A crowded lithium diaryloxo{tris(trimethylsilyl)methyl}aluminate and a bis(triarylsiloxo){tris(trimethylsilyl)methyl}alane

Article abstract of DOI:10.1039/b206770f

The reaction of [Li(thf)₂AlH₃{C(SiMe₃)₃}] ₂ with four equivalents of ArOH (Ar = C₆H₃Prⁱ₂-2,6) yielded [Li(thf)-(μ-OAr)₂2AlH{C(SiMe₃)₃}] (2) (thf = tetrahydrofuran), which has a structure containing a four-membered LiO₂Al ring both in the crystal and in toluene solution. The corresponding reaction with ArOH (Ar = C₆H₃Bu^t ₂-2,6) gave a mixture that could not be separated by fractional crystallisation. The reaction of 1 with Ph₃SiOH gave [Al(OSiPh₃)₂-{C(SiMe₃)₃}(thf)] (3), which was shown by an X-ray structure determination to be monomeric.

Full text of DOI:10.1039/b206770f

View Article Online / Journal Homepage / Table of Contents for this issue
A crowded lithium diaryloxo{tris(trimethylsilyl)methyl}aluminate
and a bis(triarylsiloxo){tris(trimethylsilyl)methyl}alane
Anthony G. Avent,a Colin Eaborn,*a Ian B. Gorrell,b Peter B. Hitchcocka and J. David Smith*a
a School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton,
UK BN1 9QJ. E-mail: c.eaborn@sussex.ac.uk; j.d.smith@sussex.ac.uk
b Department of Chemical and Forensic Sciences, University of Bradford, West Yorkshire,
UK BD7 1DP
Received 11th July 2002, Accepted 21st August 2002
First published as an Advance Article on the web 8th October 2002
The reaction of [Li(thf )2AlH3{C(SiMe3)3}]2 (1) with four equivalents of ArOH (Ar = C6H3Pri2-2,6) yielded [Li(thf )-
(µ-OAr)2AlH{C(SiMe3)3}] (2) (thf = tetrahydrofuran), which has a structure containing a four-membered LiO2Al
ring both in the crystal and in toluene solution. The corresponding reaction with ArOH (Ar = C6H3But2-2,6) gave
a mixture that could not be separated by fractional crystallisation. The reaction of 1 with Ph3SiOH gave [Al(OSiPh3)2-
{C(SiMe3)3}(thf )] (3), which was shown by an X-ray structure determination to be monomeric.
There is considerable interest in the chemistry of alkoxo- and
alkoxo(alkyl)-alanes and aluminates bearing bulky groups
because their structures provide insight into intermediates
involved in the reduction of carbonyl compounds by
aluminium hydrides,1–4 the stereochemistry of the addition
of organolithium reagents to carbonyl compounds,2,5,6 and
Ziegler–Natta catalysis.7 The presence of the alkoxo groups has
been shown to modify both the reactivity and selectivity of
aluminium hydride reagents and a range of alkoxohydrido
species has been detected in solution.1,8 A number of lithium
alkoxo- or aryloxo-aluminates containing four-membered
LiO2Al rings have been characterized in the solid state.3,5,9–11
However, it is not clear what factors determine whether
species containing both lithium and aluminium are stable in
solution or whether they separate to give a mixture of species,
some of which contain only lithium and others only
aluminium.
