Synthesis, characterization, and reactivity of aluminum alkyl/amide complexes supported by guanidinate and monoanionic OCO-pincer ligands

Article abstract of DOI:10.1021/om100278b

The synthesis and characterization of mixed alkyl/amide Al complexes supported by guanidinate and monoanionic OCO-pincer ligands are described. In situ generation of the lithium-guanidinate reagents via reaction of carbodiimides and lithium-amide reagents, followed by reaction with the corresponding AlMe_xCl_3-x reagents, resulted in the formation of compounds 1-3. Subsequent reaction with lithium arylamide reagents provided access to mixed alkyl/amide-and bis-amide-substituted complexes 4-6, which were characterized by multinuclear NMR spectroscopy and elemental analysis. Single-crystal X-ray diffraction of compounds 5a and 6a confirmed the monomeric nature of these complexes and revealed the influence of the alkyl/amide functionalities on the bonding of the guanidinate ligands. A similar synthetic approach resulted in isolation of an OCO-pincer-supported Al dialkyl complex, which was also fully characterized. In contrast to the guanidinate compounds, complex 8 showed activity toward intramolecular hydroamination of 2,2-diphenylpent-4-en-1-amine.

Full text of DOI:10.1021/om100278b

3350 Organometallics 2010, 29, 3350–3356
DOI: 10.1021/om100278b
Synthesis, Characterization, and Reactivity of Aluminum
Alkyl/Amide Complexes Supported by Guanidinate and Monoanionic
OCO-Pincer Ligands
€
Jurgen Koller and Robert G. Bergman*
Department of Chemistry, University of California, Berkeley, California 94720
Received April 7, 2010
The synthesis and characterization of mixed alkyl/amide Al complexes supported by guanidinate
and monoanionic OCO-pincer ligands are described. In situ generation of the lithium-guanidinate
reagents via reaction of carbodiimides and lithium-amide reagents, followed by reaction with the
corresponding AlMexCl3-x reagents, resulted in the formation of compounds 1-3. Subsequent
reaction with lithium arylamide reagents provided access to mixed alkyl/amide- and bis-amide-
substituted complexes 4-6, which were characterized by multinuclear NMR spectroscopy and
elemental analysis. Single-crystal X-ray diffraction of compounds 5a and 6a confirmed the
monomeric nature of these complexes and revealed the influence of the alkyl/amide functionalities
on the bonding of the guanidinate ligands. A similar synthetic approach resulted in isolation of an
OCO-pincer-supported Al dialkyl complex, which was also fully characterized. In contrast to the
guanidinate compounds, complex 8 showed activity toward intramolecular hydroamination of 2,2-
diphenylpent-4-en-1-amine.
Introduction
(e.g., atom size, electronegativity), well-characterized main
group 13 metal imides are scarce in the literature.7,8
Alkyl- and amide-substituted transition metals show re-
markably rich chemistry, ranging from traditional organo-
metallic catalysis to more exotic applications such as
precursors for materials chemistry.1 Main group metals have
shown interesting behavior themselves and thus received a
comparable amount of attention. Not only can these ligands
act as active sites on their own, but careful arrangement of
these functional groups allows entry into imide chemistry via
R-hydrogen elimination, a reaction pathway mainly ob-
served for transition metals (eq 1).2-6 Extensive applications
of these complexes in organic transformations such as
hydroamination catalysis have made metal imides desirable
targets for organometallic chemists. Despite obvious simila-
rities of main group metals with early transition metals
Although the alkyl/amide functionalities have a significant
influence on the reactivity of the metal complex, the support-
ing ligands play an equally crucial role by providing the
appropriate steric protection and electronic support for the
metal center. Guanidinate anions have been used extensively
in organometallic chemistry since their first appearance as
supporting ligands for Zr-amide complexes in 1970 by
Lappert et al.9 Besides their similarity to the widely used
cyclopentadienyl (Cp) ligand, the relative ease of steric and
electronic tunability via variation of the N-substitution
makes these molecules interesting targets for a variety of
applications.10-15 As a result, coordination chemistry invol-
ving transition, f-block, and main group metals enjoys
extensive presence in the literature.16-20 Starting in the late
1990s, guanidinate ligands coordinated to group 13 metals
*Corresponding author. Tel: þ1-510-642-2156. Fax: þ1-510-642-
7714. E-mail: rbergman@berkeley.edu.
(1) Lappert, M. F.; Protchenko, A. V.; Power, P. P.; Seeber, A. L.
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pubs.acs.org/Organometallics
Published on Web 07/14/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 15, 2010 3351
Scheme 1. Synthesis of Compounds 1-6
have received increased attention.21-23 Similarly, pincer
ligands are represented equally well due to their robust
nature when coordinated to transition metals.24,25 Extremely
large catalytic turnover numbers and facile tunability of
steric and electronic influences of the ligand on the metal
center have made these ligands desirable especially in late
transition metal catalysis.26-28 Recent reports of pincer
ligands coordinated to group 4 and 13 metals have tempted
us to consider these compounds as viable ligands for Al
chemistry.29-31 Herein we would like to present our attempts
to mimic the behavior of transition metal complexes such as
[Cp*Zr(NHAr)(R)] and [Cp*Zr(NHAr)2] in hydroamina-
tion catalysis with cheap and easily prepared group 13 metal
complexes supported by a variety of guanidinate and mono-
anionic OCO-pincer ligands.
Results and Discussion
Synthesis of Aluminum Guanidinate Complexes. The gua-
nidinate ligands were prepared via reaction of lithium-amide
reagents with carbodiimides at -78 °C as described in the
literature.12,32,33 The resulting Li salts were not isolated but
rather reacted in situ with the appropriate aluminum reagents
(AlMexCl3-x) in ethereal solutions at -78 °C (Scheme 1).
Following the completion of the salt metathesis reactions by
warming the solutions to room temperature and stirring
overnight, compounds 1a-3b were isolated as colorless
crystalline solids after recrystallization from concentrated
toluene, diethyl ether, or pentane solutions at -35 °C
1
depending on their respective solubility characteristics. H
and 13C NMR spectra of compounds 1a-3b show the
equivalence of the substituents on the guanidinate ligands
and the equivalence of the alkyl functionalities in complexes
1a and 1b, thus suggesting monomeric Al species. The
observed 13C NMR resonances in the range 166.23-173.82
ppm are diagnostic for the central guanidinate C atom and
further corroborate the structural assignment.
