Synthesis and structures of some silylallyl-lithium or -potassium complexes

Article abstract of DOI:10.1039/a806870d

The η³-1,3-bis(silyl)allyllithium[Li{η³-CH(CHSiMe ₂Bu^t)(CHSiMe₂R)}(tmen)] (R = Bu^t or Me) and 1,3-bis(trimethylsilyl)cyclohexenyllithium [Li{C(SiMe₃)CHC(SiMe₃)(CH

Full text of DOI:10.1039/a806870d

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Synthesis and structures of some silylallyl-lithium or -potassium
complexes
Peter B. Hitchcock,a Michael F. Lappert,*a Wing-Por Leung,b Dian-Sheng Liu,b
Thomas C. W. Makb and Zhong-Xia Wanga
a The Chemistry Laboratory, University of Sussex, Brighton, UK BN1 9QJ.
E-mail: M.F.Lappert@sussex.ac.uk
b Department of Chemistry, The Chinese University of Hong Kong, Shatin, NT, Hong Kong
Received 3rd September 1998, Accepted 15th January 1999
The η3-1,3-bis(silyl)allyllithium [Li{η3-CH(CHSiMe2But)(CHSiMe2R)}(tmen)] (R = But or Me) and 1,3-bis(trimethyl-
silyl)cyclohexenyllithium [Li{C(SiMe3)CHC(SiMe3)(CH2)2CH2}(tmen)] complexes were obtained by lithiation of
the appropriate 1,3-bis(silyl)propene or 1,3-bis(trimethylsilyl)cyclohexene. The lithium complexes were transformed
into the potassium complexes [K{CH(CHSiMe2But)2}] or [K{C(SiMe3)CHC(SiMe3)(CH2)2CH2}] by reaction with
KOBut. A dimethylsilyl ansa-bridged bis(cyclohexenyl)dipotassium complex [{K2{(η3-C6H4SiMe3-6)2SiMe2}(thf)3}∞]
was obtained by a similar route. Single crystal structures of three complexes have been determined.
Allyls and substituted allyls of alkali metals have been the sub-
Results and discussion
ject of extensive investigations of their chemistry,1–6 molecular
structures by X-ray crystallography,7–13 solution structures by
NMR spectroscopy14–18 and by calculation.19–24 These com-
pounds display an astonishing variety of properties that vary
with substituents, temperature and especially the nature of
coligands.
The two 1,3-bis(silyl) propenes RMe SiC(H)᎐CHCH SiMe But
᎐
2
2
2
(R = But 2a or Me 2b) were prepared from the appropriate
3-silylpropene C3H5SiMe2R (R = But 1a or Me 1b) (i in Scheme
1) by successive lithiation and quenching with ButMe2SiF.
Although 1a was a known compound, having been synthesized
The allyl ion is one of the simplest π-electron systems. Struc-
tural studies of allylalkali metal compounds showed interesting
features,7–13 which were recently reviewed by Weiss.13
by the reaction of ButMe SiCl with CH ᎐CHCH MgBr,29 no
᎐
3
2
2
physical or analytical data had been reported. We obtained 1a
from ButMe SiF and CH ᎐CHCH MgBr. Each propene 1a or
᎐
2
2
2
The structures of α-silylallyl anions in solution have been
extensively studied by Fraenkel and co-workers17,18,25 using
NMR spectroscopy. The (trimethylsilyl)allyl anion seemed to
adopt exclusively an exo orientation. This is to be contrasted
with simple alkylallyl anions, which tend to exist as a mixture of
exo and endo isomers, with the latter generally predominat-
ing.26,27 A neutral ligand, such as tmen or pmdeta [(Me2NCH2-
CH2)2NMe], when co-ordinated to 1,3-bis(trimethylsilyl)allyl-
lithium or 1,1,3-tris(trimethylsilyl)allyllithium also adopted an
exo orientation in solution. The crystal structure of crystalline
[Li{C3H3(SiMe3)2-1,3}(tmen)] showed that it has the exo,exo
orientation.11
1b was lithiated by the addition of LiBun to a stirred solution in
the presence of tmen in hexane, and then treated in situ with
ButMe2SiF to form the appropriate 1,3-bis(silyl)propene 2a or
2b. 1,3-Bis(trimethylsilyl)cyclohexene 8 was prepared similarly
(i–iii in Scheme 2). Thus, 3-bromocyclohexene was converted
into 3-trimethylsilylcyclohexene 6 by successive treatment with
magnesium and quenching with Me3SiCl; and 6 upon lithiation
and then addition of Me3SiCl afforded 8.
The silylallyllithium compound [Li{η3-C6H8(SiMe3)}(tmen)]
7 and the 1,3-bis(silyl)allyllithium complexes [Li{η3-CH(Si-
Me2But)CHCH(SiMe2R)}(tmen)] (R = But 3a or Me 3b) and
[Li{C6H7(SiMe3)2-1,3}(tmen)]
9 were prepared from the
In a preliminary publication28 we have briefly described an
exploration of the synthesis and reactions of 1,3-bis(silyl)allyl-
lithium or -potassium compounds. We now provide: (i) details
on these compounds, (ii) the synthesis of related compounds
and (iii) structures of crystalline complexes.
appropriate silyl- or bis(silyl)-alkene. n-Butyllithium was added
to a stirred solution of the silyl-substituted alkenes 2a, 2b, 6 or
8 and tmen in hexane at room temperature and the mixture was
stirred overnight (and refluxed for 2 h for the case of 2a) to yield
the silylallyllithium–tmen complexes 3a, 3b (ii in Scheme 1), 7
Scheme 1 i, LiBun, tmen, hexane, 0 ЊC to room temperature, 12 h, then ButMe2SiF, room temperature 1 h and reflux 6 h; ii, LiBun, tmen, hexane,
Ϫ78 ЊC to room temperature, 12 h; iii, KOBut, hexane, room temperature, 4 h; iv, pyridine or thf, hexane; v, pyridine.
