Studies of the ligand effect on the synthesis of dialuminoxanes by various β-diketiminato ligands

Article abstract of DOI:10.1021/ic2021879

Reactions of LH (L = HC[C(Me)N(2,6-Me₂C₆H ₃)]₂) with MenAlCl_3-n in diethyl ether afforded the adducts LH·AlMen(Cl) _3-n (n = 2, 3; 1, 4; 0, 5) in good yields. Treatment of 3 at elevated temp

Full text of DOI:10.1021/ic2021879

Article
pubs.acs.org/IC
Studies of the Ligand Effect on the Synthesis of Dialuminoxanes by
Various β-Diketiminato Ligands
Ying Yang,†,‡ Haipu Li,*,† Chen Wang,† and Herbert W. Roesky*,‡
†School of Chemistry and Chemical Engineering, Central South University, 410083 Changsha, P.R. China
‡Institut fur Anorganische Chemie, Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany
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S
* Supporting Information
ABSTRACT: Reactions of LH (L = HC[C(Me)N(2,6-Me2C6H3)]2) with MenAlCl3−n in diethyl ether afforded the adducts
LH·AlMen(Cl)3−n (n = 2, 3; 1, 4; 0, 5) in good yields. Treatment of 3 at elevated temperatures in toluene resulted in LAlMeCl
(2) by intramolecular elimination of methane. The controlled hydrolysis of LAlMeCl (2) with equimolar amounts of water in the
presence of N-heterocyclic carbene (NHC) gave a mixture of [LAl(Me)]2(μ-O) (7) and dimeric [LAlMe(μ-OH)]2 (8). A
convenient route for the preparation of [LAlMe(μ-OH)]2 (8) was the NHC-assisted controlled hydrolysis of LAlMeI (9).
Stepwise hydrolysis of LAlH2 (11) gave dialuminoxane hydride [LAl(H)]2(μ-O) (12) and dialuminoxane hydroxide
[LAl(OH)]2(μ-O) (13), respectively. Anhydrous treatment of LAlCl2 (1) or LAlMeCl (2) with Ag2O afforded chlorinated
dialuminoxane [LAl(Cl)]2(μ-O) (14) and [LAl(Me)]2(μ-O) (7), respectively.
minum monochlorides resulted in different products. For
instance, the controlled hydrolysis of methylaluminum
INTRODUCTION
■
Methyl aluminoxane, yet structurally elusive, is probably the
most widely used cocatalyst for metallocene-based catalysts in
olefin polymerization.1 Hydrolysis of alkylaluminum with water
or hydrated metal salts is a convenient route to synthesize
alkylaluminoxanes of general formula (RAlO)n or (R2Al−O−
AlR2)n.2 A number of alternative routes other than cleaving the
Al−C bond have also been investigated to generate the Al−O
bond for the preparation of well-defined aluminoxanes,3,4
especially those of the basic aluminoxanes (dialuminoxanes)
containing an Al−O−Al linkage.5 The first structurally
authenticated monomeric tetraalkylaluminoxane [tBu2(py)-
Al)]2(μ-O) was obtained either by partial hydrolysis of
Al(tBu)3 with water in pyridine or by treatment of [tBu2Al(μ-
OH)]3 with pyridine under reflux.6 The latter route is of
interest in preparing dialuminoxanes from organoaluminum
hydroxides. Subsequently, the monomeric dialuminoxane
[{(Me3Si)2HC}2Al]2(μ-O) free of a Lewis base bound to
aluminum was prepared by oxygen insertion into the Al−Al
bond.7
F
monochloride LAlMeCl (FL = HC[C(Me)N(C6F5)]2) in the
presence of N-heterocyclic carbene (NHC) can be used to
prepare dialuminoxane [FLAl(Me)]2(μ-O),15 while treatment
of PhLAlMeCl (PhL = HC[C(Me)N(Ph)]2) with LiOiPr gave a
mixture of dialuminoxane [PhLAl(Me)]2(μ-O) and mononu-
clear PhLAlMe(OiPr).16 In contrast, NHC-assisted controlled
hydrolysis of iPrLAlMeCl (iPrL = HC[C(Me)N(2,6-
iPr2C6H3)]2) led to the methylaluminum monohydroxide
iPrLAlMe(OH).17−19 It is therefore suggested that the steric
demanding β-diketiminato ligand could possibly play a leading
role in governing the direction of these reactions to generate
mononuclear organoaluminum compounds or dialuminoxanes.
To address the problem in detail, we first selected a β-
diketiminato ligand L with 2,6-dimethylphenyl substituents,
which is of middle size when compared with those of PhL and
iPrL analogues. However MesL is of comparable size (Scheme 1).
The synthesis and characterization of related precursors and
their conversion to dialuminoxanes from organoaluminum
monohalides, dihalides, and hydrides are described in this
paper.
The extraordinary protection of the metal center with a β-
diketiminato ligand is well-known especially for the stabilization
of organometallic compounds of low valent and low coordinate
metal centers.8 Supported by such a ligand, reactions of oxygen-
containing compounds with organoaluminum dihydrides9−12 or
dihalides13,14 provided facile access to the formation of
dialuminoxanes. However, the reactions involving methylalu-
Received: October 10, 2011
Published: February 9, 2012
© 2012 American Chemical Society
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Therefore, we used an alternative route, namely, the
intermolecular elimination of methane from the acidic ligand
and metal alkyls. Treatment of LH with Me2AlCl in Et2O at
−18 °C resulted in a white precipitate almost immediately after
adding the precursor. The solid was collected by filtration and
then characterized by IR, 1H, 13C, 27Al NMR spectroscopy, and
elemental analysis. It turned out to be the 1:1 adduct
LH·AlMe2Cl (3) instead of the expected LAlMeCl (2).
Compound 3 is stable in solid state or in diethyl ether solution
at room temperature. In the IR spectrum of 3, the NH
stretching frequency is found at 3339 cm−1, corresponding to
the presence of the singlet for the NH proton (4.48 ppm) in
Scheme 1. Varieties of β-Diketiminato Ligands
1
the H NMR spectrum. Two distinct single resonances (1.39,
2.58 ppm) are assigned to the protons of β-Me groups, which
do not support a time averaged C2v-symmetric structure of the
ligand backbone of 3 in C6D6 solution. The 27Al NMR
spectrum confirms the aluminum in compound 3 (67.86 ppm),
and the 1H NMR spectrum also exhibits a singlet (−0.28 ppm)
because of the AlMe2 group with correct integration ratio
relative to the ligand signals.
