -5.2 (q, JCH ) 118, AlMeterminal). 13C, 11B, and 19F
-
2H, H4 and H6), 6.40 (d, 3JHH ) 12, 2H, H3 and H7), 6.21 (t, 3JHH
)
NMR spectra in C6D5Cl confirmed that the B(C6F5)4 anion is free.
Anal. Calcd for C53H47Al2BF20N4: C, 53.73; H, 4.00; N, 4.73. Found:
C, 53.52; H, 3.95; N, 4.51.
3
9, 1H, H5), 3.59 (sept, JHH ) 6.5, 2H, Me2CHN), 1.95 (br m, 10H,
3
C6H11 ring), 1.47 (br m, 10H, C6H11 ring), 1.27 (d, JHH ) 6.5, 12H,
Me2CHN), 0.53 (br t, 3JHH ) 11, 2H, AlCH). 13C NMR (C6D6) δ 162.0
(C1 and C2), 136.5 (d, 1JCH ) 155, C4 and C6), 119.1 (d, 1JCH ) 160,
C5), 114.0 (d, 1JCH ) 152, C3 and C7), 47.4 (d, 1JCH ) 135, Me2CHN),
31.2 (t, 1JCH ) 123, CH2, C6H11 ring), 30.9 (t, 1JCH ) 125, CH2, C6H11
ring), 28.7 (t, 1JCH ) 131, CH2, C6H11 ring), 26.6 (d, 1JCH ) 96, AlCH),
Observation of an Intermediate in the Reaction of (iPr2-ATI)-
AlMe2 and [Ph3C][B(C6F5)4] in CD2Cl2 at Low Temperature. An
NMR tube was charged with (iPr2-ATI)AlMe2 (55 mg, 210 µmol) and
[Ph3C][B(C6F5)4] (97 mg, 110 µmol). CD2Cl2 (ca. 0.5 mL) was added
by vacuum transfer at -78 °C. The tube was sealed at that temperature
and inserted into the pre-cooled (-90 °C) NMR probe and spectra were
recorded at -90 °C. The NMR spectra established the presence of a
1:1 mixture of (iPr2-ATI)AlMe2 and [{1,2-(NiPr)2-5-CPh3-cyclohepta-
3,6-diene}AlMe2][B(C6F5)4]. 1H NMR (CD2Cl2, -90 °C) δ 7.70-6.60
(m, 19H, Ph ring and H3 and H7 and H4 and H6), 6.01 (br, 1H, H5),
3.85 (br, 2H, Me2CHN), 1.26 (br, 12H, Me2CHN), -0.46 (br, 3H,
AlMe), -0.65 (br, 3H, AlMe). 13C NMR (CD2Cl2, -90 °C) δ 161.6
1
22.2 (q, JCH ) 126, Me2CHN).
(iPr2-ATI)Al(CH2Ph)2 (1h). A solution of (iPr2-ATI)AlCl2 (212 mg,
704 µmol) in ca. 10 mL of hexanes was prepared and Mg(CH2Ph)2‚
2THF (322 mg, 918 µmol) was added as a powder. The mixture was
stirred for 16 h at room temperature, filtered through Celite, and
evaporated under vacuum leaving a red oily residue. The residue was
dissolved in hexanes (ca. 5 mL), and ca. 0.5 mL of dioxane was added.
The solution was kept at -37 °C for 16 h, and a white precipitate
formed. The mixture was filtered and the filtrate was evaporated under
1
(s, C1 and C2), 151.0 (d, JCH ) 159, C4 and C6), 143.6 (s, Phipso),
132.6 (d, 1JCH ) 159, Ph), 128.6 (d, 1JCH ) 166, Ph), 127.1 (d, 1JCH
)
1
1
1
144, Ph), 126.5 (d, JCH ) 152, Ph), 126.1 (d, JCH ) 149, Ph), 121.4
vacuum giving a red oily product (221 mg, 76%). H NMR (C6D6) δ
(d, 1JCH ) 165, C3 and C7), 66.9 (s, Ph3C), 51.8 (d, 1JCH ) 138, C5),
7.10 (m, 8H, Ho, Hm), 6.91 (t, 3JHH ) 7, 2H, Hp), 6.70 (m, 2H, H4 and
46.6 (d, JCH ) 134, Me2CHN), 22.2 (q, JCH ) 127, MeAMeBCHN),
1
1
3
3
H6), 6.30 (d, JHH ) 12, 2H, H3 and H7), 6.18 (t, JHH ) 9, 1H, H5),
21.0 (q, 1JCH ) 126, MeAMeBCHN), -7.6 (d, 1JCH ) 115, AlMeAMeB),
3
3.42 (sept, JHH ) 6.5, 2H, Me2CHN), 2.04 (s, 4H, AlCH2), 1.05 (d,
-8.6 (t, JCH ) 116, AlMeAMeB). The presence of six Ph signals in
1
3JHH ) 6.5, 12H, Me2CHN). 13C NMR (C6D6) δ 161.6 (s, C1 and C2),
the 13C NMR spectrum is ascribed to restricted rotation around
Ph3C-C5 bond. These spectra also contained signals of (iPr2-ATI)-
AlMe2. 13C, 11B, and 19F NMR spectra in CD2Cl2 confirmed that the
1
1
146.9 (s, Cipso), 136.6 (d, JCH ) 152, C4 and C6), 128.3 (d, JCH
)
1
1
158, Cm), 127.9 (d, JCH ) 154, Co), 122.1 (d, JCH ) 158, Cp), 120.2
1
1
1
(d, JCH ) 160, C5), 114.8 (d, JCH ) 152, C3 and C7), 47.3 (d, JCH
-
1
1
B(C6F5)4 anion is free.
) 134, Me2CHN), 25.1 (t, JCH ) 113, AlCH2), 22.0 (q, JCH ) 126,
Me2CHN).
(iPr2-ATI)Al(C6F5)(µ-H)2B(C6F5)2 (3). An NMR tube was charged
with (iPr2-ATI)AlH2 (40 mg, 170 µmol) and [Ph3C][B(C6F5)4] (159 mg,
170 µmol), and C6D6 (ca. 0.5 mL) was added by vacuum transfer at
-78 °C. The tube was sealed and warmed to 25 °C, and a dark red oil
separated from solution. The tube was heated to 60 °C and a
homogeneous solution formed. NMR spectra at 60 °C indicated that a
complex mixture of unidentified products had formed. The tube was
cooled to 25 °C and crystals of 3 formed. The structure of 3 was
established by X-ray crystallography.
[(iPr2-ATI)AlMe][B(C6F5)4] (4b). A solution of (iPr2-ATI)AlEt2 (62
mg, 220 mmol) and (iPr2-ATI)AlMe2 (56 mg, 220 mmol) in ca. 5 mL
of toluene was prepared and [Ph3C][B(C6F5)4] (397 mg, 430 mmol)
was added at room temperature. The mixture was stirred for 0.5 h.
Pentane (ca. 10 mL) was added and a yellow solid precipitated. The
solid was collected by filtration, washed with pentane (4 × 5 mL),
and dried under vacuum affording [(iPr2-ATI)AlMe][B(C6F5)4] as a
[{(iPr2-ATI)Al}2H3][B(C6F5)4] (2a). A vial was charged with (iPr2-
ATI)AlH2 (54 mg, 230 µmol) and [Ph3C][B(C6F5)4] (90 mg, 98 µmol).
Toluene (ca. 0.5 mL) was added and the mixture was stirred for 0.5 h.
