Synthesis, characterization, and hydrolysis of aluminum(III) compounds bearing the C6F5-substituted β-diketiminate HC[(CMe)(NC6F5)]2 (L) ligand

Article abstract of DOI:10.1021/ic051718o

A series of Al(III) compounds containing the C₆F ₅-substituted β-diketiminate ligands LAlMeCl (2), LAlMe ₂ (3), LAlMel (4), and LAlBr₂ (5) (L = HC[(CMe)(NC ₆F₅)]₂) were synthesiz

Full text of DOI:10.1021/ic051718o

Inorg. Chem. 2006, 45, 1823−1827
Synthesis, Characterization, and Hydrolysis of Aluminum(III)
Compounds Bearing the C6F5-Substituted
HC[(CMe)(NC6F5)]2 (L) Ligand
â-Diketiminate
Zhi Yang, Hongping Zhu, Xiaoli Ma, Jianfang Chai, Herbert W. Roesky,* Cheng He, Jo
1rg Magull,
Hans-Georg Schmidt, and Mathias Noltemeyer
Institut fu¨r Anorganische Chemie der Georg-August-UniVersita¨t Go¨ttingen, Tammannstrasse 4,
D-37077 Go¨ttingen, Germany
Received October 5, 2005
A series of Al(III) compounds containing the C6F5-substituted
(4), and LAlBr2 (5) (L HC[(CMe)(NC6F5)]2) were synthesized and characterized. The hydrolysis of 2 and 4 in the
presence of 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene as the hydrogen halide acceptor both lead to (LAlMe)2-
-O) (6), a methylalumoxane derivative, which is the first hydrolysis product with the general formula of (RAlMe)nO.
A comparison of the hydrolysis products of 2 and 4 with that of L AlMeCl (L′ ) HC[(CMe)(NAr)]2, Ar 2,6-
iPr2C6H3) shows that with the C6F5-substituted -diketiminate ligand, it was not possible to generate LAlMe(OH).
â-diketiminate ligands LAlMeCl (2), LAlMe2 (3), LAlMeI
)
(µ
′
)
â
This is obviously due to the stronger Bro¨nsted acidity of the proton and the smaller size of the C6F5 group in this
compound compared to that of the corresponding 2,6-iPr2C6H3 derivative.
Introduction
with water or hydrated inert salts afforded some aggregated
alumoxanes [RAlO]n, aluminum hydroxides, and oxide
hydroxides. In most of the cases, the bulky ligand at the
aluminum center hinders the aggregation of the hydrolysis
product, which can result in the formation of unusual
mononuclear hydroxides, such as L′AlMe(OH). This com-
pound was recently prepared by hydrolysis of L′AlMeCl with
the bulky â-dikeminate ligand HC[(CMe)(NAr)]2 (Ar ) 2,6-
iPr2C6H3).6 In 2002, Power et al. reported on a new C6F5-
substituted â-diketiminate ligand, HC[(CMe)(NC6F5)]2H (1)
(LH).7 Moreover, Cowley et al. prepared a Lewis acid
stabilized compound with a boron-oxygen double bond
using this ligand;8 more recently, they reported on the X-ray
crystal structure of the ligand (LH) and also on LLi‚(Et2O),
LAlMe2, and LGaMe2.9 In these papers, it was demonstrated
that this ligand exhibits very interesting reaction properties.
Organoaluminum compounds containing Al-O bonds
have attracted much interest since the discovery of methyl-
alumoxane as an extremely potent cocatalyst in the polym-
erization of ethylene and propylene by Group 4 metal-
locenes.1 The method for the formation of alumoxane is the
controlled hydrolysis of organoaluminum compounds with
water2 or reactive oxygen-containing species.3 Traditionally,
the reaction of AlR3 compounds (R ) Me, tBu, Mes, or Ph)4,5
* To whom correspondence should be addressed. Fax: 49 551-39-3373.
E-mail: hroesky@gwdg.de.
(1) (a) Sinn, H.; Kaminsky, W.; Vollmer, H.-J.; Woldt, R. Angew. Chem.