(19) Dagorne, S.; Guzei, T. A.; Coles, M. P.; Jordan, R. F. J. Am.
Chem. Soc. 2000, 122, 274–289.
(20) Duchateau, R.; Wee, C. T.; Teuben, J. H. Organometallics 1996,
15, 2291–2302.
(21) Chang, C. C.; Hsiung, C. S.; Su, H. L.; Srinivas, B.; Chiang,
M. Y.; Lee, G. H.; Wang, Y. Organometallics 1998, 17, 1595–1601.
(22) Jones, C.; Junk, P. C.; Platts, J. A.; Stascht, A. J. Am. Chem. Soc.
2006, 128, 2206–2207.
(23) Aeilts, S. L.; Coles, M. P.; Swenson, D. G.; Jordan, R. F.; Young,
V. G. Organometallics 1998, 17, 3265–3270.
(24) Moulton, C. J.; Shaw, B. L. J. Chem. Soc., Dalton Trans. 1976,
1020–1024.
(25) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759–
1792.
(26) Slagt, M. Q.; van Zwieten, D. A. P.; Moerkerk, A.; Gebbink, R.;
van Koten, G. Coord. Chem. Rev. 2004, 248, 2275–2282.
(27) Ohff, M.; Ohff, A.; Van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1998, 120, 3273–3273.
(28) Zhu, K. M.; Achord, P. D.; Zhang, X. W.; Krogh-Jespersen, K.;
Goldman, A. S. J. Am. Chem. Soc. 2004, 126, 13044–13053.
(29) Sarkar, S.; McGowan, K. P.; Culver, J. A.; Carlson, A. R.;
Koller, J.; Peloquin, A. J.; Veige, M. K.; Abboud, K. A.; Veige, A. S.
Inorg. Chem. 2010, 49, 5143–5156.
Roesky and co-workers previously reported that Al di-
alkyl complexes supported by diketiminate ligands can under-
go substitution with I2 under mild conditions to form the
corresponding dihalide species.34 The Al guanidinate com-
plex 1b shows similar reactivity under equally mild condi-
tions. Upon stirring a toluene solution of 1b at room
temperature in the presence of I2 for two days, the bis-iodo
complex 4a was isolated as a yellow crystalline solid. The
mixed alkyl/amide complexes 5a and 5b were prepared as
crystalline solids via reaction of compounds 2a and 2c with
lithium arylamides at ambient temperature followed by
(32) Wilder, C. B.; Reitfort, L. L.; Abboud, K. A.; McElwee-White,
L. Inorg. Chem. 2006, 45, 263–268.
(33) Duncan, A. P.; Mullins, S. M.; Arnold, J.; Bergman, R. G.
(30) Koller, J.; Sarkar, S.; Abboud, K. A.; Veige, A. S. Organome-
tallics 2007, 26, 5438–5441.
(31) Dostal, L.; Jambor, R.; Ruzicka, A.; Holecek, J. Main Group
Met. Chem. 2008, 31, 185–188.
Organometallics 2001, 20, 1808–1819.
(34) Cui, C. M.; Roesky, H. W.; Schmidt, H. G.; Noltemeyer, M.;
Hao, H. J.; Cimpoesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274–4276.

3352 Organometallics, Vol. 29, No. 15, 2010
Koller and Bergman
Scheme 2. Synthesis of Compound 8
recrystallization from pentane at -35 °C. Similarly, the bis-
amide compounds were prepared by reaction of two equiva-
lents of lithium arylamide with the dichloro-substituted
complexes 3a and 3b at room temperature. Once again,
recrystallization from pentane at -35 °C resulted in the
isolation of 6a and 6b as colorless crystalline solids.
Synthesis of Aluminum Pincer Complexes. Synthesis of the
pincer ligand precursor was achieved by refluxing a mixture
of 2,6-bis(bromomethyl)bromobenzene and 3,5-di-tert-bu-
tylphenol in the presence of anhydrous potassium carbonate
(Scheme 2). After workup and crystallization from hexanes,
the ligand 7 (2,6-bis(3,5-tBu-phenoxymethyl)bromobenzene)
was isolated on a 10 g scale in 61% yield as a microcrystalline
colorless solid. Similar to the synthesis of the Al guanidinate
complexes, the lithiated ligand was not isolated but generated
in situ via activation of the Caryl-Br bond with nBuLi followed
by salt metathesis with AlClMe2 in noncoordinating solvents.
Compound 8 was isolated as a white microcrystalline solid in
1
good yield. The H and 13C NMR spectra (at 25 °C) both
display single resonances for the tBu substituents as well as the
Al-bound alkyl groups, suggesting a highly symmetric coordi-
nation environment around the Al metal center.
Solid-State Structures of Compounds 5a and 6a. To confirm
the monomeric nature of the synthesized complexes, single
crystals of compounds 5a and 6a were grown and their
structure was determined via X-ray crystallography. Crystal
data and structure refinement for these complexes can be
found in Table S1 (Supporting Information). Unsurpris-
ingly, the structural features of 5a and 6a are similar to those
of previously reported Al complexes supported by guanidi-
nate and closely related amidinate ligands.23,35 Compound
5a adopts a distorted tetrahedral coordination sphere, as
shown in the ORTEP representation of 5a (Figure 1).
Selected bond lengths and angles for 5a can be found in
Table 1. The sterically demanding bis-trimethylsilyl substi-
tution around N3 of the guanidinate backbone causes the
amide functionality to adopt a position almost perpendicular
to the metal-ligand plane (torsion angle 76.6°). This twist
limits the electron overlap of the N3-based lone pair with the
remaining guanidinate ligand, as evidenced by a compara-
Figure 1. Thermal ellipsoid diagram of the molecular structure
of 5a. Thermal ellipsoids are drawn at 50% probability. H atoms
(except H4) are omitted for clarity.