J. Chem. Soc., Dalton Trans., 1999, 1257–1262
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Scheme 2 i, Mg, Et2O, Me3SiCl, 0 ЊC, 12 h; ii, LiBun, tmen, hexane, room temperature, 12 h; iii, Me3SiCl, hexane, Ϫ78 ЊC to room temperature, 4 h;
iv, LiBun, tmen, hexane, room temperature, 12 h; v, KOBut, hexane, room temperature, 12 h; vi, Me2SiCl2, hexane, Ϫ78 ЊC to room temperature, 12 h
then LiBun, tmen, room temperature, 12 h and then KOBut, 12 h, recrystallisation in thf–hexane.
or 9 (ii or iv in Scheme 2). Upon treatment of 3a or 9 with an
equimolar amount of KOBut in hexane at room temperature
the corresponding tmen-free potassium complex 4 (iii in
Scheme 1) or 10 (v in Scheme 2) was precipitated. From 3b and
KOBut under the same conditions only an unidentified brown
solution was obtained.
Crystallisation of complex 4 from hexane in the presence of
pyridine (py) or thf yielded (iv in Scheme 1) the adducts [K{η3-
CH(CHSiMe2But)2}L] (L = py 5a or thf 5b). The crystalline
dimethylsilyl ansa-bis(silylcyclohexenyl)dipotassium complex
[K2[(η3-C6H4SiMe3-6)2SiMe2](thf)3}∞] 11 was obtained from 7
by several steps in a one-pot reaction sequence. A dimethylsilyl-
bridged bis(cyclohexene), presumably formed from 7 and Me2-
SiCl2, was lithiated by LiBun and tmen; the product was further
treated with KOBut and crystallisation in the presence of thf
gave 11.
The identity of each of the air-stable silyl-substituted alkenes
1
1a, 2a, 2b, 6 and 8 was established by their H NMR, IR and
(for 1a, 2a and 2b) GC-MS spectra, as well as (for 2a and 2b)
elemental analysis. The lithium complexes 3a, 3b, 7 and 9 were
obtained as air-sensitive, colourless crystals, soluble in hexane
Fig. 1 An ORTEP30 representation of the molecular structure of
crystalline complex 3a.
or pentane and purified by crystallisation from hexane or pen-
little more complicated. It showed two sets of trimethylsilyl
tane. They were characterised by elemental analyses (3a and 3b)
signals and two sets of allyl proton signals, respectively, in a
and 1H (3a, 3b, 7 and 9) and (for 3a and 3b) 13C-{1H}, 7Li-{1H}
ratio of 1 to 3. This may have been due to the formation of a
and 29Si-{1H} NMR spectra. These data were consistent with
mixture of σ-allylmetal complexes 10a [10ؒnpy] (1 part) and 10b
(10ؒmpy) (3 parts) (n ≠ m).
1
the formulae shown in Schemes 1 and 2. Thus, the H NMR
spectra in C6D6 showed the η3 co-ordination mode of each
allylic ligand; in addition, complex 3a (but not the less hindered
3b) showed the presence of magnetically inequivalent methyls
attached to the same silicon atom. This is attributed to the
greater restriction to rotation about the silicon–allyl–carbon
bond in the more hindered of the two compounds. The same
distinction between 3a and 3b was also observed in the 13C
NMR spectrum. It may be that at a lower temperature the
SiMe2But methyls in 3b would also have shown inequivalence.
An interesting difference between the lithium compound
The solid white (4) or yellow (10) potassium complexes were
[Li{η3-CH(CHSiMe2But)2}(tmen)] 3a and the related potas-
insoluble in pentane or hexane. Their pyridine (5a) or thf (5b or
sium compounds 4, 5a and 5b is that each of the latter showed
11) adducts were hydrocarbon-soluble, crystalline solids. They
1
singlets, rather than the two singlets for 3a, in their H NMR
were characterised by elemental analyses (4, 5a and 5b) and 1H
spectra (see Experimental section). This may be because the
potassium complexes are loose ion pairs, with weak potassium–
(4, 5a, 5b, 10 and 11), 13C-{1H} (4, 5a and 5b) and 29Si-{1H} (5a)
1
NMR spectra. The H NMR spectrum of each neutral donor
ligand contacts.
adduct 5a and 5b was consistent with the η3-allylic co-
ordination mode in the non-co-ordinating C6D6 or C6D5CD3.
However, when the H NMR spectrum of the allylpotassium
Crystal structures of the bis(silyl)allyllithium complexes 3a and 9
1
complex 4 was recorded in [2H5]pyridine it showed three sets of
different allyl proton signals. This is attributed to the co-
ordination of pyridine to potassium (v in Scheme 1) to yield the
σ-allylmetal complex [K{C(H)(SiMe2But)C(H)CHSiMe2But}-
(py)n] (5c n ≥ 2), due to steric repulsion between the co-
ordinated pyridines and the SiMe2But group. Attempts to
crystallise the adduct 5c by adding pyridine to 4 in hexane
failed. The 1H NMR spectrum of complex 10 in C6D6 (2 parts)
and C5D5N (1 part) was somewhat similar to that of 4, but a
The molecular structures with the atom numbering schemes of
the crystalline complexes 3a and 9 are shown in Figs. 1 and 2,
respectively. Selected bond distances and angles are listed in
Tables 1 and 2.