1980, 92, 396-402; Angew. Chem., Int. Ed. 1980, 19, 390-392. (b)
Chen, E. Y.-X.; Marks, T. J. Chem. ReV. 2000, 100, 1391-1434. (c)
Roesky, H. W.; Walawalkar, M. G.; Murugavel, R. Acc. Chem. Res.
2001, 34, 201-211.
(2) (a) Storr, A.; Jones, K.; Laubengayer, A. W. J. Am. Chem. Soc. 1968,
90, 3173-3177. (b) Ziegler, K. Angew. Chem. 1956, 68, 721-729.
(c) Boleslawski, M.; Pasynkiewicz, S.; Minorska, A.; Hrynio´w, W. J.
Organomet. Chem. 1974, 65, 165-167.
(3) (a) Kosinska, W.; Kunicki, A.; Boleslawski, M.; Pasynkiewicz, S. J.
Organomet. Chem. 1978, 161, 289-297. (b) Ueyama, N.; Araki, T.;
Tani, H. Inorg. Chem. 1973, 12, 2218-2215. (c) Atwood, J. L.; Hrncir,
D. C.; Priester, R. D.; Rogers, R. D. Organometallics 1983, 2, 985-
989.
(4) (a) Mason, M. R.; Smith, J. M.; Bott, S. G.; Barron, A. R. J. Am.
Chem. Soc. 1993, 115, 4971-4984. (b) Harlan, C. J.; Mason, M. R.;
Barron, A. R. Organometallics 1994, 13, 2957-2969. (c) Landry, C.
C.; Harlan, C. J.; Bott, S. G.; Barron, A. R. Angew. Chem. 1995, 107,
1315-1317; Angew. Chem., Int. Ed. 1995, 34, 1201-1203.
(5) (a) Storre, J.; Schnitter, C.; Roesky, H. W.; Schmidt, H.-G.; Nolte-
meyer, M.; Fleischer, R.; Stalke, D. J. Am. Chem. Soc. 1996, 118,
1380-1386. (b) Storre, J.; Schnitter, C.; Roesky, H. W. Schmidt, H.-
G.; Noltemeyer, M.; Fleischer, R.; Stalke, D. J. Am. Chem. Soc. 1997,
119, 7505-7513.
(6) Bai, G. C.; Sanjay, S.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-
G. J. Am. Chem. Soc. 2005, 127, 3449-3455.
(7) Panda, A.; Stende, M.; Wright, R. J.; Olmstead, M. M.; Klavins, P.;
Power, P. P. Inorg. Chem. 2002, 41, 3909-3916.
(8) Vidovic, D.; Moore, J. A.; Jones, J. N.; Cowley, A. H. J. Am. Chem.
Soc. 2005, 127, 4566-4567.
(9) Vidovic, D.; Jones, J. N.; Moore, J. A.; Cowley, A. H. Z. Anorg. Allg.
Chem. 2005, 631, 2888-2892.
10.1021/ic051718o CCC: $33.50
Published on Web 01/24/2006
© 2006 American Chemical Society
Inorganic Chemistry, Vol. 45, No. 4, 2006 1823

Yang et al.
-154.91 (t, 2F, p-F), -160.54 (m, 4F, m-F). EI-MS: m/z (%) 471
(100, [M+ - Me]). Anal. Calcd for C19H13Al F10N2 (Mr )
486.29): C, 46.93; H, 2.69; N, 5.76. Found: C, 47.00; H, 2.73; N,
5.66.
To investigate the unusual hydrolysis of the aluminum
compound with the bulky â-diketiminate ligand in more
detail, we selected the C6F5-substituted â-diketiminate HC-
[(CMe)(NC6F5)]2 (L) as the supporting ligand. Finally, a new
method has attracted great interest; this method uses the
strongly nucleophilic N-heterocyclic carbene as a HCl
acceptor for the reaction of L′AlRCl (L′ ) HC[(CMe)-
(NAr)]2, Ar ) 2,6-iPr2C6H3, R ) Cl,11 OH,10 and I10) with
stoichiometric amounts of water to afford L′AlR(OH). We
used this new technique as well to obtain a high yield of
methylalumoxane derivative (LAlMe)2(µ-O).
