Synthesis and crystal structures of organometallic compounds containing the ligands C(SiMe3)2(SiMe2H) and C(SiMe2Ph)2(SiMe2H)

Article abstract of DOI:10.1016/j.jorganchem.2004.01.019

Metallation of (HMe₂Si)(Me₃Si)₂CH (1) by LiMe gave the organolithium compound Li(THF)₂ C(SiMe₃)₂(SiMe₂H) (2a), which exists in toluene solution as a mixture of covalent species a

Full text of DOI:10.1016/j.jorganchem.2004.01.019

Journal of Organometallic Chemistry 689 (2004) 1238–1248
www.elsevier.com/locate/jorganchem
Synthesis and crystal structures of organometallic
compounds containing the ligands C(SiMe3)2(SiMe2H)
and C(SiMe2Ph)2(SiMe2H)
Ashrafolmolouk Asadi, Anthony G. Avent, Martyn P. Coles, Colin Eaborn,
*
Peter B. Hitchcock, J. David Smith
Department of Chemistry, School of Life Sciences, University of Sussex, Brighton BN1 9QJ, UK
Received 3 December 2003; accepted 11 January 2004
Abstract
Metallation of (HMe2Si)(Me3Si)2CH (1) by LiMe gave the organolithium compound Li(THF)2C(SiMe3)2(SiMe2H) (2a), which
exists in toluene solution as a mixture of covalent species and ion pairs [Li(THF)4][Li{C(SiMe3)2(SiMe2H)}2] (2b). Treatment of a
mixture of 1 and LiMe with KOBut gave KC(SiMe3)2(SiMe2H) (3). This reacted with AlMe2Cl in hexane/THF to give
Al(THF)Me2{C(SiMe3)2(SiMe2H)} (4). Treatment of (HMe2Si)(PhMe2Si)2CH (5) with LiMe in Et2O/THF gave the THF adduct
[Li(THF)2C(SiMe2Ph)2(SiMe2H)] (6); in the presence of KOBut the solvent-free [K][C(SiMe2Ph)2(SiMe2H)] (7) was obtained.
Crystal structure determinations showed that 6 crystallizes in a molecular lattice and 7 in an ionic lattice in which the coordination
sphere of the potassium comprises phenyl groups and hydrogen atoms attached to silicon, as well as the central carbon of the bulky
carbanion. Compound 7 reacted with an excess of AlMe2Cl to give [AlClMe{C(SiMe2Ph)2(SiMe2H)}]2 (8) and AlMe3. A small
amount of the methoxo derivative [Al(OMe)Me{C(SiMe2Ph)2(SiMe2H)}]2 (9) was obtained as a byproduct, presumably after the
accidental admission of traces of air. X-ray structural determinations showed that 8 forms halogen-bridged dimers, with the bulky
ligands in the anti-configuration, and 9 forms methoxo-bridged species in which the bulky ligands are syn.
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Lithium; Potassium; Aluminium; Organosilicon
1. Introduction
In view of the recent confirmation of hydrogen
bridges between silicon centres in compounds contain-
ing cations I [15], we considered it of interest to inves-
tigate the extent to which hydrogen attached to silicon
could interact with a metal centre in derivatives con-
taining the ligands II and III.
There have been reports of Si–Hꢀ ꢀ ꢀM interactions
both when M is a main group element [1,2] and when it
is a transition metal [3–8]. Evidence from X-ray dif-
fraction studies indicates that in some cases the hydro-
gen atoms are strongly attached to silicon [1,2,6,7,9],
and in others strongly attached to the metal [5,10–12]. In
a few compounds, the hydrogen appears to be bound to
the two centres to a similar degree [13]. The range of
possibilities is taken to reflect a likely reaction pathway
for industrially important hydrogen transfer processes
such as hydrosilylation [14].
Me2
Si
Me
Si2
Me
Si 2
(PhMe2Si)2C
H
(Me3Si)
2C
(Me3Si)2C
H
H
+
Si
R2
I
These are related to a general class of potentially
bidentate ligands of the type –C(SiMe3)2(SiMe2Z), in
which the group Z is capable of donating lone pairs or
p-electrons to an appropriate electron-deficient metal
* Corresponding author. Tel.: +44-01273678124; fax: +44-
01273677196.
E-mail address: j.d.smith@sussex.ac.uk (J. David Smith).
0022-328X/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.01.019

A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
1239
centre M [16]. The structures of such compounds depend
on the balance between Mꢀ ꢀ ꢀC and Mꢀ ꢀ ꢀZ interactions;
Mꢀ ꢀ ꢀZ interactions predominate when the Lewis acidity
of the metal is high, and Mꢀ ꢀ ꢀC interactions predomi-
nate when the Lewis acidity of M is low. In the latter
case Z may interact only weakly or not at all [17]. We
describe here some compounds of main group elements
containing ligands II and III; these are potential pre-
cursors for the syntheses of transition metal compounds
by ligand transfer reactions [18,19].
for the bond to the central carbon (98 Hz in 1, and 101
Hz in (Me3Si)3CH [21]) compared with 118–119 Hz in
methyl groups attached to silicon. The value for 5 could
not be found because of overlapping peaks. The low
1
values of JSiC (38 Hz in 1 and 5, cf. 39 Hz in
(Me3Si)3CH and 42 Hz in (Me2NSiMe2)3CH [22]) are
found in other compounds in which three silicon atoms
are attached to the same carbon centre. In contrast, the
1
values of JSiC when only one silicon is attached to
carbon, e.g. within SiMe3 groups, are 51–52 Hz. The 1H
and 13C NMR spectra of 5 confirm that the methyl
groups within each SiMe2Ph fragment are inequivalent
and that the adjacent carbon atom is prochiral.
(HMe2Si)(Me3Si)2CH (1)
KC(SiMe3)2(SiMe2H) (3)
Li(THF)2C(SiMe3)2(SiMe2H) (2a)
Al(THF)Me2{C(SiMe3)2(SiMe2H)} (4)
H
2.2. The lithium derivatives 2a and 6
Me2Si
THF
(5)
(HMe2Si)(PhMe2Si)2CH
C
Li
Compound 2a was made more than 10 years ago by
the reaction between the chloride (HMe2Si)(Me3Si)2CCl
and butyl-lithium at )110 °C. It was not isolated but
treated at once with zinc or cadmium halides to give the
dialkyl compounds M{C(SiMe3)2(SiMe2H)}2 (M ¼ Zn
or Cd) [23]. We considered that a more convenient
synthesis would be from 1 and lithium diisopropyla-
mide, since the compound Li(THF)2{C(SiMe2H)3}
(10a) can be readily obtained in this way [24].
PhMe2Si
PhMe2Si
THF
[K] [C(SiMe2Ph)2(SiMe2H)] (7)
6
Me
O
Cl
Me
R
Me
R
Me
R
R
Al
Al
Al
Al
Me
O
Cl
8
Me
9
R = C(SiMe2Ph)2(SiMe2H)
Compounds 2a and 3–4 were made from the known
compound 1 but, on encountering problems arising
from disorder in their crystal structures, we switched
attention to compounds derived from the new precursor
5. As we expected from our past experience, these gave
better-defined structures and we were able to charac-
terize the organometallic compounds 6–9.