Crystalline complex 3a is a monomer with an η3-co-
ordination mode of ligand to metal and exo,exo orientation of
the tert-butyldimethylsilyls. The lithium atom lies almost sym-
metrically above the allyl group, the Li–C(2) distance of
2.11(2) Å being slightly shorter than the Li–C(1) and Li–C(3)
1258
J. Chem. Soc., Dalton Trans., 1999, 1257–1262

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Table 1 Selected intramolecular distances (Å) and angles (Њ) for
complex 3a
Li–N(1)
Li–C(1)
Li–C(3)
C(1)–C(2)
C(2)–C(3)
2.13(2)
2.23(2)
2.22(2)
1.415(10)
1.408(9)
Li–N(2)
Li–C(2)
Si(1)–C(1)
Si(2)–C(3)
2.09(2)
2.11(2)
1.844(7)
1.848(8)
N(1)–Li–N(2)
N(1)–Li–C(2)
N(2)–Li–C(1)
N(2)–Li–C(3)
C(1)–Li–C(3)
Li–N(1)–C(16)
Li–C(1)–Si(1)
Li–C(2)–C(1)
Li–C(3)–C(2)
C(1)–C(2)–C(3)
86.2(6)
130.4(7)
119.9(7)
119.1(6)
69.0(5)
103.1(7)
124.9(5)
75.4(6)
N(1)–Li–C(1)
N(1)–Li–C(3)
N(2)–Li–C(2)
C(1)–Li–C(2)
C(2)–Li–C(3)
Li–N(2)–C(17)
Li–C(1)–C(2)
Li–C(2)–C(3)
Li–C(3)–Si(2)
133.0(6)
134.6(8)
143.4(8)
38.0(4)
37.8(4)
104.0(7)
66.6(6)
75.4(6)
126.4(5)
Fig. 3 An ORTEP representation of the structure of crystalline
complex 11.
66.8(5)
126.5(6)
Table 2 Selected intramolecular distances (Å) and angles (Њ) for
complex 9
Li(1)–N(2)
Li(1)–C(6)
C(1)–Li(1)
C(2)–Si(2)
C(1)–C(6)
C(3)–C(4)
C(5)–C(6)
2.145(7)
2.428(7)
2.140(6)
1.305(4)
1.379(5)
1.460(6)
1.537(6)
Li(1)–C(2)
C(2)–C(3)
Li(1)–N(1)
C(6)–Si(1)
C(1)–C(2)
C(4)–C(5)
2.395(7)
1.541(5)
2.116(7)
1.792(4)
1.412(4)
1.490(5)
N(1)–Li(1)–C(1)
C(1)–Li(1)–N(2)
N(2)–Li(1)–C(2)
N(2)–Li(1)–C(6)
C(1)–C(2)–C(3)
C(1)–C(2)–Si(2)
Si(2)–C(2)–Li(1)
C(3)–C(4)–C(5)
C(1)–C(6)–C(5)
C(5)–C(6)–Si(1)
152.2(4)
121.5(3)
130.6(3)
127.3(3)
112.8(3)
125.4(3)
118.2(2)
114.8(4)
115.2(3)
116.6(3)
N(1)–Li(1)–N(2)
N(1)–Li(1)–C(2)
N(1)–Li(1)–C(6)
C(2)–Li(1)–C(6)
C(6)–C(1)–C(2)
C(3)–C(2)–Si(2)
C(4)–C(3)–C(2)
C(4)–C(5)–C(6)
C(1)–C(6)–Si(1)
Si(1)–C(6)–Li(1)
86.0(2)
129.3(3)
126.6(4)
63.20(17)
129.8(3)
121.1(2)
114.9(3)
113.6(4)
126.6(3)
121.3(2)
Fig. 4 The unit cell of crystalline complex 11.
bonds, average 2.412(7) Å. Noteworthy features are the very
different bond distances for C(1)–C(2) [1.412(4) Å] and C(1)–
C(6) [1.379(5) Å] in complex 9, corresponding to a formal
double and single bond, respectively. The C(2)–C(1)–C(6) angle
of 129.8(3)Њ is almost the same as that subtended at the central
carbon of [Li{η3-CH(CHSiMe3)2}(tmen)] [129.4(4)Њ],11 but is
bigger than that in 3a [126.5(6)Њ]. Perhaps 9 is better formulated
as a σ- (or η1)-allyllithium, rather than an η3-allyllithium
compound.
Crystal structure of the dimethylsilyl-ansa-bis(cyclohexenyl)-
potassium complex 11
The molecular structure of the crystalline complex 11, with the
atom numbering scheme, is shown in Fig. 3, the unit cell in Fig.
4 and selected bond distances and angles in Table 3. The crys-
talline complex 11 is a polymer with different co-ordination
environments for successive potassium atoms, one co-ordinated
by the ansa-bridged bis(cyclohexenyl) and the other between
two such ligands. The three disordered thf molecules in an
asymmetric unit of the cell have a half occupancy. The potas-
sium atoms make contact with the allyl units of the cyclo-
hexenyls in an asymmetric manner, the K–C distances ranging
from 2.932(6) to 3.350(7) Å, which are comparable to those
Fig. 2 An ORTEP representation of the molecular structure of
crystalline complex 9.
distances, average 2.22(3) Å; this corresponds to the situation
found in other allyllithium compounds7–13 and most allyltransi-
tion metal complexes.31 The C(1)–C(2) and C(2)–C(3) bond
lengths are closely similar, average 1.41(2) Å. Comparison with
the structure of [Li{C3H3(SiMe3)2-1,3}(tmen)]11 reveals that
complex 3a has the more symmetrical structure.
The molecular structure of crystalline complex 9 shows it
also to be monomeric. Compared with 3a, the structure of 9 has
somewhat longer Li–C distances, the central Li–C [C(1)] bond
of 2.140(6) Å being shorter than the Li–C(Si) [C(2) and C(6)]
28
in [K{η4-N(SiMe2But)C(But)(CH)3SiMe2But}]∞ or [{K[C(Si-
Me3)3]}∞].32 The various C–C distances of the allyl units of the
cyclohexenyls are in the narrow range 1.374(8) to 1.386(9) Å.