˚
Table 1. Selected Bond Distances (A) and Angles (deg) for
Compound 5a
Al1-N1
Al1-N2
C1-N1
C1-N2
C1-N3
Al1-C20
1.9296(16)
1.9172(16)
1.336(2)
1.345(2)
1.402(2)
1.949(2)
N1-Al1-N2
N1-C1-N2
N1-C1-N3
N2-C1-N3
C20-Al1-N4
69.60(7)
109.91(16)
125.55(16)
124.54(16)
117.61(9)
demand of the 2,6-di-isopropylphenyl substituent on the
metal-bound amide moiety slightly distorts the tetrahedral
coordination environment around Al toward a square-pla-
nar arrangement. Consequently, the larger trans influence of
the amide ligand is reflected in the elongated Al1-N1 bond
˚
(1.9296(16) A) compared to the Al1-N2 bond (1.9172(16)
˚
tively long N3-C1 bond (1.402(2) A). The Al1-C20 bond
length (1.949(2) A) of the Al-bound methyl moiety is within
˚
A). The noticeably different C1-N1 and C1-N2 bond
distances (1.336(2) and 1.345(2) A, respectively) further
˚
˚
the expected range for Al alkyl complexes.36,37 The steric
corroborate this finding and suggest a more amide-like
character of the Al1-N2 bond compared to the more
amine-like Al1-N1 bond.
Some of the structural features discussed for compound 5a
are also evident in the solid-state structure of 6a, as depicted
in its ORTEP drawing (Figure 2). Selected bond lengths and
(35) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1997, 16, 5183–5194.
(36) Gao, A.; Mu, Y.; Zhang, J.; Yao, W. Eur. J. Inorg. Chem. 2009,
3613–3621.
(37) Jin, C.; Wang, Z.-X. New J. Chem. 2009, 33, 659–667.

Article
Organometallics, Vol. 29, No. 15, 2010 3353
Scheme 3. Reaction of Compound 1a with 2,6-Diisopropylaniline
Scheme 4. Attempted Intramolecular Hydroamination Reactions
Figure 2. Thermal ellipsoid diagram of the molecular structure
of 6a. Thermal ellipsoids are drawn at 50% probability. H atoms
(except H4 and H5) are omitted for clarity.
Scheme 5. Catalytic Intramolecular Hydroamination of 2,2-Di-
phenylpent-4-en-1-amine with 8
˚
Table 2. Selected Bond Distances (A) and Angles (deg) for
Compound 6a
Al1-N1
Al1-N2
Al1-N4
Al1-N5
N1-C1
N2-C1
N3-C1
1.8960(13)
1.9258(13)
1.8119(14)
1.8022(14)
1.336(2)
N4-Al1-N5
N1-Al1-N2
N1-C1-N2
N1-C1-N3
N2-C1-N3
123.71(7)
69.75(5)
109.38(13)
125.07(14)
125.54(14)
1.342(2)
1.4103(19)
complexes show significantly different behavior compared to
their transition metal analogues.
angles can be found in Table 2. Although the bis-amide
substitution might suggest a highly symmetric molecule, the
steric bulk of the two 2,6-di-isopropylphenyl substituents
considerably distorts the tetrahedral coordination environ-
ment around Al and renders the two amide functionalities
inequivalent. The larger trans influence of the amide moiety
bound through N5, caused by the shorter Al1-N5 bond
(1.8022(14) A) compared to Al1-N4 (1.8119(14) A), is
reflected in the significantly different Al1-N1 and Al1-N2
bond distances (1.8960(13) and 1.9258(13) A, respectively).
The differences in C1-N1 and C1-N2 bond lengths
(1.336(2) and 1.342(2) A, respectively) further substantiate
this finding. Once again, the sterically demanding trimethyl-
silyl substituents bound to N3 force a perpendicular arrange-
ment of the ligand backbone (torsion angle 88.6°), allowing
little electron delocalization, as evidenced by the relatively
Despite the absence of an isolable guanidinate-supported
Al imide species, we were encouraged by the reactivity of the
Al guanidinate complexes with primary amines. Heating
solutions of 2,2-diphenylpent-4-en-1-amine (150 °C in
C6D6) in the presence of catalytic amounts (10 mol %) of
compounds 1, 5, and 6, however, did not result in the
formation of intramolecular hydroamination products, an
observation that further corroborates the stability of these
four-coordinate Al guanidinate complexes (Scheme 4). On
the basis of recent reports of intramolecular hydroamination
of aminoalkenes catalyzed by cationic aminotroponiminate-
supported Zn complexes,38 we attempted the reaction in the
presence of [Ph3C][B(C6F5)4] as a methyl-abstracting reagent
in an effort to generate a cationic Al species in situ. Upon
heating solutions of 2,2-diphenylpent-4-en-1-amine, 1b, and
[Ph3C][B(C6F5)4] (10 mol % each) at 135 °C, complete
isomerization of the terminal olefin to the internal position
was observed accompanied by the absence of any observable
hydroamination products.
˚
˚
˚
˚
˚
long C1-N3 bond (1.4103(19) A).
Reactivity of Aluminum Complexes. To establish the re-
activity of these Al compounds with primary amines, 1a was
treated with 2,6-di-isopropylphenylaniline. As expected, the
mixed alkyl/amide complex 5a is formed via the elimination
of methane gas (Scheme 3). Surprisingly, however, the reac-
tion requires high temperatures (135 °C in C6D6) and
extended heating times (two weeks) to reach quantitative
In an attempt to disrupt the preferred tetrahedral coordi-
nation sphere of Al and possibly force increased reactivity,
complex 8, bearing a tridentate monoanionic OCO-pincer
ligand, was subjected to similar conditions to evaluate its
reactivity toward aminoalkenes. Upon heating a solution of
1
conversion, as determined by H NMR spectroscopy (see
Supporting Information). All attempts to generate an imido
species via the elimination of a second equivalent of methane
have been unsuccessful thus far, suggesting that these Al
(38) Loehnwitz, K.; Molski, M. J.; Luehl, A.; Roesky, P. W.;
Dochnahl, M.; Blechert, S. Eur. J. Inorg. Chem. 2009, 1369–1375.