Hexanes (ca. 5 mL) was added, the mixture was stirred, and a yellow
precipitate formed. The supernatant was removed using a pipet. The
yellow solid was washed with hexanes (3 × 5 mL), collected by
filtration, and dried under vacuum affording [{(iPr2-ATI)Al}2H3)]-
1
[B(C6F5)4] as a yellow powder (76 mg, 68%). H NMR (C6D5Cl) δ
7.14 (t, 3JHH ) 10.5, 4H, H4 and H6), 6.72 (d, 3JHH ) 11, 4H, H3 and
3
3
H7), 6.69 (t, JHH ) 10, 2H, H5), 4.59 (br, 3H, AlH), 3.51 (sept, JHH
) 6.5, 4H, Me2CHN), 1.05 (d, JHH ) 6.5, 24H, Me2CHN). 13C{H}
3
NMR (C6D5Cl) δ 160.7 (C1 and C2), 138.6 (C4 and C6), 126.2 (C5),
118.3 (C3 and C7), 47.0 (Me2CHN), 22.5 (Me2CHN). 13C, 11B, and
19F NMR spectra in C6D5Cl confirmed that the B(C6F5)4- anion is free.
Anal. Calcd for C26H41Al2BF20N4: C, 52.56; H, 3.62; N, 4.90. Found:
C, 52.64; H, 3.93; N, 4.69.
1
3
yellow powder (356 mg, 89%). H NMR (C6D5Cl) δ 7.18 (t, JHH
)
10.5, 2H, H4 and H6), 6.79 (t, 3JHH ) 9, 1H, H5), 6.77 (d, 3JHH ) 12,
[{(iPr2-ATI)AlMe}2(µ-Me)][B(C6F5)4] (2b). A mixture of (iPr2-
ATI)AlMe2 (153 mg, 588 µmol) and [Ph3C][B(C6F5)4] (252 mg, 273
µmol) in toluene (ca. 0.5 mL) was stirred for 0.5 h at room temperature.
Hexanes (ca. 5 mL) was added, the mixture was stirred for 1 h, and a
pale green precipitate formed. The supernatant was removed using a
pipet. The pale green solid was washed with hexanes (4 × 5 mL),
collected by filtration, and dried under vacuum affording [{(iPr2-ATI)-
3
3
2H, H3 and H7), 3.53 (sept, JHH ) 6.5, 2H, Me2CHN), 1.08 (d, JHH
) 6.5, 12H, Me2CHN), -0.16 (s, 3H, AlMe). 13C NMR (C6D5Cl) δ
159.9 (s, C1 and C2), 138.9 (d, 1JCH ) 158, C4 and C6), 128.2 (d, 1JCH
1
1
) 173, C5), 119.5 (d, JCH ) 153, C3 and C7), 47.4 (d, JCH ) 138,
Me2CHN), 22.9 (q, 1JCH ) 127, Me2CHN), -6.7 (q, 1JCH ) 120, AlMe).
13C, 11B, and 19F NMR spectra in C6D5Cl confirmed that the B(C6F5)4
-
1
anion is free.
AlMe}2(µ-Me)][B(C6F5)4] as a pale green powder (235 mg, 73%). H
NMR (C6D5Cl) δ 7.06 (t, 3JHH ) 10.5, 4H, H4 and H6), 6.63 (d, JHH
[(iPr2-ATI)AlEt][B(C6F5)4] (4c). Procedure A. A vial was charged
with (iPr2-ATI)AlEt2 (104 mg, 361 µmol) and [Ph3C][B(C6F5)4] (303
mg, 328 µmol) and benzene (ca. 0.5 mL) was added. The mixture was
stirred for 0.5 h at room temperature. Hexanes (ca. 5 mL) was added,
the mixture was stirred, and a yellow precipitate formed. The
supernatant was removed using a pipet. The yellow solid was washed
with hexanes (4 × 5 mL), collected by filtration, and dried under
vacuum affording [(iPr2-ATI)AlEt][B(C6F5)4] as a yellow powder (226
mg, 74%). Procedure B. (iPr2-ATI)AlEt2 (395 mg, 1.37 mmol) was
3
) 11.5, 4H, H3 and H7), 6.59 (t, 3JHH ) 9.5, 2H, H5), 3.60 (sept, 3JHH
) 6.5, 4H, Me2CHN), 1.08 (d, 3JHH ) 6.5, 24H, Me2CHN), -0.09 (s,
9H, AlMe). 1H NMR (CD2Cl2, -90 °C, slow bridge/terminal exchange)
δ 7.35 (t, 3JHH ) 10.5, 4H, H4 and H6), 6.95 (d, 3JHH ) 11.5, 4H, H3
3
and H7), 6.80 (t, JHH ) 9.5, 2H, H5), 3.97 (br, 4H, Me2CHN), 1.25
(br, 24H, Me2CHN), 0.63 (br s, 3H, AlMebridge), -0.38 (br s, 6H,
AlMeterminal). 1H NMR (CD2Cl2, -15 °C, fast bridge/terminal Me
exchange) δ 7.41 (t, 3JHH ) 10.5, 4H, H4 and H6), 7.00 (d, 3JHH ) 11,

8306 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
(nonet, JHH ) 7, 2H, AlCH2CHMe2), 1.15 (d, JHH ) 6.5, 12H, Me2-
3
3
dissolved in ca. 20 mL of pentane. A finely divided powder of [Ph3C]-
[B(C6F5)4] (1.25 g, 1.35 mmol) was added and the mixture was stirred
for 2 days at room temperature. A yellow precipitate formed and was
collected by filtration, washed with pentane (3 × 20 mL), and dried
under vacuum affording [(iPr2-ATI)AlEt][B(C6F5)4] as a pale yellow
powder (1.25 g, 99%). 1H NMR (C6D5Cl) δ 7.16 (t, 3JHH ) 10.5, 2H,
3
3
CHN), 0.95 (d, JHH ) 7, 6H, AlCH2CHMe2), 0.60 (d, JHH ) 8, 2H,
1
3
AlCH2CHMe2). H NMR (CD2Cl2, -90 °C) δ 7.70 (t, JHH ) 10.5,
2H, H4 and H6), 7.41 (d, 3JHH ) 12, 2H, H3 and H7), 7.26 (t, 3JHH
)
9, 1H, H5), 4.13 (br, 2H, Me2CHN), 2.10 (br, 2H, AlCH2CHMe2), 1.41
(d, 3JHH ) 4.5, 12H, Me2CHN), 0.98 (d, 3JHH ) 4.5, 6H, AlCH2CHMe2),
0.79 (d, 3JHH ) 7, 2H, AlCH2CHMe2). 13C{H} NMR (C6D5Cl) δ 160.0
(C1 and C2), 139.0 (C4 and C6), 128.7 (C5), 119.7 (C3 and C7), 47.4
(Me2CHN), 27.9 (AlCH2CHMe2), 25.7 (AlCH2CHMe2), 24.1 (AlCH2-
CHMe2), 22.8 (Me2CHN). 13C{H} NMR (CD2Cl2, -90 °C) δ 159.1
(C1 and C2), 147.0 138.8 (C4 and C6), 128.2 (C5), 119.9 (C3 and
C7), 46.7 (Me2CHN), 27.1 (AlCH2CHMe2), 25.0 (AlCH2CHMe2), 23.2
(AlCH2CHMe2), 22.0 (Me2CHN). 13C, 11B, and 19F NMR spectra in
3
3
H4 and H6), 6.78 (t, JHH ) 10, 1H, H5), 6.74 (d, JHH ) 11, 2H, H3
3
3
and H7), 3.51 (sept, JHH ) 6.5, 2H, Me2CHN), 1.09 (d, JHH ) 6.5,
12H, Me2CHN), 1.04 (t, 3JHH ) 8, 3H, AlCH2CH3), 0.44 (q, 3JHH ) 8,
2H, AlCH2CH3). 13C NMR (C6D5Cl) δ 159.9 (s, C1 and C2), 139.0 (d,
1JCH ) 157, C4 and C6), 128.7 (d, JCH ) 160, C5), 119.7 (d, JCH
)
1
1
155, C3 and C7), 47.3 (d, 1JCH ) 139, Me2CHN), 22.8 (q, 1JCH ) 126,
Me2CHN), 7.6 (q, 1JCH ) 127, AlCH2CH3), 3.3 (t, 1JCH ) 116, AlCH2-
CH3). 13C, 11B, and 19F NMR spectra in C6D5Cl confirmed that the
-
C6D5Cl confirmed that the B(C6F5)4 anion is free. Anal. Calcd for
-
B(C6F5)4 anion is free. Anal. Calcd for C39H24N2AlF20B: C, 49.92;
C41H28AlBF20N2: C, 50.95; H, 2.92; N, 2.90. Found: C, 51.04; H, 3.15;
N, 2.92.