J. Chem. Soc., Dalton Trans., 1999, 1257–1262
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Table 3 Selected intramolecular distances (Å) and angles (Њ) for
complex 11
mol) and the mixture refluxed for 15 h. After cooling, water
(100 cm3) was added. The organic layer was separated and dried
(CaCl2); diethyl ether was then removed in vacuo and the resi-
due distilled to give the colourless oil 1a (26.0 g, 90%), bp 150–
155 ЊC. 1H NMR (298 K, CDCl3): δ Ϫ0.03 (s, 6 H, SiMe2), 0.91
(s, 9 H, SiBut), 1.56 (d, 2 H, J = 8.3 Hz), 4.82–4.90 (m, 2 H) and
5.76–5.88 (m, 1 H). GC-MS: m/z = 156 (Mϩ). IR (liquid film):
νmax/cmϪ1 3079w, 2955vs, 2930vs, 2884s, 2858s, 1632m, 1471m,
1392w, 1363w, 1253s, 1155m, 1039w, 1008w, 992w, 893s, 838s,
750w and 658m.
K(1)–O(2)
K(1)–C(13)
K(1)–C(12)
K(1)–C(4)
K(1)–Si(2)
K(2)–C(13)
K(2)–C(12)
K(2)–C(17)
C(4)–C(9)
C(6)–C(7)
C(8)–C(9)
C(12)–C(17)
C(14)–C(15)
C(15)–C(16)
2.726(7)
2.932(6)
3.141(7)
3.329(7)
3.727(3)
2.951(6)
3.184(7)
3.484(10)
1.520(10)
1.510(9)
1.533(13)
1.498(9)
1.536(10)
1.476(12)
K(1)–O(1)
K(1)–C(5)
K(1)–C(6)
K(1)–C(14)
K(2)–O(3)
K(2)–C(14)
K(2)–C(15)
C(4)–C(5)
C(5)–C(6)
C(7)–C(8)
C(12)–C(13)
C(13)–C(14)
C(14)–Si(3)
C(16)–C(17)
2.734(8)
2.942(6)
3.201(7)
3.350(7)
2.706(9)
3.084(7)
3.412(11)
1.386(9)
1.380(9)
1.493(12)
1.374(8)
1.381(9)
1.799(8)
1.453(12)
RMe SiCH᎐CHCH SiMe But (R ؍ But 2a or Me 2b). n-
᎐
2
2
2
Butyllithium (26.5 cm3 of a 1.6 mol dmϪ3 solution in hexane,
42.4 mmol) was added dropwise at 0 ЊC with stirring to a solu-
tion of tert-butyldimethylsilylpropene (6.5 g, 41.7 mmol) and
tmen (6.3 cm3, 41.8 mmol) in hexane (50 cm3), and stirred over-
night at room temperature. tert-Butyldimethylsilyl fluoride (5.6
g, 41.8 mmol) was added at room temperature. The mixture was
stirred for 1 h and then heated at 75–80 ЊC for 6 h. The tmen
was removed by column chromatography and the eluent dis-
tilled under vacuum to obtain colourless crystals of compound
2a (11.3 g, 91%) (Found: C, 66.2; H, 12.7. C15H34Si2 requires C,
66.6; H, 12.7%), mp 52.5–54 ЊC. 1H NMR (298 K, C6D6):
δ Ϫ0.04 (s, 6 H, SiMe2), 0.10 (s, 6 H, SiMe2), 0.88 (s, 9 H, SiBut),
0.99 (s, 9 H, SiBut), 1.65 (d, 2 H, J = 7.9, CH2), 5.54 (d, 1 H,
J = 17.6 Hz, CH) and 6.08–6.18 (m, 1 H, CH). 13C NMR (298
K, CDCl3): δ Ϫ6.46, Ϫ5.92, 16.61, 16.81, 24.69, 26.50, 26.58,
125.06 and 145.43. IR (Nujol): νmax/cmϪ1 2953vs, 2926vs,
2855vs, 1604m, 1463m, 1377w, 1251w, 1143w, 1007w, 989w,
938w, 840w, 823w, 806w, 752vw and 723vw.