3354 Organometallics, Vol. 29, No. 15, 2010
Koller and Bergman
2,2-diphenylpent-4-en-1-amine (in C6D6) in the presence of
catalytic amounts of complex 8 (10 mol %), formation of the
cyclized hydroamination product (2-methyl-4,4-diphenyl-
pyrrolidine) was observed (Scheme 5). However, high con-
version of the aminoalkene to the corresponding hydroami-
nation product was only observed after extended reaction
times (∼100 h) at relatively high temperature (150 °C), as
determined by integration of the reactant/product 1H NMR
signals against 1,3,5-trimethoxybenzene as an internal stan-
dard (see Supporting Information, Figure S1). For this
reason, hydroamination chemistry using this catalyst system
was not pursued any further.
prepared according to published literature procedures and dis-
tilled from CaH2 prior to use.40
Crystallographic Analysis. Single crystals of 5a and 6a were
coated in Paratone-N oil, mounted on a Kaptan loop, trans-
ferred to a Bruker APEX CCD area detector, centered in the
beam, and cooled by a nitrogen flow low-temperature apparatus
that was previously calibrated by a thermocouple placed at the
same position as the crystal. Preliminary orientation matrixes
and cell constants were determined by collection of 60 10 s
frames, followed by spot integration and least-squares refine-
ment. An arbitrary hemisphere of data was collected, and the
raw data were integrated using SAINT. Cell dimensions re-
ported were calculated from all reflections with I > 10σ. The
data were corrected for Lorentz and polarization effects, but no
correction for crystal decay was applied. Data were analyzed for
agreement and possible absorption using XPREP. An empirical
absorption correction based on S3 comparison of redundant
and equivalent reflections was applied using SADABS. The
structures were solved using SHELXS and refined on all data by
full-matrix least-squares with SHELXL-97.41 Thermal para-
meters for all non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were calculated in ideal positions and were
riding on their respective carbon atoms. Nitrogen-bound H
atoms were located on the electron density map and fully
refined. For compound 5a, a total of 356 parameters were
refined in the final cycle of refinement using 5279 reflections
with I > 2σ(I) to yield R1 and wR2 of 4.16% and 10.07%,
respectively. For compound 6a, a total of 468 parameters were
refined in the final cycle of refinement using 9033 reflections
with I > 2σ(I) to yield R1 and wR2 of 3.48% and 8.21%,
respectively. Refinement was done using F2. ORTEP diagrams
were created using the ORTEP-3 software package and ren-
dered using Pov-Ray 3.6.
Conclusions
In conclusion, we have prepared and fully characterized a
series of mixed alkyl/amide Al complexes (1-6) supported
by guanidinate ligands. X-ray crystallographic characteriza-
tion of compounds 5a and 6a allowed comparison of the
structural features of these Al guanidinate complexes with
varying alkyl/amide substitution. The reactivity of these
complexes was determined to be comparable to that of other
Al compounds; however, significantly different behavior
with regard to their transition metal analogues was observed
most likely due to the high stability of four-coordinate
Al(III) complexes. Although catalytic hydroamination reac-
tions involving compounds 1-6 were unsuccessful, controlled
variation of the coordination sphere around Al via the intro-
duction of a monoanionic OCO-pincer ligand (compound 8)
resulted in increased activity toward the intramolecular hydro-
amination of 2,2-diphenylpent-4-en-1-amine.
[CyNC(N(SiMe3)2)NCy]AlMe2 (1a). A slurry of LiN(SiMe3)2
(1.51 g, 9.00 mmol) in Et2O (25 mL) was cooled to -78 °C, and a
solution of N,N0-dicyclohexylcarbodiimide (1.86 g, 9.00 mmol)
in Et2O (15 mL) was added dropwise. The resulting mixture was
allowed to warm to room temperature and stirred for 1 h. The
resulting suspension was cooled to -78 °C, and AlClMe2 (10 mL,
0.9 M solution in heptane, 9.00 mmol) was added dropwise. The
resulting mixture was allowed to warm to room temperature and
stirred for 18 h. All volatiles were removed in vacuo, and the
product was extracted with pentane (2 ꢀ 10 mL). The combined
extracts were filtered and cooled to -35 °C to yield pure 1a as
colorless crystals, which were isolated by filtration. Yield: 1.11 g
(29%, 2.62 mmol). 1H NMR (benzene-d6): δ 3.18 (m, 2H, NCH),
1.79 (m, 4H, CH2), 1.65 (m, 4H, CH2), 1.46 (m, 2H, CH2), 1.23 (m,
8H, CH2), 1.05 (m, 2H, CH2), 0.18 (s, 18H, Si(CH3)3), -0.19 (s,
6H, AlCH3). 13C NMR (benzene-d6): δ 166.23 (s, N3C), 52.68 (s,
NCH), 36.95 (s, CH2), 26.16 (s, CH2), 26.13 (s, CH2), 2.36 (s,
Si(CH3)3), -8.89 (s, AlCH3). Anal. Calcd for C21H46N3AlSi2: C,
59.52; H, 10.94; N, 9.92. Found: C, 59.58; H, 11.07; N, 10.08.
[CyNC(N(iPr)2)NCy]AlMe2 (1b). This compound was pre-
pared by the procedure outlined for 1a, using 0.96 g of LiN(iPr)2
(9.00 mmol), 1.86 g of N,N0-dicyclohexylcarbodiimide (9.00
mmol), and 10 mL of AlClMe2 (0.9 M solution in heptane,
9.00 mmol). The product was isolated as colorless crystals.
Yield: 1.84 g (56%, 5.06 mmol). 1H NMR (benzene-d6): δ 3.25
(sept, 2H, NCH(CH3)2), 3.18 (m, 2H, NCH), 1.81 (m, 4H, CH2),
1.67 (m, 4H, CH2), 1.49 (m, 2H, CH2), 1.34-1.15 (m, 8H, CH2),
Experimental Section
General Procedures. Unless otherwise noted, all reactions and
manipulations were performed in an inert atmosphere (N2)
glovebox or using standard Schlenk and high-vacuum-line
techniques. Glassware was dried overnight at 150 °C before
use. 1H and 13C NMR spectra were recorded at room tempera-
ture (except where noted) on Bruker AV 300 MHz, AVQ 400
MHz, or DRX 500 MHz spectrometers using residual protons
of deuterated solvents for reference. Elemental analyses were
performed at the University of California, Berkeley, Microana-
lytical Facility, on a Perkin-Elmer 2400 Series II CHNO/S
analyzer. X-ray structural determinations were performed at
CHEXRAY, University of California, Berkeley. Sealed NMR
tubes were prepared by attaching the NMR tube directly to a
Kontes high-vacuum stopcock via a Cajon Ultra-Torr reducing
union followed by flame-sealing on a vacuum line. Reaction
yields were not systematically optimized.