[Li(thf)Al(OC6H3Pri2)2H{C(SiMe3)3}] (2)
We have studied the reactions of the alkyltrihydroaluminate
[Li(thf )2AlH3{C(SiMe3)3}]2 (1)12 with alcohols,9,10 aldehydes
and ketones,10 thiols and disulfides,13 and aniline,14 and have
isolated a series of crowded functionalised tris(trimethylsilyl)-
methylaluminates. In most cases, all three Al–H bonds in the
parent 1 are replaced by bonds between aluminium and a group
X containing donor atoms such as oxygen, sulfur, or nitrogen,
but in two cases only two Al–H bonds are replaced and alkyl-
hydroaluminates containing larger groups X (X = NHPh or
SBut) have been isolated.13,14 In this article we describe the
extension of this work to reactions of compound 1 with the
bulky phenols ArOH (Ar = C6H3Pri2-2,6 and C6H3But2-2,6) and
the silanol Ph3SiOH, and bring together results from several
of our previous papers. There are few structural data on (tri-
organosiloxo)organoalanes, even though these compounds
have a number of applications as catalysts.15
A solution of 2,6-diisopropylphenol (0.20 cm3, 1.08 mmol) in
toluene (20 cm3) was added to a stirred solution of 1 (0.22 g,
0.27 mmol) in toluene (10 cm3). Gas was evolved and the
mixture was stirred at room temperature for 16 h then heated to
70 ЊC for 2 h and allowed to cool to room temperature. The
solvent was removed under vacuum and the residue extracted
into heptane. The extract was cooled to Ϫ30 ЊC to give colour-
less very air-sensitive crystals of 2 (0.28 g, 75%), mp 172 ЊC
(found: C, 64.00, H, 10.28; C38H70AlLiO3Si3 requires C, 65.85,
H, 10.18%). vmax/cmϪ1 1915w, 1814m (Al–H), 1591m, 1260s,
1196m, 1113m, 1044s, 1028s, 859s, 798s; δH (298 K) 0.43 (27 H,
s, SiMe3), 0.76 and 2.52 (4 H, thf ), 1.1 and 1.4 (12 H, vb, Pri)
[0.97, 1.07, 1.41 and 1.49 (6 H, d, 3JHH = 6.7 Hz) at 248 K], 3.9
and 4.5 (4 H, vb, Pri) [3.91 and 4.53 (2 H, sept, 3JHH = 6.7 Hz) at
3
248 K], 5.3 (1 H, vb, AlH), 6.94 (2 H, t, JHH = 7.6 Hz, p-H),
3
4
7,14 (4 H, s, m-H) [7.04 and 7.09 (2 H, dd, JHH = 7.6, JHH
=
1.6 Hz) at 248 K]; δC (248 K) 5.8 (1JSiC = 44.5 Hz, SiMe3), 22.2,
22.7 and 26.0 (×2) (CHMe2), 23.7 and 67.8 (thf ), 25.8 and 26.7
(1JCH = 123 Hz, CHMe2), 121.4 (p-C), 123.6 and 124.7 (m-C),
137.4 and 138.8 (o-C), 151.5 (i-C); δLi (258 K) 0.24; δAl (298 K)
108 (∆v1/2 ca. 5 kHz); δSi (298 K) Ϫ4.2. The spectra showed
that 2 was essentially free from impurities, despite the low C
analysis.
Experimental
Air and moisture were excluded as far as possible from all
manipulations by the use of flame-dried glassware, Schlenk
techniques and Ar as blanket gas. NMR spectra from samples
dissolved in benzene-d6 or toluene-d8 were recorded at 300.1
(1H), 75.4 (13C), 194.5 (7Li), 130.4 (27Al) and 99.4 MHz (29Si).
Chemical shifts are relative to SiMe4 (H, C, and Si), aqueous
LiCl or Al(NO3)3. IR spectra were recorded from Nujol mulls.
Reactions of 1 with two equivalents of ArOH gave a complex
mixture showing eight signals in the SiMe3 region of the NMR
DOI: 10.1039/b206770f
J. Chem. Soc., Dalton Trans., 2002, 3971–3974
This journal is © The Royal Society of Chemistry 2002
3971

View Article Online
spectrum, including one from 2. The product from the reaction
with six equivalents of ArOH gave a mixture showing five
SiMe3 signals; a few crystals that appeared to be of LiOAr were
obtained but no attempt was made to isolate other products.