In our hands, however, 1 did not react with LiNPri2 in
heptane/THF, either under the conditions employed
previously in the metallation of (HMe2Si)3CH [24], or
under reflux. It did however react with methyllithium in
THF to give a good yield of the THF adduct 2a. The
compound 6 was made similarly, but we observed no
reaction between 5 and methyllithium when toluene or
Et2O was used as solvent. Both 2a and 6 were obtained
as colourless air- and moisture-sensitive crystals. They
were characterized by elemental analysis and NMR
spectroscopy but the signals from quaternary carbon
atoms could not be detected.
2. Results and discussion
2.1. The ligand precursors (HMe2Si)(Me3Si)2CH (1)
and (HMe2Si)(PhMe2Si)2CH (5)
Crystals obtained from solutions of 2 were disor-
dered, with the SiMe3 and SiMe2H fragments distrib-
uted randomly over the three sites adjacent to the
central carbon. Although details of the structure are not
publishable, it is clear that an ate complex [Li(THF)4]
[Li{C(SiMe3)2(SiMe2H)}2] (2b) is formed in the solid
state, analogous to that found previously for
[Li(THF)4][Li{C(SiMe3)3}2] (11b) [25]. The structure of
compound 6 was determined without difficulty and
found to comprise molecular species like those in the
compounds [Li(THF)C(SiMe2Ph)3] (12) [26] and
[Li(OEt2){C(SiMe3)2(SiMe2Ph)}] (13) [27], in which
Compound 1 was made previously by the reaction
between (Me3Si)2CHM (M ¼ Li or K) with Me2SiHCl
[20]. Our synthesis from (Me3Si)2CHBr, Me2SiHCl and
metallic magnesium (Eq. (1)) gave an identical product.
The new compound 5 was made similarly in 90% yield.
ðXMe2SiÞ CHBr þ Me2SiHCl þ Mg=THF
2
! ðHMe2SiÞðXMe2SiÞ CH
ð1Þ
2
1 X ¼ Me or 5 X ¼ Ph
The withdrawal of electron density from the C–H
1
into the Si–C bonds is shown by the low value of JCH

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A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
there are significant Liꢀ ꢀ ꢀPh interactions, and
[Li(THF){C(SiMe3)2(SiMe2C5H4N-2 (14) [18] or
2LiðTHFÞ fCðSiMe3Þ ðSiMe2HÞg
2
2
2a
ꢀ ½LiðTHFÞ ꢁ½LifCðSiMe3Þ ðSiMe2HÞg2ꢁ
4
2
with Z ¼ NMe (15) or
[Li(THF)2{C(SiMe3)2(SiMe2Z)}]
2
2b
OMe (16) [28]. The molecular structure is shown in
Fig. 1 and selected bond lengths and angles are given in
Table 1. Compound 6 is the first in this series in which
there is no chelation, i.e. interaction between lithium
and substituents attached to silicon. The Liꢀ ꢀ ꢀH1 dis-
The 1H, 13C, 7Li and 29Si spectra of 2a at 298 K show
sharp peaks in toluene-d8 solution, as expected if the
species in solution has a molecular structure like that
found for crystalline 6. As the solution of 2a is cooled
below 258 K, however, new signals, ascribed to the ionic
form 2b, appear. The peaks remain sharp, indicating
that chemical exchange is slow on the NMR time scale
and that the two species coexist (Eq. (2)). The propor-
tion of 2b increases as the temperature is lowered, and
more concentrated solutions require less cooling before
peaks for 2b are observed. The predominance of mo-
lecular species at higher temperature and lower con-
centrations suggest that the ion-pairs 2b are (at least in
toluene) held together in a solvent cage, rather than
dissociated. The ionic species must be the less soluble
since it crystallizes from solution preferentially. A sim-
ilar equilibrium between 10a and 10b was proposed to
account for the discrepancy between the 7Li NMR
spectra of a solid sample and a solution in C6D6 [24].
The compound 11b also dissolves in toluene to give a
solution containing covalent species and ion-pairs [29]
but, because the spectra vary in a complex way with the
concentration, temperature and solvent, a quantitative
comparison between thermodynamic data for com-
pounds 2, 10 and 11 is not yet possible.
ꢀ
tance, 3.27 A, is much greater than the sum of the van
der Waals radii, and the shortest distances from lithium
to the carbon atoms of the phenyl groups (Liꢀ ꢀ ꢀC6 or
ꢀ
ꢀ
C7 ¼ 2.8 A) are much greater that those in 12 [2.40(2) A]
ꢀ
or 13 [2.487(11) A]. Two moles of coordinated solvent
are bound to lithium, rather than one as in 12–14. The
ꢀ
Li–O distance (1.958(5) A) is significantly longer than
ꢀ
those in 12–14 (1.85(2)–1.885(10) A), but similar to
ꢀ
those in 15–16 (1.949(11)–1.980(8) A), in which the co-
ordination number of lithium is four rather than three.
ꢀ
The Li–C distance in 6 (2.226(5) A) is a little shorter
ꢀ
than those (2.287(9)–2.304(11) A) in 15–16, but not as
ꢀ
short as those in 12–14 (Li–C1 2.096(10)–2.144(8) A), in
which there is only one coordinated solvent molecule.
The other intraligand bond lengths and angles in 6 are
very similar to those in 13.
2.3. The potassium compounds 3 and 7
Treatment of the precursors 1 and 5 with methylli-
thium in the presence of potassium t-butoxide gave the
organopotassium compounds 3 and 7 (Eq. (3)).
ðHMe2SiÞðXMe2SiÞ CH þ LiMe þ KOBut
2
X ¼ Me 1 or Ph 5
! ½Kꢁ½CðSiMe2XÞ ðSiMe2HÞꢁ þ LiOBut þ CH4
ð3Þ
2
X ¼ Me 3 or Ph 7
Fig. 1. Molecular structure of 6.
It is likely that the metallating agent was methylpo-
tassium, generated in situ at room temperature from the
reaction between methyllithium and potassium t-bu-
toxide. The alternative reaction sequence, viz. metalla-
tion of 1 or 5 by methyllithium, followed by reaction of
2a or 6 with KOBut, is unlikely since the metallation
step requires forcing conditions, e.g. reaction in THF
under reflux (see Section 3). Compounds 3 or 7 could be
washed free from LiOBut with heptane and obtained,
after crystallization from benzene, as yellow crystals.
