Reactivity studies of a four-coordinate methyl chloro aluminium aminophenolate complex with B(C6F5)3

Article abstract of DOI:10.1016/j.jorganchem.2006.07.001

The X-ray characterized four-coordinate aminophenolate aluminium complex {6-(CH₂NMe₂)-2-CPh₃-4-Me-C₆H₂O}Al(Me)(Cl) (1), which is readily available by reaction of the corresponding aminophenolate Li salt with MeAlCl₂, slowly reacts with B(C₆F₅)₃ to yield a 1/1 mixture of the Al methyl cation {6-(CH₂NMe₂)-2-CPh₃-4-Me-C₆H₂O}Al(Me)(THF)⁺ (2, as MeB (C₆ F₅)₃^- salt) and the Al dichloro derivative {6-(CH₂NMe₂)-2-CPh₃-4-Me-C₆H₂O}AlCl₂ (3). This reaction most likely proceeds via a Me^- abstraction/ligand exchange sequence.

Full text of DOI:10.1016/j.jorganchem.2006.07.001

Journal of Organometallic Chemistry 691 (2006) 4797–4801
www.elsevier.com/locate/jorganchem
Note
Reactivity studies of a four-coordinate methyl chloro aluminium
aminophenolate complex with B(C6F5)3
*
Samuel Dagorne
Laboratoire DECOMET, Institut Le Bel, CNRS, Universite´ Louis Pasteur, 4, rue Blaise Pascal, 67000 Strasbourg, France
Received 15 June 2006; received in revised form 4 July 2006; accepted 5 July 2006
Available online 12 July 2006
Abstract
The X-ray characterized four-coordinate aminophenolate aluminium complex {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}Al(Me)(Cl) (1),
which is readily available by reaction of the corresponding aminophenolate Li salt with MeAlCl2, slowly reacts with B(C6F5)3 to yield a
1/1 mixture of the Al methyl cation {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}Al(Me)(THF)+ (2, as MeBðC6F5Þꢀ salt) and the Al dichloro
3
derivative {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlCl2 (3). This reaction most likely proceeds via a Meꢀ abstraction/ligand exchange
sequence.
ꢀ 2006 Elsevier B.V. All rights reserved.
Keywords: Aluminium; Cationic; Lewis acid; Aminophenolate
1. Introduction
In contrast with the numerous studies on the ionization
chemistry of {LX}AlR2 derivatives with B(C6F5)3, the
reactivity of {LX}Al(X)(R) derivatives (X ¼ alkyl) with
the latter borane has never been investigated although this
approach may, in principle, constitute a straightforward
way to access {LX}Al(X)(L)+ (via a Rꢀ abstraction reac-
tion) [6]. In this regard, we are interested in the synthesis
of Al chloro cations of the type {LX}Al(Cl)(L)+ via reac-
tion of {LX}Al(Cl)(R) derivatives with B(C6F5)3. Low-
coordinate Al chloro cationic species, nearly unknown to
date with the exception of studies by Bertrand et al. on
that matter [3], may be of interest as they could exhibit
an enhanced Lewis acidity vs. that of Al alkyls
{LX}Al(R)(L)+ and thus be of potential use in catalysis
[3b].
For our studies, the choice of a sterically bulky biden-
tate N,O-aminophenolate ligand seemed appropriate since
this class of LXꢀ ligand has been shown to be suitable for
the obtention of stable Al alkyls cations {LX}Al(R)(L)+
[7]. Here, we report the results of our reactivity studies
on the ionization of a mono-chloro aminophenolate Al
methyl complex with B(C6F5)3.