Results and discussion
The reaction between the compound 1 and four equivalents of
2,6-Pri2C6H3OH (ArOH) gave in good yield the novel alkyl-
bis(aryloxy)hydridoaluminate [Li(thf )Al(OAr)2H{C(SiMe3)3}]
2, analogous to the alkanethiolato compound [Li(thf )Al-
(SBut)2H{C(SiMe3)3}] previously described.13 The molecular
structure is shown in Fig. 1. The LiO2Al ring has a fold angle of
Reaction of 1 with 2,6-But2C6H3OH
A solution of 2,6-di-t-butylphenol (0.16 g, 0.77 mmol) in
toluene (5 cm3) was slowly added to a stirred solution of 1
(0.32 g, 0.39 mmol) in toluene (20 cm3) at Ϫ70 ЊC. The mixture
was stirred at Ϫ70 ЊC for 1 h, then the solvent was removed
under vacuum to give a sticky white solid. This was stirred with
heptane (10 cm3) and the mixture filtered. The filtrate was
cooled to Ϫ30 ЊC to give as major product a colourless crystal-
line solid with a 1H NMR spectrum3 and unit cell dimensions16
identical with those of [LiOC6H3But2ؒthf] made independently
from ArOH and LiBun. A second crop of crystals was identical.
The third crop, consisting of only a few crystals, was an
unidentified product with δH 0.40 (SiMe3), 1.51 (But), 6.85 (m)
and 7.25 (d, Ar). [LiOC6H3But2ؒthf] was similarly identified as a
product from the reaction between 1 and four equivalents of
ArOH.
[Al(OSiPh3)2{C(SiMe3)3}(thf)] (3)
A solution of Ph3SiOH (0.48 g, 1.74 mmol) in toluene (10 cm3)
was added dropwise to a stirred solution of 1 (0.24 g,
0.29 mmol) in toluene (20 cm3) at 0 ЊC. Gas was evolved. The
mixture was allowed to warm to room temperature and stirred
for 18 h, and the suspended white solid was filtered off. The
solvent was removed from the filtrate and the white solid
residue recrystallised from a 1 : 1 heptane–toluene mixture
to give colourless crystals of 2 (0.50 g, 98%), mp 202 ЊC
(Found: C, 67.63; H, 7.54. C50H65AlO3Si5 requires C, 68.13;
H, 7.43%). vmax/cmϪ1 1962m, 1901m, 1828m, 1663w, 1588m,
1567w, 1428m, 1298m, 1250s, 1187m, 1157w, 1111s, 1056s,
1033s, 1016s, 938w, 917w, 850s bd, 741m, 704m, 664m, 614w;
δH (298 K) 0.27 (27 H, s, SiMe3), 0.88 and 3.97 (4 H, thf ), 7.11
(18 H, m- and p-C), 7.87 (12 H, o-H); δC 6.8 (SiMe3), 24.2
and 73.9 (thf ), 127.7 (m-C), 129.5 (p-C), 136.8 (o-C), 138.4
(i-C); δSi Ϫ25.1 (SiPh3), Ϫ3.9 (SiMe3); the 27Al signal was not
observed and therefore assumed to be very broad; m/z 793 (6,
M–Me–thf ), 607 (15), 217 (90), 129 (50), 92 (70), 71 (80), 42
(100).
Fig. 1 Molecular structure of the predominant conformer of [Li-
(thf )(µ-OC6H3Pri2-2,6)2AlH{C(SiMe3)3}] (2).