H, 2.58; N, 2.99. Found: C, 50.08; H, 2.73; N, 2.90.
Observation of an Intermediate in the Reaction of (iPr2-ATI)-
AlEt2 and [Ph3C][B(C6F5)4] at Low Temperature. An NMR tube
was charged with (iPr2-ATI)AlEt2 (32.4 mg, 112 µmol) and [Ph3C]-
[B(C6F5)4] (102 mg, 110 µmol), and CD2Cl2 (ca. 0.5 mL) was added
by vacuum transfer at -78 °C. The tube was sealed at that temperature
and inserted into a pre-cooled (-90 °C) NMR probe. The probe was
warmed gradually to -30 °C, and spectra were recorded at several
temperatures during the warm-up period. These spectra indicated that
an intermediate formed between -90 and -45 °C that was identified
as [{1,2-(NiPr)2-5-CPh3-cyclohepta-3,6-diene}AlEt2][B(C6F5)4] by NMR.
1H NMR (CD2Cl2, -75 °C) δ 7.60-6.90 (m, 17H, H of Ph ring and
H4 and H6), 6.57 (d, 3JHH ) 13.0, H3 and H7), 6.00 (br, 1H, H5), 3.93
Reaction of (iPr2-ATI)AlEt2 with B(C6F5)3. A solution of B(C6F5)3
(126 mg, 246 µmol) in pentane (6 mL) was added to a solution of
(iPr2-ATI)AlEt2 (71 mg, 250 µmol) in pentane (2 mL) at room
temperature producing a cloudy mixture. A small amount of a red oil
separated and the mixture was stirred for 36 h. The supernatant was
decanted from the oil and evaporated under vacuum leaving a red oily
residue that was dissolved in ca. 0.5 mL of C6D6. NMR spectra were
taken. Signals of (iPr2-ATI)AlEt(C6F5) (5c) and BEt(C6F5)2 were
observed.43
1
Data for 5c: H NMR (C6D6) δ 6.83 (m, 2H, H4 and H6), 6.47 (d,
3
3JHH ) 11.5, 2H, H3 and H7), 6.31 (t, JHH ) 9, 1H, H5), 3.55
3
3
(sept, JHH ) 6.5, 2H, Me2CHN), 1.26 (t, JHH ) 8, 3H, AlCH2CH3),
3
(br, 2H, Me2CHN), 1.37 (br, 12H, Me2CHN), 1.07 (t, JHH ) 8, 3H,
1.14 (d, JHH ) 6.5, 6H, MeAMeBCHN), 1.03 (d, JHH ) 6.5, 6H,
3
3
3
3
AlCH2CH3A), 0.72 (t, JHH ) 8, 3H, AlCH2CH3B), 0.17 (q, JHH ) 8,
MeAMeBCHN), 0.65 (q, JHH ) 8, 2H, AlCH2CH3). 13C NMR (C6D6)
3
4H, AlCH2ACH3), 0.17 (q, JHH ) 8, 4H, AlCH2BCH3). 13C{H} NMR
3
1
1
δ 161.7 (s, C1 and C2), 150.0 (d, JCF ) 231, AlC6F5), 141.5 (d, JCF
) 253, AlC6F5), 137.2 (d, 1JCF ) 252, AlC6F5), 137.1 (d, 1JCH ) 154,
C4 and C6), 121.0 (d, 1JCH ) 160, C5), 115.2 (d, 1JCH ) 152, C3 and
(CD2Cl2, -75 °C) δ 162.2 (s, C1 and C2), 151.0 (C4 and C6), 143.7
(s, Phipso), 132.6 (Ph), 128.8 (Ph), 127.2 (Ph), 126.7 (Ph), 126.5 (Ph),
121.7 (C3 and C7), 66.8 (s, Ph3C), 52.0 (C5), 46.9 (Me2CHN),
22.2 (MeAMeBCHN), 20.7 (MeAMeBCHN), 8.4 (AlCH2CAH3), 7.4
(AlCH2CBH3), 1.8 (AlCAH2CH3), 0.2 (AlCBH2CH3). The presence of
six Ph signals in the 13C NMR spectrum is ascribed to restricted rotation
around the Ph3C-C5 bond. 13C, 11B, and 19F NMR spectra in CD2Cl2
C7), 47.5 (d, JCH ) 135, Me2CHN), 22.3 (q, JCH ) 126, MeAMeB-
1
1
CHN), 22.1 (q, JCH ) 126, MeAMeBCHN), 8.1 (q, JCH ) 125,
AlCH2CH3), 5.6 (br t, 1JCH ) 112, AlCH2CH3). The signal correspond-
ing to Cipso of AlC6F5 was not observed. 19F NMR (C6D6) δ -122.7
(2F, Fo, AlC6F5), -155.3 (1F, Fp, AlC6F5), -162.6 (2F, Fm, AlC6F5).
1
1
-
confirmed that the B(C6F5)4 anion is free.
Data for BEt(C6F5)2: 1H NMR (C6D6) δ 1.80 (q, 3JHH ) 8, 2H, BCH2-
[{1,2-(NiPr)2-5-CPh3-cyclohepta-3,6-diene}AlEt2][B(C6F5)4] was con-
CH3), 0.95 (t, 3JHH ) 8, 3H, BCH2CH3). 13C NMR (C6D6) δ 147.1 (d,
verted to [(iPr2-ATI)AlEt][B(C6F5)4] at -30 °C. Then, the probe was
1JCF ) 247, BC6F5), 143.5 (d, JCF ) 258, BC6F5), 137.6 (d, JCF
)
1
1
1
cooled to -90 °C and the spectra of this species were recorded. H
1
1
252, BC6F5), 24.2 (t, JCH ) 115, BCH2CH3), 9.1 (q, JCH ) 125,
BCH2CH3). The signal corresponding to Cipso of BC6F5 was not
observed. 11B NMR (C6D6) δ 72.2 (br s). 19F NMR (C6D6) δ -131.0
(4F, Fo, BC6F5), -148.2 (2F, Fp, BC6F5), -161.7 (4F, Fm, BC6F5),
NMR (CD2Cl2, -90 °C) δ 7.69 (t, 3JHH ) 10.5, 2H, H4 and H6), 7.41
(d, 3JHH ) 12, 2H, H3 and H7), 4.14 (sept, 3JHH ) 5.5, 2H, Me2CHN),
3
3
1.44 (d, JHH ) 5.5, 12H, Me2CHN), 1.18 (t, JHH ) 7.5, 3H,
3
AlCH2CH3), 0.74 (q, JHH ) 7.5, 2H, AlCH2CH3). The H5 resonance
Reaction of (iPr2-ATI)AlCy2 with [Ph3C][B(C6F5)4]. A solution
of (iPr2-ATI)AlCy2 (23 mg, 62 µmol) in pentane (2 mL) was prepared
and [Ph3C][B(C6F5)4] (54 mg, 59 µmol) was added as a powder. The
mixture was stirred for 24 h at 25 °C. A yellow precipitate formed
during the first hour and then disappeared leaving a green-yellow
solution and a small amount of a dark green oily residue. The
supernatant was decanted from the oily residue and evaporated under
vacuum leaving a dark green solid that was dissolved in ca. 0.5 mL of
C6D6. The NMR spectra of this solution contained resonances for
(iPr2-ATI)AlCy(C6F5) (5g), Ph3CH, and B(C6F5)3.
is obscured by a Ph3CH resonance. 13C{H} NMR (CD2Cl2, -90 °C) δ
159.1 (C1 and C2), 138.8 (C4 and C6), 123.3 (C5), 119.8 (C3 and
C7), 46.6 (Me2CHN), 22.1 (Me2CHN), 7.2 (AlCH2CH3), 3.0 (AlCH2-
CH3). These spectra also contained resonances for Ph3CH and ethy-
lene. 13C, 11B, and 19F NMR spectra in CD2Cl2 confirmed that the
B(C6F5)4- anion is free. [(iPr2-ATI)AlEt][B(C6F5)4] decomposed at -15
°C in CD2Cl2.