O(2)–K(1)–O(1)
O(1)–K(1)–C(13)
O(1)–K(1)–C(5)
O(2)–K(1)–C(12)
C(13)–K(1)–C(12)
O(2)–K(1)–C(6)
C(13)–K(1)–C(6)
C(12)–K(1)–C(6)
O(1)–K(1)–C(4)
C(5)–K(1)–C(4)
C(6)–K(1)–C(4)
O(1)–K(1)–C(14)
C(5)–K(1)–C(14)
C(6)–K(1)–C(14)
O(2)–K(1)–Si(2)
C(13)–K(1)–Si(2)
C(13)–K(2)–C(14)
C(14)–K(2)–C(12)
C(14)–K(2)–C(15)
O(3)–K(2)–C(17)
C(14)–K(2)–C(17)
C(15)–K(2)–C(17)
C(9)–C(4)–K(1)
C(6)–C(5)–C(4)
C(4)–C(5)–K(1)
C(7)–C(6)–K(1)
C(8)–C(7)–C(6)
C(4)–C(9)–C(8)
C(13)–C(12)–K(1)
C(13)–C(12)–K(2)
K(1)–C(12)–K(2)
C(12)–C(13)–K(1)
K(1)–C(13)–K(2)
109.2(2)
118.4(2)
99.1(2)
O(2)–K(1)–C(13)
O(2)–K(1)–C(5)
C(13)–K(1)–C(5)
O(1)–K(1)–C(12)
C(5)–K(1)–C(12)
O(1)–K(1)–C(6)
C(5)–K(1)–C(6)
O(2)–K(1)–C(4)
C(13)–K(1)–C(4)
C(12)–K(1)–C(4)
O(2)–K(1)–C(14)
C(13)–K(1)–C(14)
C(12)–K(1)–C(14)
C(4)–K(1)–C(14)
O(1)–K(1)–Si(2)
C(12)–K(1)–Si(2)
C(13)–K(2)–C(12)
C(13)–K(2)–C(15)
C(12)–K(2)–C(15)
C(13)–K(2)–C(17)
C(12)–K(2)–C(17)
C(5)–C(4)–K(1)
Si(1)–C(4)–K(1)
C(6)–C(5)–K(1)
C(5)–C(6)–K(1)
Si(2)–C(6)–K(1)
C(7)–C(8)–C(9)
C(6)–Si(2)–K(1)
116.1(2)
119.0(2)
93.48(19)
99.8(2)
78.53(17)
115.6(2)
25.52(17)
95.9(2)
142.0(2)
25.86(16)
124.1(2)
68.68(17)
58.20(18)
101.0(2)
24.56(16)
45.22(16)
112.7(2)
117.64(17)
92.53(17)
146.48(19)
47.99(12)
26.34(16)
47.05(18)
26.74(18)
137.6(2)
52.46(19)
43.2(2)
100.8(4)
130.6(7)
93.5(4)
101.9(5)
113.4(7)
110.5(7)
68.5(4)
67.7(4)
135.1(2)
85.6(4)
113.00(17)
102.29(17)
99.6(2)
24.25(16)
45.23(17)
135.31(17)
103.91(18)
29.90(12)
25.52(16)
44.93(19)
53.1(2)
43.29(17)
25.46(16)
61.9(4)
101.0(3)
87.8(4)
Compound 2b was prepared similarly. Trimethylsilylallyl-
lithium [prepared from trimethylsilylpropene (3.6 g, 31.6
mmol), tmen (4.8 cm3, 31.8 mmol) and LiBun (20 cm3 of a 1.6
mol dmϪ3 solution in hexane, 32 mmol)] was treated with tert-
butyldimethylsilyl fluoride (4.3 g, 32.1 mmol). The resultant
solution was distilled, after removing tmen by column chrom-
atography, to produce the colourless oil 2b (5.84 g, 81%)
(Found: C, 62.1; H, 12.0. C6H14Si requires C, 63.1; H, 12.4%),
66.7(4)
91.2(2)
115.3(8)
59.2(2)
1
bp 50–52 ЊC (0.5 Torr). NMR (298 K, CDCl3): H, δ Ϫ0.02 (s,
6 H, SiMe2), 0.07 (s, 9 H, SiMe3), 0.93 (s, 9 H, SiBut), 1.68 (d,
2 H, J = 6.8, CH2), 5.47 (d, 1 H, J = 18.4 Hz, CH) and 6.01–6.11
(m, 1 H, CH); 13C, δ Ϫ6.45, Ϫ0.97, 16.90, 24.56, 26.63, 128.11
and 144.11. GC-MS: m/z = 228 (Mϩ). IR (liquid film): νmax/cmϪ1
2954vs, 2929vs, 2897vs, 2858vs, 1605s, 1471s, 1464s, 1402w,
1363w, 1251vs, 1143s, 1005w, 987w, 938vw, 873vs, 840vs, 766w,
749m, 720w, 692s, 667w and 633w.
C(17)–C(12)–K(1) 101.2(5)
C(17)–C(12)–K(2) 88.5(4)
C(12)–C(13)–C(14) 130.6(6)
C(14)–C(13)–K(1)
K(2)–C(14)–K(1)
95.1(4)
130.6(2)
167.2(2)
Experimental
[Li{CH(CHSiMe2But)2}(tmen)] 3a. n-Butyllithium (5 cm3 of
a 1.6 mol dmϪ3 solution in hexane, 8 mmol) was added dropwise
with stirring to a solution of 1,3-bis(tert-butyldimethylsilyl)-
propene (2.1 g, 7.78 mmol) and tmen (1.2 cm3, 7.96 mmol) in
hexane (25 cm3) at Ϫ78 ЊC. The mixture was allowed to warm
to room temperature, stirred overnight and then filtered. The
filtrate was concentrated to ca. 3 cm3 to yield colourless crystals
of complex 3a (2.8 g, 92%) (Found: C, 66.6; H, 13.0; N, 6.67.
C21H49LiN2Si2 requires C, 64.2; H, 12.6; N, 7.13%), mp
83–85 ЊC. NMR (298 K, C6D6): 1H, δ 0.14 (s, 6 H, SiMe2), 0.29
(s, 6 H, SiMe2), 1.22 (s, 18 H, SiBut), 1.59 (s, 4 H, tmen), 1.81 (s,
12 H, tmen), 2.83 (d, 2 H, J = 16, CH) and 7.04 (t, 1 H, J = 16
Hz, CH); 13C, δ Ϫ4.21, Ϫ2.58, 18.62, 27.46, 46.15, 56.56, 64.53
and 156.52; 7Li, δ Ϫ0.22; 29Si, δ Ϫ3.20.
All reactions were performed under argon using standard
Schlenk techniques. The thf and diethyl ether were dried using
sodium–benzophenone, hexane and pentane using sodium–
potassium alloy. The compound ButMe2SiF was prepared
according to a published procedure.32 Allyltrimethylsilane was
purchased from Aldrich. The NMR spectra were recorded on
AC-P250, WM-360 and AMX-500 instruments, and the solvent
resonances were used as the internal references for H and 13C
1
spectra; LiCl (1 mol dmϪ3 aqueous solution) was the external
7
reference for Li NMR spectra. The IR spectra were recorded
on a Perkin-Elmer 1720 FT spectrometer as liquid films or
Nujol mulls using KBr windows. The GC-MS data were
recorded on a MD800 apparatus: EI, 70 eV. Elemental analyses
were carried out by Medac Ltd., Brunel University. Melting
points were determined under argon in sealed capillaries on an
electrothermal apparatus and were uncorrected.