15Њ across the O1 ؒ ؒ ؒ O2 vector with the C(SiMe3)3 group on
the less crowded convex side and the thf and the hydrogen
attached to aluminium on the concave side of the ring. In
the crystal there is a small amount of another conformer
with the hydrogen and C(SiMe3)3 group attached to aluminium
interchanged, but the conformers pack in a disordered fashion
leaving the aryloxo groups well-defined. The bond lengths and
angles for the major conformation are given in Table 1. The
corresponding bond lengths on either side of a plane through
Al and Li and perpendicular to the OLiO and OAlO planes
are not significantly different but the molecule as a whole has
no symmetry since the two aryl groups are not quite equally
twisted about the C–O bonds. The Li–O(Ar) distances (mean
1.885 Å) are only just outside and the Al–O distances (mean
1.804 Å) are within the range of values previously found in
compounds with LiO2Al rings having three-coordinate Li and
four-coordinate Al [Li–O 1.910(8) to 1.97(2) Å; Al–O 1.786(1)
to 1.808(2) Å].3,9,18 The differences between the Li–O and Al–O
Crystallography
Crystal data: for 2: M = 693.1; orthorhombic, space group Pbca
(no. 61), a = 19.071(4), b = 20.379(8), c = 22.142(6) Å; U =
8605(4) Å3; Z = 8; µ = 0.16 mmϪ1; 5963 unique reflections, 3586
with I > 2σ(I), R1, wR2 = 0.081, 0.207 [I > 2σ(I)] and 0.138,
0.244 (all data). For 3: M = 881.5; monoclinic, space group
P21/c (no. 14), a = 9.596(2), b = 21.418(5), c = 24.212(9) Å,
β = 101.16(2)Њ; U = 4882(2) Å3; Z = 4; µ = 0.20 mmϪ1; 9111
reflections, 8576 unique [Rint = 0.046], 5354 with I > 2σ(I), R1,
wR2 = 0.061, 0.112 [I > 2σ(I)] and 0.117, 0.133 (all data).
Data were collected from a CAD4 diffractometer and struc-
tures were refined by full matrix least squares refinement
(SHELXL-97)17 with most (2) or all (3) non-H atoms aniso-
tropic and H atoms included in riding mode. For 2, the
molecule was disordered, with an alternative low occupancy Al
site on the opposite side of the LiO2 plane, associated with a
different orientation of the C(SiMe3)3 group sharing a common
C1 position. The alternative orientation was further disordered
with two sets of Si positions. The C atoms were located only
for the major occupancy C(SiMe3)3 group, and the hydrogen
attached to Al was fixed at a position obtained from a difference
map. The lower occupancy Al and Si sites were left isotropic.
CCDC reference numbers 189680 and 189681.
Table 1 Bond lengths (Å) and angles (Њ) for [Li(thf )(µ-OC6H3-
Pri2-2,6)2AlH{C(SiMe3)3}] (2)
Al–O1,2
Al–C1
Li–O1,2
Li–O3
O–C(Ar)
Al ؒ ؒ ؒ Li
Li ؒ ؒ ؒ C29b
Si–C1
1.804(4)a
2.005(6)
O1–Al–O2
O1–Al–C
O2–Al–C
O1–Li–O2
O1–Li–O3
O2–Li–O3
Si–C1–Si
88.24(17)
120.9(2)
121.0(2)
83.6(4)
132.4(4)
1.885(11)a
1.832(11)
1.375(6)a
2.677(11)
140.1(6)
3.36
108.9(3)–112.7(3)
102.5(3)–107.7(3)
93.0(3)a
1.885(6)a
Me–Si–Me
Li–O–Al
Si–Me
1.875(6)a
C–O–Al
C–O–Li
148.4(3), 150.2(3)
110.6(4), 114.6(4)
a Mean; no individual value (standard deviation in parentheses) differs
significantly. b Others are Li ؒ ؒ ؒ C20, 3.61; Li ؒ ؒ ؒ C17, 3.71;
Li ؒ ؒ ؒ C32, 3.96 Å.
See http://www.rsc.org/suppdata/dt/b2/b206770f/ for crystal-
lographic data in CIF or other electronic format.
