Organometallics 2003, 22, 207-210
207
F ir st Isola tion a n d Str u ctu r a l Ch a r a cter iza tion of
Tr ia r yla lu m in u m -Wa ter a n d -Meth a n ol Com p lexes
Debashis Chakraborty and Eugene Y.-X. Chen*
Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523-1872
Received October 7, 2002
Summary: The structurally characterized (C6F5)3Al‚OH2
(1) and (C6F5)3Al‚OHCH3 (2) exhibit medium-strong
intermolecular and weak intramolecular O-H‚‚‚FC
hydrogen bonds in the solid state. Both complexes have
substantial stability in toluene solutions at room tem-
perature, while the spectroscopic data of 1 show strong
activation of the weak Brønsted acid H2O by Al(C6F5)3.
dimers or trimers; warming the solution of B to room
temperature induces further alkane elimination to give
alkylalumoxanes (C) as the final products.
Although the existence of the alkylaluminum-water
complex A was supported by the low-temperature solu-
tion 1H NMR studies, isolation and structural charac-
terization of such a complex still remain a challenge.5
The use of the bulky trimesityl ligand makes possible
the isolation and structural characterization of the
trimesitylgallium-water complex Mes3Ga‚OH2‚2THF,
which is stabilized by two THF molecules.11 The analo-
gous aluminum complex, however, is again thermally
too unstable to isolate and characterize structurally.
In tr od u ction
Organoaluminum complexes have played pivotal roles
in many chemical processes,1 especially in organic
synthesis,2 olefin polymerization catalysis,3 and polym-
erization of polar monomers.4 There has been long-
standing interest in the controlled reactions of water
with aluminum trialkyl/triaryl compounds due to both
scientific curiosity and technological importance.5 The
partial hydrolysis of trialkylaluminum (R3Al) leads to
formation of industrially important, oligomeric alumox-
anes6 that are potent activators for olefin polymeriza-
tion7 as well as active catalysts for polymerization of
epoxides.8 The controlled reaction of water with bulky
trialkylaluminum compounds such as tri-tert-butylalu-
minum produces a series of structurally characterized
tert-butylaluminum hydroxides, oxide hydroxides, and
alumoxanes.9 Variable-temperature 1H NMR spectro-
scopic studies10 have shown that the hydrolysis of R3Al
Inspired by the above-mentioned work of Roesky,
Barron, and others,5-11 and by the work of Green,12a,b
Siedle,12c and co-workers, in which B(C6F5)3 forms
isolable and structurally characterizable adducts with
water, we sought to utilize the electronic effects in
attempts to isolate trialkyl/triaryl aluminum complexes
with oxygen Brønsted acids in general (e.g., H2O, CH3-
OH). Herein, we report the first isolation and structural
characterization of triarylaluminum-water and -metha-
nol complexes: (C6F5)3Al‚OH2 (1) and (C6F5)3Al‚OHCH3
(2). Complexes 1 and 2 have been isolated in good yields
from the controlled reactions of the highly Lewis acidic
13
alane Al(C6F5)3 with water and methanol. Unique
properties of 1 and 2 include (1) substantial stability in
toluene solutions at room temperature with half-lives
of t1/2 ) 33, 193 h, respectively, (2) strong activation of
the weak Brønsted acid H2O with (C6F5)3Al as shown
by a 8.96 ppm downfield shift of the water proton in 1
versus the free water proton, and (3) in the solid state,
i
(R ) Me, Et, Bu) proceeds with the formation of an
alkylaluminum-water complex (A), which subsequently
[R3Al‚OH2] [R2Al(µ-OH)]n [RAl(µ-O)]n
A
B
C
eliminates an alkane to form a dialkylaluminum hy-
droxide (B). Hydroxide B normally associates to give
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10.1021/om020834l CCC: $25.00 © 2003 American Chemical Society
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