Materials. Unless otherwise noted, reagents were purchased
from commercial suppliers and used without further purification.
Pentane, diethyl ether, and toluene were purified by passing
through a column of activated alumina (type A2, size 12-32,
Purifry Co.) under nitrogen pressure and sparged with N2 prior to
use. Deuterated solvents (Cambridge Isotope Laboratories) were
degassed by three freeze-pump-thaw cycles and stored over
1.07 (m, 2H, CH2), 1.02 (d, 12H, J = 6.6 Hz, NCH(CH3)2). 13
C
˚
activated 3 A molecular sieves. 2,6-Diisopropylaniline was dis-
˚
tilled from sodium and stored over activated 3 A molecular sieves.
2,6-Bis(bromomethyl)bromobenzene was prepared according
to literature procedures.39 2,2-Diphenylpent-4-en-1-amine was
NMR (benzene-d6): δ 168.05 (s, N3C), 53.57 (s, NCH), 49.09 (s,
CH(CH3)2), 36.83 (s, CH2), 26.35 (s, CH2), 26.31 (s, CH2), 23.34
(s, CH(CH3)2), -8.51 (s, AlCH3). Anal. Calcd for C21H42N3Al:
C, 69.38; H, 11.64; N, 11.56. Found: C, 69.58; H, 11.85; N, 11.81.
[CyNC(N(SiMe3)2)NCy]AlMeCl (2a). A slurry of LiN-
(SiMe3)2 (1.26 g, 7.50 mmol) in Et2O (25 mL) was cooled
to -78 °C, and a solution of N,N0-dicyclohexylcarbodiimide
ꢀ
(39) Bibal, C.; Mazieres, S.; Gornitzka, H.; Couret, C. Polyhedron
2002, 21, 2827–2834.
(40) Crimmin, M. R.; Arrowsmith, M.; Barrett, A. G. M.; Casely,
I. J.; Hill, M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 9670–
9685.
(41) SHELXTL6; Bruker-AXS: Madison, WI, 2000.

Article
Organometallics, Vol. 29, No. 15, 2010 3355
(1.55 g, 7.50 mmol) in Et2O (15 mL) was added dropwise. The
resulting mixture was allowed to warm to room temperature and
stirred for 1 h. The resulting suspension was cooled to -78 °C,
and AlMeCl2 (7.5 mL, 1.0 M solution in hexanes, 7.50 mmol)
was added dropwise. The resulting mixture was allowed to warm
to room temperature and stirred for 18 h. All volatiles were
removed in vacuo, and the solid was extracted with diethyl ether
(2 ꢀ 10 mL). The combined extracts were filtered and cooled to
-35 °C to yield pure 2a as colorless crystals, which were isolated
by filtration. Yield: 1.78 g (54%, 4.01 mmol). 1H NMR
(benzene-d6): δ 3.14 (m, 2H, NCH), 1.87 (m, 2H, CH2), 1.71-
1.58 (m, 6H, CH2), 1.49 (m, 4H, CH2), 1.25-1.08 (m, 6H, CH2),
1.01 (m, 2H, CH2), 0.19 (s, 9H, Si(CH3)3), 0.12 (s, 9H, Si(CH3)3),
-0.06 (s, 3H, AlCH3). 13C NMR (benzene-d6): δ 169.93
(s, N3C), 52.62 (s, NCH), 36.75 (s, CH2), 36.39 (s, CH2), 26.01
(s, CH2), 25.95 (s, CH2), 25.92 (s, CH2), 2.36 (s, Si(CH3)3), 2.21
(s, Si(CH3)3), -9.27 (s, AlCH3). Anal. Calcd for C20H43N3-
AlSi2Cl: C, 54.08; H, 9.76; N, 9.46. Found: C, 54.32; H, 9.65;
N, 9.52.
C19H40N3AlSi2Cl2: C, 49.12; H, 8.68; N, 9.04. Found: C, 49.17;
H, 8.71; N, 8.92.
[CyNC(N(iPr)2)NCy]AlCl2 (3b). This compound was pre-
pared by the procedure outlined for 3a, using 0.80 g of LiN(iPr)2
(7.50 mmol), 1.55 g of N,N0-dicyclohexylcarbodiimide (7.50
mmol), and 1.00 g of AlCl3 (7.50 mmol). The product was
isolated as colorless crystals. Yield: 0.65 g (22%, 1.61 mmol).
1H NMR (benzene-d6): δ 3.34 (sept, 2H, NCH(CH3)2), 3.03 (m,
2H, NCH), 1.85 (m, 4H, CH2), 1.61 (m, 4H, CH2), 1.51-1.40
(m, 6H, CH2), 1.12-0.98 (m, 6H, CH2), 0.93 (d, 12H, J = 6.8
Hz, NCH(CH3)2). 13C NMR (benzene-d6): δ 172.65 (s, N3C),
52.27 (s, NCH), 50.55 (s, CH(CH3)2), 35.99 (s, CH2), 26.22 (s,
CH2), 25.85 (s, CH2), 23.33 (s, CH(CH3)2). Anal. Calcd for
C19H36N3AlCl2: C, 56.43; H, 8.97; N, 10.39. Found: C, 56.81; H,
9.17; N, 10.39.
[CyNC(N(iPr)2)NCy]AlI2 (4a). A Schlenk flask was charged
with I2 (1.40 g, 5.50 mmol), and subsequently, a solution of
compound 1b (1.00 g, 2.75 mmol) in 15 mL of toluene was added
at room temperature. The mixture was stirred for 48 h at room
temperature, during which time a color change from deep purple
to yellow and the precipitation of a yellow solid was observed.
The precipitation was completed by cooling the suspension to
-20 °C for 24 h. The crude product was collected by filtration
and dried in vacuo. Recrystallization from toluene (10 mL)
afforded pure 4a as yellow needles. Yield: 0.46 g (0.78 mmol,
[CyNC(N(iPr)2)NCy]AlMeCl (2b). This compound was pre-
pared by the procedure outlined for 2a, using 0.80 g of LiN(iPr)2
(7.50 mmol), 1.55 g of N,N0-dicyclohexylcarbodiimide (1.55 g,
7.50 mmol), and AlClMe2 (7.50 mL, 1.0 M solution in hexane,
7.50 mmol). The product was isolated as colorless crystals.