3972
J. Chem. Soc., Dalton Trans., 2002, 3971–3974

View Article Online
Table 2 Bond lengths (Å) and angles (Њ) for Al(OSiPh3)2C(SiMe3)3ؒthf
(3)
bond distances in such compounds vary from 0.11 to 0.17 Å,
and probably reflect differences in the crowding around the
metal centres; the difference between the Li–O and Al–O bond
distances in 2 (0.08 Å) is smaller but it is intermediate between
the difference in the widely used ionic radii (0.2 Å) and the
difference in the covalent radii (0.04 Å).19 The short Li–O(thf)
distance [1.832(11) Å] in 2 (cf. 1.897(4) to 1.976(8) Å in the
previously described compounds) may be attributed to strong
electron-withdrawal by the aryl groups, as there is also a short
bond [1.822(7) Å] in [Li(thf )V(OC6H3Pri2-2,6)4].20 The Li–OEt2
bond in [Li(OEt2)AlH(OC6H3Pri2-2,6)3] is longer [1.892(4) Å],
but this may reflect the larger size of Et2O than of thf. The
aryloxo groups lean away from the bulky alkyl group as do the
alkoxo groups in [Li(thf )nAl(OR)3{C(SiMe3)3}] (n = 1, R = But
and n = 2, R = Et).10 The Al–C, Si–C1 and Si–Me bond lengths
are all normal.
Al–O1,2
Al–O3
Al–C
Si–C1
Si–Me
Si–O
1.726(3)a
1.927(3)
1.998(4)
1.894(4)a
1.880(4)a
1.616(3)a
1.877(4)a
C–Al–O2
C–Al–O3
Ol–Al–O2
O2–Al–O3
Ol–Al–O3
Al–O1–Si4
Al–O2–Si5
O–Si–Ph
115.52(15)
110.00(14)
112.37(13)
99.13(13)
100.27(13)
163.71(18)
170.42(18)
111.0b
Si–Ph
C–Al–O1
116.78(15)
Si–C–Si
Me–Si–Me
109.61(19)a
105.0(2)a
a Mean; no individual value (standard deviation in parentheses) differs
significantly. b Mean; range from 109.51 (17) to 112.64(16)Њ.
In order to determine whether the structure found in the
crystal is also present in solution we recorded a range of NMR
1
spectra. In the H and 13C spectra of samples at room temper-
ature the peaks in the aromatic (meta-proton) and isopropyl
regions were broad, suggesting that within each set protons
were undergoing chemical exchange on the NMR timescale
between alternative sites. It was clear from spectra of samples
at 248 K that (i) within the isopropyl groups there were four
distinct methyl as well as two distinct methine environments
and (ii) there were two distinct meta-proton environments but
only one para-. Selective decoupling experiments show that the
CH resonance at δ 4.53 is associated with the CH3 resonances at
δ 1.07 and 1.49, so that these three resonances are from one
isopropyl group, and saturation transfer measurements show
that the signal at δ 1.49 is from protons that are exchanging with
those giving the signal at δ 0.97, i.e. protons from a different
isopropyl group. These NMR data indicate that at 248 K the
two aryloxo groups are equivalent but that rotation about the
O–C bond is restricted so that the isopropyl groups on the con-
vex and concave sides of the LiO2Al ring are different. The
6Li{1H} nuclear Overhauser spectra21 for 2 show that the low
frequency septet at δ 3.91 is associated with protons, attached
to C17 and C29 (Fig. 1), that are slightly nearer to the lithium
and thf (mean Li ؒ ؒ ؒ C 3.53 Å). than those, attached to
C20 and C32, giving the high frequency septet (mean Li ؒ ؒ ؒ C
3.78 Å). An alternative explanation is that the exchange
between isopropyl groups on opposite sides of the shallow
LiO2Al ring involves Al–O bond opening and recombination to
give the minor conformer detected by crystallography, followed
by ring inversion. Both rotation about O–C bonds and ring
opening (the latter having the higher activation energy) have
been postulated to account for exchange processes in solutions
of [Al(OPri)(acac)2]2.22 The value of ∆G‡ calculated from the
coalescence temperature (315 K) of the methine signal of the
isopropyl group in 2 is 60.4 kJ molϪ1.