Cationic aluminium species have recently received an
increased interest because their enhanced Lewis acidity ver-
sus that of neutral analogues may be of potential interest in
catalysis as well as in the mediation of other reactions
requiring a Lewis acid species [1]. In this regard, some of
these cations have already been used as alkene oxide [2],
(D,L)-lactide [3b], e-caprolactone [4] and ethylene [5]
polymerization catalysts. Among this class of compounds,
four-coordinate Al alkyl cations of the type {LX}Al(R)(L)+
(LXꢀ = bidentate monoanionic ligand, L = labile ligand),
have been the most studied as they combine a low-coordina-
tion with a cationic metal center, thus resulting in highly
Lewis acidic species [2e,5b]. The interest in these cations
has been triggered by the fact that they were shown to be
readily accessible via an alkyl abstraction reaction of neu-
tral precursors {LX}AlR2 with reagents such as B(C6F5)3
in the presence of a Lewis base L [5b].
*
Fax: +33 3 90 24 50 01.
E-mail address: dagorne@chimie.u-strasbg.fr.
0022-328X/$ - see front matter ꢀ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.07.001

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S. Dagorne / Journal of Organometallic Chemistry 691 (2006) 4797–4801
2. Results and discussion
2.1. Synthesis and structure of the mono-chloro
aminophenolate Al complex {6-(CH2NMe2)-2-CPh3-4-Me-
C6H2O}Al(Me)(Cl) (1)
The neutral Al complex 1 was synthesized via a classical
salt metathesis route involving the reaction of the corre-
sponding aminophenolate lithium salt and AlMeCl2. Thus,
the reaction of the lithium salt [6-(CH2NMe2)-2-CPh3-4-
Me-C6H2O]Li, generated in situ by deprotonation of the
aminophenol ligand 6-(CH2NMe2)-2-CPh3-4-Me-C6H2OH
n
with BuLi at RT in pentane, with an equimolar amount
of AlMeCl2 yields the four-coordinate Al complex {6-
(CH2NMe2)-2-CPh3-4-Me-C6H2O}Al(Me)(Cl) (1, Scheme
1), which was isolated in good yield (78%) as a colorless
crystalline solid.
The molecular structure of the Al complex 1 was deter-
mined by X-ray crystallography analysis, thus establishing
its monomeric nature as well as the effective chelation of
one aminophenolate to the Al center (Fig. 1). Overall, com-
pound 1 exhibits similar structural and geometrical features
as those of related aminophenolate Al dialkyl complexes
[2e]. The Al–O and Al–N bond distances in 1 (1.7206(16)
Fig. 1. Molecular structure of the Al complex 1 as determined by X-ray
crystallography with a partial labelling for clarity. The hydrogen atoms
˚
are also omitted for clarity. Selected bond distances (A): Al–O = 1.721(2),
Al–C(1) = 1.947(4), Al–N = 1.972(3), Al–Cl = 2.134(1). Selected bond
angles (ꢁ): O–Al–C(1) = 118.3(1), O–Al–N = 97.99(9), O–Al–Cl = 109.25,
C(1)–Al–Cl = 113.3(1).
The reaction of complex 1 with 1 equivalent of B(C6F5)3
in the presence of 1 equivalent of THF (CD2Cl2, RT, 18 h)
affords the quantitative conversion to a 1/1 mixture of
the Al-THF methyl cation {6-(CH2NMe2)-2-CPh3-4-Me-
˚
and 1.972(3) A, respectively) are slightly shorter than those
in the related aminophenolate Al dimethyl complex
{6-(CH2NC5H10)-2-tBu-4-C6H2O}AlMe2 (1.768(2) and
˚
C6H2O}Al(Me)(THF)+ (as MeBðC6F5Þꢀ salt (2) Scheme
2.019(2) A, respectively) [2e], which may reflect the more
3
electron deficient and Lewis acidic Al center in 1.
The NMR data for 1 are consistent with a C1-symmetric
structure for this complex in solution and thus with its state
structure being retained in solution at RT.
2) and the neutral Al dichloro derivative {6-(CH2NMe2)-
2-CPh3-4-Me-C6H2O}AlCl2 (3, Scheme 1), along with 0.5
equivalent of unreacted B(C6F5)3, as monitored by 1H
and 19F NMR [8]. As can be expected, this reaction pro-
ceeds in a similar manner when performed with 0.5 equiva-
lent of B(C6F5)3.