The formation of 3 was further authenticated by single
crystal X-ray structural analysis, and its molecular structure is
shown in Figure 1. Compound 3 crystallizes in the monoclinic
space group P21/c, containing an open chain-like ligand,
together with a slightly distorted tetrahedral geometry
completed by one nitrogen, two methyl carbon atoms, and
one chlorine around the aluminum center. The N(1)−Al(1)
bond length of 3 (1.951(2) Å) is found in the normal
range.22,23 However, the bond length is much longer than that
of iPrLAlMeCl (1.905 Å) in a typical delocalized system.21 The
relatively short bonds of N(1)−C(2) (1.330(3) Å) and C(3)−
C(4) (1.379(3) Å) are indicative of a partial double-bond
character, when compared with their corresponding single-
bond counterparts of N(2)−C(4) (1.349(3) Å) and C(2)−
C(3) (1.405(4) Å). At the same time, N(1) and N(2) atoms
deviate only slightly from the C(2)−C(3)−C(4) plane by
RESULTS AND DISCUSSION
■
Synthesis of Organoaluminum Chlorides. In general, β-
diketiminate aluminum chlorides can be easily prepared by
lithium salt elimination.18−21 However, in contrast to the high
yield preparation of LAlCl2 (1, L = HC[C(Me)N(2,6-
Me2C6H3)]2, Scheme 2), the analogous reaction of LLi·THF
with MeAlCl2 in diethyl ether solution led to a unexpected
mixture of free ligand (LH), a small portion of the targeted
product LAlMeCl (2), and a number of side products.
Scheme 2. Formation of Compounds 1−13 (L = HC[C(Me)N(2,6-Me2C6H3)]2, NHC = [C(Me)N(iPr)]2C)
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corresponding β-diketiminato adduct, from which the methyl
monochloride derivative was obtained in high yield and purity.
Hydrolysis of Organoaluminum Halides and Hy-
drides. In comparison to the labile alkylaluminum adducts
(3 and 4) stabilized by the neutral monodentate β-diketiminato
ligand, the dimethylaluminum compound LAlMe2 (6)
supported by the monoanionic bidentate ligand is more stable.
Treatment of 6 with water resulted in a mixture of free ligand
and the starting material. We were curious to see what product
would be obtained using the middle-sized L other than iPrL or
FL in NHC-assisted hydrolysis.15,17−19 The controlled hydrol-
ysis of LAlMeCl (2) using 1 equiv of water in the presence of
equimolar amounts of NHC proceeds to a mixture of
[LAl(Me)]2(μ-O) (7) and [LAl(Me)(μ-OH)]2 (8). Both
compounds can be separated by fractional crystallization from
n-hexane.
Figure 1. Molecular structure of LH·AlMe2Cl (3). Thermal ellipsoids
are drawn at the 50% level, and all hydrogen atoms, except those of the
NH and γ-CH groups, are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Al(1)−C(22) 1.950(3), Al(1)−C(23) 1.980(2),
Al(1)−Cl(1) 2.2031(11), Al(1)−N(1) 1.951(2), N(1)−C(2)
1.330(3), C(2)−C(3) 1.405(4), C(3)−C(4) 1.379(3), N(2)−C(4)
1.349(3); C(22)−Al(1)−C(23) 116.84(15), C(2)−N(1)−Al(1)
128.38(17), N(1)−C(2)−C(3) 120.4(2), C(4)−C(3)−C(2)
129.6(3), N(2)−C(4)−C(3) 118.5(2).
The molecular structure of [LAl(Me)]2(μ-O) (7) is depicted
in Figure 2. Compound 7 is a typical dialuminoxane containing
0.055 and 0.223 Å, respectively, suggesting a possible
conjugated system therein. Compound LH·AlMe2Cl (3) offers
a unique style for the β-diketiminato family member to play as a
monodentate neutral ligand. The most striking observation for
compound 3 is the stack-arrangement of two aryl planes, rather
than the trans conformation found in relevant examples.23,24
Compound 3 seems to be an intermediate that represents the
initial step of the reaction of LH with Me2AlCl. In toluene or
C6D6 solution, 3 degraded spontaneously at room temperature,
and gradually transformed into LAlMeCl (2) by breaking one
of the Al−C bonds under elimination of methane. Treatment of
a suspension of 3 in toluene under reflux for 2 h afforded
LAlMeCl (2) in high yield with high purity (Scheme 2). The
structural analysis of LAlMeCl (2) disclosed a monomeric
composition in the solid state (Supporting Information, Figure
S1).
Figure 2. Molecular structure of [LAl(Me)]2(μ-O) (7). Thermal
ellipsoids are drawn at the 50% level, and all hydrogen atoms are
omitted for clarity. Selected bond lengths (Å) and angles (deg):
Al(1)−O(1) 1.700(2), Al(1)−C(43) 1.955(4), Al(2)−O(1) 1.700(2),
Al(2)−C(44) 1.941(3); N(1)−Al(1)−N(2) 93.90(12), O(1)−Al(1)−
C(43) 114.73(14), O(1)−Al(2)−C(44) 112.75(14), Al(1)−O(1)−
Al(2) 152.91(15).
By following the same strategy, the neutral adducts of
LH·AlMeCl2 (4) and LH·AlCl3 (5) were successfully isolated as
white crystalline solids. In the IR spectra, the NH stretches are
exhibited at 3283 cm−1 (4) and 3321 cm−1 (5), respectively.
Both compounds are found to be stable in the solid state or in
diethyl ether solution.25 The C6D6 solution of 4 exhibited
intense resonances of LAlMeCl (2) in the NMR spectra after
prolonged standing under an inert atmosphere. In an attempt
to prepare LH·AlMe3, however, no precipitate could be
observed after mixing LH and AlMe3 in Et2O at −18 °C
either under storing or rigorous stirring for more than 20 h.
From the concentrated reaction solution block-like colorless
crystals of composition LAlMe2 (6) were obtained (Supporting
Information, Figure S2).
a bent Al−O−Al skeleton, the angle of which (152.91(15)°) is
found to be more acute than those in [PhLAl(Me)]2(μ-O)
(168.90(12)°)16 and [FLAl(Me)]2(μ-O) (174.42(11)°).15 The
Al−O bond length of 7 (1.700(2) Å) is slightly longer relative
to those in [PhLAl(Me)]2(μ-O) (1.6797(18)−1.6807(18) Å)16
and [FLAl(Me)]2(μ-O) (1.685(2)−1.689(2) Å).15 A more
closely comparable example is [PhLAl(CH2tBu)]2(μ-O)
(155.8(1)°, 1.697(2)−1.701(2) Å).9
[LAl(Me)(μ-OH)]2 (8) is stable under an inert atmosphere.