Yield: 0.71 g (25%, 1.86 mmol). 1H NMR (benzene-d6): δ 3.29
(sept, 2H, NCH(CH3)2), 3.10 (m, 2H, NCH), 1.92 (m, 2H, CH2),
1.75-1.61 (m, 6H, CH2), 1.55-1.44 (m, 4H, CH2), 1.30-1.03
(m, 8H, CH2), 0.97 (d, 12H, J = 6.6 Hz, NCH(CH3)2). 13C
NMR (benzene-d6): δ 171.29 (s, N3C), 53.85 (s, NCH), 49.79 (s,
NCH(CH3)2), 36.59 (s, CH2), 36.21 (s, CH2), 26.32 (s, CH2),
26.25 (s, CH2), 26.07 (s, CH2), 23.35 (s, CH(CH3)2), -8.49 (s,
AlCH3). Anal. Calcd for C20H39N3AlCl: C, 62.56; H, 10.24; N,
10.94. Found: C, 62.74; H, 10.41; N, 10.68.
1
29%). H NMR (benzene-d6): δ 3.26 (sept, 2H, NCH(CH3)2),
3.18 (m, 2H, NCH), 1.91 (m, 4H, CH2), 1.67-1.60 (m, 8H,
CH2), 1.42 (m, 2H, CH2), 1.10-0.97 (m, 6H, CH2), 0.91 (d, 12H,
J = 6.7 Hz, NCH(CH3)2). 13C NMR (benzene-d6): δ 171.55 (s,
N3C), 54.71 (s, NCH), 50.30 (s, CH(CH3)2), 36.19 (s, CH2),
26.29 (s, CH2), 25.86 (s, CH2), 23.13 (s, CH(CH3)2). Anal. Calcd
for C19H36N3AlI2: C, 38.86; H, 6.18; N, 7.15. Found: C, 38.96;
H, 5.99; N, 6.77.
[(2,6-iPr2C6H3)NC(N(iPr)2)N(2,6-iPr2C6H3)]AlMeCl (2c).
This compound was prepared by the procedure outlined for
2a, using 0.54 g of LiN(iPr)2 (5.00 mmol), 1.81 g of N,N0-bis(2,6-
diisopropylphenyl)carbodiimide (5.00 mmol), and AlMeCl2
(5.00 mL, 1.0 M solution in hexanes, 5.00 mmol). The product
was isolated as colorless crystals. Yield: 0.98 g (36%, 1.81
[CyNC(N(SiMe3)2)NCy]AlMe[NH(2,6-iPr2C6H3)] (5a). Method
A. A 20 mL scintillation vial was charged with LiNH-
(2,6-iPr2C6H3) (206 mg, 1.13 mmol) and 10 mL of diethyl ether.
A solution of 2a (500 mg, 1.13 mmol) in 5 mL of diethyl ether was
added via pipet. The resulting mixture was stirred for 18 h at
ambient temperature. LiCl was filtered off and the solvent
removed in vacuo. The resulting solid was extracted with pentane
(2 ꢀ 4 mL). The combined extracts were filtered and subsequently
cooled to -35 °C to yield pure 5a as colorless crystals, which were
isolated by filtration. Yield: 468 mg. (71%, 0.80 mmol). 1H NMR
(benzene-d6): δ 7.25 (d, 2H, Ph), 7.03 (m, 1H, Ph), 3.56 (sept, 2H,
CH(CH3)2), 3.23 (bs, 1H, NH), 3.19 (m, 2H, NCH), 1.85 (m, 4H,
CH2), 1.68 (m, 4H, CH2), 1.52 (m, 4H, CH2), 1.44 (d, 12H, J =
6.8 Hz, CH(CH3)2), 1.37 (m, 2H, CH2), 1.14 (m, 8H, CH2), 0.21
(s, 9H, Si(CH3)3), 0.17 (s, 9H, Si(CH3)3), -0.26 (s, 2H, AlCH3).
13C NMR (benzene-d6): δ 169.05 (s, N3C), 146.46 (s, Ph), 137.28
(s, Ph), 123.62 (s, Ph), 118.77 (s, Ph), 53.01 (s, NCH), 36.97 (s,
CH2), 36.74 (s, CH2), 29.88 (s, CH(CH3)2), 26.45 (s, CH2), 26.33
(s, CH2), 26.30 (s, CH2), 24.43 (s, CH(CH3)2), 2.47 (s, Si(CH3)3),
2.34 (s, Si(CH3)3), -7.94 (s, AlCH3). Anal. Calcd for
C32H61N4AlSi2: C, 65.70; H, 10.51; N, 9.58. Found: C, 65.38;
H, 10.39; N, 9.27.
1
mmol). H NMR (benzene-d6): δ 7.11-7.03 (m, 6H, Ph), 3.99
(sept, 2H, NCH(CH3)2), 3.90 (sept, 2H, CH(CH3)2), 3.57 (sept,
2H, CH(CH3)2), 1.52 (d, 6H, J = 6.6 Hz, CH(CH3)2), 1.32 (d,
6H, J = 6.9 Hz, CH(CH3)2), 1.26 (d, 6H, J = 6.8 Hz, CH-
(CH3)2), 1.18 (d, 6H, J = 6.7 Hz, CH(CH3)2), 0.77 (d, 12H, J =
7.1 Hz, NCH(CH3)2), -0.03 (s, 3H, AlCH3). 13C NMR
(benzene-d6): δ 167.70 (s, N3C), 146.45 (s, Ph), 145.33 (s, Ph),
138.30 (s, Ph), 126.79 (s, Ph), 125.14 (s, Ph), 124.43 (s, Ph), 50.51
(s, NCH(CH3)2), 28.89 (s, CH(CH3)2), 28.86 (s, CH(CH3)2),
28.17 (s, CH(CH3)2), 27.28 (s, CH(CH3)2), 24.35 (s, CH(CH3)2),
24.02 (s, CH(CH3)2), 23.77 (s, NCH(CH3)2), -7.55 (s, AlCH3).