Elemental analysis of 3 showed that the crystals did not
contain coordinated solvent but a satisfactory X-ray
structure determination was precluded by crystallo-
graphic disorder. The NMR spectrum revealed that the
compound contained about 20% of [K][C(SiMe3)3] [30],
Table 1
ꢀ
Bond lengths (A) and angles (°) in Li(THF)2C(SiMe2Ph)2(SiMe2H) (6)
Bond lengths
Li–Oa
Li–C
Si–Ca
1.958(5)
2.226(5)
1.821(2)
Si–Mea
Si–Pha
1.882(3)
1.913(3)
Bond angles
O–Li–O
101.6(2)
130.7(2)
Si2–C–Si3
Si1–C–Li
Si2–C–Li
Si3–C–Li
Me–Si–Mea
118.66(13)
94.15(15)
95.99(16)
111.53(16)
104.96(17)
O1–Li–C1
O2–Li–C1
Si1–C–Si2
Si1–C–Si3
123.5(2)
114.43(13)
116.68(13)
a Average value with e.s.dÕs of individual measurements in paren-
theses. None differs significantly from the mean.

A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
1241
showing that some of the methylpotassium formed from
the reaction between LiMe and KOBut had reacted at
the Si–H rather than the C–H bond. Compound 7 was
made similarly but in this case there was no evidence
from the NMR spectra that there was any
KC(SiMe3)(SiMe2Ph)2 impurity [27], indicating that
there had been clean reaction at the C–H bond.
An X-ray study confirmed that 7 crystallized as the
ionic solid [K][C(SiMe2Ph)2(SiMe2H)]. The asymmetric
unit comprises three independent ion-pairs, two of them
disordered with lower occupancy Si sites sharing the
unresolved methyl and phenyl groups. The disordered
ion-pairs are repeated by unit cell translations to form
zig-zag chains along the a axis (Fig. 2); the undisordered
ion-pair, shown in Fig. 3, is repeated by the a glide
plane. The bond lengths and angles in Table 2 are for
this undisordered species; those for the other ion-pairs
are identical within experimental uncertainty. There are
significant differences between bond distances from the
central carbon atoms (e.g. C39) to silicon within each of
the three independent species. These differences must be
treated with caution because of the uncertainties re-
sulting from disorder, but the short average Si–C dis-
Fig. 3. Structure of the undisordered ion-pair of 7.
Table 2
ꢀ
Bond lengths (A) and angles (°) in the undisordered molecule in the
structure of KC(SiMe2Ph)2(SiMe2H) (7)
Bond lengths
K–C39a
3.167(8)
C39–Si(Ph) 1.869(8)
1.770(8)
K–C(Ph)ag6
K–C(Ph)a g2
3.248(8)–3.395(7)
3.293(8)–3.326(10)
3.461(10)
Si–Mec
Si–Phc
Kꢀ ꢀ ꢀSi
Kꢀ ꢀ ꢀH
1.896(8)
1.925(8)
3.457
,
K–C(Me)a b
C39–Si(H)
ꢀ
1.817(8)
2.57(9)
tance [1.817(8) A] and wide average Si–C–Si angle
[118.8(5)°] strongly indicate that electronic charge is
transferred from potassium to the adjacent carbon and
delocalized into the Si–C bonds.
Bond angles
Si–C–Si
116.8(4) 116.9(4)
122.8(4)
83.1(3)
K–C–Si8
K–C–Si9
94.5(3)
K–C–Si7
110.7(3)
Each potassium atom interacts with (a) the adjacent
carbanionic centre (C39 in Fig. 3), (b) two phenyl
groups from the next ion-pair in the chain, (c) a methyl
group in a neighbouring chain (C200, C21 and C4000 in
Fig. 2) and (d) the hydrogen atoms attached to silicon
(H7s in Fig. 3). The coordination sphere can be con-
sidered as a distorted trigonal bipyramid with (a) and (b)
occupying the three equatorial and (c) and (d) the two
axial positions [the sum of angles subtended by C39,
C4700 and C5300 is 358° and H21a–K3–H7s 153°]. The
a
ꢀ
Kꢀ ꢀ ꢀC distances >3.5 A are not shown.
b To C21 in adjacent ion-pair.
c Average value; with e.s.d. of individual measurements in paren-
theses. None differs significantly from the mean.
ꢀ
interaction (a) gives a K–C distance of 3.167(8) A,
slightly longer than that in [K][C(SiMe3)3] [Av.
ꢀ
3.097(11) A] but similar to the shortest distances in
[K][C(SiMe2Ph)3] [3.26(2) A] [30], [K][C(SiMe3)2
(SiMe2NMe2)] [3.1870(12) A] [31] or [K][C(SiMe3)2
ꢀ
ꢀ
ꢀ
(SiMe2C5H4N-2)] [3.207(3) A] [18]. If it is assumed
ꢀ
(somewhat arbitrarily) that Kꢀ ꢀ ꢀC distances <3.5 A
(Table 2) indicate significant interactions (b) between
potassium and the two adjacent phenyl groups, one
phenyl group, C52–C57, can be designated as g6 and the
other, C44–C49, from which only meta- or para-C atoms
are involved, can be considered to be g2. The
Kꢀ ꢀ ꢀC(aryl) distances are typical of those found in a
range of organopotassium derivatives [32]. The interac-
tions (c) link the chains into layers perpendicular to the c
axis (Fig. 2). The interchain Kꢀ ꢀ ꢀMe distances [3.461(10)
ꢀ
to 3.484(7) A] are only slightly longer than the intra-
chain Kꢀ ꢀ ꢀMe distances in [K][C(SiMe3)3] [3.16(2)–
ꢀ
3.311(11) A] [30] or [K][C(SiMe3)2 (SiMe2NMe2)]
ꢀ
[3.113(2)–3.49 A] [31].
The hydrogen atoms attached to silicon were located
and their positions refined. Those shown as H7s in Fig. 3
appear to be attracted towards the adjacent potassium
Fig. 2. Lattice of 7 showing interactions between ion-pairs.

1242
A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
centres, as shown by the narrow K–C–Si(H) angles
[81.8(3) to 83.1(3)° c.f. K–C–Si(Ph) 94.5(3) to 110.7(3)°]
crystallography in 7 appears to be broken in toluene
solution.
ꢀ
and the Kꢀ ꢀ ꢀH distances 2.57(9)–2.77(9) A. These are
similar to those observed in [K(18-crown-6)][H2SiPh3]
ꢀ
(2.69 and 3.21 A) [2], and [KOsH3(PMe2Ph)3]2 (2.52–
2.4. The aluminium compounds 4, 8 and 9
ꢀ
3.02 A) [11] by X-ray diffraction and in [K(18-crown-
6)][W(PMe3)3H5] by neutron diffraction (2.684(6) to
ꢀ
2.750(6) A) [12]. All are less than the sum of the van der
The reaction of the lithium compound 2 with alu-
minium chloride gave an intractable oil. With AlMe2Cl
in THF a crystalline product was obtained and this was
shown by chemical analysis and NMR spectroscopy to
be the compound [Al(THF)Me2{C(SiMe3)2(SiMe2H)}]
(4). The structure was shown by an X-ray study to be
like that of [Al(THF)Me2{C(SiMe3)3}] [37] but crystal-
lographic disorder, again arising from different orien-
tations of the C(SiMe3)2(SiMe2H) group, made the data
too imprecise for publication. The NMR spectra
indicated that there was a small amount of Al(THF)-
MeCl{C(SiMe3)2(SiMe2H)} (17) present as an impurity.