In the IR spectrum of 8, the OH stretching band is observed at
1
3679 cm−1. The C6D6 solution of 8 presents two sets of H
On the one hand, the reaction of iPrLH with Me2AlCl in Et2O
at −18 °C resulted in an oily paste, which turned out to be a
NMR resonances that slowly equilibrated at room temper-
ature,18 referring to the monomeric composition with a
terminal hydroxyl group (0.34 ppm) and the dimeric one
with bridging hydroxyl groups (1.21 ppm), respectively. In solid
state 8 is dimeric (Supporting Information, Figure S3) and
1
complex mixture of products as characterized by H NMR
spectroscopy. On the other hand, treatment of PhLH with
Me2AlCl in toluene resulted in a mixture of PhLAlMeCl and
PhLAlMe2.16 A reference reaction using iPrLH and Me2AlCl in
toluene under reflux for 2 h gave iPrLAlMeCl (1′, Supporting
Information) nearly quantitatively. A comparison of these three
ligands shows that the middle-sized L provides an access to the
19
essentially isostructural with its analogues [iPrLAlCl(μ-OH)]2
and [MesLAlR(μ-OH)]2
(
MesL = HC[C(Me)N(2,4,6-
Me3C6H2)]2; R = F,10 Ph18) in terms of the OH-bridged
planar Al2O2 four-membered ring.
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It is interesting to examine how the dialuminoxane
[LAl(Me)]2(μ-O) (7) was produced under controlled hydrol-
ysis. According to our experience, most β-diketiminato
aluminum methyl hydroxides are stable enough to preclude
the possibility of intermolecular elimination of methane to form
Al−O−Al moiety.17−19 It is therefore suggested that the
generation of dialuminoxane [LAl(Me)]2(μ-O) (7) could
plausibly be realized by the NHC-supported intermolecular
HCl elimination between the initially formed LAlMe(OH) (8)
and LAlMeCl (2). As expected, treatment of a mixture of 2 and
NHC in toluene or C6D6 with equimolar amount of 8 afforded
[LAl(Me)]2(μ-O) (7) almost quantitatively. In a straightfor-
ward way, [LAl(Me)]2(μ-O) (7) can be alternatively obtained
from the reaction of 2 in the presence of NHC in toluene with
0.5 equiv of H2O at room temperature. As anticipated, reducing
the amount of water to one-half we observed the exact
formation of 7 from the in situ produced LAlMe(OH) (8) with
unreacted starting material.
directly with LiAlH4 at 80 °C.28 The IR spectrum of 11 shows
typical asymmetric and symmetric Al−H absorptions (1819,
1787 cm−1),26 and the single crystal X-ray structural analysis
indicates the formation of monomeric dihydride in the solid
state (Supporting Information, Figure S4). Treatment of 11
with 0.5 equiv of water at room temperature smoothly afforded
dialuminoxane hydride [LAl(H)]2(μ-O) (12) in moderate
yield. In a parallel reaction, compound 11 was treated with 1.5
equiv of water to produce [LAl(OH)]2(μ-O) (13) in modest
yield. With regard to the obtained products from reactions of
organoaluminum dihydrides with water, compounds with L are
highly comparable to those of their MesL analogues.11,29
1
In the H NMR spectrum of [LAl(H)]2(μ-O) (12) a very
broad resonance (3.95 ppm) was observed for the AlH groups.
The latter are supported by the distinct absorption bands at
1803 and 1795 cm−1 in the IR spectrum. These data are highly
consistent with those observed for [MesLAl(H)]2(μ-O) (1H
NMR: br 3.99 ppm; IR: 1815, 1775 cm−1).11 The X-ray single-
crystal structure of 12 exhibits a monomer with a bent Al−O−
Al skeleton (168.05(19)°) and Al−O separations (1.685(2)−
1.700(2) Å) in the expected range (Figure 3).30 Structurally
To explain the phenomenon we assume that the spectator
ligand of β-diketiminato type generally provides kinetic
protection around the Al center against the intermolecular
elimination of methane from aluminum methyl hydroxides.
Therefore, a delicate tuning of the steric property of the ligand
may influence the proximity of molecules either to allow
inhibiting or encouraging the intermolecular reactions between
two β-diketiminato species. In the current case, the less bulky
environment furnished by the 2,6-Me2C6H3 ligand is suitable
for the approach of molecule 8 to molecule 2, and enables the
competitive coordination between oxygen atoms from LAlMe-
(OH) (8) and those from H2O onto aluminum atoms of
LAlMeCl (2) to initiate the HCl elimination reaction. In a
F
broader view, as far as the ligand size is concerned, PhL and L
can be treated as smaller ligand so that they easily allow such
kind of intermolecular reactions.15,16 In contrast MesL, iPrL, and
tBuL (tBuL = HC[C(tBu)N(2,6-iPr2C6H3)]2) are larger ligands
that obviously hinder this type of reactions.18
We were also interested in the reactivity and performance of
different aluminum halides toward hydrolysis. The methyl-
aluminum monoiodide precursor LAlMeI (9) was therefore
prepared from the partial iodization of LAlMe2 (6). Similarly,
the reaction of 6 with 2 equiv of I2 led to the formation of LAlI2
(10) in high yield, in sharp contrast to the unfeasible formation
of FLAlI2.15 It was found that the controlled hydrolysis of
LAlMeI (9) with water at 0 °C using NHC as the HI acceptor
(in a ratio of 1:1:1) afforded [LAl(Me)(μ-OH)]2 (8) as
expected. When compared to the analogous hydrolysis of
LAlMeCl (2), an improvement in purity and yield is noticeable,
which might be due to the greater steric bulk of the larger
iodine atom and weaker Al−I bond strength. However, the
formation of [LAl(Me)]2(μ-O) (7) would still accumulate into
a large quantity when the same hydrolysis reaction of LAlMeI
(9) was carried out at ambient temperature. It was further
observed that a more practical and reproducible isolation of
[LAl(Me)(μ-OH)]2 (8) can be obtained using tetrahydrofuran
(THF) as a solvent instead of the usual toluene, which could
suggest a role of the O-donor solvent to alleviate the
intermolecular HI elimination.
Figure 3. Molecular structure of [LAl(H)]2(μ-O) (12). Thermal
ellipsoids are drawn at the 50% level, and all hydrogen atoms, except
those at the Al atoms, are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Al(1)−O(1) 1.685(2), Al(2)−O(1) 1.700(2),
Al(1)−N(1) 1.905(3), Al(1)−N(2) 1.915(3), Al(2)−N(3) 1.916(3),
Al(2)−N(4) 1.895(3); N(1)−Al(1)−N(2) 94.08(12), N(4)−Al(2)−
N(3) 94.30(14), Al(1)−O(1)−Al(2) 168.05(19).
characterized dialuminoxane hydrides are very rare. A related
example is [{1η-3,5-tBu2pz(μ-Al)H}2O]2,4 which could be
roughly seen as a dimer of dialuminoxane hydride driven by
the oxophilicity of aluminum to a less steric demanding
environment.