[Li{CH(CHSiMe2But)(CHSiMe3)}(tmen)] 3b. Complex 3b
was synthesized using a similar method as that for 3a. A mixture
of 3-tert-butyldimethylsilyl-1-trimethylsilylpropene (3.3 g, 14.5
mmol) and tmen (2.2 cm3, 14.6 mmol) in pentane (30 cm3) was
treated with LiBun (9 cm3 of a 1.6 mol dmϪ3 solution in hexane,
14.4 mmol). After work-up the colourless crystalline complex
3b (4.0 g, 79%) was obtained (Found: C, 61.1; H, 12.8; N, 7.66.
C18H43LiN2Si2 requires C, 61.7; H, 12.4; N, 7.99%), mp 70–
Preparations
ButMe SiCH CH᎐CH 1a. Allylmagnesium bromide (0.25
᎐
2
2
2
mol), prepared from CH ᎐CHCH Br (30.25 g, 0.25 mol) and
᎐
2
2
magnesium turnings (6.5 g, 0.27 mol) in diethyl ether (150 cm3),
was mixed with tert-butyldimethylsilyl fluoride (25 g, 0.187
1260
J. Chem. Soc., Dalton Trans., 1999, 1257–1262

View Article Online
Table 4 Crystallographic data for complexes 3a, 9 and 11c
72 ЊC. NMR (298 K, C6D6): 1H, δ 0.13 (s, 6 H, SiMe2), 0.28 (s,
9 H, SiMe3), 1.17 (s, 9 H, SiBut), 1.64 (s, 4 H, tmen), 1.82 (s, 12
H, tmen), 2.77 (d, 1 H, J = 15.7, CH), 2.90 (d, 1 H, J = 15.7,
CH) and 7.03 (t, 1 H, J = 15.7 Hz, CH); 13C, δ Ϫ4.04, Ϫ2.49,
3a
9
11
Empirical formula C21H49LiN2Si2 C18H41Li2Si2
C32H62K2O3Si3
657.3
7
2.29, 18.57, 27.53, 46.19, 56.52, 63.76, 69.24 and 155.22; Li,
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
392.8
348.65
δ Ϫ0.22; 29Si, δ Ϫ9.98 and Ϫ1.25.
Monoclinic
P21/n (no. 14)
11.295(3)
21.365(3)
12.254(4)
103.33(2)
2877(1)
4
Orthorhombic Orthorhombic
Pna21 (no. 33)
19.325(4)
8.660(2)
14.750(3)
—
2468.5(9)
4
0.938
0.145
4366
Pna21 (no. 33)
17.298(1)
20.032(1)
11.727(1)
—
4064(2)
4
1.074
0.348
5680
[{K[CH(CHSiMe2But)2]}∞] 4. Potassium tert-butoxide (0.83
g, 7.41 mmol) was added at room temperature with stirring to a
hexane (30 cm3) solution of complex 3a [prepared from 2a (1.98
g, 7.33 mmol), tmen (1.1 cm3, 7.3 mmol) and LiBun (4.6 cm3 of
a 1.6 mol dmϪ3 solution in hexane, 7.36 mmol)]. After several
minutes a white precipitate appeared. Stirring was continued
for 4 h. The mixture was filtered and the precipitate washed
with hexane (2 × 15 cm3) and dried in vacuo to afford the white
solid 4 (1.95 g, 86%) (Found: C, 56.7; H, 10.7. C15H33KSi2
requires C, 58.4; H, 10.8%), mp 271–275 ЊC. NMR (298 K,
C5D5N): 1H, δ 0.10 (s, 6 H, SiMe2), 0.19 (s, 6 H, SiMe2), 0.91 (s,
9 H, SiBut), 1.05 (s, 9 H, SiBut), 5.38 (d, 1 H, J = 17.6, CH), 6.08
(d, 1 H, J = 10.8, CH) and 6.97 (dd, 1 H, J = 10.8, 17.6 Hz, CH);
13C, δ Ϫ5.20, Ϫ4.04, 17.22, 19.17, 26.89, 27.30, 113.08, 117.86
and 149.75.
β/Њ
V/Å3
Z
Dc/g cmϪ3
µ/mmϪ1
Reflections
collected
Independent,
0.910
0.13
5478
5217 (0.02)
1780
2263 (0.17)
614
5680 (0.06)
5179
n (Rint
)
Observed, n
[I > 2σ(I)]
No. parameters, p 235
203
0.0482
0.1019
362
0.0989
0.2606
R1 [I > 2σ(I)]
0.094
0.083
wR2a or wRb
a For I > 2σ(I) (complexes 9 and 11). b For complex 3a. c All data were
collected at 293 K.
[K{CH(CHSiMe2But)2}(py)] 5a. Pyridine (0.5 cm3) was added
to a suspension of complex 4 (0.5 g, 1.62 mmol) in hexane (ca.
10 cm3). The complex slowly dissolved and a red-brown mixture
was formed. After filtration all volatiles were removed from the
filtrate in vacuo. The resultant solid was redissolved in hexane
(ca. 10 cm3) and concentrated in vacuo. Crystallisation at room
temperature yielded the yellow crystalline complex 5a (0.5 g,
80%) (Found: C, 61.3; H, 9.89; N, 3.54. C18H43LiN2Si2 requires
C, 62.0; H, 9.88; N, 3.61%), mp 85–88 ЊC. NMR (298 K,
crystallised at Ϫ78 ЊC to give white crystals of 7 (5.0 g, 90%). 1H
NMR (298 K, C6D6): δ 0.37 (s, 9 H, SiMe3), 1.66 (s, 4 H, tmen),
1.81 (s, 12 H, tmen), 2.01 (br, 3 H), 2.43 (br, 1 H), 2.85 (br, 2 H),
3.94 (m, 1 H) and 6.62 (d, 1 H).