2.2. Reaction of the Al complex 1 with B(C6F5)3
The identity of the Al complexes 2 and 3 was confirmed
by their independent synthesis. Thus, the Al cation 2 could
be generated by ionization of the Al dimethyl complex {6-
(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlMe2 with B(C6F5)3
in the presence of THF, while the Al dichloro derivative
3 was synthesized by a salt metathesis reaction between
an equimolar amount of [6-(CH2NMe2)-2-CPh3-4-Me-
C6H2O]Li and AlCl3 and was isolated in a moderate yield
(Scheme 3).
The reaction of the aminophenolate complex 1 with
B(C6F5)3 was investigated to probe the ability of 1 to be
ionized (via a Meꢀ abstraction reaction) and to tentatively
access an Al chloro cation via this route.
CPh3
OLi
CPh3
O
MeAlCl2
- LiCl
Cl
Al
Me
N
N
The borane B(C6F5)3 thus appears to slowly ionize com-
plex 1 via a Meꢀ abstraction reaction, as evidenced by the
1
presence of the MeBðC6F5Þꢀ anion in the reaction mixture
3
Scheme 1.
[9]; however, the Al chloro cation expected to be derived
CPh3
CPh3
O
CPh3
O
B(C6F5)3
(0.5 equiv)
O
N
Me
Cl
Me
Cl
Cl
Al
+
Al
Al
THF
N
N
MeB(C6F5)3
3
1
2
Scheme 2.

S. Dagorne / Journal of Organometallic Chemistry 691 (2006) 4797–4801
4799
{6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}Al(Cl)(THF)+ was
never observed in the reaction mixture. These results imply
that the alkyl abstraction route, successful to access Al cat-
ionic alkyls from {LX}AlR2, may not be a viable way to
generate Al chloro cations of the type {LX}Al(Cl)(L)+.
CPh3
O
1) THF
2) B(C6F5)3
Me
Me
2
Al
N
CPh3
OLi
3. Experimental section
AlCl3
- 2 LiCl
3
3.1. General procedures
N
All experiments were carried out under N2 using stan-
dard Schlenk techniques or in a Mbraun Unilab glovebox.
Toluene, pentane and diethyl ether were distilled from Na/
benzophenone and stored over activated molecular sieves
Scheme 3.
from it is not observed at any point along the reaction pro-
cess, as deducted from a careful H NMR monitoring of
˚
1
(4 A) in a glovebox prior to use. CH2Cl2, CD2Cl2 were dis-
tilled from CaH2 and stored over activated molecular sieves
the reaction at RT. This suggests that the putative Al
chloro cation, if formed, reacts quite fast. The formation
of complexes 2 and 3 as well as the stoichiometry of the
reaction strongly suggests a ligand exchange reaction
involving unreacted 1 and an Al cationic species derived
from Meꢀ abstraction at 1 by B(C6F5)3.
A possible mechanism for this ionization reaction may
involve an initial Meꢀ abstraction by B(C6F5)3 at the Al
center of 1 to form a putative transient l-Cl dinuclear Al
cation (Scheme 4), which, upon coordination of THF to
the AlClMe metal center, would yield a 1/1 ratio of the
Al-THF methyl cation 2 and the neutral dichloro deriva-
tive 3. The latter species is formed irreversibly as it does
not further react with B(C6F5)3; this feature is most likely
the driving force of the reaction.
Although we have no experimental evidence for the pro-
posed chloro-bridged Al dinuclear cation, this proposal is
consistent with the reaction outcome, its stoichiometry
(2/1 ratio in 1 vs. B(C6F5)3) as well as with the known abil-
ity of Al complexes to form l-Cl-typed aggregates. In addi-
tion, although l-Cl Al cations of the type conjectured here
have not been previously observed in group 13 chemistry,
related dinuclear cations such as [Cp2Zr(Cl)-(l-Cl)-
(Cl)ZrCp2]+ have been spectroscopically characterized by
Brintzinger and al. in cationic zirconium metallocene
chemistry [10].