The 1H NMR spectrum of [LAl(OH)]2(μ-O) (13) displays a
singlet resonance in the high-field region (−0.72 ppm), which
can be assigned to hydroxyl groups. In the IR spectrum a weak
stretching frequency at 3674 cm−1 is due to the OH
functionalities. The solid X-ray structure of 13 (Supporting
Information, Figure S5) is comparable to those stabilized by
iPrL and MesL ligands.14,29 The Al−O−Al angle in 13
(129.84(13)°) is smaller when compared with that in
In comparison to the less reactive dimethyl compounds
iPr-
iPrLAlMe2 and LAlMe2 (6), organoaluminum dihydrides
LAlH2 and MesLAlH2 have been demonstrated to be facile
precursors for the preparation of chalcogen bridged binuclear
organoaluminum compounds.10−12,26,27 LAlH2 (11) was there-
fore prepared using a modified route by reacting LH in toluene
[
MesLAl(OH)]2(μ-O) (136.8(1)°),29 but wider than that in
iPrLAl(OH)]2(μ-O) (112.3°).14 The Al−O distances
[
(1.7028(10)−1.7252(17) Å) are close to those in [MesLAl-
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(OH)]2(μ-O) (1.691(2)−1.701(2) Å)29 and [iPrLAl(OH)]2(μ-
[LAl(Me)]2(μ-O) (7) can be readily isolated from this reaction
(Scheme 3). In the same way, treatment of LAlCl2 (1) with 0.5
O) (1.694−1.698 Å).14
The high reactivity of aluminum hydrides toward water
initiated the reaction of LAlH2 (11) with equivalent amounts of
water (2: 2) in an attempt to generate [LAl(μ-O)]2. However,
this reaction at low temperatures (<0 °C) gave a mixture of
[LAl(OH)]2(μ-O) (13) and a small amount of LH. The
controlled hydrolysis of LAlI2 (10) (in a ratio of 1:1:2 =
10:H2O:NHC) resulted in a similar mixture. Obviously the
species containing a strained Al2O2 four-membered ring should
be highly sensitive to moisture and could not be isolated as the
final product in a hydrolytic environment, although they might
occur as intermediates. The previously reported [iPrLAl(μ-O)]2
was obtained by treatment of carbene-like iPrLAl with
anhydrous molecular oxygen.31 In comparison, the reaction of
tBuLAl with water afforded tBuLAlH(OH),32 which is not stable
in solution and slowly decomposed.
Scheme 3. Formation of Dialuminoxanes 7 and 14 (L =
HC[C(Me)N(2,6-Me2C6H3)]2)
equiv of Ag2O led to the formation of chlorinated
dialuminoxane [LAl(Cl)]2(μ-O) (14), and its molecular
structure is depicted in Figure 4. Structurally characterized
All synthetic attempts to prepare LAl(OH)2 by hydrolyzing
LAlI2 (10) or LAlH2 (11) failed. A mixture of products was
formed mainly consisting of the free ligand LH and 13. This
should be due to the less steric demanding ligand that could
not sufficiently prevent the intermolecular reactions between
reactants of AlI/AlH and active Al(OH) species in a
nonstoichiometric ratio. These results are in sharp contrast to
the facile preparation of iPrLAl(OH)2 by hydrolyzing iPrLAlI2,
iPrLAlCl2, iPrLAlCl(I), and iPrLAl(SH)2, respectively.19,33
Furthermore, we performed a reference reaction by treating
iPrLAlH2 with water (in a ratio of 2:3) to investigate the steric
effect of the ligand. Unlike the straightforward formation of
[LAl(OH)]2(μ-O) (13) from LAlH2 and water (2:3), this
reaction led to the isolation of iPrLAl(OH)2 (2′, Supporting
Information) in high yield. It was obviously confirmed that iPr
L
Figure 4. Molecular structure of [LAl(Cl)]2(μ-O) (14). Thermal
ellipsoids are drawn at the 50% level, and all hydrogen atoms, except
those of the OH groups, are omitted for clarity. Selected bond lengths
(Å) and angles (deg): Al(1)−O(1) 1.6795(15), Al(1)−Cl(1)
2.1518(14); N(2)−Al(1)−N(1) 97.78(12), O(1)−Al(1)−Cl(1)
112.47(11), Al(1)−O(1)−Al(1A) 138.5(2).
with a large size is efficient to decrease the possibility of
intermolecular reactions of different β-diketiminato species.
The unusual formation of [iPrLAl(OH)]2(μ-O) was previously
realized under harsh conditions using a two-phase toluene/
liquid ammonia system to overcome the steric hindrance.14
Although iPrLAl(OH)2 (2′) has long ago been reported, its
reactivity is so far unknown. Treatment of iPrLAl(OH)2 (2′)
with 1 equiv of HAl(OAr*)2 (Ar* = 4-Me-2,6-tBu2C6H2)
resulted in the isolation of dialuminoxane iPrLAl(OH)(μ-
O)Al(Ar*)2 (3′, Supporting Information). X-ray structural
analysis shows that 3′ contains one four- and one three-
coordinate Al along with a wide Al(1)−O(2)−Al(2) angle
(153.80(11)°) (Supporting Information, Figure S6).
Anhydrous Synthesis of Dialuminoxanes. Parallel to the
hydrolytic synthesis of alumoxanes, an anhydrous approach has
also been explored by using other oxygen sources. Treatment of
[{(Me3Si)2HC}2Al]2 with oxygen donors like trimethylamine
o x i d e o r D M S O a f f o r d e d t h e d i a l u m o x a n e
[{(Me3Si)2HC}2Al]2(μ-O),7 without the formation of alk-
oxides.34 Reaction of PhLAlH(R) (R = H, CH2tBu, CH2SiMe3)
with hydrogenperoxide/HOOtBu resulted in the isolation of
[PhLAl(R)]2(μ-O) (R = OtBu, CH2tBu, CH2SiMe3) other than
peroxoaluminum compounds because of the preferential
formation of the Al−OH group as well as facile intermolecular
reactions of different β-diketiminato species.9,35 These
observations initiated the synthesis of alkyldialuminoxanes
using Ag2O.
halogenated dialuminoxanes are so far rare.10,13 The Al−O−Al
angle of 14 (138.5(2)°) is in the expected range, but smaller
than that in [MeLAl(Cl)]2(μ-O) (180°, MeL = HC[C(Me)N-
(Me)]2) because of the increased steric bulk.13 Their Al−O
(1.6796(16) vs 1.6770(6) Å) and Al−Cl (2.1520(14) vs
2.1640(9) Å) bond lengths are highly comparable.