HC[(CMe)(NC6F5)]2AlMeI (4). Toluene (30 mL) was added
to a solid mixture of LAlMe2 (2.43 g, 5 mmol) and I2 (1.27 g, 5
mmol) at room temperature. After 3 days of being stirred, a light
yellow solution formed. The solvent and volatiles were removed
from the solution in a vacuum, and the residue was washed with
1
n-hexane to yield solid 4 (2.66 g, 89%). Mp: 164-165 °C. H
NMR (300.13 MHz, C6D6, 298 K): δ -0.15 (tr, 3H, Al-Me), 1.21
(s, 6H, â-Me), 4.72 (s, 1H, γ-CH). 13C NMR (75.48 MHz, C6D6,
298 K): δ -5.51 (Al-Me), 22.94 (â-Me), 101.47 (γ-C), 117.97,
136.61, 138.92, 140.01, 141.23, 142.27, 144.60 (C6F5), 173.15 (CN).
19F NMR (188.28 MHz, C6D6, 298K): δ -139.84 (m, 2F, o-F),
-145.80 (m, 2F, o-F), -152.63 (t, 2F, p-F), -159.36 (m, 2F, m-F),
-159.57 (m, 2F, m-F). EI-MS: m/z (%) 598 (1, [M+]), 583 (30,
[M+ - Me]), 471 (100, [M+ - I]). Anal. Calcd for C18H10AlF10-
IN2 (Mr ) 598.16): C, 36.14; H, 1.69; N, 4.68. Found: C, 35.49;
H, 2.11; N, 4.46.
Experimental Section
General Procedures. All manipulations were carried out under
a purified nitrogen atmosphere using Schlenk techniques or inside
a Mbraun MB 150-GI glovebox. All solvents were distilled from
Na/benzophenone ketyl prior to use. Commercially available
chemicals were purchased from Aldrich or Fluka and used as
received. LH7 (1) and [CN(iPr)C2Me2N(iPr)] (:C)12 were prepared
as described in the literature. Elemental analyses were performed
by the Analytisches Labor des Instituts fu¨r Anorganische Chemie
der Universita¨t Go¨ttingen. 1H, 13C, and 19F NMR spectra were
recorded on Bruker AM 200, 300, and 500 spectrometers and IR
spectra on a Bio-Rad Digilab FTS-7 spectrometer. EI mass spectra
were measured on a Finnigan MAT 8230 or a Varian MAT CH5
instrument. Melting points were measured in sealed glass tubes and
were not corrected.
HC[(CMe)(NC6F5)]2AlBr2 (5). To a toluene solution (40 mL)
of LH (4.31 g, 10 mmol) at 0 °C was added dropwise n-BuLi (2.5
M, 4 mL, 10 mmol). The mixture was stirred and allowed to warm
to room temperature. After being stirred for an additional 12 h, the
solution was cooled to -0 °C and AlBr3 (2.67 g, 10 mmol) in
toluene (10 mL) was added. The resulting solution was allowed to
warm to room temperature and was stirred for 12 h. After workup,
the insoluble LiBr was removed by filtration; the filtrate was dried
in a vacuum and washed with n-hexane to yield crystalline 5. (6.02
HC[(CMe)(NC6F5)]2AlMeCl (2). To a toluene solution (40 mL)
of LH (4.31 g, 10 mmol) at 0 °C was added dropwise n-BuLi (2.5
M, 4 mL, 10 mmol). The mixture was stirred and allowed to warm
to room temperature. After being stirred for an additional 12 h, the
solution was cooled to 0 °C and AlCl2Me (1 M, 10 mL, 10 mmol)
was added. The resulting solution was allowed to warm to room
temperature and was stirred for 12 h. After workup, the insoluble
LiCl was removed by filtration; the filtrate was dried in a vacuum
and washed with n-hexane to yield solid 2 (4.60 g, 91%). Mp: 180-
1
g, 91%). Mp: 190-191 °C. H NMR (300.13 MHz, C6D6, 298
K): δ 1.18 (s, 6H, â-Me), 4.67 (s, 1H, γ-CH). 13C NMR (125.77
MHz, C6D6, 298 K): δ 23.00 (â-Me), 101.80 (γ-C), 116.75, 137.34,
139.34, 140.06, 142.10, 144.09 (C6F5), 174.55 (CN). 19F NMR
(188.28 MHz, C6D6, 298 K): δ -142.54 (m, 4F, o-F), -151.43 (t,
2F, p-F), -159.46 (m, 4F, m-F). EI-MS: m/z (%) 615.9 (100, [M+]).