Like the previously described related compound
Al(THF)MeCl{C(SiMe3)3} [38], this gave two signals in
ꢀ
ꢀ
Waals radii (ꢂ3.95 A [33]) or the distance [2.854(1) A]
between the six-coordinate ions in KH [34]. However, a
search of the Cambridge Crystallographic Data Centre
ꢀ
data base gives a number of Kꢀ ꢀ ꢀHC distances of ꢂ2.6 A
in organopotassium compounds [18,35] and crown ether
complexes [36]. In 7 itself, the K3–H21 distance between
potassium and the hydrogen in a methyl group in an
00
ꢀ
adjacent ion-pair-chain is 2.69(9) A and the K2–H2
and K1–H4000 distances are 2.85 and 2.87 A, respec-
tively. In compounds in which the lattices are held to-
gether by predominantly electrostatic attraction the
coordination number of potassium is large and not very
well defined, and hydrogen atoms at the periphery of the
anions are brought into the Ôcoordination sphere.Õ
Where, as in 7, the anions contain local centres of partial
negative charge (e.g. hydridic hydrogen) it is not sur-
prising that they adopt configurations in which these
centres point towards the cation to give the interactions
discussed here. It is not clear, however, that these should
be described as ÔKꢀ ꢀ ꢀH bondsÕ.
ꢀ
1
the H NMR spectrum at 298 K for the a-CH2 protons
of the coordinated THF, showing that the species in
solution contained the chiral AlCMeClO fragment in
which the THF was firmly bound to aluminium. At
higher temperatures the THF (but not the Si–H) signals
broadened and at 338 K irradiation at the THF signals
of the minor species resulted in saturation transfer at the
signal of the major species. This chemical exchange
probably proceeds by the dissociation of a small fraction
of the THF complexes 4 and 17.
ꢀ
The average Si–Me distance [1.894(8) A] may be
ꢀ
compared with those in [K][C(SiMe3)3] [1.873(13) A],
ꢀ
[K][C(SiMe2Ph)3] [1.89(2) A], [K][C(SiMe3)2(SiMe2N-
ꢀ
Me2)] [1.8920(14) A], [K][C(SiMe3)2(SiMe2C5H4N-2)]
We argued that we were unlikely to obtain species
containing Si–H–Al bridges in the presence of solvents,
such as THF, that can coordinate to aluminium more
strongly than hydride, so we turned to [K][C(SiMe2Ph)2-
(SiMe2H)] (7) as an alkylating agent. The reaction be-
tween 7 and one equivalent of AlMe2Cl in hexane gave a
white air- and moisture-sensitive solid that was almost
insoluble in hydrocarbons, strongly suggesting that the
structure was ionic or polymeric. The experiment was
repeated several times with the same result. In one in-
stance, however, the mass spectrum of the solid showed
peaks ascribed to the compound AlMe2{C(SiMe2Ph)2-
(SiMe2H)}. A small amount of soluble material was ex-
tracted into heptane and shown by an X-ray structure
determination to be the methoxo-derivative [Al(OMe)-
Me{C(SiMe2Ph)2(SiMe2H)}]2 (9), presumably formed by
the admission of traces of air. Because very little material
was available, further characterisation was not possible,
but it was clear that oxygen had reacted preferentially at
the more electron-rich unsubstituted methyl groups, ra-
ther than at the relatively electron-poor, more hindered,
silyl-substituted methyl group.
ꢀ
ꢀ
[1.890(4) A] and the mean Si–Ph distance [1.925(8) A] with
ꢀ
that in [K][C(SiMe2Ph)3] [1.92(2) A].
Compounds 3 and 7 are poorly soluble in aliphatic
hydrocarbons, as is consistent with the adoption of
structures in which there are significant interactions
between ion-pairs. They are more soluble in benzene and
toluene, which are presumably able to break potassium–
phenyl interactions by solvation. The solubility of 7 is,
however, still quite low and samples for NMR spectra
were warmed to 50 °C to reveal the weaker signals. The
peak assigned to the methyl protons of the SiMe2Ph
group appears as a sharp singlet (contrast 5 above),
which does not significantly broaden when a sample in
toluene-d8 is cooled to 198 K. This shows that in solu-
tion there is ready inversion at the centre of the
[C(SiMe2Ph)2(SiMe2H)]ꢃ carbanion. In the slightly
more crowded compound [K][C(SiMe2Ph)2(SiMe3)],
inversion became sufficiently slow below 189 K for two
1
signals to be observed in the SiMe2Ph region of the H
NMR spectrum [27].
The reaction of 7 with an excess of AlMe2Cl gave
a well-defined crystalline solid, shown by elemental
analysis, NMR spectroscopy and an X-ray structure
determination to be the dialkylaluminium chloride 8
(Eq. (4)).
It has been shown that Si–Hꢀ ꢀ ꢀM interactions may be
1
detected by low coupling constants JSiH [4,6]. Our
compounds 1–4 and 5–8 all give values (155–184 Hz) in
the usual range [8]; the weak interaction detected by

A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
1243
½Kꢁ½CðSiMe2PhÞ ðSiMe2HÞꢁ þ AlMe2Cl
2
7
! KCl þ AlMe3 þ 0:5½AlClMefCðSiMe2PhÞ ðSiMe2HÞgꢁ
2
2
8
ð4Þ
Compound 8 could be formed either by rapid reac-
tion of AlMe2Cl with
a (non-polymeric) AlMe2
{C(SiMe2Ph)2(SiMe2H)} intermediate or by reaction of
7 with AlMeCl2 initially present in the AlMe2Cl.
In one experiment compound 7 was made from 5,
LiMe and KOBut (by a procedure like that described in
Section 3.3), and without purification treated with Al-
Me2Cl to give colourless crystals. These were not suit-
able for an X-ray structure determination and an
attempt to obtain larger crystals by sublimation at 0.001
mm Hg gave only oily decomposition products. The
crystals were dissolved in toluene-d8 to give NMR
spectra that showed the presence of ButO groups. In this
sample, therefore, t-butoxide was incompletely removed
from the crude 7 and a molecular, rather than a poly-
meric, species was apparently obtained. Although it was
not possible to determine the structure of the initially
formed crystals from NMR spectra alone, the data are
consistent with the presence of alkoxide–alkyl com-
plexes like those postulated to explain the reactivity of
Ôsuper-basesÕ [39]. What little information is available on
these species indicates that their structures can be quite
complex [40]. The spectra underwent a complex series of
changes when they were rerecorded as the sample was
heated to 348 K then allowed to stand for 22 h at 298 K.
In the final product t-butoxide appeared to be attached
to aluminium and the bulky anion to potassium. The
1H, 13C and 29Si spectra are quite similar to those of 7,
but the broadening and splitting of the SiMe2Ph peak on
cooling below 294 K shows that free 7 is not present.
