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

The main Groups IV and V
Treatment of dihalides of Ge, Sn or Pb with Grignard reagents does not afford
monomeric divalent compounds R 2 M, but leads rather to polymers in which the
metal is tetravalent because ofthe presence of metal-metal bonds. The challenge
to synthesise truly divalent organic compounds of these elements has been
tackled in severa! ways.
Dimethylsilylene Me 2 Si has been generated by photolysis of polysilanes such as
(Me 2 Si) 6 •
hv
(Me 2 Si) 6 --> (Me 2 Si) 5 + Me 2 Si
It is a short lived species which can be trapped as it is formed by, for example, 2-
butyne or triethylsilane. If the irradiation is performed in a solid argon matrix at
1 O K, spectra ofMe 2 Si can be obtained, as it is stable under these conditions. Me 2 Si
is a bright yellow species absorbing at 450 nm.
Me Me
"'-c=c/
\/
Si
Me2
MeCE:CMe
Bis(cyclopentadienyl) complexes Cp 2 M (M = Ge, Sn, Pb) have been prepared by
reaction of cyclopentadienylsodium and an appropriate dihalide in tetrahydrofuran.
Electron diffraction shows that in the vapour these molecules ha ve angular
structures on account of the electron pair on the metal. In the solid state the
germanium compound polymerizes within 3 h at ambient temperature, the tin
compound within five days. The cyclopentadienyl groups are coordinated in a
symmetrical pentahapto fashion (p. 191 ). Association through the rings occurs
in the crystalline lead compound to give a polymeric chain structure (Fig. 4.8).
M
M-C/A
et•
Colour
m.p
Ge
White
dec.
Sn
2.706
125
White
105°
Pb
2.7 78 } Vopour
135
Yellow } Solid
138-9°
sinters
Fig. 4.8 Structures of Cp 2Ge(g)• Cp 2 Sn(gl and Cp 2 Pb(c)·
122
Choin slructure of orlhorhombic