Fig. 2 Molecular structure of [Al(OSiPh3)2C(SiMe3)3(thf )] (3).
The coordination at aluminium is that of a distorted tetra-
hedron with Al–OSi distances [mean 1.726(3) Å, Table 2]
somewhat greater than those found for similar compounds,
e.g. [Al(OSiPh3)2(acac)][1.680(4)and1.700(4)Å],22 [Al(OSiPh3)3-
(thf )] (4) [1.696(4) to 1.709(4) Å] or Al(OSiPh3)3(H2O)(thf )2 (5)
[1.708(5) Å],23 and much longer than that in the solvent-free
compound Al(OC6H2But2-2,6-Me-4)3 [1.648(7) Å].24 The Al–
O(thf ) distance in 3 [1.927(3) Å] is significantly longer than the
corresponding distances in 4 [1.861(5) Å], 5 [1.83(1) Å to H2O],
and the dihalides [AlX2{C(SiMe3)3}(thf )] [X = Cl, 1.883(2),25 Br
1.881(6) or I 1.886(4) Å14,25], indicating that the thf is held more
weakly than in these related compounds. [It was, however, not
removed when 3 was heated to 150 ЊC for 6 h.] The crowding
around aluminium in 3 is reflected in the wide Al–O–Si angles
[163.7(2) and 170.4(2)Њ] (cf. 149.7(3) to 157.3(3)Њ in 4 and
160.4(3)Њ in 5); the angles involving the Al–thf bonds are
significantly less than the tetrahedral value. Crowding around
the carbon of the C(SiMe3)3 group is shown by the fact that the
Si–C–Si angles are close to the tetrahedral value. Widening to
alleviate intraligand strain is prevented.26 The Al–O–Si angles
in 3, 4 and 5 become wider as the length of the Al–O bond
increases.
We have found no evidence for cleavage of the Al–C bonds
in 2 or 3 by the use of an excess of the reagents ArOH or Ph3-
SiOH, suggesting that the metal centre is effectively protected
from attack. In contrast, reaction of [(C6H2But3-2,4,6)AlH2]2
with Ph2Si(OH)2 yields mainly C6H3But3,27 indicating that only
slightly less well protected centres are vulnerable.
The reactions between the lithium {tris(trimethylsilyl)-
methyl} trihydroaluminate 1 and the compounds HX (X =
halogen, OR, SR or NHPh) are summarised in Scheme 1.
When X is large, e.g. OC6H3Pri2, SBut 13 or NHPh,14 the reac-
tion can be halted at the alkylhydridoaluminate stage (A) and,
An attempt to prepare the analogue of 2 with Ar = C6H3But2-
2,6 at room temperature gave a mixture that could not be
separated by fractional crystallisation. One of the components
appeared to be [LiOAr(thf )], identified by comparison of its
NMR spectrum3 and unit cell dimensions16 with those of
an authentic sample, but a pure sample of the aluminium-
containing product could not be obtained. Even with a
1 : ArOH mole ratio of 1 : 2, [LiOAr(thf )] was the only isolable
product. [The lithium aryloxides LiOAr or LiOArЈ (ArЈ =
C6H2But2-2,6-Me-4) have been reported as the major products
from the reaction between bulky phenols and LiAlH4.2,3] The
results with ArOH suggested, however, that the reaction of 1
with bulky phenols could, under certain circumstances, give
mixtures from which two products could be separated, one
containing the lithium and the other the aluminium.
Such separation was realised when 1 was treated with tri-
phenylsilanol (6 equiv.) to give an almost quantitative yield of
crystalline [Al(OSiPh3)2{C(SiMe3)3}(thf )] (3) in a form suitable
for structural characterization. The molecule is shown in Fig. 2.