The central carbon of the anion appeared to be four-
rather than three-coordinate.
Fig. 4. Molecular structure of 8.
Fig. 5. Molecular structure of 9.
Table 3
Bond
ꢀ
(A)
lengths
and
angles
(°)
in
[AlCXMe
{C(SiMe2Ph}2(SiMe2H)}]2 X ¼ Cl (8) or OMe (9)
8 X ¼ Cl
9 X ¼ OMed
Bond lengths
Al–Ca
Al–Me
Al–X
1.972(3)
2.023(7)b
1.951(9)b
1.869(5)b
1.896(8)b
1.871(9)b
1.874(9)b
1.890(8)b
1.938(4)
2.3216(12)b
1.902(3)b
1.874(4)b
1.877(4)b
1.892(3)b
C–Sia
Si(H)–Mec
Si(Ph)–Mec
Si–Ph
The structures of the derivatives AlXMe
{C(SiMe2Ph)2(SiMe2H)} X ¼ Cl (8) or OMe (9) are
shown in Figs. 4 and 5 and selected bond lengths and
angles are given in Table 3. Both compounds form di-
mers. Those of 8 have a centre of symmetry and adopt
an anti configuration about the strictly planar Al2Cl2
ring with the bulky groups pointing away from each
other. Those of 9 have no crystallographically imposed
symmetry; the central Al2O2 ring is slightly folded (di-
hedral angle 15.7°), and the conformation about the
mean plane of the ring is syn, i.e. the two bulky groups
are on the same side. There is no significant difference in
the bond lengths from the central carbon atom to the
silicon atoms that bear the hydrogen substituent and
those that do not, and no significant difference between
Si-alkyl and Si-aryl bonds. In both 8 and 9 the bonds
from aluminium to the central carbon of the
C(SiMe2Ph)2(SiMe2H) group are significantly longer
Bond angles
Al–X–Al
X–Al–X0
93.47(4)
86.53(4)
99.6(2)b
79.0(2)b
X–Al–Me
C–Al–Xa
Me–Al–Ca
Si–C–Sia
107.66(13) 102.82(12)
114.33(9) 111.55(10)
126.50(14)
106.0(3)–109.2(3)
117.9(3)–121.0(3)
117.6(3)
111.13(15) 116.77(14)
109.48(15)
105.28(18)b
105.74(16)b
114.56(15)–116.00(16)
111.7(4)b
Me–Si–Me
Me–Si–Ph
C–Si(H)–Mea;c
C–Si(Ph)–Mea;c 110.79(15)–112.83(15)
C–Si–Pha
Al–C–Sia
105.5(4)b
105.1(4)b
113.2(4)–118.8(4)
110.7(3)–114.3(4)
113.0(3)–117.8(3)
104.8(3)–109.4(4)
113.42(14) 118.21(14)
104.12(14) 111.60(13)
103.34(14)
a C1 or C20.
b Average value with e.s.d.Õs of individual measurements in paren-
theses. None differs significantly from the mean.
c Si(H): Si1 or Si4; Si(Ph): Si2,3,5,6.
d
b
b
ꢀ
C–O 1.451(8) A ; C–O–Al 122.2(4)°.

1244
A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
than the Al–Me bonds, as is commonly found in com-
pounds that contain bulky groups. The Al–C, Al–Cl and
Al–O bond lengths are all in the usual range [41–43].
The corresponding intraligand dimensions in the two
compounds are identical within experimental error. The
smaller size of oxygen than of chlorine results in weaker
cross-ring inner shell repulsions and thus wider Al–X–Al
and narrower X–Al–X angles in the methoxo derivative
than in the chloride. Angles at aluminium involving the
carbon atoms C1 or C20 are wider, and angles involving
only X and Me are narrower than the tetrahedral value.
This may partly be explained on steric grounds but C–
Al–C angles of 120–125° are commonly found in com-
pounds AlMe2X [42,43]. The distances between the
hydrogen atoms attached to Si1 or Si4 and aluminium
(SiMe2H) III. Both have the potential to give com-
pounds in which the Si–H group might bind to the metal
centre, but only weak interactions in the crystalline
potassium compound 7 have so far been detected. The
Hꢀ ꢀ ꢀK distances are similar to those recently reported in
[K(18-crown-6)][H2SiPh3] [2], but also similar to those in
organopotassium compounds that are usually described
as showing Kꢀ ꢀ ꢀMe or Kꢀ ꢀ ꢀPh interactions. Further
examples of Si–Hꢀ ꢀ ꢀM interactions are likely to be
found in compounds that do not contain ligands having
lone pairs that can preferentially coordinate to metal
centres. Compounds containing the ligand III are less
likely to suffer from crystallographic disorder than those
containing ligand II.
ꢀ
ꢀ
(3.409 A in 8 and 3.204, 3.395 A in 9) are greater than
the sum of the van der Waals radii so there in no evi-
dence of engagement of the Si–H bond with the metal
centre.
3. Experimental
Air and moisture were excluded as far as possible by
use of flame-dried glassware, Schlenk techniques with
argon as blanket gas, and a nitrogen-filled drybox.
NMR spectra were recorded at 500.1 (1H), 125.8 (13C),
194.5 (7Li), 130.4 (27Al) or 99.4 Hz (29Si); chemical shifts
are relative to SiMe4, aqueous LiCl or aqueous
Al(NO3)3. EI mass spectra were obtained at 70 eV; m=z
values are given for 28Si and 35Cl.
There is no simple explanation for the difference in
the conformations adopted by 8 and 9. Most com-
pounds containing four-membered Al2O2 rings crystal-
lize with the anti configuration [37,44], presumably
because it is the less crowded. However, there are re-
ports in the literature that indicate that the difference in
energy between the syn and anti forms may be small [41].
In some cases both isomers are present in the equilib-
rium mixture in solution and either may constitute the
least soluble species and thus crystallize preferentially.