Anal. Calcd for C32H51N3AlCl: C, 71.15; H, 9.52; N, 7.78.
Found: C, 71.32; H, 9.33; N, 7.83.
[CyNC(N(SiMe3)2)NCy]AlCl2 (3a). A slurry of LiN(SiMe3)2
(1.26 g, 7.50 mmol) in Et2O (25 mL) was cooled to -78 °C, and a
solution of N,N0-dicyclohexylcarbodiimide (1.55 g, 7.50 mmol)
in Et2O (15 mL) was added dropwise. The resulting mixture was
allowed to warm to room temperature and stirred for 1 h. The
resulting suspension was cooled to -78 °C, and a solution of
AlCl3 (1.00 g, 7.50 mmol) in Et2O (15 mL) was added dropwise.
The resulting mixture was allowed to warm to room tempera-
ture and stirred for 18 h. The solution was filtered through a pad
of Celite, and all volatiles were removed in vacuo to yield the
crude product as an off-white solid. Pure 3a was obtained via
recrystallization from toluene (10 mL) at -35 °C as colorless
crystals, which were isolated by filtration. Yield: 0.54 g (16%,
1.16 mmol). 1H NMR (benzene-d6): δ 3.13 (m, 2H, NCH), 1.78
(m, 4H, CH2), 1.58 (m, 4H, CH2), 1.36 (m, 6H, CH2), 1.07 (m,
4H, CH2), 0.94 (m, 2H, CH2), 0.12 (s, 18H, Si(CH3)3). 13C NMR
(benzene-d6): δ 172.38 (s, N3C), 52.71 (s, NCH), 36.22 (s, CH2),
25.85 (s, CH2), 25.66 (s, CH2), 2.21 (s, Si(CH3)3). Anal. Calcd for
Method B. Compound 1a (10 mg, 0.024 mmol) and 2,6-di-
isopropylaniline (4.5 μL, 0.024 mmol) were dissolved in 1 mL of
C6D6 and charged into a J-Young NMR tube. The sealed tube
was subsequently heated at 135 °C for two weeks. Compound 5a
was formed in near-quantitative NMR yield. 1H NMR signals
were identical to those described in method A (Supporting
Information, Figure S2).
[(2,6-iPr2C6H3)NC(N(iPr)2)N(2,6-iPr2C6H3)]AlMe[NH-
(2,6-iPr2C6H3)] (5b). This compound was prepared by the
procedure outlined for 5a, using 85 mg of LiNH(2,6-iPr2C6H3)
(0.46 mmol) and 250 mg of 2c (0.46 mmol). The product was
isolated as colorless crystals. Yield: 155 mg (49%, 0.23 mmol).
1H NMR (benzene-d6): δ 7.13-7.09 (m, 8H, Ph), 6.97 (m, 1H,
Ph), 4.05 (sept, 2H, NCH(CH3)2), 3.73 (sept, 2H, CH(CH3)2),
3.68 (sept, 2H, NCH(CH3)2), 3.20 (sept, 2H, CH(CH3)2), 3.04

3356 Organometallics, Vol. 29, No. 15, 2010
Koller and Bergman
(bs, 1H, NH), 1.49 (d, 6H, J = 6.7 Hz, CH(CH3)2), 1.34 (d, 6H,
J = 6.9 Hz, CH(CH3)2), 1.32 (d, 6H, J = 6.7 Hz, CH(CH3)2),
1.27 (d, 6H, J = 6.8 Hz, CH(CH3)2), 1.12 (d, 12H, J = 6.7 Hz,
CH(CH3)2), 0.80 (d, 12H, J = 7.0 Hz, NCH(CH3)2), -0.20 (s,
3H, AlCH3). 13C NMR (benzene-d6): δ 167.68 (s, N3C), 145.48
(s, Ph), 145.34 (s, Ph), 145.17 (s, Ph), 139.87 (s, Ph), 139.42 (s,
Ph), 126.30 (s, Ph), 124.98 (s, Ph), 124.63 (s, Ph), 123.63 (s, Ph),
120.00 (s, Ph), 50.61 (s, NCH(CH3)2), 29.46 (s, CH(CH3)2),
29.20 (s, CH(CH3)2), 28.70 (s, CH(CH3)2), 27.43 (s, CH-
(CH3)2), 26.73 (s, CH(CH3)2), 24.61 (s, CH(CH3)2), 24.53 (s,
CH(CH3)2), 24.03 (s, NCH(CH3)2). Anal. Calcd for
C44H69N4Al: C, 77.60; H, 10.21; N, 8.23. Found: C, 77.31;
H, 10.03; N, 8.02. [Note: 13C NMR resonance for Al-CH3
could not be observed even after extended acquisition times.]
[CyNC(N(SiMe3)2)NCy]Al[NH(2,6-iPr2C6H3)]2 (6a). A 20 mL
scintillation vial was charged with LiNH(2,6-iPr2C6H3) (78.9 mg,
0.43 mmol) and 5 mL of diethyl ether. A solution of 3a (100 mg,
0.22 mmol) in 5 mL of diethyl ether was added via pipet. The
resulting mixture was stirredfor 18 hatambient temperature. LiCl
was filtered off and the solvent removed in vacuo. The resulting
solid was extracted with pentane (2 ꢀ 6 mL). The combined
extracts were filtered and subsequently cooled to -35 °C to yield
pure 6a as colorless crystals, which were isolated by filtration.
Yield: 159 mg (99%, 0.21 mmol). 1H NMR (benzene-d6): δ 7.15
(d, 4H, Ph), 6.95 (m, 2H, Ph), 3.49 (sept, 4H, CH(CH3)2), 3.34 (bs,
2H, NH), 3.19 (m, 2H, NCH), 1.85 (m, 4H, CH2), 1.66 (m, 4H,
CH2), 1.48 (m, 6H, CH2), 1.32 (d, 24H, J = 6.5 Hz, CH(CH3)2),
1.14 (m, 8H, CH2), 0.20 (s, 18H, Si(CH3)3). 13C NMR (benzene-
d6): δ 171.33 (s, N3C), 145.99 (s, Ph), 136.86 (s, Ph), 123.65 (s, Ph),
118.87 (s, Ph), 53.19 (s, NCH), 36.43 (s, CH2), 29.80 (s, CH-
(CH3)2), 26.39 (s, CH2), 26.04 (s, CH2), 24.48 (s, CH(CH3)2), 2.49
(s, Si(CH3)3). Anal. Calcd for C43H76N5AlSi2: C, 69.21; H, 10.27;
N, 9.38. Found: C, 69.06; H, 9.88; N, 9.55.
was heated at reflux for 22 h. The resulting suspension was
cooled to room temperature and then quenched with water (200
mL). The product was extracted with methylene chloride (2 ꢀ
100 mL), and the combined organic fractions were washed with
saturated NaHCO3 (200 mL) and brine (200 mL). The organic
phase was then dried over anhydrous MgSO4 and the solvent
removed in vacuo to yield the crude product as an off-white solid.