In summary, the ionization reaction of the mono-chloro
Al methyl complex 1 with B(C6F5)3 in the presence of THF
yields the Al methyl cation 2 along with the neutral
dichloro derivative 3 via a presumably Meꢀ abstraction/
ligand exchange reaction sequence. The Al chloro cation
˚
(4 A) in a glovebox prior to use. C6D6 was degassed under
˚
a N2 flow and stored over activated molecular sieves (4 A)
in a glovebox prior to use. The aminophenol derivative 6-
(CH2NMe2)-2-CPh3-4-Me-C6H2OH was prepared follow-
ing a literature procedure [2e]. B(C6F5)3 was purchased
from Strem and extracted with dry pentane prior to use.
All other chemicals were purchased from Aldrich and were
used as received except for NMe2Ph, which was stored over
˚
activated molecular sieves (4 A) prior to use. NMR spectra
were recorded on Bruker AC 200 or 400 MHz NMR spec-
trometers, in Teflon-valved J-Young NMR tubes at ambi-
1
ent temperature, unless otherwise indicated. H and 13C
chemical shifts are reported vs. SiMe4 and were determined
1
by reference to the residual H and 13C solvent peaks. 11B
and 19F chemical shifts are reported versus BF3–Et2O in
CD2Cl2 and neat CFCl3, respectively. Elemental analysis
was performed by the microanalysis laboratory of the Uni-
´
versite Pierre et Marie Curie (Paris, France).
3.2. [6-(CH2NMe2)-2-CPh3-4-Me-C6H2O]Li
In a glovebox, n-BuLi (0.62 mL of a 2.5 M hexane solu-
tion, 1.56 mmol) was added dropwise to a precooled
(ꢀ40 ꢁC) pentane suspension of the aminophenol 6-
(CH2NMe2)-2-CPh3-4-Me-C6H2OH (579 mg, 1.42 mmol)
under vigorous stirring. After the addition, the mixture
was left under stirring for 12 h, after which the resulting
colorless suspension was filtered through glass frit. The
obtained colorless solid was washed with pentane and dried
1
and was further used as is (477 mg, 81% yield). H NMR
4
(200 MHz, C6D6): d 7.34 [d, J(HH) = 2.0 Hz, 1H, O-Ph],
4
7.30–6.84 (m, 15H, CPh3), 6.83 [d, J(HH) = 2.0 Hz, 1H,
O-Ph], 3.67 (br, 2H, PhCH2), 2.23 (s, 3H, MePh), 1.54 (s,
6H, NMe2).
CPh3
Ph3C
O
Cl
Al
0.5 B(C6F5)3
2 + 3
3.3. {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlMeCl (1)
O
N
Cl
Me
N
1
Al
In a glovebox, Cl2AlMe (0.71 mL of a 1 M hexanes
solution, 0.71 mmol) was rapidly added via a pipette to
a precooled (ꢀ40 ꢁC) toluene solution (5 mL) of 6-
(CH2NMe2)-2-CPh3-4-Me-C6H2OLi (295 mg, 0.71 mmol).
THF
MeB(C6F5)3
Scheme 4.