J. Chem. Soc., Dalton Trans., 2002, 3971–3974
3973

View Article Online
Scheme 1
ˇ
Libr., 1985, 15, 5; (b) Z. Cerný, J. Fusek, J. Machácˇek, O. Krˇíz and
ˇ
in the case of 2, the crowding is shown by the crystal structure
ˇ
B. Cásenský, J. Organomet. Chem., 1996, 516, 115.
and the restricted rotation about C–O bonds detected by vari-
able temperature NMR data. When X is a small alkoxo or
alkanethiolato group, there is no barrier to attack by the third
equivalent of HX but the reaction stops at the alkylaluminate
stage to give an associated ion pair (B).9,10,13 When X = F, a
tetramer [Li(thf )AlF3R]4 is formed9 and when X = OMe10 or
NHPh (with an excess of HX under forcing conditions14),
products containing separated ion pairs (C) can be obtained.
Elimination of LiX from B gives the complex D. This elimin-
ation is achieved cleanly when X is Cl, Br, or I,14 probably
because of the low solubility of LiX in hydrocarbons. When X
contains a lipophilic organic group, the elimination, which
relieves crowding in the species B, depends critically on the
relative solubilities of LiX and AlRX2. It is not achieved cleanly
when X = OC6H3But2 but when X = OSiPh3 the compound 3 is
formed quantitatively. The size of the OSiPh3 group is not quite
enough to squeeze out the thf, originally present in 1, to give a
compound like AlMe(OC6H2But2-2,6-Me-4)2 containing three-
coordinate aluminium.5 Attempts to prepare compounds of
type A when X is small have resulted in complex mixtures
containing products B.10 This indicates that in the absence of
significant steric hindrance the second and third Al–H bonds in
1 are more reactive than the first. The increasing reactivity of
Al–H bonds with increasing substitution has also been
observed in the preparation of [AlH(OC6H3Pri2-2,6)2(thf )2].28
9 A. G. Avent, W.-Y. Chen, C. Eaborn, I. B. Gorrell, P. B. Hitchcock
and J. D. Smith, Organometallics, 1996, 15, 4343.
10 W.-Y. Chen, C. Eaborn, I. B. Gorrell, P. B. Hitchcock, M. Hopman
and J. D. Smith, J. Chem. Soc., Dalton Trans., 1997, 4689.
11 (a) J. Pauls and B. Neumüller, Z. Anorg. Allg. Chem., 2000, 626, 270;
(b) H. Nöth, A. Schlegel and M. Suter, J. Organomet. Chem., 2001,
621, 231; (c) S. M. Ivanova, B. G. Nolan, Y. Kobayashi, S. M. Miller,
O. P. Anderson and S. H. Strauss, Chem. Eur. J., 2001, 7, 503;
(d ) T. J. Barbarich, S. M. Miller, O. P. Anderson and S. H. Strauss,
J. Mol. Catal. A: Chem., 1998, 128, 289; (e) J. A. Francis, S. B. Bott
and A. R. Barron, J. Organomet. Chem., 2000, 597, 29; ( f ) H. Nöth,
A. Schlegel and S. R. Lima, Z. Anorg. Allg. Chem., 2001, 627, 1793;
(g) J. Pauls and B. Neumüller, Z. Anorg. Allg. Chem., 2001, 627,
2127.
12 C. Eaborn, I. B. Gorrell, P. B. Hitchcock, J. D. Smith and
K. Tavakkoli, Organometallics, 1994, 13, 4143.
13 W.-Y. Chen, C. Eaborn, I. B. Gorrell, P. B. Hitchcock and
J. D. Smith, J. Chem. Soc., Dalton Trans., 2000, 2313.
14 S. S. Al-Juaid, C. Eaborn, I. B. Gorrell, S. A. Hawkes,
P. B. Hitchcock and J. D. Smith, J. Chem. Soc., Dalton Trans., 1998,
2411.