Compounds that crystallize with the syn configuration,
i.e. with bulky groups on the same side of the Al2O2
3.1. Synthesis of (HMe2Si)(Me3Si)2CH (1)
A solution of (Me3Si)2CHBr (15.0 g, 62.8 mmol) in
THF (50 ml) was added dropwise to a mixture of
Me2SiHCl (15 ml, 138 mmol) and magnesium metal
(1.50 g) in THF (50 ml). The mixture was then heated
under reflux for 2 h, stirred as it was allowed to cool
overnight, and filtered. The filtrate was washed with
water, the product extracted with hexane and the extract
dried over Na2SO4. The solvent was removed from the
extract under reduced pressure and the residue, distilled
at 97 °C/28 mmHg (10.9 g, 80%), was shown to be
ring, are
(R ¼ Me or
[Al{C(SiMe3)2(SiMe2R)}(CH2)4O]2
Cy) [45] and the mentholato compound [R2AlOC10H19]2
(R ¼ Me, but when R ¼ Bui the configuration is anti)
[43]. For 9 it is possible that the energy of the anti
configuration is raised by repulsive interactions between
the methyl groups C41 and C42 and those of the bulky
ligand. (The distances from C42 to C5, C23, and C24 are
ꢀ
all less than 3.65 A.) The energy of the syn configuration
1
identical with that obtained previously [20]: H NMR
is lowered by the presence of hydrogen substituents on
Si1 and Si4, so that the bulky ligands may lie on the
same side of the ring without being pushed too close
3
2
(C6D6) d)0.89 (1H, d, JHH ¼ 0:8 Hz, JSiH ¼ 9:7 Hz,
3
CH), 0.11 (18H, s, SiMe3), 0.14 (6H, d, JHH ¼ 3:8 Hz,
3
3
SiMe2), 4.25 (1H, dsept, JHH (sept) ¼ 3.8 Hz, JHH
ꢀ
together. (The H1–H4 distance (2.48 A) is close to the
(d) ¼ 1 Hz, JSiH ¼ 183:5 Hz, SiH). 13C NMR: d)0.4
1
sum of the van der Waals radii.) Both syn- and anti-
configurations are found also in compounds containing
Al2N2 rings [46]. For example, NMR spectroscopic
studies showed that a solution of [AlBrEtNHBut]2 in
benzene contained a mixture of species that included the
all-cis isomer in which the two But groups and the two
Br atoms are all on the same side of the Al2N2 ring.
1
1
(qm, JCH ¼ 119 Hz, JSiC ¼ 50:7 Hz, SiMe2), 2.1 (d,
1JCH ¼ 98 Hz, 1JSiC ¼ 38 Hz, CH), 2.7 (qm,
1JCH ¼ 118:4 Hz, JSiC ¼ 51:2 Hz, SiMe3). 29Si NMR:
1
d)15.7 (1JSiH ¼ 183:8 Hz, JSiH ¼ 10 Hz, SiMe2H), 0.1
2
(SiMe3). MS: m=z 217 (90, M–H), 203 (100, M–Me), 129
(50, Me2Si@CHSiMe2), 73 (50, SiMe3).
2.5. Conclusion
3.2. Li(THF)2C(SiMe3)2(SiMe2H) (2a)
There was no reaction between (HMe2Si)(Me3Si)2CH
and LiNPri2 in heptane/THF (1:10) during 16 h either at
room temperature or under reflux.
We have synthesized a number of main group orga-
nometallic compounds that contain the ligand
C(SiMe3)2(SiMe2H) II and the new ligand C(SiMe2Ph)2

A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
1245
A solution of LiMe (7.84 mmol) in Et2O (4.9 ml) was
added to a solution of 1 (1.50 g. 6.88 mmol) in THF (50
ml). The mixture was heated under reflux for 2 h, then
the solvents were removed under vacuum to leave a
white solid that was crystallised from toluene to give
colourless crystals (2.13 g, 84%), mp 123 °C. Anal. Calc.
for C17H41LiO2Si3: C, 55.38; H, 11.21. Found: C, 55.0;
11.35. 1H NMR (toluene-d8, 298 K): d 0.33 (18H, s,
84%). Anal. Calc. for C15H39AlSi3O: C, 52.0; H, 11.34.
1
Found: C, 51.60; H, 11.58. H NMR (298 K): d)0.51
2
(6H, s, AlMe2), 0.28 (18H, s, JSiH ¼ 6:1 Hz, SiMe3),
3
0.33 (6H, d, JHH ¼ 3:6 Hz, SiMe2), 1.02–1.05 (4H, m,
1
THF), 3.54 (4H, t, THF), 4.41 (1H, hept, JSiH 177 Hz,
3JHH ¼ 3:6 Hz, SiH). 13C NMR: d)4.1 (b, AlMe2), 5.3
(SiMe3), 6.2 (SiMe2), 24.4 (THF), 72.4 (THF). 29Si
NMR: d)18.1 (SiMe2H), )4.2 (SiMe3). 27Al NMR: d
(353 K) 174, Dm1=2 ¼ 1:9 kHz. MS: m=z 331 (30, M–Me),
317 (70, M–Me–CH2), 260 (100, RAlO [R ¼ C(SiMe3)2-
(SiMe2H)]). The sample appeared to contain about 20%
of Al(THF)ClMe{(C(SiMe3)2(SiMe2H)} as a byproduct.
1H NMR: d)0.50 (3H, s, AlMe), 0.30 (18H, s, SiMe3), 0
3
SiMe3); 0.39 (6H, d, JCH ¼ 3:6 Hz, SiMe2), 1.26 (8H,
m, THF), 3.33 (8H, m, THF), 4.73 (1H, hept,
3
1JSiH ¼ 161 Hz, JCH ¼ 3:6 Hz). 13C NMR: d 4.8
(SiMe2), 7.0 (SiMe3), 25.1 and 68.3 (THF). 7Li NMR: d
0.8. 29Si NMR: d )23.7 (SiMe2), )9.8 (SiMe3).
3
As the toluene solution was cooled below 258 K, new
signals, ascribed to the ionic form [Li(THF)4]
[Li{C(SiMe3)2(SiMe2H)}2] (2b), appeared. 1H NMR
(208 K) 2a: d 0.59 (SiMe3), 0.66 (SiMe2), 1.68 and 3.28
(THF), 4.98 (SiH); 2b: 0.70 (SiMe2/SiMe3), 1.05 and
3.12 (THF), 5.12 (SiH). 13C NMR (220 K) 2a: d 3.0
(SiMe2), 6.9 (SiMe3), 25.6 and 68.1 (THF); 2b: 4.8
33 (6H, d, JHH ¼ 3:8 Hz, SiMe2), 1.00–1.02 (4H, m,
THF), 3.59 and 3.82 (2H, m, THF), 4.38 (1H, hept, SiH).
13C NMR: d 2.1 (SiMe2), 6.2 (SiMe3), 24.3 (THF), 73.6
(THF). 29Si NMR: d)18.3 (SiMe2H), )4.7 (SiMe3). 27Al
NMR: d (353 K) 151, Dm1=2 ¼ 1:6 kHz. Selective decou-
pling at d 1.1 gave doublets at d 3.59 and 3.82 with
2JHH ¼ 8:1 Hz. MS: m=z 279 (55, RAlCl), 264 (50,
RAlCl)Me) [R ¼ C(SiMe3)2(SiMe2H)].
7
(SiMe2), 7.2 (SiMe3), 24.8 and 67.9 (THF). Li NMR
(208 K) 2a: d 0.8; 2b: )0.9 and 3.5. The ratio 2b/2a was
concentration dependent but in a typical experiment the
1H spectra showed that it was 0.20 at 248 and 1.5 at
208 K.
3.5. HMe2Si(PhMe2Si)2CH (5)
A solution of (PhMe2Si)2CHBr [27] (10.5 g, 28.9
mmol) in THF (50 ml) was added slowly to a mixture of
SiMe2HCl (15 ml, 135 mmol) and Mg (0.69 g, 28.9
mmol) in THF (100 ml) at room temperature. The
mixture was heated under reflux for 4 h then treated
with water, and the product was extracted with hexanes.