4800
S. Dagorne / Journal of Organometallic Chemistry 691 (2006) 4797–4801
The reaction mixture was allowed to warm to room temper-
ature and stirred for 18 h. The resulting colorless light sus-
pension was then filtered through glass frit and the filtrate
evaporated to dryness under vacuum to yield a colorless res-
idue. Recrystallization of this residue from a 1/1 toluene/
Et2O mixture at ꢀ40ꢁC afforded pure 1 as a colorless solid
(210 mg, 55% yield). Anal. Calc. for C30H31AlClNO: C,
74.45; H, 6.46. Found: C, 74.96; H, 6.52. 1H NMR
(400 MHz, CD2Cl2): d 7.21–7.13 (m, 15H, CPh3), 6.99 [d,
4J(HH) = 2.0 Hz, 1H, O-Ph], 6.77 [d, 4J(HH) = 2.0 Hz,
from toluene at ꢀ40 ꢁC. Anal. Calc. for C29H28AlCl2NO:
C, 69.05; H, 5.59. Found: C, 69.24; H, 5.41. 1H NMR
(400 MHz, CD2Cl2): d 7.32–7.18 (m, 15H, CPh3), 7.09 [d,
1H, 4J(HH) = 2.0 Hz, O-Ph], 6.81 [d, 1H, 4J(HH) =
2.0 Hz, O-Ph], 3.91 (s, 2H, Ph-CH2), 2.43 (s, 6H, NMe2),
2.18 (s, 3H, Ph-Me). 13C{1H} NMR (100 MHz, CD2Cl2):
d 152.9 (O-Ph), 145.6 (Ph), 136.4 (Ph), 130.5 (Ph), 128.6
(Ph), 127.8 (Ph), 127.0 (Ph), 126.7 (Ph), 124.9 (Ph), 119.5
(Ph), 63.0 (CPh3), 62.3 (PhCH2), 44.5 (NMe2), 20.2
(MePh).
2
1H, O-Ph], 4.28 [d, J(HH) = 14.0 Hz, 1H, PhCH2], 3.35
2
[d, J(HH) = 14.0 Hz, 1H, PhCH2], 2.50 (s, 3H), 2.16 (s,
3.6. NMR-scale reaction of the Al complex 1 with B(C6F5)3
in the presence of THF
3H), 2.10 (s, 3H), ꢀ1.11 (s, 3H, AlMe). 13C{1H} NMR
(100 MHz, C6D6): d 154.5 (Ph), 146.8 (Ph), 137.5 (Ph),
132.7 (Ph), 131.6 (Ph), 131.5 (Ph), 129.2 (Ph), 127.4 (Ph),
125.6 (Ph), 120.5 (Ph), 64.1 (CPh3), 62.0 (PhCH2), 44.9
(NMe), 42.3 (NMe), 20.9 (PhMe), ꢀ13.7 (AlMe).
In a glovebox, the mono-chloro Al compound 1
(31.4 mg, 0.065 mmol), B(C6F5)3 (33.1 mg, 0.065 mmol)
and THF (5.3 lL, 0.065 mmol) were charged in a small vial
sample and dissolved in CD2Cl2. Hexamethylbenzene, used
as an internal standard (0.3 equivalents, 3.2 mg,
0.02 mmol) was also added to the sample. The resulting
colorless solution was then transferred to a J-Young
3.4. [{6-(CH2NMe2)-2-CPh3-4-Me-
C6H2O}Al(Me)(THF)][MeB(C6F5)3] (2)
1
In a glovebox, in a small Schlenk flask, the Al dimethyl
compound {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlMe2
(88.0 mg, 0.19 mmol) was dissolved in CH2Cl2 (1 mL) and
an equimolar amount of THF (15.4 lL, 0.19 mmol) was
added. B(C6F5)3 (97.2 mg, 0.19 mmol) was introduced and
the resulting colorless solution was stirred at room temper-
ature for 30 min, after which it was evaporated to dryness in
vacuo to yield a colorless foam. Trituration of the foamy
residue with cold pentane (precooled at ꢀ40 ꢁC) provoked
the precipitation of a colorless solid. The mixture was then
filtered through frit under reduced pressure and the
obtained solid was further dried to afford pure 2. Anal.