C(SiMe3)CHC(SiMe3)(CH2)2CH2 8. A solution of complex 7
in hexane (ca. 20 cm3) [prepared from tmen (2.25 cm3, 14.94
mmol), LiBun (9.7 cm3 of a 1.4 mol dmϪ3 solution in hexane,
13.58 mmol) and 6 (2.3 g, 14.94 mmol)] was added dropwise to
a solution containing an equimolar portion of Me3SiCl in hex-
ane (ca. 10 cm3) at Ϫ78 ЊC. The mixture was warmed to room
temperature and stirred for 4 h, then hydrolysed and the organic
phase separated. After drying (CaCl2) it was distilled to give 8
1
toluene-d8): H, δ 0.11 (s, 12 H, SiMe2), 1.00 (s, 18 H, SiBut),
2.92 (d, 2 H, J = 16, CH), 6.89 (t, 1 H, J = 16 Hz, CH), 6.67–
6.71 (m, 2 H, py), 6.94–6.96 (m, 1 H, py) and 8.43–8.45 (m, 2 H,
py); 13C, δ Ϫ2.51, 18.38, 28.03, 67.30, 123.81, 137.46, 149.96
and 157.28; 29Si, δ Ϫ4.21.
[K{CH(CHSiMe2But)2}(thf)] 5b. Tetrahydrofuran (ca. 0.5
cm3) was added to a suspension of complex 4 (0.9 g, 2.92 mmol)
in hexane (ca. 10 cm3). The solid slowly dissolved and a colour-
less solution was formed. After filtering off a small precipitate
the filtrate was concentrated in vacuo. Crystallisation at room
temperature yielded colourless crystals of complex 5b (0.93 g,
84%) [Found: C, 58.5; H, 10.6. C15H33KSi2 (the co-ordinated
thf was lost during elemental analysis) requires C, 58.4; H,
1
(2.6 g, 77%), bp 49–50 ЊC (1 Torr). H NMR (298 K, CDCl3):
δ Ϫ0.01 (s, 9 H, SiMe3), 0.03 (s, 9 H, SiMe3), 1.40 (m, 2 H), 1.54
(m, 1 H), 1.69 (m, 2 H), 1.93 (m, 2 H) and 5.91 (m, 1 H).
[Li{C(SiMe3)CHC(SiMe3)(CH2)2CH2}(tmen)] 9. Employing
a procedure similar to that for complex 7, 8 (1.9 g, 8.39 mmol),
tmen (1.26 cm3, 8.39 mmol) and LiBun (5.43 cm3 of a 1.54 mol
dmϪ3 solution in hexane, 8.36 mmol) in pentane (ca. 20 cm3)
1
10.8%], mp 138–140 ЊC. NMR (298 K, C6D6): H, δ 0.19 (s,
1
gave white crystals of 9 (2.6 g, 89%). H NMR (298 K, C6D6):
12 H, SiMe2), 1.08 (s, 18 H, SiBut), 1.39 (m, 4 H, thf), 2.75 (d,
2 H, J = 16.4, CH), 3.55 (m, 4 H, thf) and 6.89 (t, 1 H, J = 16.4
Hz, CH); 13C, δ Ϫ2.24, 18.87, 28.37, 25.76, 67.95, 66.30 and
157.57.
δ 0.31 (s, 18 H, SiMe3), 1.52 (s, 4 H, tmen), 1.77 (s, 12 H, tmen),
2.05 (m, 4 H), 2.78 (m, 2 H) and 6.82 (s, 1 H).
[K{C(SiMe3)CHC(SiMe3)(CH2)2CH2}] 10. The compound
tmen (0.86 cm3, 5.7 mmol) and LiBun (3.7 cm3 of a 1.54 mol
dmϪ3 solution in hexane, 5.7 mmol) were added to a solution of
8 (1.30 g, 5.7 mmol) in hexane (ca. 30 cm3) at room temperature.
The mixture was stirred for 12 h and then KOBut (0.64 g, 5.71
mmol) was added. An additional 12 h of stirring yielded a
CH᎐CHCH(SiMe )(CH ) CH 6. Magnesium (2.8 g, 0.117
᎐
3
2
2
2
mol) in Et2O (ca. 15 cm3) was treated with a few particles of I2
until the brown colour was discharged. The compound Me3SiCl
(13 cm3, 0.103 mol) was added. A solution of 3-bromocyclo-
hexene (15 g, 0.093 mol) in Et2O (ca. 60 cm3) was slowly added
into the stirred mixture during 12 h at ice-bath temperature.
The mixture was carefully hydrolysed with crushed ice. The
organic phase was collected and dried (CaCl2). Distillation
under reduced pressure gave 6 (8.7 g, 61%), bp 64–66 ЊC (20
Torr). 1H NMR (298 K, CDCl3): δ 0.01 (s, 9 H, SiMe3), 1.55 (m,
3 H), 1.73 (m, 2 H), 1.96 (m, 2 H) and 5.64 (s, 2 H).
1
yellow precipitate of complex 10 (0.90 g, 60%). H NMR (298
K, C6D6–pyridine-d5 2:1): δ Ϫ0.05, 0.05 (s, 6 H, SiMe3), 0.94,
0.20 (s, 12 H, SiMe3), 1.70 (m, 3 H), 2.05, 2.15, 2.37, 2.56 (m,
3 H), 6.05 (m, 1/3 H) and 6.58 (s, 2/3 H).
[{K2[(ç3-C6H4SiMe3-6)2SiMe2](thf)3}∞] 11. A solution of
complex 7 (3.00 g, 10.87 mmol) in hexane (ca. 40 cm3) was
added dropwise to the solution of Me2SiCl2 (0.66 cm3, 5.44
mmol) in hexane (ca. 10 cm3) at Ϫ78 ЊC. The mixture was
warmed to room temperature stirred for 12 h and then filtered.