[(iPr2-ATI)AlPr][B(C6F5)4] (4d). This compound was synthesized
from (iPr2-ATI)AlPr2 in 96% yield using procedure B described above
1
3
for 4c. H NMR (C6D5Cl) δ 7.16 (t, JHH ) 10.5, 2H, H4 and H6),
Data for 5g: 1H NMR (C6D6) δ 6.81 (m, 2H, H4 and H6), 6.46 (d,
3
3
6.79 (t, JHH ) 9.5, 1H, H5), 6.75 (d, JHH ) 11.5, H3 and H7), 3.52
(sept, 3JHH ) 6.5, 2H, Me2CHN), 1.46 (sext, 3JHH ) 7.5, 2H, AlCH2CH2-
CH3), 1.12 (d, 3JHH ) 6.5, 12H, Me2CHN), 0.95 (t, 3JHH ) 7, 3H, AlCH2-
CH2CH3), 0.55 (t, 3JHH ) 8, 2H, AlCH2CH2CH3). 13C NMR (C6D5Cl)
3
3JHH ) 12, 2H, H3 and H7), 6.29 (t, JHH ) 9, 1H, H5), 3.52 (sept,
3JHH ) 6.5, 2H, Me2CHN), 2.13 (br m, 2H, Cy), 1.93 (br m, 3H, Cy),
1.48 (br m, 5H, Cy), 1.15 (d, 3JHH ) 6.5, 6H, MeAMeBCHN), 1.02 (d,
3JHH ) 6.5, 6H, MeAMeBCHN), 0.81 (br m, 1H, AlCH). 13C NMR
1
δ 160.0 (s, C1 and C2), 138.9 (d, JCH ) 159, C4 and C6), 128.7 (d,
1
1JCH ) 163, C5), 119.7 (d, JCH ) 155, C3 and C7), 47.4 (d, JCH
)
1
1
(C6D6) δ 161.7 (C1 and C2), 149.9 (d, JCF ) 233, C6F5), 141.4 (d,
1JCF ) 250, C6F5), 137.2 (d, 1JCH ) 251, C6F5), 137.0 (d, 1JCH ) 154,
C4 and C6), 120.9 (d, 1JCH ) 160, C5), 115.2 (d, 1JCH ) 152, C3 and
1
1
137, Me2CHN), 22.8 (q, JCH ) 126, Me2CHN), 20.0 (q, JCH ) 125,
AlCH2CH2CH3), 18.0 (t, 1JCH ) 126, AlCH2CH2CH3), 14.6 (t, 1JCH
)
1
1
115, AlCH2CH2CH3). 13C, 11B, and 19F NMR spectra in C6D5Cl
C7), 47.5 (d, JCH ) 135, Me2CHN), 30.6 (t, JCH ) 125, 2CH2, Cy),
1
1
-
28.6 (t, JCH ) 127, CH2, Cy), 27.1 (d, JCH ) 111, AlCH), 22.5 (q,
confirmed that the B(C6F5)4 anion is free.
[(iPr2-ATI)AliBu][B(C6F5)4] (4e). This compound was synthesized
1JCH ) 126, MeAMeBCHN), 21.9 (q, JCH ) 126, MeAMeBCHN). The
1
signal for Cipso of AlC6F5 was not observed. 19F NMR (C6D6) δ -122.7
(2F, Fo), -154.9 (2F, Fp), -162.2 (2F, Fm).
using procedure A (244 mg, 67%) or procedure B (1.10 g, 98%)
1
3
described above for 4c. H NMR (C6D5Cl) δ 7.16 (dd, JHH ) 11.5,
9.5, 2H, H4 and H6), 6.79 (d, JHH ) 9.5, 2H, H5), 6.75 (t, JHH
11.5, 2H, H3 and H7), 3.53 (sept, JHH ) 6.5, 2H, Me2CHN), 1.94
)
Data for B(C6F5)3: 13C NMR (C6D6) δ 148.4 (d, 1JCF ) 250, C6F5),
3
3
3
1
1
145.1 (d, JCF ) 260, C6F5), 137.7 (d, JCF ) 255, C6F5), 113.1 (br,

Cationic Aluminum Alkyl Complexes
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8307
Cipso). 19F NMR (C6D6) δ -129.1 (6F, Fo), -142.0 (3F, Fp), -160.4
(6F, Fm).
0.42 (q, 3JHH ) 8, 2H, AlCH2CH3). 1H NMR (CD2Cl2, -90 °C) δ 7.44
(t, 3JHH ) 10, 2H, H4 and H6), 7.05 (d, 3JHH ) 11.5, 2H, H3 and H7),
3
Reaction of (iPr2-ATI)Al(CH2Ph)2 with [Ph3C][B(C6F5)4]. A
solution of (iPr2-ATI)Al(CH2Ph)2 (262 mg, 635 µmol) in hexanes (10
mL) was prepared and [Ph3C][B(C6F5)4] (536 mg, 581 µmol) was added
as a powder. The suspension was stirred for 48 h at room temperature
producing a slurry of a brown solid in a yellow solution. The solid
was collected by filtration, washed with pentane, and dried under
vacuum to give 243 mg (45% of the starting amount) of unreacted
[Ph3C][B(C6F5)4] that was identified by 1H NMR. The pentane washes
were combined with the hexane filtrate and evaporated under vacuum
to yield a yellow residue. The NMR spectra of this material contained
signals for (iPr2-ATI)Al(CH2Ph)(C6F5) (5h) and Ph3CCH2Ph in ca. 2:1
molar ratio, and signals for a mixture of boranes B(CH2Ph)x(C6F5)3-x
(x ) 0-3).40 Trace amounts of B(C6F5)4- were detected by 19F NMR.
The Ph ring 1H resonances were not assigned due to the complexity of
the spectrum in the aromatic region.
6.93 (t, JHH ) 9.5, 1H, H5), 3.97 (br m, 2H, Me2CHN), 2.58 (s, 3H,
MeCN), 1.31 (br d, 12H, Me2CHN), 1.01 (t, 3JHH ) 8, 3H, AlCH2CH3),
3
0.29 (q, JHH ) 8, 2H, AlCH2CH3). 13C{H} NMR (C6D5Cl) δ 160.6
(C1 and C2), 138.5 (C4 and C6), 125.9 (C5), 123.1 (MeCN), 117.8
(C3 and C7), 47.0 (Me2CHN), 22.5 (Me2CHN), 7.9 (AlCH2CH3), 1.6
(AlCH2CH3), 0.7 (MeCN). 13C{H} NMR (CD2Cl2) δ 161.4 (C1 and
C2), 139.0 (C4 and C6), 126.2 (C5), 120.7 (MeCN), 118.4 (C3 and
C7), 47.6 (Me2CHN), 23.2 (Me2CHN), 8.1 (AlCH2CH3), 3.3 (MeCN),
the AlCH2CH3 resonance was not observed. 13C{H} NMR (CD2Cl2,
-90 °C) δ 159.9 (C1 and C2), 137.9 (C4 and C6), 124.7 (C5), 122.5
(br, MeCN), 117.1 (C3 and C7), 46.4 (Me2CHN), 22.1 (Me2CHN), 7.7
(AlCH2CH3), 3.4 (MeCN), 0.9 (AlCH2CH3). 13C, 11B, and 19F NMR
-
spectra in CD2Cl2 confirmed that the B(C6F5)4 anion is free. Anal.
Calcd for C41H27N3F20BAl: C, 50.30; H, 2.78; N, 4.21. Found: C,
50.44; H, 2.80; N, 4.22.