Anal. Calcd for C17H7AlBr2F10N2 (Mr ) 616.05): C, 33.15; H,
1.15; N, 4.55. Found: C, 32.50; H, 1.40; N, 4.33.
1
{HC[(CMe)(NC6F5)]2AlMe}2(µ-O) (6). To a mixture of 2 (0.51
g, 1 mmol) or 4 (0.60 g, 1 mmol) and [CN(iPr2)C2Me2N(iPr)] (:C,
0.18 g, 1 mmol) in toluene (20 mL) at 0 °C was added distilled
H2O (18 µL, 1 mmol). The suspension was allowed to warm to
room temperature and was stirred for 12 h. The insoluble solid
was removed by filtration; the filtrate was dried in a vacuum and
extracted with n-hexane (10 mL). The extract was kept at -28 °C
to afford colorless crystals of 6. (0.33 g, 69%). Mp: 184-185 °C.
1H NMR (300.13 MHz, CDCl3, 298 K): δ -1.38 (t, 6H, Al-Me),
1.85 (s, 12H, â-Me), 5.22 (s, 2H, γ-CH). 13C NMR (75.48 MHz,
CDCl3, 298K): δ -14.57 (Al-Me), 22.98 (â-Me), 99.22 (γ-C),
119.88, 136.11, 137.77, 139.71, 141.12, 142.89, 144.57 (C6F5),
171.04 (CN). 19F NMR (188.28 MHz, CDCl3, 298 K): δ -146.27
(m, 2F, o-F), -149.12 (m, 2F, o-F), -157.99 (t, 2F, p-F), -163.03
(m, 2F, m-F), -163.19 (m, 2F, m-F). EI-MS: m/z (%) 943 (100,
[M+ - Me]). Anal. Calcd for C36H20Al2F20N4O (Mr ) 958.51):
C, 45.11; H, 2.10; N, 5.85. Found: C, 44.79; H, 2.37; N, 5.67.
Single-Crystal X-ray Structure Determination and Refine-
ment. The crystallographic data for compounds 3, 5, and 6‚(0.5
toluene) were collected on a Stoe IPDS II-array detector system
with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å).
These three structures were solved by direct methods (SHELXS-
96)13 and refined against F2 using SHELXL-97.14 All non-hydrogen
181 °C. H NMR (500.13 MHz, C6D6, 298 K): δ -0.33 (s, 3H,
Al-Me), 1.21 (s, 6H, â-Me), 4.69 (s, 1H, γ-CH). 13C NMR (125.77
MHz, C6D6, 298 K): δ -11.22 (Al-Me), 22.65 (â-Me), 100.93 (γ-
CH), 118.09, 137.06, 139.21, 141.65, 142.34, 143.71, 144.33 (C6F5),
173.21 (CN). 19F NMR (188.28 MHz, C6D6, 298 K): δ -143.25
(m, 2F, o-F), -146.31 (m, 2F, o-F), -153.04 (t, 2F, p-F), -159.54
(m, 2F, m-F), -160.33 (m, 2F, m-F). EI-MS: m/z (%) 506 (4,
[M+]), 491 (100, [M+ - Me]). Anal. Calcd for C18H10AlClF10N2
(Mr ) 506.71): C, 42.67; H, 1.99. Found: C, 42.09; H, 2.33.
HC[(CMe)(NC6F5)]2AlMe2 (3). To a toluene solution (40 mL)
of LH (4.31 g, 10 mmol) at 0 °C was added dropwise AlMe3 (2
M, 5 mL, 10 mmol). The solution was stirred and allowed to warm
to room temperature. After being stirred for an additional 12 h, the
solution was dried in a vacuum and washed with n-hexane (5 mL)
1
to yield crystalline solid 3 (4.52 g, 93%). Mp: 141-142 °C. H
NMR (500.13 MHz, C6D6, 298 K): δ -0.53 (s, 6H, Al-Me), 1.28
(s, 6H, â-Me), 4.75 (s, 1H, γ-CH). 13C NMR (125.77 MHz, C6D6,
298 K): δ -11.26 (Al-Me), 22.59 (â-Me), 100.41 (γ-C), 119.85,
137.19, 138.88, 139.19, 140.83, 141.99, 143.95 (C6F5), 172.07 (CN).