Note that in the series of dialuminoxanes [LAl(R)]2(μ-O) (R
= Me, 7; OH, 13; Cl, 14), the two Al−R bonds are in a trans
position relative to the Al−O−Al plane, with the torsion angle
of R−Al···Al−R around 55° (C(43)−Al(1)···Al(2)−C(44)
54.97°, 7; O(2)−Al(1)···Al(1A)−O(2A) 55.09°, 13; Cl(1)−
Al(1)···Al(1A)−Cl(1A) 55.55°, 14).
These latter reactions provide an interesting anhydrous route
to methylalumoxane derivatives as exemplified by the initial
formation of the adduct LH·AlMe2Cl (3), then transforming it
to LAlMeCl (2), and eventually to [LAl(Me)]2(μ-O) (7). The
attempt to prepare [LAl(μ-O)]2 by reacting LAlCl2 (1) with
one or more equivalents of Ag2O was not successful. Moreover,
treatment of iPrLAlMeCl (1′) with excess of Ag2O in CH2Cl2 at
room temperature failed to produce the expected [iPrLAl-
(Me)]2(μ-O). It was obviously shown that the anhydrous route
with Ag2O creates mild conditions although they were not
successful where steric hindrance dominated.
LAlMeCl (2) was treated with 0.5 equiv of Ag2O suspended
in CH2Cl2 at −18 °C, followed by additional stirring at room
temperature for 3 d. As expected, the methyldialuminoxane
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workup, the solvent of the clear solution was removed to give a white
crystalline solid. Yield 4.99 g (93%); mp 220 °C. 1H NMR (500 MHz,
C6D6) δ 6.85−6.98 (m, Ar), 4.89 (s, 1 H, γ-CH), 2.50 (s, 6 H, ArMe),
2.07 (s, 6 H, ArMe), 1.41 (s, 6 H, β-Me), −0.56 (s, 3 H, AlMe) ppm.
13C NMR (126 MHz, C6D6) δ 169.85 (CN), 141.92, 134.70, 132.85,
128.95, 128.38, 127.96, 126.41 (Ar), 97.58 (γ-CH), 22.19 (β-Me),
19.25, 18.28 (ArMe), −10.24 (AlMe) ppm. 27Al NMR (130.3 MHz,
C6D6): δ 65.99 ppm. Anal. Calcd for C22H28AlClN2 (382.91): C,
69.01; H, 7.37; N, 7.32. Found: C, 68.60; H, 7.60; N, 7.16. X-ray
quality crystals were grown from a mixed solution of toluene and n-
hexane (5:1).
SUMMARY
■
The β-diketiminato ligand with less bulky substituents (L =
HC[C(Me)N(2,6-Me2C6H3)]2) provides a unique chance to
investigate the formation and reaction of discrete organo-
aluminum compounds. For the first time a series of novel 1:1
adducts of composition LH·AlMen(Cl)3−n (n = 2, 3; 1, 4; 0, 5)
was prepared, where the ligand features a unprecedented
monodentate neutral binding mode. These adducts can be seen
as trapped intermediates, and they are useful for preparing the
corresponding derivatives via further intramolecular elimination
of methane or HCl. A mixture of [LAl(Me)]2(μ-O) (7) and
[LAlMe(μ-OH)]2 (8) was obtained from the NHC-supported
hydrolysis of LAlMeCl (2). This observation indicates the role
of the sterically demanding ligand in the competitive
coordination between oxygen atoms from H2O and the initially
formed LAlMe(OH) (8) onto LAlMeCl (2). This idea was
confirmed by the nearly quantitative formation of [LAl-
(Me)]2(μ-O) (7) by using 2, NHC, and 8 in toluene. When
the steric bulk of these ligands is compared, it was found that
this is obviously the key to proceed or inhibit the
intermolecular reactions of different β-diketiminato species.
Nevertheless, using the iodide analogue LAlMeI (9) in the
presence of an O-donor solvent at 0 °C was found to be useful
in suppressing such intermolecular side reactions. Treatment of
LAlH2 (11) with water resulted in intermolecular formed
dialuminoxanes [LAl(H)]2(μ-O) (12) or [LAl(OH)]2(μ-O)
(13) instead of generating LAl(OH)2. In contrast, reaction of
iPrLAlH2 with water afforded no dialuminoxanes but rather
iPrLAl(OH)2 was formed. The smooth preparation of [LAl-
(X)]2(μ-O) (X = Me, 7; Cl, 14) from LAlX(Cl) (X = Me 2; Cl,
1) and Ag2O proved to be a mild method for preparing
dialuminoxanes under anhydrous conditions. The hydrolysis of
LH·AlMen(Cl)3−n and LAlR(H) derivatives is in progress.
LH·AlMe2Cl (3). To a diethyl ether solution (40 mL) of LH (3.06
g, 10 mmol) at −18 °C, Me2AlCl (11.1 mL, 0.9 M in heptane, 10
mmol) was added drop by drop. The mixture was stirred and allowed
to warm to room temperature. After stirring overnight, the precipitate
was filtered off and washed with n-hexane (5 mL) to afford a white
1
solid. Yield 3.63 g (91%); mp 141 °C. H NMR (500 MHz, C6D6) δ
6.50−7.01 (m, Ar), 4.48 (s, 1 H, NH), 4.08 (s, 1 H, γ-CH), 2.58 (s, 3
H, β-Me), 2.01 (s, 6 H, ArMe), 1.60 (s, 6 H, ArMe), 1.39 (s, 3 H, β-
Me), −0.28 (s, 6 H, AlMe2) ppm. 13C NMR (126 MHz, C6D6) δ
144.37 (CN), 135.07, 131.32, 128.08, 127.96, 127.86, 127.67, 127.58,
127.48, 125.59 (Ar), 93.54 (γ-CH), 23.93, 20.14 (β-Me), 17.95, 16.85
(ArMe), −5.95 (AlMe2) ppm. 27Al NMR (130.3 MHz, C6D6): δ 67.86
ppm. IR (Nujol mull, cm−1): υ
̃
3339.73 (NH). Anal. Calcd for
C23H32AlClN2 (398.95): C, 69.24; H, 8.08; N, 7.02. Found: C, 69.14;
H, 8.16; N, 7.14. X-ray quality crystals were grown from diethyl ether.