15 R. Mulhaupt, J. Calabrese and S. D. Ittel, Organometallics, 1991, 10,
3403.
16 J. C. Huffman, R. L. Geerts and K. G. Caulton, J. Crystallogr.
Spectrosc. Res., 1984, 14, 541.
17 G. M. Sheldrick, SHELXL 97, University of Göttingen, Germany,
1997.
18 M. B. Power, S. G. Bott, J. L. Atwood and A. R. Barron, J. Am.
Chem. Soc., 1990, 112, 3446.
19 J. E. Huheey, E. A. Keiter and R. L. Keiter, Inorganic Chemistry,
HarperCollins, New York, 4th edn., 1993, p. 292.
20 W. C. A. Wilisch, M. J. Scott and W. H. Armstrong, Inorg. Chem.,
1988, 27, 4333.
21 M. M. Andrianarison, A. G. Avent, M. C. Ellerby, I. B. Gorrell,
P. B. Hitchcock, J. D. Smith and D. R. Stanley, J. Chem. Soc., Dalton
Trans., 1998, 249.
22 J. H. Wengrovius, M. F. Garbauskas, E. A. Williams, R. C. Going,
P. E. Donahue and J. F. Smith, J. Am. Chem. Soc., 1986, 108,
982.
23 A. W. Apblett, A. C. Warren and A. R. Barron, Can. J. Chem., 1992,
70, 771.
24 M. D. Healy and A. R. Barron, Angew. Chem., Int. Ed. Engl., 1992,
31, 921.
25 C. Schnitter, K. Klimek, H. W. Roesky, T. Albers, H.-G. Schmidt,
C. Röpken and E. Parisini, Organometallics, 1998, 17, 2249.
26 (a) P. T. Brain, M. Mehta, D. W. H. Rankin, H. E. Robertson,
C. Eaborn, J. D. Smith and A. D. Webb, J. Chem. Soc., Dalton
Trans., 1995, 349; (b) C. A. Morrison, D. W. H. Rankin,
H. E. Robertson, C. Eaborn, A. Farook, P. B. Hitchcock and
J. D. Smith, J. Chem. Soc., Dalton Trans., 2000, 4312.
27 R. J. Wehmschulte and P. P. Power, Polyhedron, 2000, 19, 1649.
28 J. P. Campbell and W. L. Gladfelter, Inorg. Chem., 1997, 36, 4094.
Acknowledgements
We thank the EPSRC for financial support.
References
1 (a) J. Málek, Org. React., 1985, 34, 1; (b) J. Seyden-Penne, Reductions
by the Alumino- and Borohydrides in Organic Synthesis, VCH, New
York, 1991; (c) J. Málek, Org. React., 1988, 36, 249.
2 M. D. Healy, M. B. Power and A. R. Barron, Coord. Chem. Rev.,
1994, 130, 63.
3 H. Nöth, A. Schlegel, J. Knizek, I. Krossing, W. Ponikwar and
T. Seifert, Chem. Eur. J., 1998, 4, 2191.
4 H. Nöth, A. Schlegel, J. Knizek and H. Schwenk, Angew. Chem., Int.
Ed. Engl., 1997, 36, 2640.
5 W. Clegg, E. Lamb, S. T. Liddle, R. Snaith and A. E. H. Wheatley,
J. Organomet. Chem., 1999, 573, 305 and references therein.
6 S. Saito and H. Yamamoto, Chem. Commun., 1997, 1585.
7 A. P. Shreve, R. Mulhaupt, W. Fultz, J. Calabrese, W. Robbins and
S. D. Ittel, Organometallics, 1988, 7, 409.
ˇ
ˇ
8 (a) O. Strouf, B. Cásenský and V. Kubánek, J. Organomet. Chem.
3974
J. Chem. Soc., Dalton Trans., 2002, 3971–3974