1
3
Data for 5h: H NMR (C6D6) δ 6.40 (d, JHH ) 12, 2H, H3 and
To generate 8c in the complete absence of free MeCN, the above
reaction was carried out with 10 mol % deficiency of MeCN. NMR
spectra indicated that 8c formed quantitatively (based on MeCN) and
signals for the expected ca. 10% unreacted 4c were also observed. Due
to the presence of 4c, no free MeCN is present and intermolecular
H7), 6.25 (t, 3JHH ) 9, 1H, H5), 3.44 (sept, 3JHH ) 6.5, 2H, Me2CHN),
2.40 (s, 2H, PhCH2Al), 0.97 (d, JHH ) 6.5, 6H, MeAMeBCHN), 0.95
3
(d, JHH ) 6.5, 6H, MeAMeBCHN). The H4 and H6 resonance was
3
obscured by Ph ring H resonances. 19F NMR (C6D6) δ -122.4 (2F,
1
1
Fo), -154.3 (1F, Fp), -162.0 (2F, Fm).
MeCN exchange is thus slow. H NMR (C6D5Cl) δ 7.13 (m, 2H, H4
3
3
Data for Ph3CCH2Ph: 1H NMR (C6D6) δ 3.79 (s, 2H, Ph3CCH2Ph).
and H6), 6.73 (d, JHH ) 11, 2H, H3 and H7), 6.67 (t, JHH ) 9, 1H,
H5), 3.62 (sept, 3JHH ) 6.5, 2H, Me2CHN), 1.77 (s, 3H, MeCN), 1.16
(d, 3JHH ) 6.5, 6H, MeAMeBCHN), 1.06 (d, 3JHH ) 6.5, 6H, MeAMeB-
Data for B(CH2Ph)(C6F5)2: 1H NMR (C6D6) δ 3.26 (s, CH2Ph). 19
F
NMR (C6D6) δ -129.8 (2F, Fo), -147.0 (1F, Fp), -161.4 (2F, Fm).
CHN), 1.03 (t, 3JHH ) 8, 3H, AlCH2CH3), 0.22 (q, 3JHH ) 8, 2H, AlCH2-
Data for B(CH2Ph)2(C6F5): 1H NMR (C6D6) δ 2.88 (s, CH2Ph). 19
F
CH3). 13C NMR (C6D5Cl) δ 160.7 (s, C1 and C2), 138.5 (d, JCH
)
1
NMR (C6D6) δ -133.0 (4F, Fo), -152.3 (2F, Fp), -162.0 (4F, Fm).
1
Data for B(CH2Ph)3: 1H NMR (C6D6) δ 2.09 (s, CH2Ph).
156, C4 and C6), 125.9 (d, JCH ) 162, C5), 123.3 (s, MeCN), 117.8
1
1
Generation of [(iPr2-ATI)Al(R)(NMe2Ph)][B(C6F5)4] (7a,b,c,e,h;
(d, JCH ) 153, C3 and C7), 47.0 (d, JCH ) 137, Me2CHN), 22.8 (q,
1JCH ) 125, MeAMeBCHN), 22.3 (q, JCH ) 125, MeAMeBCHN), 7.9
1
i
R ) H, Me, Et, Bu, CH2Ph). The following procedure for 7a is
1
1
(q, JCH ) 126, AlCH2CH3), 1.7 (t, JCH ) 116, AlCH2CH3), 0.7 (q,
representative; details for the other examples are provided in the
Supporting Information. An NMR tube was charged with (iPr2-ATI)-
AlH2 (15 mg, 65 µmol) and [HNMe2Ph][B(C6F5)4] (59 mg, 74 µmol),
and C6D5Cl (ca. 0.5 mL) was added by vacuum transfer at -78 °C.
The tube was warmed to 23 °C and a rapid reaction occurred affording
a homogeneous solution after a few seconds. The NMR spectra
indicated that quantitative formation of [(iPr2-ATI)AlH(NMe2Ph)]-
[B(C6F5)4] had occurred. 1H NMR (C6D5Cl) δ 7.22 (t, 3JHH ) 11, 2H,
H4 and H6), 7.17 (t, 3JHH ) 7.5, 2H, Hm), 7.11 (t, 3JHH ) 7.5, 1H, Hp),
1JCH ) 140, MeCN). 13C, 11B, and 19F NMR spectra in C6D5Cl
-
confirmed that B(C6F5)4 anion is free.
[(iPr2-ATI)Al(R)(OdCMe2)][B(C6F5)4] (9b,c,d; R ) Me, Et, Pr).
The following procedure for 9c is representative; details for the other
examples are provided in the Supporting Information. An NMR tube
was charged with [(iPr2-ATI)AlEt][B(C6F5)4] (50 mg, 53 µmol), and
C6D5Cl (0.5 mL) and acetone (20.3 mL at 44 Torr and 25 °C, 48 µmol)
were added by vacuum transfer at -78 °C. The tube was warmed to
room temperature and a yellow solution formed. NMR spectra were
obtained after ca. 5 min at 23 °C and indicated that 9c had formed
quantitatively (based on Me2CO); signals for the expected ca. 10%
unreacted 4c were also observed. 9c is stable in C6D5Cl solution for
ca. 1 day at 23 °C. Due to the presence of 4c, no free Me2CO is present
and intermolecular Me2CO exchange is thus slow. 1H NMR (C6D5Cl)
δ 7.15 (m, 2H, H4 and H6), 6.77 (d, 3JHH ) 12, 2H, H3 and H7), 6.68
3
3
6.96 (d, JHH ) 7.5, 2H, Ho), 6.84 (d, JHH ) 11.5, 2H, H3 and H7),
3
3
6.79 (t, JHH ) 9.5, 1H, H5), 4.33 (br s, 1H, AlH), 3.34 (sept, JHH
)
6.5, 2H, Me2CHN), 2.40 (s, 6H, NMe2Ph), 0.93 (br s, 6H, MeAMeB-
CHN), 0.79 (br s, 6H, MeAMeBCHN). 13C NMR (C6D5Cl) δ 161.7 (s,
C1 and C2), 144.1 (s, Cipso), 138.8 (d, 1JCH ) 157, C4 and C6), 130.5
1
1
1
(d, JCH ) 169, Cm), 129.0 (d, JCH ) 165, Co), 127.4 (d, JCH ) 161,
C5), 121.0 (d, 1JCH ) 165, Cp), 119.6 (d, 1JCH ) 154, C3 and C7), 48.7
3
3
1
1
(t, JHH ) 9, 1H, H5), 3.62 (sept, JHH ) 6.5, 2H, Me2CHN), 2.02 (s,
(d, JCH ) 134, Me2CHN), 45.9 (q, JCH ) 142, NMe2Ph), 23.9 (q,
6H, Me2CO), 1.05 (d, JHH ) 6.5, 6H, MeAMeBCHN), 1.01 (m, 9H, d
3
1JCH ) 126, MeAMeBCHN), 21.4 (q, JCH ) 126, MeAMeBCHN). 13C,
1
of MeAMeBCHN and t of AlCH2CH3), 0.26 (q, 3JHH ) 8.3, 2H, AlCH2-
CH3). 13C{H} NMR (C6D5Cl) δ 236.7 (Me2CO), 160.3 (C1 and C2),
138.5 (C4 and C6), 126.0 (C5), 117.8 (C3 and C7), 46.9 (Me2CHN),
32.3 (Me2CO), 22.9 (MeAMeBCHN), 22.1 (MeAMeBCHN), 8.0
(AlCH2CH3), 1.6 (AlCH2CH3).
11B, and 19F NMR spectra in C6D5Cl confirmed that the B(C6F5)4- anion
is free.