LH·AlMeCl2 (4). Preparation of 4 was accomplished like that of 3
from LH (0.92 g, 3 mmol) and MeAlCl2 (3 mL, 1.0 M, 3 mmol). Yield
1
1.17 g (93%); mp 213 °C. H NMR (500 MHz, C6D6) δ 6.52−6.82
(m, Ar), 4.70 (s, 1 H, NH), 4.08 (s, 1 H, γ-CH), 2.73 (s, 3 H, β-Me),
2.05 (s, 6 H, ArMe), 1.58 (s, 6 H, ArMe), 1.42 (s, 6 H, β-Me), −0.40
(s, 3 H, ArMe) ppm. 13C NMR (126 MHz, C6D6) δ177.44 (CN),
161.43, 143.18, 134.92, 133.56, 132.11, 128.11, 128.04, 127.96, 127.86,
127.67, 127.58, 127.48, 126.19 (Ar), 93.59 (γ-CH), 24.21, 20.57 (β-
Me), 17.98, 16.84 (ArMe), −6.35 (AlMe) ppm. 27Al NMR (130.3
MHz, C6D6): δ 61.07 ppm. IR (Nujol mull, cm−1): υ
̃
3283.58 (NH).
Anal. Calcd for C22H29AlCl2N2 (419.37): C, 63.01; H, 6.97; N, 6.68.
Found: C, 64.12; H, 6.88; N, 6.52.
LH·AlCl3 (5). Preparation of 5 was accomplished like that of 3 from
LH (0.92 g, 3 mmol) and AlCl3 (0.40 g, 3 mmol). Yield 1.20 g (91%);
mp 175 °C. 27Al NMR (130.3 MHz, C6D6): δ 61.60 ppm. IR (Nujol
̃
EXPERIMENTAL SECTION
■
All manipulations were carried out under an atmosphere of purified
nitrogen using standard Schlenk techniques. The samples for analytical
measurements as well as for the reactions were stored in a MBraun
Unilab glovebox. The solvents were purified and dried with sodium/
mull, cm−1): υ 3321.38 (NH). Anal. Calcd for C H AlCl N
2
(439.79): C, 57.35; H, 5.96; N, 6.37. Found: C, 58.73; H, 6.01; N,
6.24.
21 26
3
1
potassium benzophenone, and were freshly distilled prior to use. H,
LAlMe2 (6). To a toluene solution (40 mL) of LH (3.06 g, 10
mmol) at room temperature, AlMe3 (10 mL, 1.0 M in hexane, 10
mmol) was added drop by drop. The mixture was stirred at 100 °C
overnight. After workup, all volatiles were removed in vacuo to give a
13C, and 27Al NMR spectra were recorded on a Bruker AV 500
spectrometer. Melting points were measured in a sealed glass tube
using a Buchi B-540 instrument without correction. IR absorption
̈
1
white solid. Yield 3.30 g (91%); mp 106 °C. H NMR (500 MHz,
spectra were obtained as Nujol mulls between KBr plates using a
Fourier transform infrared spectrometer Nicolet 380 (Thermo Fisher
Scientific). Elemental analysis was performed using a Vario EL III
instrument. AlCl3, MeAlCl2, Me2AlCl, AlMe3, Ag2O, nBuLi, and
LiAlH4 were purchased from Aldrich and used as received. LH,
LLi·THF,36 and 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene (N-
heterocyclic carbene, abbreviated as NHC)37 were prepared as
described in literature.
C6D6) δ 6.87−6.99 (m, Ar), 4.82 (s, 1 H, γ-CH), 2.22 (s, 12 H, ArMe),
1.43 (s, 6 H, β-Me), −0.58 (s, 6 H, AlMe) ppm. 13C NMR (126 MHz,
C6D6) δ 168.60 (CN), 143.13, 133.51, 128.63, 125.79 (Ar), 96.02 (γ-
CH), 22.14 (β-Me), 18.40 (ArMe), −8.27 (AlMe) ppm. 27Al NMR
(130.3 MHz, C6D6): δ 71.82 ppm. Anal. Calcd for C23H31AlN2
(362.49): C, 76.21; H, 8.62; N, 7.73. Found: C, 76.29; H, 8.89; N,
7.87.
[LAl(Me)]2(μ-O) (7). Method A. To a toluene solution (40
mL) of LAlMeCl (2) (1.15 g, 3 mmol) and [C(Me)N(iPr)]2C
(NHC, 0.54 g, 3 mmol) at room temperature was added
degassed water (27 μL, 1.5 mmol) using a microsyringe. The
mixture was stirred for 6 h, and the resultant precipitate was
removed by filtration. The solvent of the filtrate was removed
to produce a crystalline solid. Yield 0.70 g (66%);
LAlCl2 (1). To a diethyl ether solution (20 mL) of AlCl3 (0.40 g, 3
mmol) at −78 °C LLi·THF (1.15 g, 3 mmol) in diethyl ether (20 mL)
was added drop by drop. The mixture was stirred and allowed to warm
to room temperature. After additional stirring for 12 h, the LiCl was
filtered off. The volatile components of the filtrate were removed in
vacuo to obtain a crystalline white solid. Yield 1.08 g (89%); mp 234
1
°C. H NMR (500 MHz, C6D6) δ 6.92 (m, Ar), 4.84 (s, 1 H, γ-CH),
2.32 (s, 12 H, ArMe), 1.35 (s, 6 H, β-Me) ppm. 13C NMR (126 MHz,
C6D6) δ 171.55 (CN), 140.47, 133.97, 129.02, 126.97 (Ar), 97.95 (γ-
CH), 22.32 (β-Me), 18.80 (ArMe) ppm. 27Al NMR (130.3 MHz,
C6D6): δ 65.19 ppm. Anal. Calcd for C21H25AlCl2N2 (403.32): C,
62.54; H, 6.25; N, 6.95. Found: C, 63.19; H, 6.38; N, 7.03.
Method B. To a toluene solution (20 mL) of LAlMeCl (2) (0.38 g,
1 mmol) and [C(Me)N(iPr)]2C (NHC, 0.18 g, 1 mmol) at room
temperature was added the toluene solution (15 mL) of LAlMe(OH)
(8) (1.15 g, 1 mmol) drop by drop under rigorous stirring. The
resultant mixture was stirred for additional 6 h and the precipitate was
filtered off. All volatile components of the filtrate were removed to
LAlMeCl (2). The suspension of LH·AlMe2Cl (3) (5.59 g, 14
mmol) in toluene (60 mL) was stirred under reflux for 2 h. After
1
produce a crystalline solid. Yield 0.65 g (91%), mp 286 °C. H NMR
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(500 MHz, C6D6) δ 6.87−7.06 (m, Ar), 4.94 (s, 2 H, γ-CH), 2.24 (s,
12 H, ArMe), 2.17 (s, 12 H, ArMe), 1.51 (s, 12 H, β-Me), −0.99 (s, 6
H, AlMe) ppm. 13C NMR (126 MHz, C6D6) δ 167.65 (CN), 144.25,
135.05, 133.11, 128.47, 128.16, 127.97, 127.87, 127.67, 127.59, 127.48,
125.57 (Ar), 96.10 (γ-CH), 22.20 (β-Me), 19.52, 18.30 (ArMe),
−11.16 (AlMe) ppm. 27Al NMR (130.3 MHz, C6D6): δ 60.61 ppm.