Calc. for C53H42AlBF15NO2: C, 60.76; H, 4.04. Found: C,
NMR tube. The reaction was monitored by H and 19F
NMR spectroscopy showing the slow formation of a 1/1
mixture of the Al-THF cation {6-(CH2NMe2)-2-CPh3-4-
Me-C6H2O}Al(Me)(THF)+ (2) and the Al dichloro com-
plex {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlCl2 (3, 95%
conversion based on the internal standard after 18 h at
RT). After this time, the Al complex 1 has completely
reacted, whereas the 19F NMR spectrum of the reaction
mixture only exhibits resonances for a 1/1 mixture of
B(C6F5)3 and the anion MeBðC6F5Þꢀ.
3
3.6.1. Crystal data for 1
Crystals of 1 suitable for X-ray diffraction were obtained
at ꢀ35 ꢁC from a saturated 1/1 Et2O–toluene solution of 1.
1
59.91; H, 3.85. H NMR (400 MHz, CD2Cl2): d 7.23–6.88
4
(m, 16H, CPh3 and O-Ph), 6.87 [d, J(HH) = 2.0 Hz, 1H,
Compound 1: C30H31AlClNO, M = 483.99 g molꢀ1
;
O-Ph], 3.81 (br s, THF, 4H), 3.72 (br s, 2H, PhCH2), 2.41
(br s, NMe2, 6H), 2.20 (s, MePh, 3H), 1.94 (br s, THF,
4H), 0.48 (MeB), ꢀ0.92 (AlMe). 13C{1H} NMR
(100 MHz, C6D6): d 151.6 (Ph), 148.1 [d, 1J(CF) = 242 Hz,
C6F5], 145.5 (Ph), 137.3 [d, 1J(CF) = 255 Hz, C6F5],
colorless prismatic crystal; 0.10 · 0.08 · 0.06 mm3; mono-
˚
clinic; space group P21/n; a = 8.950(5) A, b = 24.015
˚
˚
(5) A, c = 14.220(5) A; b = 104.66(5)ꢁ; Z = 4; Dcalc
=
1.087 g cmꢀ3; l(Mo Ka) = 0.179 mmꢀ1; a total of 23811
reflections; 1.70 < h < 30.03, 8628 independent reflections
with 5915 having I > 2r(I); 307 parameters; final results:
R(F) = 0.1090; Rw(F) = 0.0767, Goodness-of-fit = 0.865,
1
136.8 (Ph), 136.0 [d, J(CF) = 238 Hz, C6F5], 133.2 (Ph),
130.5 (Ph), 129.4 (Ph), 128.8 (Ph), 126.9 (Ph), 125.5 (Ph),
119.0 (Ph), 71.3 (br s, THF), 63.1 (PhCH2 or CPh3), 62.9
(PhCH2 or CPh3), 44.0 (br s, NMe2), 25.5 (THF), 20.5
(PhMe), 10.0 (MeB), ꢀ17.8 (AlMe). 19F NMR (376 MHz,
CD2Cl2): d ꢀ133.5 [d, 3J(FF) = 19 Hz, o-C6F5], ꢀ165.7
ꢀ3
˚
maximum residual electronic density = 0.884 e A
.
Selected crystals were mounted on a Nonius Kappa-CCD
˚
area detector diffractometer (Mo Ka, k = 0.71073 A). The
complete conditions of data collection (Denzo software)
and structures refinements are given below. The cell param-
eters were determined from reflections taken from one set
of ten frames (1.0ꢁ steps in phi angle), each at 20 s expo-
sure. The structures were solved using direct methods
(SIR97) and refined against F2 using the SHELXL97 software.
All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were generated according to stereo-chem-
istry and refined using a riding model in SHELXL97. All
hydrogen atoms were placed from Fourier differences and
refined isotropically.
3
3
[t, J(FF) = 20 Hz, m-C6F5], ꢀ168.2 [m, J(FF) = 19 Hz,
p-C6F5].