The extract was dried over Na2SO4 and solvent was
removed under vacuum to leave an oil that was distilled
at 120 °C/0.001 mm to give 5 as a colourless liquid (9.1
g, 92%). Anal. Calc. for C19H30Si3: C, 66.59; H, 8.82.
3.3. KC(SiMe3)2(SiMe2H) (3)
A solution of 1 (2.00 g, 9.17 mmol) and LiMe (9.17
mmol) in Et2O (25 ml) was added to a slurry of KOBut
(1.03 g, 9.20 mmol) in Et2O (20 ml). The mixture was
stirred overnight and the slightly cloudy solution was
filtered. Volatile material was removed from the filtrate
under vacuum and the white residue was washed with
heptane then crystallized from benzene to give 3 (2.10 g,
89%) as colourless needles, mp 230–235 °C (decomp).
Anal. Calc. for C9H25KSi3: C, 42.12; H, 9.82. Found:
1
Found: C, 66.73; H, 9.12. H NMR (CD2Cl2): d)0.06
3
3
(1H, d, JHH ¼ 1 Hz, CH), )0.03 (12H, d, JHH ¼ 3:8
Hz, SiMe2H), 0.24 and 0.35 (12H, s, SiMe2Ph), 4.04
1
3
(1H, heptd, JSiH ¼ 183:5 Hz, JHH ¼ 3:8 and 1.2 Hz),
7.30–7.33 (6H, m, m-and p–H), 7.47–7.49 (4H, m, o–H).
13C NMR: d)0.8 (1JSiC ¼ 51 Hz, SiMe2H), 0.2
(1JSiC ¼ 38 Hz, CH), 0.5 and 1.1 (1JSiC ¼ 53 Hz, Si-
Me2Ph), 127.9, (m-C), 128.9 (p-C), 133.8 (o-C), 141.6 (i-
C). 29Si NMR: d)15.2 (SiMe2H) and )4.0 (SiMe2Ph).
MS: m=z 327 (10, M)Me), 269 (20, M)SiMe3), 249 (80,
Me2Si@C(SiMe2Ph)(SiMeH)), 191 (30, Me2Si@CHSi-
MePh), 135 (100, SiMe2Ph).
1
2
41.82; H, 10.04. H NMR: d 0.31 (s, 18H, JSiH ¼ 5:8
3
Hz, SiMe3); 0.40 (6H, d, JHH ¼ 3:5 Hz, SiMe2); 4.67
1
3
(1H, sept, JSiH ¼ 155 Hz, JHH ¼ 3:5 Hz, SiH). 13C
NMR: d 5.0 (1JCSiMe ¼ 53:4, 1JCSiH ¼ 51:3 Hz, CSi3), 5.7
(1JSiC ¼ 46:2 Hz, SiMe2), 7.7 (1JSiC ¼ 46:8 Hz, SiMe3).
29Si NMR: d)25.3 (SiMe2), 12.1 (SiMe3). Minor peaks
(ꢂ20%) at dH 0.31, dC 8.4 (1JSiC ¼ 46:5 Hz) and dSi
)12.7, were assigned to KC(SiMe3)3 [30].
3.4. Al(THF)Me2{(C(SiMe3)2(SiMe2H)} (4)
3.6. Li(THF)2C(SiMe2Ph)2(SiMe2H) (6)
A solution of AlMe2Cl (2.8 ml, 1 M) in hexane was
added to a solution of 2a (0.60 g, 1.63 mmol) in THF (25
ml) and the mixture was stirred overnight. The volatile
components were removed under vacuum to leave a
white solid that was crystallized from heptane at )20 °C
to give colourless crystals of 4, mp 198–202 °C (0.47 g,
Methyllithium (1.8 ml 1.6 M solution in Et2O) was
added to a solution of 5 (1.00 g, 2.92 mmol) in THF (30
ml). The mixture was heated under reflux for 2 h then
stirred at room temperature overnight. The solvents
were removed and the white solid residue was dissolved
in heptane (5 ml). The solution was kept at )30 °C to

1246
A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
give colourless crystals of 6 (0.75 g, 52%), mp 65 °C.
Anal. Calc. for C27H45Si3O2Li: C, 65.80; H, 9.20.
Found: C, 65.85; H, 9.27. 1H NMR: d 0.33 (6H, d,
3JHH ¼ 3:6 Hz, SiMe2H), 0.56 (12H, s, SiMe2Ph), 1.21
(SiMe2Ph}2(SiMe2H)}]2 (8), mp 150–152 °C. Anal.
Calc. for C20H32AlClSi3: C, 57.31; H, 7.69. Found: C,
1
57.07; H, 7.81. H NMR (toluene-d8): d)0.68 (6H, s,
3
AlMe), 0.06 (6H, d, JHH ¼ 3:6 Hz, SiMe2H), 0.51 and
1
3
and 3.18 (8H, m, THF), 4.80 (1H, hept, JSiH ¼ 165:5,
0.58 (6H, s, SiMe2Ph), 4.55 (1H, hept, JHH ¼ 3:7,
3JHH ¼ 3:6 Hz, SiH), 7.02 (2H, tt, p-H), 7.10 (4H, m, m-
1JSiH ¼ 184 Hz, SiH), 7.03–7.12 (6H, m, m-and p-H),
7.54 (4H, dd, o-H). 13C NMR: d)2.3 (b, AlMe), 1.7, 2.9
and 4.0 (SiMe2), 128.1 (m-C), 129.1 (p-C), 135.4 (o-C),
140.0 (i-C). 27Al NMR: d 183, Dm1=2 ¼ 5 kHz. 29Si
NMR: d)19.0 (SiMe2H), )8.5 (SiMe2Ph). MS: m/z 418
(5, monomer (M)), 403 (70, M–Me), 383 (10, M–Cl),
367 (10, M–Me–HCl), 340 (50, (PhMe2Si)2C@SiMe2),
325 (70, (PhMe2Si)2CHAlMe), 309 (70, PhMeSi@
C(SiMe2Ph)AlMe), 264 (30, (PhMe2Si)(HMe2Si)C@
SiMe2), 249 (70, PhMeSi@ C(SiMe2H)SiMe2), 175 (100,
Me2Si@CHAlPh), 135 (80, PhMe2Si), 73 (80).
3
4
H), 7.59 (4H, dd, JHH ¼ 7:9 Hz, JHH ¼ 1:4 Hz, o-H).
13C NMR: d 4.8 (SiMe2H), 5.1 (SiMe2Ph), 25.2 and 68.0
(THF), 127.4 (p-C), 128.2 (m-C), 133.4 (o-C), 149.3 (i-
C). The signal from the quaternary carbon was not
7
found. Li NMR: d 0.39. 29Si NMR: d)24.5 (SiMe2H),
)11.7 (SiMe2Ph). Compound 5 did not react with LiMe
in toluene or Et2O.