Anal. Calcd for C44H56Al2N4O (710.90): C, 74.34; H, 7.94; N, 7.88.
Found: C, 76.43; H, 8.18; N, 7.96. The alternative preparation of 7
was accomplished like that of 14 from LAlMeCl (2) with 0.5 equiv of
Ag2O. X-ray quality crystals were grown from toluene.
and dried in vacuo to give a white solid. Yield 0.29 g (76%); mp 280
°C. 1H NMR (500 MHz, C6D6) δ 6.82−7.00 (m, Ar), 4.91 (s, 2 H, γ-
CH), 3.95 (vb, 2 H, AlH), 2.25 (s, 12 H, ArMe), 2.21 (s, 12 H, ArMe),
1.49 (s, 12 H, β-Me) ppm. 13C NMR (126 MHz, C6D6) δ 168.19
(CN), 143.82, 134.86, 134.57, 128.49, 128.14, 125.72 (Ar), 95.82 (γ-
CH), 21.86 (β-Me), 18.68, 18.45 (ArMe) ppm. 27Al NMR (130.3
MHz, C6D6): δ 65.80 ppm. IR (Nujol mull, cm−1): υ
̃
1803.47 (AlH),
1795.02 (AlH). Anal. Calcd for C42H52Al2N4O (682.85): C, 73.87; H,
7.68; N, 8.20. Found: C, 72.15; H, 7.61; N, 8.07. X-ray quality crystals
were grown from toluene.
[LAl(OH)]2(μ-O) (13). Preparation of 13 was accomplished like that
of 12 from LAlH2 (11) (0.33 g, 1 mmol) in toluene (30 mL) and
degassed water (27 μL, 1.5 mmol). Yield 0.21 g (58%); mp 264 °C. 1H
NMR (500 MHz, C6D6) δ 6.88−7.05 (m, Ar), 4.78 (s, 2 H, γ-CH),
2.44 (s, 12 H, ArMe), 1.88 (s, 12 H, ArMe), 1.37 (s, 12 H, β-Me),
−0.72 (s, 2 H, OH) ppm. 13C NMR (126 MHz, C6D6) δ 168.18 (CN),
143.82, 134.85, 134.56, 128.49, 128.14, 125.72 (Ar), 95.82 (γ-CH),
21.87 (β-Me), 18.69, 18.45 (ArMe) ppm. 27Al NMR (130.3 MHz,
[LAl(Me)(μ-OH)]2 (8). To a mixture of LAlMeI (9) (1.32 g, 2.78
mmol) and NHC (0.50 g, 2.78 mmol) in THF (40 mL) at 0 °C was
added distilled H2O (50 μL, 2.78 mmol). The suspension was stirred
at 0 °C for additional 2 h and then 12 h at room temperature. After
workup, the insoluble solid was removed by filtration. All volatile
components of the filtrate were removed in vacuo, followed by being
washed with a small portion of n-hexane (5 mL) and dried, to obtain a
white solid. Yield 0.73 g (72%); mp 273 °C. (A) 1H NMR (500 MHz,
C6D6) δ 6.75−7.13 (m, Ar), 4.93 (s, 1 H, γ-CH), 2.14 (s, 6 H, ArMe),
1.98 (s, 6 H, ArMe), 1.30 (s, 6 H, β-Me), 1.21 (s, 1 H OH), −0.44 (s, 3
H, AlMe) ppm; 13C NMR (126 MHz, C6D6) δ 166.80 (CN), 124.82−
143.01 (Ar), 97.49 (γ-CH), 23.26 (β-Me), 18.66, 18.10 (ArMe) ppm.
(B) 1H NMR (500 MHz, C6D6) δ 6.75−7.13 (m, Ar), 4.86 (s, 1 H, γ-
CH), 2.50 (s, 6 H, ArMe), 2.14 (s, 6 H, ArMe), 1.45 (s, 6 H, β-Me),
0.34 (s, 1 H OH), −0.78 (s, 3 H, AlMe) ppm; 13C NMR (126 MHz,
C6D6) δ 168.66 (CN), 124.82−143.01 (Ar), 96.21 (γ-CH), 22.00 (β-
Me), 18.80, 18.10 (ArMe) ppm. 27Al NMR (130.3 MHz, C6D6): δ
C6D6): δ 67.22 ppm. IR (Nujol mull, cm−1): υ
̃
3674.4 (OH). Anal.
Calcd for C42H52Al2N4O3 (714.85): C, 70.57; H, 7.33; N, 7.84. Found:
C, 71.39; H, 7.31; N, 7.91. The alternative route to 13 was the reaction
of 12 with water in a 1:2 ratio. X-ray quality crystals of 13 were grown
from toluene.
[LAl(Cl)]2(μ-O) (14). To a suspension of Ag2O (0.12 g, 0.5 mmol)
in CH2Cl2 solution (20 mL) at −18 °C, LAlCl2 (1) (0.40 g, 1 mmol)
in CH2Cl2 solution (20 mL) was added drop by drop. The mixture
was stirred for 3 d in the darkness. After workup, the insoluble
component was removed by filtration, and the filtrate was
concentrated to form a pale brown residue. Washing the residue
with n-hexane (5 mL) and drying it in vacuum afforded an off-white
solid. Yield 0.32 g (84%); mp 319 °C (decomp). 1H NMR (500 MHz,
C6D6) δ 6.85−7.07 (m, Ar), 4.85 (s, 2 H, γ-CH), 2.38 (s, 12 H, ArMe),
1.91 (s, 12 H, ArMe), 1.36 (s, 12 H, β-Me) ppm. 13C NMR (126 MHz,
C6D6) δ 169.50 (CN), 142.72, 134.72, 133.92, 129.02, 128.19, 126.08
(Ar), 97.32 (γ-CH), 22.22 (β-Me), 19.35, 18.93 (ArMe) ppm. 27Al
NMR (130.3 MHz, C6D6): δ 69.37 ppm. Anal. Calcd for
C42H51Al2ClN4O2 (733.30): C, 68.79; H, 7.01; N, 7.64. Found: C,
67.22; H, 6.86; N, 7.73. X-ray quality crystals were grown from a
mixture of toluene and dichloromethane (1:1).