19F NMR (188.28 MHz, C6D6, 298 K): δ -146.17 (m, 4F, o-F),
(10) Zhu, H. P.; Chai, J. F.; He, C.; Bai, G. C.; Roesky, H. W.; Jancik, V.;
Schmidt, H.-G.; Noltemeyer, M. Organometallics 2005, 24, 380-384.
(11) Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.;
Neculai, A. M.; Herbst-Irmer, R. Angew. Chem. 2004, 116, 2194-
2197; Angew. Chem., Int. Ed. 2004, 43, 2142-2145.
(13) Sheldrick, G. M. SHELXS-90, Program for Structure Solution. Acta
Crystallogr., Sect. A 1990, 46, 467-473.
(12) Kuhn, N.; Kratz, T. Synthesis 1993, 561-562.
1824 Inorganic Chemistry, Vol. 45, No. 4, 2006

Aluminum(III) Compounds Bearing â-Diketiminate
Table 1. Crystallgraphic Data for Compounds 3, 5 and 6‚(0.5 toluene)
3
5
6‚ 0.5 toluene
formula
fw
C19H13AlF10N2
486.29
C17H7AlBr2F10N2
616.05
C
39.5H24Al2F20N4O
1004.59
T (K)
133(2)
133(2)
133(2)
cryst syst
space group
a (Å)
b (Å)
c (Å)
monoclinic
P2(1)/n
monoclinic
P2(1)/n
monoclinic
P2(1)/n
9.4204(5)
24.4924(10)
8.5734(5)
95.304(4)
1969.66(17)
4
1.640
0.205
976
11.2157(8)
14.7816(14)
12.8121(9)
103.656(5)
2061.4(3)
13.1892(6)
17.0111(9)
18.4350(9)
102.906(4)
4031.6(3)
4
1.655
0.205
2012
â (deg)
V (Å3)
Z
4
Fc (Mg/m3)
1.985
4.072
1184
µ (mm-1
F(000)
)
θ range (deg)
1.66-24.84
-11 e h e 11, -28 e k e 28,
-10 e l e 10
37437
1.87-24.74
-12 e h e 11, -17 e k e 17,
-15 e l e 14
12231
1.65-24.86
-15 e h e 15, -20 e k e 20,
-21 e l e 21
26861
index ranges
no. of reflns collected
no. of indep reflns (Rint
)
3387 (0.0597)
3387/0/293
1.021
0.0353, 0.0914
0.0442, 0.0945
0.158/-0.267
3339 (0.0403)
3339/0/291
1.030
0.0248, 0.0401
0.0469, 0.0444
0.240/-0.307
6804 (0.0506)
6804/0/602
1.017
0.0371, 0.0785
0.0590, 0.0850
0.205/-0.292
no. of data/restraints/params
GOF/F2
R1a, wR2b(I >2σ(I))
R1a, wR2b(all data)
largest diff peak/hole(e Å-3
)
a R ) ∑||F0| - |Fc||/∑|F0|. b wR2 ) [∑w(F0 - Fc )2/∑(F0 )]1/2
.
2
2
2
Scheme 1
atoms were located by difference Fourier synthesis and refined
anisotropically, and hydrogen atoms were included using the riding
model with Uiso related to the Uiso of the parent atoms. A summary
of cell parameters, data collection, and structure solution and
refinement is given in Table 1.
Results and Discussion
Compounds LAlMeCl (2) and LAlBr2 (5) were prepared
according to the procedure given in Scheme 1. The toluene
solution of LLi prepared from LH and n-BuLi was used
directly in the reaction with AlCl2Me and AlBr3. LAlMeI
(4) was obtained by reacting LAlMe2 (3) with iodine
(Scheme 1), whereas 3 was prepared from LH and AlMe3
(14) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of Go¨ttingen, Germany, 1997.