The compound tmen (1.63 cm3, 10.87 mmol) and LiBun (5.4
cm3 of a 2.0 mol dmϪ3 solution in hexane, 10.8 mmol) were
added to the filtrate. The mixture was stirred for 12 h and
[Li{C(SiMe3)(CH)2(CH2)2CH2}(tmen)] 7. The compound
tmen (3 cm3, 20.31 mmol) and LiBun (10 cm3 of a 2 mol dmϪ3
solution in hexane, 20 mmol) were added to a solution of 6
(3.1 g, 20.31 mmol) in hexane (ca. 30 cm3) at room temperature.
The mixture was stirred for 12 h and then concentrated and
J. Chem. Soc., Dalton Trans., 1999, 1257–1262
1261

View Article Online
KOBut (1.22 g, 10.89 mmol) added. After 12 h of stirring the
yellow precipitate 11 (2.4 g, 99%) was filtered off and crystal-
lised from thf. NMR (298 K, C6D6): 1H, δ 0.28 (s, 18 H, SiMe3),
0.35 (s, 6 H), 1.84 (br, 4 H), 2.56 (br, 8 H), 6.46 (s, 2 H), 1.39 (m,
6 H, thf) and 3.56 (m, 6 H); 13C, δ 0.82, 0.89, 15.31, 26.54, 30.12,
25.76, 28.56, 67.96, 70.60, 77.54, 143.52 and 176.48.
9 J. F. Sebastian, J. R. Grunwell and B. Hsu, J. Organomet. Chem.,
1974, 78, C1.
10 G. Boche, H. Etzrodt, M. Marsch, W. Massa, G. Baum, H. Dietrich
and W. Mahdi, Angew. Chem., Int. Ed. Engl., 1986, 25, 104.
11 G. Boche, G. Fraenkel, J. Cabral, K. Harms, N. J. R. v. Eikema
Hommes, J. Lohrenz, M. Marsch and P. v. R. Schleyer, J. Am. Chem.
Soc., 1992, 114, 1562.
12 P. Jutzi, Adv. Organomet. Chem., 1986, 26, 217.
13 E. Weiss, Angew. Chem., Int. Ed. Engl., 1993, 32, 1501.
14 P. West, J. I. Purmort and S. V. McKinley, J. Am. Chem. Soc., 1968,
90, 797.
15 D. H. O’Brien, A. J. Hart and C. R. Russell, J. Am. Chem. Soc.,
1975, 97, 4410.
16 R. Benn and A. Rufinska, J. Organomet. Chem., 1982, 239, C19.
17 G. Fraenkel and W. R. Winchester, Organometallics, 1990, 9, 1314.
18 G. Fraenkel, A. Chow and W. R. Winchester, J. Am. Chem. Soc.,
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19 C. B. Erusalimski and V. H. Kormer, Zh. Org. Khim., 1984, 20, 2028.
20 E. R. Tidwell and B. R. Russell, J. Organomet. Chem., 1974, 80, 175.
21 G. Decher and G. Boche, J. Organomet. Chem., 1983, 259, 31.
22 T. Clark, E. D. Jemmis, P. v. R. Schleyer, J. S. Binkley and J. A.
Pople, J. Organomet. Chem., 1978, 15, 1.
Crystallography
Details are given in Table 4. Single crystals of each of the com-
plexes 3a, 9 and 11 were mounted in Lindemann capillaries
under argon. Data were collected on Enraf-Nonius CAD4
(for 3a), Rigaku AFC7R (for 9) or Rigaku Raxis IIc (for
11) diffractometers in the θ–2θ mode with monochromated
Mo-Kα radiation. The structure was solved by direct methods
(SHELXS 8634 or Siemens SHELXSTL plus) and refined by
full-matrix least squares on F for 3a or on F2 for 9 and 11. All
non-H atoms were anisotropic. The diffraction for the crystal
of 9 was rather weak resulting in a limited data set.
CCDC reference number 186/1314.
See http://www.rsc.org/suppdata/dt/1999/1257/ for crystallo-
graphic files in .cif format.
23 T. Clarke, C. Rhode and P. v. R. Schleyer, Organometallics, 1983, 2,
1344.
24 R. J. Bushby and M. P. Tytko, J. Organomet. Chem., 1984, 270,
265.
25 G. Fraenkel, A. Chow and W. R. Winchester, J. Am. Chem. Soc.,
1990, 112, 2582.
26 M. Schlosser and J. Hartmann, J. Am. Chem. Soc., 1976, 98, 4674.
27 R. B. Bates and W. A. Beavers, J. Am. Chem. Soc., 1974, 96,
5001.
28 P. B. Hitchcock, M. F. Lappert and Z.-X. Wang, Chem. Commun.,
1996, 1647.
29 T. Morita, Y. Okamoto and H. Sakurai, Tetrahedron Lett., 1980,
835.
Acknowledgements
We thank the Chinese Government and the British Council
for the award of a studentship to Z.-X. W. and EPSRC for
other support at Sussex and the Hong Kong Research Grants
Council Earmarked Grants CUHK 4126/98P.
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Paper 8/06870D
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J. Chem. Soc., Dalton Trans., 1999, 1257–1262