[(iPr2-ATI)Al(R)(NCMe)][B(C6F5)4] (8c,d,e; R ) Et, Pr, iBu). The
following procedure for 8c is representative; details for the other
examples are provided in the Supporting Information. A sample tube
was charged with [(iPr2-ATI)AlEt][B(C6F5)4] (330 mg, 352 µmol) and
toluene (ca. 5 mL). Phase separation to a yellow liquid clathrate and a
pale-yellow solution occurred. Acetonitrile (ca. 1 mL) was added by
vacuum transfer at -78 °C, and the tube was warmed to room
temperature. The clathrate dissolved. The volatiles were removed under
vacuum leaving a red-yellow oil that crystallized over a 12 h period to
give 340 mg (99%) of the product. The NMR spectra of isolated
material indicated that intermolecular NCMe exchange is fast on the
NMR time scale which is ascribed to an associative exchange with a
The above reaction was also carried out with 4 mol % excess acetone.
NMR spectra indicated that quantitative formation of 9c occurred and
that intermolecular Me2CO exchange is fast on the NMR time scale at
23 °C. 1H NMR (C6D5Cl) δ 7.15 (m, 2H, H4 and H6), 6.77 (d, 3JHH
)
12, 2H, H3 and H7), 6.68 (t, 3JHH ) 9, 1H, H5), 3.62 (sept, 3JHH ) 6.5,
2H, Me2CHN), 2.00 (s, 6H, Me2CO), 1.03 (m, 15H, d of Me2CHN and
3
t of AlCH2CH3), 0.27 (q, JHH ) 8.3, 2H, AlCH2CH3). 13C{H} NMR
(C6D5Cl) δ 160.3 (C1 and C2), 138.5 (C4 and C6), 126.0 (C5), 117.8
(C3 and C7), 46.8 (NCHMe2), 32.1 (Me2CO), 22.5 (NCHMe2), 8.0
(AlCH2CH3), 1.6 (AlCH2CH3); the Me2CO resonance was not observed.
[{(iPr2-ATI)Al(µ-OiPr2)}2][B(C6F5)4]2‚2CD2Cl2 (10‚2CD2Cl2). A
resealable NMR tube was charged with [(iPr2-ATI)AlEt][B(C6F5)4] (62
mg, 66 µmol), and C6D6 (1 mL) was added by pipet at 25 °C. Phase
separation occurred to produce a pale yellow solution above a dark
red oil. Acetone (20.3 mL at 61 Torr and 25 °C, 66 µmol) was added
by vacuum transfer at -78 °C. The tube was continuously shaken and
was warmed to room temperature. The lower oil layer did not dis-
1
trace amount of free MeCN. H NMR (C6D5Cl) δ 7.13 (m, 2H, H4
3
3
and H6), 6.73 (d, JHH ) 11, 2H, H3 and H7), 6.67 (t, JHH ) 9, 1H,
H5), 3.62 (sept, 3JHH ) 6.5, 2H, Me2CHN), 1.74 (s, 3H, MeCN), 1.11
3
3
(d, JHH ) 6.5, 12H, Me2CHN), 1.03 (t, JHH ) 8, 3H, AlCH2CH3),
0.23 (q, 3JHH ) 8, 2H, AlCH2CH3). 1H NMR (CD2Cl2) δ 7.52 (m, 2H,
H4 and H6), 7.16 (d, 3JHH ) 11.5, 2H, H3 and H7), 7.01 (t, 3JHH ) 9,
3
1H, H5), 4.08 (sept, JHH ) 6.5, 2H, Me2CHN), 2.56 (s, 3H, MeCN),
1.41 (d, 3JHH ) 6.5, 12H, Me2CHN), 1.14 (t, 3JHH ) 8, 3H, AlCH2CH3),

8308 J. Am. Chem. Soc., Vol. 123, No. 34, 2001
KoroleV et al.
tBuCtCH. H NMR (C6D5Cl) δ 7.25 (t, JHH ) 11, 2H, H4 and H6),
1
3
solve. The volatiles were removed under vacuum leaving a yellow solid.
CD2Cl2 (0.5 mL) was added by vacuum transfer producing a yellow
solution. The tube was maintained at 25 °C for 3 days. NMR spectra
were obtained periodically and established that 9c was gradually
converted to 10 during this period. The volatiles were removed under
vacuum leaving a yellow oil that was washed with pentane (3 × 1
mL) to afford 59 mg (94%) of a yellow powder. This material was
recrystallized from CH2Cl2 to yield yellow crystalline 10‚2CH2Cl2. 10
3
3
6.93 (d, JHH ) 11, 2H, H3 and H7), 6.83 (t, JHH ) 9, 1H, H5), 6.07
(s, 1H, AlCH), 3.62 (sept, 3JHH ) 6.5, 2H, Me2CHN), 1.22 (d, 3JHH
)
6.5, 12H, Me2CHN), 1.06 (s, 9H, AlCHdC(CMe3)), 0.71 (s, 9H,
AlCHdC(CMe3)CtCCMe3). 13C NMR (C6D5Cl) δ 159.7 (C1 and C2),
159.0 (AlCHdCH(CMe3)CtCCMe3), 148.9 (d, 1JCF ) 240, B(C6F5)4-),
139.1 (C4 and C6), 138.7 (d, 1JCF ) 245, B(C6F5)4-), 136.8 (d, 1JCF
)
240, B(C6F5)4-), 128.7 (C5), 126.5 (br, ipso-B(C6F5)4-), 119.9 (C3 and
C7), 118.0 (br, AlC), 86.0 (AlCHdC(CMe3)CtC), 59.8 (AlCHd
C(CMe3)CtC), 47.7 (Me2CHN), 31.5 (AlCHdC(CMe3)), 29.8 (AlCHd
C(CMe3)CtCCMe3), 28.0 (AlCHdC(CMe3)), 22.6 (Me2CHN); the
AlCHdC(CMe3)CtCCMe3 resonance was not assigned. 13C, 11B, and
19F NMR spectra in C6D5Cl confirmed that the B(C6F5)4- anion is free.
1
was also synthesized from 4d using the above procedure. H NMR
(CD2Cl2) δ 7.95 (m, 2H, H4 and H6), 7.79 (d, 3JHH ) 11, 2H, H3 and
3
3
H7), 7.58 (t, JHH ) 9, 1H, H5), 4.86 (sept, JHH ) 6, 1H, Me2CHO),
3
3
4.32 (sept, JHH ) 7, 2H, Me2CHN), 1.68 (d, JHH ) 7, 12H, Me2-
CHN), 1.44 (d, JHH ) 6, 6H, Me2CHO). 13C{H} NMR (CD2Cl2) δ
3
Catalytic Dimerization of tBuCtCH. An NMR tube was charged
with [(iPr2-ATI)AlEt][B(C6F5)4] (30 mg, 32 µmol). C6D5Cl (0.5 mL)
was added by vacuum transfer at -78 °C and the mixture was warmed
159.5 (C1 and C2), 140.9 (C4 and C6), 132.4 (C5), 124.3 (C3 and
C7), 78.0 (Me2CHO), 48.6 (Me2CHN), 25.7 (Me2CHO), 23.1 (Me2-
CHN). 13C, 11B, and 19F NMR spectra confirmed that the B(C6F5)4
-
t
anion is free. Anal. Calcd for 10‚2CD2Cl2 (C41H26D2AlBCl2F20NO):
C, 46.66; H + D, 2.86; N 2.65. Found: C, 46.76; H + D 2.70; N,
2.67.
to room temperature to produce a yellow solution. BuCtCH (ca. 8
equiv) was added by vacuum transfer at -78 °C. The mixture was
warmed to room temperature and monitored by NMR. The formation
[(iPr2-ATI)Al(CHdCHtBu)][B(C6F5)4] (12). A resealable NMR
tube was charged with [(iPr2-ATI)AlEt][B(C6F5)4] (42 mg, 45 µmol),
and C6D5Cl (0.5 mL) was added by vacuum transfer to produce a yellow
t
of ethylene and BuCHdCH2 (1 equiv) was observed. After 3 days at
t
ambient temperature, the signals corresponding to BuCtCH had
completely disappeared, and the resonances for the head-to-tail dimer,
2-tert-butyl-5,5-dimethyl-1-hexen-3-yne (11), were observed. Hexanes
(ca. 2 mL) and a few drops of 5% aqueous HCl solution were added
to the solution. The mixture was shaken for 5 min. The clear colorless
organic layer was separated and analyzed by GC-MS. 11 was observed
as the major organic product (>90%). The data for 11 are consistent
with those reported by Eisen.72 Characterization of 11: 1H NMR (C6D5-
t
solution. BuCtCH (20.3 mL at 42 Torr and 25 °C, 45 µmol) was
added by vacuum transfer at -78 °C. The tube was continuously shaken
and was warmed to room temperature. NMR spectra were obtained
after 5 min at room temperature and indicated that quantitative
formation of 12 and ethylene had occurred. The volatiles were removed
under vacuum leaving a dark red oil, and C6D5Cl (0.5 mL) was added
1
by vacuum transfer. H and 13C NMR spectra confirmed the presence
2
2
Cl) δ 5.22 (d, 1H, JHH ) 1.8, HAHBCdC), 5.09 (d, 1H, JHH ) 1.8,
HAHBCdC), 1.19 (s, 9H, H2CdC(CMe3)), 1.12 (s, 9H, CtCCMe3).