Inorganic Chemistry, Vol. 45, No. 4, 2006 1825

Yang et al.
as a crystalline solid. All compounds were characterized by
EI-MS and 1H, 19F, and 13C NMR measurements as well as
by elemental analysis. The reaction of 3 with 1 equiv of I2
within 3 days at room temperature resulted in the formation
of 4 as light yellow crystals. To our surprise, the reaction of
3 with 2 equiv of I2 yields only 4, and no formation of LAlI2
was observed. In contrast, the reaction of L′AlMe2 with I2
15
resulted in the formation of L′AlI2. The most important
reason for this behavior is an increase in the Al-C bond
strength, which does not allow for the cleavage of this bond
under the reported condition with iodine. When either 2 or
4 were hydrolyzed in the presence of an N-heterocycliccar-
bene, 6 was obtained as a methylalumoxane derivative
instead of the LAlMe(OH). This is obviously due to the
stronger Bro¨nsted acidity of the proton and the smaller size
of the C6F5 group in this compound compared to that of the
corresponding 2,6-iPr2C6H3 derivative. In the 1H NMR
spectrum, compounds 2, 3, 4, and 6 show one resonance
between δ 0 to -1, which can be assigned to Al-Me. All
compounds exhibit one resonance between δ 4 and 5 and
one signal between δ 1 and 2 with a 1:6 intensity ratio,
showing the characteristic â-diketiminate resonances. In the
19F NMR spectra, the LH as well as 3 and 5 exhibit three
resonances in a 2:1:2 ratio, whereas compounds 2, 4, and 6
show five resonances in a 1:1:1:1:1 ratio. These differences
can be attributed to the symmetric arrangement of LH, 3,
and 5, and the asymmetric structures of 2, 4, and 6. In the
EI-MS spectra, the most intense peak of compounds 2, 3, 4,
and 6 is attributed to [M+ - Me]. Compound 5 exhibits its
most intense peak for the molecular ion [M+]. In summary,
the MS data indicate that under these conditions, the methyl
group of the aluminum is easily eliminated. The X-ray crystal
structures of 3 and 5 showed mononuclear compounds with
aluminum at the center that coordinates to the chelating
â-diketiminate ligand with the C6F5 groups attached to the
ring. Compounds 3 and 5 exhibit a distorted tetrahedral
geometry. The molecular structures of 3 and 5 are shown in
Figures 1 and 2, respectively, and their corresponding bond
distances and angles are shown in Tables 2 and 3, respec-
tively. The terminal Al-Me bond length (avg 1.956(2) Å)
Figure 1. Molecular structure of 3. Thermal ellipsoids are drawn at the
50% probability level, and the hydrogen atoms are omitted for clarity.
16
is a little shorter than that (avg 1.964(3) Å) in L′AlMe2.
This is also found for the Al-N bond length (avg 1.9213-
(15) Å, avg 1.929(2) Å in L′AlMe2). For compound 5, the
Al-N bond length (1.865(2) Å) is a little shorter than those
in 3, which is in good agreement with the electron-donating
properties of the Me group and with the electron-withdrawing
properties of bromine. The X-ray structural analysis of 6
unambiguously confirms the formation of the Al(1)-O-
Al(2) unit (see Table 4 for selected bond distances and
angles), which is almost linear, with an angle of 174.42-
(11)°. The Al-O bond length (1.689(2), 1.685(2) Å) is
shorter than those in [L′Al(OH)]2O (1.698(3), 1.694(3) Å),17
Figure 2. Molecular structure of 5. Thermal ellipsoids are drawn at the
50% probability level, and the hydrogen atoms are omitted for clarity.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Compound
3
Al(1)-N(1)
Al(1)-C(6)
1.9212(15) Al(1)-N(2)
1.9214(15)
1.951(2)
1.961(2)
Al(1)-C(7)
N(1)-Al(1)-N(2)
93.95(6)
N(1)-Al(1)-C(7) 110.55(7)
N(2)-Al(1)-C(6) 110.46(8)
N(1)-Al(1)-C(6) 108.57(8)
C(6)-Al(1)-C(7) 118.90(9)
N(2)-Al(1)-C(7) 111.55(8)
(15) Cui, C. Ph.D. Thesis, University of Go¨ttingen, Go¨ttingen, Germany,
2001.
(16) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998, 17,
3070-3076.
(17) Bai, G. C.; Roesky, H. W.; Li, J. Y.; Noltemeyer, M.; Schmidt, H.-G.
