_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

Divalent organic compounds of Group IV
In crystalline decaphenylstannocene, (1] 5 -C ,Ph,) 1 Sn, the C, rings are parallel
and adopt a staggered conformation. The phenyl groups are arranged like a
paddle wheel about each ring. In this structure an S 10 inversion rotation axis is
present passing through the centre of each ring and the metal atom.
It has been suggested that the dialkyls MR 1 are unstable kinetically to
disproportionation or polymerization because the monomers are coordinatively
unsaturated, possessing both filled non-bonding and low lying empty orbitals. If
association between monomer units could be prevented, it might be possible to
isolate dialkyls. The use of bulky groups such as Me,SiCH 2 - or Me ,CCH 1 -has
proved most successful in stabilizing transition metal alkyls (p. 219) of low
coordination number. Me 3 SiCH 1 MgCl and SnC1 4 , however, gave Sn(CH 2 SiMe 3 ) 4
and SnC1 2 afforded the distannane Sn 1 (CH 1 CMe 3 ) 6 with neopentylmagnesium
chloride. Success was achieved, however. with the even bulkier group
(Me 3 Si) 2 CH-.
Li
(Me,Si) 2 CHCI-----------+ (Me,Si) 2 CHLi -----------+ M{CH(SiMe,) 2 }, + 2LiCI
Et,o
Et 2 o
(M = Sn, PbJ
lsoelectronic amin o derivatives of divalent Ge. Sn and Pb were similarly prepared,
starting from hexamethyldisilazane.
MC!,
20 c
(Me 1 SH 2 CHLi
--------> { (Me,Si) 2 CH],M. (M =Ce. Sn. PbJ
These were in turn converted into the alkyl compounds as shown.
The yellow germanium (m.p. 180 C) and brick-red tin complexes (m.p. l 36 C)
are thermally stable but air-sensitive solids which can be sublimed in vacuo, but
the purple lead analogue is rather heat and photosensitive. They are monomeric
in the vapour and in their solutions in benzene. X-ray diffraction of the tin
compound shows that it dimerizes in the solid state. The monomer has both a lone
pair and vacant p orbita!. It acts as a Lewis base towards transition metal
complexes and as a Lewis acid towards pyridine. Dimerization may therefore
occur through mutual acid-base interaction to forma bent tin-tin double bond.
Cr(C0) 6 + SnR 2
In
-------> (OCJ,Cr+- SnR 2 + CO
hexane
,
py+SnR 2
low
-----------+ py+-SnR 2 :R=-CH(SiMe,) 2 )
temp.
Trivalent radicals Mr; (M =Si, Ge, Sn) and M"{N(SiMe 3 ) 1 L (M = Ge, Sn) are
obtained similarly from R 3 MCI. Apart from the silicon species t 1 2 = 1 O min. they
persist for very long periods in hexane in the absence of air.
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