3.5. {6-(CH2NMe2)-2-CPh3-4-Me-C6H2O}AlCl2 (3)
The dichloro derivative 3 was generated using the same
procedure as that for complex 1 using an equimolar
amount of [6-(CH2NMe2)-2-CPh3-4-Me-C6H2O]Li (250.0
mg, 0.603 mmol) and AlCl3 (80.4 mg, 0.603 mmol). Pure
3 was obtained after recrystallization of the crude product

S. Dagorne / Journal of Organometallic Chemistry 691 (2006) 4797–4801
4801
(d) K.-C. Kim, C.A. Reed, G.S. Long, A. Sen, J. Am. Chem. Soc.
124 (2002) 7662;
Acknowledgements
(e) S. Dagorne, L. Lavanant, R. Welter, C. Chassenieux, P. Haquette,
G. Jaouen, Organometallics 22 (2003) 3732.
The Centre National de la Recherche Scientifique is
acknowledged for financial support. Prof. R. Welter and
Dr. A. De Cian are gratefully acknowledged for their help
in the X-ray structure determination of complex 1.
´
[3] (a) N. Emig, R. Reau, H. Krautscheid, D. Fenske, G. Bertrand, J.
Am. Chem. Soc. 118 (1996) 5822;
´
(b) N. Emig, H. Nguyen, H. Krautschied, R. Reau, J.-B. Cazaux, G.
Bertrand, Organometallics 17 (1998) 3599.
[4] S. Milione, F. Grisi, R. Centore, A. Tuzi, Organometallics 25 (2006) 266.
[5] (a) For selected examples, see M. Bochmann, D.M. Dawson, Angew.
Chem. Int. Ed. Engl. 35 (1996) 2226;
Appendix A. Supplementary data
(b) M.P. Coles, R.F. Jordan, J. Am. Chem. Soc. 119 (1997) 8125;
(c) M. Bruce, V.C. Gibson, C. Redshaw, G.A. Solan, A.J.P. White,
Chem. Commun. (1998) 2523.
Crystallographic data (excluding structure factors) have
been deposited with the Cambridge Crystallographic Data
Centre, CCDC no. 610951 for compound 1. Copies of this
information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge CB2 1EZ,
UK (fax: +44 1223 336033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cal.ac.uk).
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.
2006.07.001.
[6] B(C6F5)3 is one of the best suited reagents for alkyl anion
abstraction from the dialkyl Group 4 metallocenes and related
compounds. For a review on reactions involving B(C6F5)3 as a
Lewis acid reagent: see, G. Erker, Dalton Trans. (2005) 1883, In
our case, it was anticipated that the greater stability of the
RBðC6F5Þꢀ vs. ClBðC6F5Þꢀ anion should favor the formation of
3
3
{LX}AlCl+ cations in the reaction between {LX}AlClR alumin-
ium derivatives and B(C6F5)3.
[7] S. Dagorne, I. Janowska, R. Welter, J. Zakrzewski, G. Jaouen,
Organometallics 23 (2004) 4706.
[8] The reaction of the Al compound 1 with B(C6F5)3 in the absence of
THF or any external Lewis base yielded an intractable mixture of
products.
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186.
[2] (a) For representative examples, see D.A. Atwood, J.A. Jegier, D.
Rutherford, J. Am. Chem. Soc. 117 (1995) 6779;
(b) J.A. Jegier, D.A. Atwood, Inorg. Chem. 36 (1997) 2034;
[9] We should point out that the mono-chloro Al complex 1 is stable in
CD2Cl2 for days at 40 ꢁC and thus does not undergo any ligand
exchange (to yield the corresponding Al dimethyl complex and the Al
chloro complex 3, as may be thought given the outcome of the
reaction between 1 and B(C6F5)3). The Meꢀ abstraction by B(C6F5)3
thus initially occurs at the Al metal center of 1.
´
(c) M.-A. Munoz-Hernandez, B. Sannigrahi, D.A. Atwood, J. Am.
˜
[10] O. Wrobel, F. Schaper, U. Wieser, H. Gregorius, H.H. Brintzinger,
Organometallics 22 (2003) 1320.
Chem. Soc. 121 (1999) 6747;