13C NMR (C6D5Cl) δ 142.3 (H2CdC(CMe3)), 115.9 (H2CdC), 99.2
(CtCCMe3), 79.4 (CtCCMe3), 31.1 (CtCCMe3), 29.1 (H2Cd
C(CMe3)); the H2CdC(CMe3)CtCCMe3 resonances were not assigned.
GCMS m/e: 164 (M+), 149 (100%, M+ - Me), 134 (M+ - 2 Me),
of 12 and the absence of ethylene. Compound 12 was generated in
similar experiments from 4d and 4e; in these cases propylene and
1
3
isobutylene are formed. H NMR (C6D5Cl) δ 7.19 (t, JHH ) 10, 2H,
H4 and H6), 6.81 (m, 3H, H3 and H7 and H5), 6.45 (d, 3JHH ) 21, 1H,
3
AlCHdCHCMe3), 5.56 (d, JHH ) 21, 1H, AlCHdCHCMe3), 3.57
(sept, 3JHH ) 6.5, 2H, Me2CHN), 1.16 (d, 3JHH ) 6.5, 12H, Me2CHN),
0.95 (s, 9H, AlCHdCHCMe3). 13C{H} NMR (C6D5Cl) δ 169.9
(AlCHdCHCMe3), 160.0 (C1 and C2), 139.1 (C4 and C6), 128.7 (C5),
119.8 (C3 and C7), 118.0 (br, AlCHdCHCMe3), 47.6 (Me2CHN), 37.0
(AlCHdCHCMe3), 28.2 (AlCHdCHCMe3), 23.1 (Me2CHN). 13C, 11B,
133 (M+ - Me - CH4), 121 (M+ - Me - CH2dCH2), 108 (M+
-
CH2dCMe2), 107 (M+ - Bu), 93 (M+ - Me - CH2dCMe2).
t
Reaction of [(iPr2-ATI)AlEt][B(C6F5)4] with AlEt3. An NMR tube
was charged with [(iPr2-ATI)AlEt][B(C6F5)4] (128 mg, 140 µmol) and
AlEt3 (15 mg, 140 µmol), and CD2Cl2 (ca. 0.5 mL) was added by
vacuum transfer at -78 °C. The tube was sealed at -78 °C and inserted
into a pre-cooled (-90 °C) NMR probe. NMR spectra at this
temperature indicated that two compounds had formed in a 2:1 ratio,
which were assigned as [AlEt(µ-iPr2-ATI)(µ-Et)AlEt2][B(C6F5)4] (15)
and [(iPr2-ATI)Al(µ-Et)2AlEt2][B(C6F5)4] (16), respectively. Crystals
of 15 were obtained after slow evaporation of a 1:1 mixture of [(iPr2-
ATI)AlEt][B(C6F5)4] and AlEt3 in toluene. 1H NMR (CD2Cl2, -90 °C)
δ 8.41 (t, 2H, H4 and H6 of 16), 8.16 (t, 1H, H5 of 16), 8.05 (d, 2H,
H3 and H7 of 16), 7.74 (t, 2H, H4 or H6 of 15), 7.53 (t, 2H, H4 or H6
of 15), 7.39 (m, 6H, H3, H5, H7 of 15), 4.01 (br, 6H, Me2CHN of
both), 2.00-1.00 (m, 96H, Me2CHN, AlCH2CH3, AlCH2CH3 of both).
13C NMR (CD2Cl2, -90 °C) δ 168.1, 164.9, 155.4 (s, C1 and C2 of
and 19F NMR spectra confirmed that the B(C6F5)4 anion is free.
-
[{(iPr2-ATI)Al(µ-C≡CtBu)}2][B(C6F5)4]2‚2C6H5Cl (13‚2C6H5Cl).
A resealable NMR tube was charged with [(iPr2-ATI)AlPr][B(C6F5)4]
(131 mg, 138 µmol), and C6H5Cl (0.5 mL) and tBuCtCH (20.3 mL at
64 Torr and 25 °C, 140 µmol) were added by vacuum transfer at -78
°C. The tube was warmed to room temperature and shaken for 5 min.
A second equivalent of tBuCtCH (20.3 mL at 64 Torr and 25 °C, 140
µmol) was added by vacuum transfer at -78 °C. The tube was warmed
to room temperature and shaken for 5 min. The volatiles were removed
under vacuum leaving a yellow-red glass. C6H5Cl (0.5 mL) was added
by vacuum transfer at -78 °C. A yellow crystalline precipitate formed
upon dissolution of the glass at room temperature. The mother liquor
was decanted, and the precipitate was washed with benzene (7 × 0.5
mL) and pentane (5 × 0.5 mL) and dried under vacuum to give 83
mg (55%) of 13‚2C6H5Cl. Anal. Calcd for 13‚2C6H5Cl (C49H33-
AlBClF20N2): C, 53.36; H, 3.02; N, 2.54. Found: C, 53.48; H, 3.13;
N 2.71. X-ray analysis of crystals from the yellow precipitate estab-
lished that this material is 13‚5C6H5Cl (prior to drying). The crystals
crumble in the absence of C6H5Cl solvent with loss of 3 equiv of
C6H5Cl molecules forming 13‚2C6H5Cl. 13 is insoluble in toluene,
benzene, and chlorobenzene, and decomposes to unidentified species
in CH2Cl2.
1
1
1
both), 147.0 (d, JCH ) 161), 142.9 (d, JCH ) 157), 139.2 (d, JCH
)
1
1
165), 137.4 (d, JCH ) 152), 134.4 (d, JCH ) 160) (C4, C5, C6 of
1
1
1
both), 130.3 (d, JCH ) 155), 129.0 (d, JCH ) 157), 125.9 (d, JCH
)
158) (C3 and C7 of both), 49.8 (d, 1JCH ) 134), 48.5 (d, 1JCH ) 134),
48.2 (d, 1JCH ) 137) (Me2CHN of both), 23.1 (q, 1JCH ) 129), 22.3 (q,
1JCH ) 126, 2 overlapping signals), 21.3 (q, 1JCH ) 128), 20.5 (q, 1JCH
) 129) (Me2CHN of both), 8.7, 8.3, 8.2, 8.0, 7.5, 7.1 (q, AlCH2CH3
terminal and bridging of both), 5.6 (t, 1JCH ) 119), 3.4 (t, 1JCH ) 105),
1.6 (t, 1JCH ) 113), 0.7 (t, 1JCH ) 115), -1.7 (t, 1JCH ) 115), -3.5 (t,
1JCH ) 114) (AlCH2CH3 terminal and bridging of both). 13C, 11B, and
19F NMR spectra in CD2Cl2 confirmed that the B(C6F5)4- anion is free.