Pure 6 was obtained as a colorless microcrystalline solid, which
was isolated via filtration after recrystallization from hexane
(150 mL) at -20 °C. Reduction of the volume of the mother
liquor to 75 mL followed by crystallization at -20 °C yielded a
second crop of product. Combined yields: 10.3 g (17.4 mmol,
61%). 1H NMR (benzene-d6): δ 7.48 (d, 2H, Ph), 7.21 (m, 2H,
Ph), 7.06 (d, 4H, Ph), 6.99 (m, 1H, Ph), 5.13 (s, 4H, CH2), 1.30 (s,
36H, C(CH3)3). 13C NMR (benzene-d6): δ 159.44 (s, Ph), 152.90
(s, Ph), 138.14 (s, Ph), 129.12 (s, Ph), 123.18 (s, Ph), 115.91 (s,
Ph), 110.29 (s, Ph), 70.26 (s, CH2), 35.45 (s, C(CH3)3), 31.96 (s,
C(CH3)3). Anal. Calcd for C36H49BrO2: C, 72.83; H, 8.32.
Found: C, 72.64; H, 8.21.
{[(3,5-tBuC6H3)OCH2]2C6H3}AlMe2 (8). A Schlenk flask was
charged with a solution of 2,6-bis(3,5-tBu-phenoxymethyl)bro-
mobenzene (2.00 g, 3.37 mmol) in hexanes (40 mL). The solution
n
was cooled to 0 °C, and BuLi (2.10 mL, 3.37 mmol, 1.6 M
solution in hexanes) was added dropwise via syringe. The
solution was allowed to warm to room temperature and was
stirred for another 2 h. The solution was then recooled to 0 °C,
and AlClMe2 (3.74 mL, 3.37 mmol, 0.9 M solution in heptane)
was added dropwise via syringe. The solution was slowly
warmed to room temperature and stirred for another 18 h. LiCl
was filtered off, and the solvent was removed in vacuo to yield the
crude product as a white solid. Pure 8 was obtained as colorless
crystals via recrystallization from a mixture of toluene/pentane
1
(1:1, 10 mL) at -35 °C. Yield: 1.61 g (2.82 mmol, 84%). H
[CyNC(N(iPr)2)NCy]Al[NH(2,6-iPr2C6H3)]2 (6b). This com-
pound was prepared by the procedure outlined for 6a, using 100
mg of 3b (0.25 mmol) and 91 mg of LiNH(2,6-iPr2C6H3) (0.50
mmol). 6b was isolated as colorless crystals. Yield: 35 mg (22%,
0.051 mmol). 1H NMR (benzene-d6): δ 7.18 (d, 4H, Ph), 7.00 (m,
2H, Ph), 3.57 (sept, 4H, CH(CH3)2), 3.51 (sept, 2H, NCH-
(CH3)2), 3.04 (m, 2H, NCH), 2.92 (bs, 2H, NH), 1.78 (m, 4H,
CH2), 1.67 (m, 4H, CH2), 1.50 (m, 2H, CH2), 1.39 (m, 4H, CH2),
1.32 (d, 24H, J = 6.8 Hz, CH(CH3)2), 1.15-1.08 (m, 6H, CH2),
1.06 (d, 12H, J = 6.8 Hz, NCH(CH3)2). 13C NMR (benzene-d6):
δ 173.82 (s, N3C), 146.09 (s, Ph), 139.19 (s, Ph), 123.48 (s, Ph),
119.90 (s, Ph), 54.29 (s, NCH), 51.11 (s, NCH(CH3)2), 36.04 (s,
CH2), 29.26 (s, CH(CH3)2), 26.74 (s, CH2), 26.22 (s, CH2), 24.19
(s, CH(CH3)2), 23.96 (NCH(CH3)2). Anal. Calcd for
C43H72N5Al: C, 75.28; H, 10.58; N, 10.21. Found: C, 75.36;
H, 10.83; N, 10.50.
NMR (benzene-d6): δ 7.33 (s, 6H, Ph), 7.29 (m, 1H, Ph), 6.88 (m,
2H, Ph), 5.15 (s, 4H, CH2), 1.29 (s, 36H, C(CH3)3), 0.02 (s, 6H,
AlCH3). 13C NMR (benzene-d6): δ 157.07 (s, Ph), 153.19 (s, Ph),
143.99 (s, Ph), 127.77 (s, Ph), 121.32 (s, Ph), 118.51 (s, Ph),
114.06 (s, Ph), 77.62 (s, CH2), 35.55 (s, C(CH3)3), 31.88 (s,
C(CH3)3), -6.84 (s, AlCH3). Anal. Calcd for C38H55AlO2: C,
79.96; H, 9.71. Found: C, 79.63; H, 9.64.
Acknowledgment. This work was supported by the
Director, Officeof Science, Officeof Basic EnergySciences,
and the Division of Chemical Sciences, Geosciences, and
Biosciences of the U.S. Department of Energy at LBNL
under Contract DE-AC02-05CH11231.
Supporting Information Available: X-ray data are available as
crystallographic information files (CIF) for compounds 5a and
6a. H NMR data of NMR-scale reactions as pdf files. This
2,6-Bis(3,5-tBu-phenoxymethyl)bromobenzene (7). A mixture
of 2,6-bis(bromomethyl)bromobenzene (9.86 g, 28.8 mmol),
3,5-di-tert-butylphenol (12.8 g, 61.8 mmol), and anhydrous
potassium carbonate (9.94 g, 71.9 mmol) in acetone (100 mL)
1
material is available free of charge via the Internet at http://
pubs.acs.org.