3.7. KC(SiMe2Ph)2(SiMe2H) (7)
The procedure was the same as that used for 3. The
product from 5 (1.00 g, 2.92 mmol), LiMe (2.88 mmol)
and KOBut (2.92 mmol) was obtained from hot benzene
as yellow crystals (Yield 1.05 g, 95%), mp 173–175 °C.
Anal. Calc. for C19H29KSi3: C, 59.93; H, 7.68. Found:
In another experiment, AlMe2Cl (4.7 ml, 1.0 M so-
lution in hexane) was added to 7 (1.8 g, 4.7 mmol),
prepared from 5, KOBut, and LiMe in toluene (30 ml) as
described for 3 above, and the mixture was stirred
overnight. The solvents were removed, the residue was
extracted with hexane, and the extract was kept at 5 °C
1
C, 59.77; H, 7.47. H NMR (toluene-d8, 323 K): d 0.18
3
1
(6H, d, JHH ¼ 3:6 Hz, SiMe2H), 0.52 (18H, s, Si-
to give colourless crystals: H NMR: d)0.22 (AlMe),
Me2Ph), 4.50 (1H, hept, 1JSiH ¼ 156 Hz, 3JHH ¼ 3:6 Hz,
0.52 (d, SiMe2H), 0.65 (SiMe2Ph), 0.81 (But), 6.9 and
7.6 (b, Ph). The spectra were rerecorded as the sample
was heated to 348 K then allowed to stand for 22 h at
SiH), 6.88 (4H, tt, 3JHH ¼ 7:3 Hz, 4JHH ¼ 1:5 Hz, p–H),
3
6.97 (8H, m, m-H), 7.49 (4H, dd, JHH ¼ 7:9 Hz,
4JHH ¼ 1:4 Hz, o-H). 13C NMR: d 3.8 (CSi3), 5.2 (Si-
Me2Ph), 5.6 (SiMe2H), 126.6 (p-H), 128.0 (m-H), 133.1
(o-H), 152.9 (i-C). 29Si NMR: d)26.7 (SiMe2H), )13.8
(SiMe2Ph).
298 K. H NMR: d)0.51 (AlMe), 0.26 (SiMe2H), 0.38
1
(SiMe2Ph), 1.1 (But), 4.5 (heptet, Si–H), 6.9, 7.0 and 7.4
(Ph). 13C NMR: d)1.0 (AlMe), 4.9 (SiMe2Ph) and 5.0
(SiMe2H), 31.2 and 74.3 (But), 128.2, 129.0, 133.7, and
148.2 (Ph). 29Si NMR: d)24.5 (SiMe2H), )12.0 (Si-
Me2Ph). 27Al NMR: d 153.3, Dm1=2 1.5 kHz. The Si–H
peak, not observed initially (presumably because it was
too broad), now appeared as a heptet, and the peaks in
the aromatic region gave multiplets like those in 7. NOE
experiments indicated that the Si–Me protons giving
signals at d0.33 were close to the Si–Ph protons but not
to the But or Al–Me protons, suggesting that the ligand
{C(SiMe2Ph}2(SiMe2H)}was not attached to alumin-
3.8. Reaction between KC(SiMe2Ph)2(SiMe2H) (7) and
AlMe2Cl
A solution of AlMe2Cl (0.79 ml, 1.0 M) in hexane was
added to a solution of 7 (0.39 g, 0.80 mmol) in toluene
(20 ml) and the mixture was stirred overnight. Solvent
was removed from the clear solution under vacuum to
give a white solid that was almost insoluble in heptane.
Some of the solid did dissolve, however, and cooling the
heptane solution (5 ml) to )20 °C gave a small crop of
white crystals, which were shown by an X-ray structure
determination to be 9. The low yield (precise value not
recorded) suggested that traces of air had been admitted
inadvertently during Schlenk-tube manipulation. At-
tempts to crystallize the major product were unsuc-
cessful but the compound AlClMe2{C(SiMe2Ph)2
(SiMe2H)} was detected by mass spectrometry: m=z 398
(60, M), 383 (95, M)Me), 325 (100, (PhMe2Si)2-
CHAlMe), 309 (40), 247 (35), 175 (60), 135 (60), 73 (40).
When an excess of AlMe2Cl was added to a solution
of 7 in toluene (30 ml) at room temperature and the
mixture stirred overnight, a white precipitate was
formed. The solvent was removed and the residue
extracted with heptane (10 ml). The extract was kept
at 5 °C to give colourless crystals of [AlClMe{C-
1
ium. On cooling, the SiMe2Ph signals in the H spec-
trum broadened and split into two with a coalescence
temperature of 294 K.
3.9. Crystallography
Data were collected on a Kappa CCD diffractometer
and processed without correction for absorption. Details
are given in Table 4. The structures were determined by
direct methods and full-matrix least-squares refinement
with anisotropic thermal parameters for non-hydrogen
atoms. Hydrogen atoms attached to silicon were refined
and the others were placed in calculated positions in
riding mode. In the structure of 7, there is disorder, with
resolved Si atom sites and unresolved overlapping C
atom sites, so all carbon atoms were left as isotropic in
the final cycles of least-squares refinement. The crystal of

A. Asadi et al. / Journal of Organometallic Chemistry 689 (2004) 1238–1248
1247
Table 4
Summary of crystallographic data for 6, 7, 8 and 9
6
7
8
9
Chemical formula
Formula weight
T (K)
C27H45LiO2Si3
492.8
173(2)
C19H30KSi3
381.8
173(2)
C40H64Al2Cl2Si6
838.3
223(2)
C42H70Al2O2Si6
829.5
223(2)
Crystal system
Space group
Monoclinic
C2=c (No 15)
36.6018(8)
10.1624(2)
16.1529(4)
100.047(1)
5916.1(2)
8
Orthorhombic
Pna21 (No 33)
15.649(2)
23.540(9)
17.411(3)
90
Monoclinic
P21=n (No 14)
13.2226(2)
11.1732(3)
16.5654(3)
107.822(1)
2329.9(1)
2
Monoclinic
P21=c (No 14)
17.4792(11)
16.2942(10)
18.2873(13)
113.309(3)
4783.3(5)
4
ꢀ
a (A)
ꢀ
b (A)
ꢀ
c (A)
b (°)
U (A )
3
ꢀ
6414(3)
12
0.42
Z
l (mmꢃ1
)
0.18
0.36
0.24
R1 wR2 I > 2rðIÞ
0.052, 0.124
0.077, 0.137
17570/5134/0.074
3889
0.065, 0.152
0.092, 0.171
61023/10684/0.069
7994
0.057, 0.148
0.073, 0.155
18078/5506/0.046
4447
0.093, 0.193
0.170, 0.233
23605/6578/0.155
3678
All data
Measured/independent reflections (Rint
Reflections with I > 2rðIÞ
)
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9 diffracted only weakly. In Figs. 1–5 thermal ellipsoids
are for 50% probability.
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Crystallographic data for the structural analyses have
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6, 7, 8, and 9, respectively. 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; email: deposit@ccdc.cam.ac.uk
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