Angew. Chem. 2003, 115, 5660-5664; Angew. Chem., Int. Ed. 2003,
42, 5502-5506.
and the two â-diketiminate planes are arranged vertically to
each other. The two Al-C bonds are in a trans position
1826 Inorganic Chemistry, Vol. 45, No. 4, 2006

Aluminum(III) Compounds Bearing â-Diketiminate
Table 3. Selected Bond Distances (Å) and Angles (deg) for Compound
5
Al(1)-N(1)
Al(1)-Br(1)
1.865(2)
2.267(1)
Al(1)-N(2)
Al(1)-Br(2)
1.865(2)
2.271(1)
N(1)-Al(1)-N(2)
N(1)-Al(1)-Br(2)
N(2)-Al(1)-Br(1)
98.53(9)
112.09(9)
110.75(9)
N(1)-Al(1)-Br(1)
Br(1)-Al(1)-Br(2)
N(2)-Al(1)-Br(2)
114.08(8)
109.12(3)
111.99(8)
Table 4. Selected Bond Distances (Å) and Angles (deg) for Compound
6‚(0.5 toluene)
Al(1)-N(1)
Al(1)-C(36)
1.926(2)
1.953(2)
Al(1)-N(2)
Al(1)-O(1)
1.930(2)
1.689(2)
N(1)-Al(1)-N(2)
N(1)-Al(1)-C(36)
N(2)-Al(1)-C(36)
Al(1)-O(1)-Al(2)
94.00(9)
109.95(10)
113.15(9)
174.42(11)
N(1)-Al(1)-O(1)
N(2)-Al(1)-O(1)
O(1)-Al(1)-C(36)
111.16(9)
109.04(8)
117.16(10)
toward the Al(1)-O-Al(2) plane, with bond lengths (avg
1.951(3) Å) slightly shorter than those in 3 (avg 1.956(2)
Å).
In contrast to L′Al(OH)2, which was prepared from
L′AlCl2 by hydrolysis, the corresponding reaction of LAlBr2
with water did not yield LAl(OH)2.11 The only isolated
product was LH (1). The difference in the reactivity should
be attributed to the strong electron-withdrawing properties
of the C6F5 groups. We have also tried the reaction of H2S
with 2 and 4 to get compound (RAlMe)2S, similar to the
structure of 6 (see Figure 3). A mixture of (RAlMe)2(µ-S)
and (RAlMe)2(µ-O) was formed because of small amounts
of H2O, which we were not able to remove from starting
material H2S. Moreover, we were not successful in separating
the products.
Figure 3. Molecular structure of 6. Thermal ellipsoids are drawn at the
50% probability level, and the hydrogen atoms and 0.5 molecular toluene
are omitted for clarity.
MAO, which is the first hydrolysis product with the general
formula (RAlMe)nO. This reaction demonstrates the powerful
acceptor properties of the N-heterocyclic carbene. By com-
paring the product of hydrolysis 6 with that of L′AlMeCl,
we have shown that the Bro¨nsted acidic nature of the proton
in the intermediate LAlMe(OH) and the less steric demand
of the C6F5 groups are responsible for the further reaction.
Conclusion
In summary, we report on the synthesis of a series of Al
compounds containing the C6F5-substituted â-diketiminate
as the supporting ligand (2, 3,18 4, 5) and the study of the
hydrolysis of 2 and 4 in the presence of 1,3-diisopropyl-
4,5-dimethylimidazol-2-ylidene (:C). The deprotonation of
the coordinated H2O by :C with formation of the insoluble
[H:C]+Cl- salts leads to (LAlMe)2(µ-O), a derivative of
Acknowledgment. We are grateful for financial support
by the Fonds der Chemischen Industrie and the Go¨ttinger
Akademie der Wissenschaften.
Supporting Information Available: Cif files for compounds
3, 5, and 6‚(0.5 toluene). This material is available free of charge
via the Internet at http://pubs.acs.org.
(18) After this paper was submitted, the structure of compound 3 was
reported by Cowley et al.;9 however, the reaction temperatures are
different and the shapes of the crystal are not completely the same.
IC051718O
Inorganic Chemistry, Vol. 45, No. 4, 2006 1827