Structure Determination. The crystallographic data of com-
pounds 2, 3, 6−8, 11−14, and 3′ were collected on an Oxford Gemini
S Ultra system. In all cases graphite-monochromated Mo−Kα radiation
(λ = 0.71073 Å) was used. Absorption corrections were applied using
the spherical harmonics program (multiscan type). The structures
were solved by direct methods (SHELXS-97)38 and were refined by
full-matrix least-squares on F2 with the program of SHELXL-97.39 In
general, the non-hydrogen atoms were located by difference Fourier
synthesis and refined anisotropically, and hydrogen atoms were
included using the riding model with Uiso tied to the Uiso of the parent
atoms unless otherwise specified. A summary of cell parameters, data
collection, and structure solution and refinement is given in
Supporting Information, Table S1.
63.23 ppm. IR (Nujol mull, cm−1): υ
̃
3679.64 (OH). Anal. Calcd for
C44H58Al2N4O2 (728.92): C,72.5; H, 8.02; N, 7.69. Found: C, 71.8; H,
8.11; N, 7.71. X-ray quality crystals were grown from toluene at −18
°C.
LAlMeI (9). Toluene (40 mL) was added to the mixture of LAlMe2
(6) (2.90 g, 8 mmol) and I2 (2.03 g, 8 mmol). The resulting solution
was stirred for 6 d at room temperature. After workup, the solvent was
removed to give a pale brown solid. Yield 3.64 g (96%); mp 162 °C.
1H NMR (500.13 MHz, C6D6): δ 6.86−7.02 (m, Ar), 4.90 (s, 1 H, γ-
CH), 2.54 (s, 6 H, ArMe), 2.07 (s, 6 H, ArMe), 1.37 (s, 6 H, β-Me),
−0.25 (s, 3 H, AlMe) ppm. 13C NMR (126 MHz, C6D6) δ 170.14
(CN), 141.51, 134.40, 132.93, 129.48, 128.48, 126.57 (Ar), 98.16 (γ-
CH), 22.50 (β-Me), 20.97, 18.50 (ArMe). −8.17 (AlMe) ppm. 27Al
NMR (130.3 MHz, C6D6): δ 59.62 ppm. Anal. Calcd for C22H28AlIN2
(474.36): C, 55.70; H, 5.95; N, 5.91. Found: C, 54.99; H, 5.87; N,
5.80.
LAlI2 (10). Preparation of 10 was accomplished like that of 9 from
LAlMe2 (6) (2.90 g, 8 mmol) and I2 (4.06 g, 16 mmol). Yield 4.36 g
(93%); mp 234 °C. 1H NMR (500 MHz, C6D6) δ 6.85−6.99 (m, Ar),
4.96 (s, 1 H, γ-CH), 2.38 (s, 12 H, ArMe), 1.34 (s, 6 H, β-Me) ppm.
13C NMR (126 MHz, C6D6) δ 171.23 (CN), 140.79, 133.82, 129.21,
127.08 (Ar), 99.42 (γ-CH), 23.10 (β-Me), 20.79 (ArMe) ppm. 27Al
NMR (130.3 MHz, C6D6): δ 66.20 ppm. Anal. Calcd for C21H25AlI2N2
(586.23): C, 43.03; H, 4.30; N, 4.78. Found: C, 42.11; H, 4.39; N,
4.62.
LAlH2 (11). To a mixture of LH (1.53 g, 5 mmol) and a little excess
of LiAlH4 (0.23 g, 5.9 mmol) was added toluene (40 mL). The
suspension was stirred and heated to 90 °C for 12 h. After cooling to
room temperature, the suspension was filtered. The filtrate was
evaporated to dryness to yield a colorless crystalline solid. Yield 1.37 g
(82%); mp 206 °C. 1H NMR (500 MHz, C6D6) δ 6.87−7.04 (m, Ar),
4.74 (s, 1 H, γ-CH), 4.58 (vb, 2 H, AlH2), 2.31 (s, 12 H, ArMe), 1.41
(s, 6 H, β-Me) ppm. 13C NMR (126 MHz, C6D6) δ 169.17 (CN),
142.05, 133.59, 128.84, 126.36 (Ar), 95.53 (γ-CH), 21.69 (β-Me),
18.17 (ArMe) ppm. 27Al NMR (130.3 MHz, C6D6): δ 68.15 ppm. IR
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystal data (CIF) for compounds 2, 3, 6−8, 11−14, and 3′,
important structural parameters (Table S1), molecular
structures of 2, 6, 8, 11, 13, and 3′ (Figures S1−S6) with
selected bond lengths and angles, experimental and character-
ization data of compounds 1′−3′, IR data for compounds 1−14,
and discussion of compounds 3−5. This material is available
free of charge via the Internet at http://pubs.acs.org.
(Nujol mull, cm−1): υ
̃
1819.18 (AlH), 1787.27 (AlH). Anal. Calcd for
C21H27AlN2 (334.43): C, 75.42; H, 8.14; N, 8.38. Found: C, 75.58; H,
8.07; N, 8.50. X-ray quality crystals were grown from toluene.
[LAl(H)]2(μ-O) (12). The degassed water (10 μL, 0.56 mmol) was
added to a solution of LAlH2 (9) (0.37 g, 1.12 mmol) in toluene (30
mL) at room temperature. The mixture was stirred for 12 h and
filtered. All volatiles were removed under vacuum to leave a white
residue, which was washed with a small portion of n-hexane (5 mL)
AUTHOR INFORMATION
Corresponding Author
*Fax: (+86) 731-88879616 (H.L.), (+49) 551-393-373
(H.W.R.). E-mail: lihaipu@csu.edu.cn (H.L.), hroesky@gwdg.
de (H.W.R.).
■
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Article
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Roesky, H. W.; Gurubasavaraj, P. M.; Stalke, D.; Ye, H. Organometallics
2008, 27, 769−777.
́
ez-Per
́
ez, V. M.;
Notes
The authors declare no competing financial interest.
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Schmidt, H.-G.; Noltemeyer, M. Organometallics 2005, 24, 380−384.
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A.; Biadene, M.; Herbst-Irmer, R.; Noltemeyer, M.; Schmidt, H.-G.
Inorg. Chem. 2006, 45, 1853−1860.
ACKNOWLEDGMENTS
■
This work was supported by National Natural Science
Foundation of China (20902112), National Undergraduate
Innovative Test Program of China (CSU, LA10022) and the
Deutsche Forschungsgemeinschaft.
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