1H NMR Spectrum of 13 Before Precipitation. The 1H NMR
spectrum of 13 in C6D5Cl was assigned by comparison of the spectra
At -3 °C, NMR spectra contain only one set of broad resonances
t
recorded for reaction of 12 with BuCtCH before and after precipi-
for the (iPr2-ATI)- ligand and the Al-Et group, which is indicative of
tation of 13‚5C6D5Cl. As noted in the text, the nuclearity of the
1
fast exchange between 15 and 16. H NMR (CD2Cl2, 26 °C) δ 7.86
[(iPr2-ATI)Al(CtCtBu)]+ cation in solution (i.e. mononuclear vs
(br s, 2H, H4 and H6), 7.62 (br s, 3H, H3 and H7, H5), 4.10 (br s, 2H,
1
dinuclear) is not established. H NMR (C6D5Cl) δ 7.41 (m, 2H, H4
3
Me2CHN), 1.49 (br d, JHH ) 5.5, 12H, Me2CHN), 1.04 (br s, 12H,
and H6), 7.25 (m, 3H, H3 and H7 and H5), 3.98 (br, 2H, Me2CHN),
AlCH2CH3), 0.33 (br s, 8H, AlCH2CH3). 13C NMR (CD2Cl2, 26 °C) δ
3
1.48 (d, JHH ) 6.5, 12H, Me2CHN), 0.84 (s, 9, AlCtCCMe3).
[(iPr2-ATI)Al(CHdC(tBu)CtCtBu)][B(C6F5)4] (14) was observed
by NMR as an intermediate in the catalytic reaction of 4c-e with
(72) Straub, T.; Haskel, A.; Eisen, M. S. J. Am. Chem. Soc. 1995, 117,
6365.

Cationic Aluminum Alkyl Complexes
Table 3. Summary of X-ray Diffraction Data for Aluminum Aminotroponiminate Complexes
2b 4c(ClPh)‚0.5PhCl 8c 10‚2CH2Cl2
C53H47Al2BF20N4 C31H21AlBF15N2 C48H31.5AlBCl1.5F20N2 C41H27AlBF20N3 C82H56Al2B2Cl4F40N4O2 C116H81Al2B2Cl5F40N4 C45H39Al2BF20N2
J. Am. Chem. Soc., Vol. 123, No. 34, 2001 8309
3
13‚5PhCl
15
formula
fw
cryst system triclinic
space group P1h
color
a, Å
1184.72
744.29
1107.22
monoclinic
P21/c
979.45
monoclinic
P21/c
2106.68
monoclinic
P21/n
2543.68
monoclinic
P21/c
1052.55
triclinic
P1h
triclinic
P1h
yellow
yellow
yellow
yellow
yellow
yellow
colorless
10.9714(6)
12.3277(6)
17.3766(9)
80.783(1)
79.894(1)
88.790(1)
2283.8(2)
173(2)
10.4815(2)
14.0422(3)
18.7747(4)
104.450(1)
94.848(1)
96.639(1)
2639.44(9)
173(2)
10.0419(3)
10.0407(3)
15.9755(4)
105.921(1)
96.061(1)
95.456(1)
1527.31(8)
173(2)
14.2338(9)
20.026(1)
16.546(1)
11.1053(6)
28.576(2)
13.7262(7)
13.4003(7)
14.4792(8)
22.604(1)
12.5421(6)
27.494(1)
16.7627(8)
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
temp, K
Z
98.450(1)
106.606(1)
91.756(1)
103.906(1)
4665.1(5)
173(2)
4
4174.2(4)
163(2)
4
4383.7(4)
173(2)
2
5610.8(5)
163(2)
2
2
2
2
R1, wR2
0.0447, 0.0891
0.0446, 0.0951 0.0879, 0.1855
0.0320, 0.0851 0.0688, 0.2079
0.0430, 0.1171
0.0391, 0.1108
(I>2σ(I))
GOF on F2 0.980
0.997 1.017
1.037 1.008
1.003
1.066
148.9 (C4 and C6), 138.9 (C5), 137.0 (C3 and C7), 50.3 (Me2CHN),
22.9 (Me2CHN), 8.5 (AlCH2CH3), 2.2 (AlCH2CH3). The C1 and C2
resonance was not observed.
and the resulting solid was collected by filtration, washed with MeOH
and acetone, and dried under vacuum for 5 h affording 58 mg of
polyethylene. Activity: 908 g PE/mol‚h‚atm.
Reaction of [(iPr2-ATI)AliBu][B(C6F5)4] with Ethylene. An NMR
tube was charged with [(iPr2-ATI)AliBu][B(C6F5)4] (52 mg, 54 µmol),
and C6D5Cl (ca. 0.5 mL) and ethylene (ca. 160 µmol) were added by
vacuum transfer at -196 °C. The tube was sealed and warmed to 25
°C. NMR spectra taken immediately contained signals corresponding
to [(iPr2-ATI)AliBu][B(C6F5)4] and [(iPr2-ATI)AlEt][B(C6F5)4] as well
as C2H4. After 12 h at 25 °C, a colorless precipitate had formed, and
NMR spectra contained only signals corresponding to [(iPr2-ATI)AlEt]-
[B(C6F5)4] as well as C2H4, polyethylene, and polyisobutylene. In a
similar experiment, the reaction of [(iPr2-ATI)AliBu][B(C6F5)4] and
ethylene-d4 resulted in complete conversion to [(iPr2-ATI)AlCD2CD2H]-
[B(C6F5)4] after 8 h at 25 °C. Data for [(iPr2-ATI)AlCD2CD2H]-
Ethylene polymerization by (iPr2-ATI)AlEt2 (15 mg, 52 µmol) and
[Ph3C][B(C6F5)4] (48 mg, 52 µmol) was performed using the same
procedure. Yield of polyethylene: 136 mg. Activity: 2615 g PE/mol‚
h‚atm.
X-ray Crystallography. The structures of 2b and 3 were determined
by V. G. Young, Jr. (University of Minnesota) and the structures of
4c, 8c, 10, 13, and 15 were determined by I. A. Guzei (Iowa State
University). X-ray data are summarized in Table 3. Full details of the
crystallographic analyses of 2b, 10, and 13 can be found in Supporting
Information of the preliminary communications.22 Full details of the
analyses for 3, 4c, 8c, and 15 are given in the Supporting Information.
Thermal ellipsoids in Figures 1-7 are drawn at the 30% probability
level.
3
[B(C6F5)4]: 1H NMR (C6D5Cl) δ 7.16 (t, JHH ) 10.5, 2H, H4 and
3
3
H6), 6.78 (t, JHH ) 10, 1H, H5), 6.74 (d, JHH ) 11, 2H, H3 and
H7), 3.51 (sept, 3JHH ) 6.5, 2H, Me2CHN), 1.09 (d, 3JHH ) 6.5, 12H,
Me2CHN); the AlCD2CD2H resonance was obscured by polyisobu-
tylene signals. 13C{H} NMR (C6D5Cl) δ 159.9 (s, C1 and C2), 139.0
(C4 and C6), 128.7 (C5), 119.7 (C3 and C7), 47.3 (Me2CHN), 22.8
Acknowledgment. This work was supported by Eastman
Chemical Company and DOE grant DE-FG02-00ER15036.
1
(Me2CHN), 6.9 (quint, JCD ) 20, AlCD2CD2H); the AlCD2CD2H
Supporting Information Available: Additional experimen-
tal details and characterization data for new compounds and
crystal data, data collection, solution and refinement details,
tables of atomic coordinates, isotropic displacement parameters,
anisotropic displacement parameters, and bond distances and
bond angles for 3, 4c, 8c, and 15 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
resonance was not observed.
Ethylene Polymerization at 1 atm. Toluene (ca. 15 mL) was added
to a mixture of (iPr2-ATI)AliBu2 (22 mg, 64 µmol) and [Ph3C][B(C6F5)4]
(66 mg, 72 µmol) in a round-bottom flask by a pipet in a glovebox.
The flask was moved to a high vacuum line, the mixture was stirred at
23 °C for 30 min, and phase separation occurred. The mixture was
degassed three times by the freeze/pump/thaw method. The mixture
was heated to 80 °C, 1 atm of ethylene was introduced, and the reaction
mixture was stirred for 1 h at 80 °C. MeOH was added to the mixture
JA010242E