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

Divalent organic compounds of Group IV
Tin(II) halides and Grignard or organolithium reagents afford air-sensitive oils
or amorphous solids. usually yellow or red in colour, which ha ve the approximate
empirica! composition R 2 Sn. They are similar to the materials obtained from
alkali metals and organotin halides. These products do not contain divalent tin
but are mixtures of linear and cyclic polystannanes. The linear compounds are
coloured, the more branching which is present the deeper the colour. The extent
of branching can be determined by degradation by chlorine at - 70'C which
gives a mixturc of R,SnCI. R,SnCI, and RSnCI,.
t•J
(R,Sn) 2 SnR(SnR 2 ),SnR, ~ 3R,SnCI + 2R,SnCI 2 + RSnCI,
(JCll
(R 2 Sn) 6 ----> 6R,SnCI,
These polystannanes presumably arise through the intermediacy of
trialkyl/aryltin lithium or Grignard reagents. One way of preparing R 3 SnLi is to
treat tin (II) chloride with three molar equivalents of RLi in ether. Further reaction
with SnCI, yields (Ph,Sn),SnLi (R = Ph) which may be trapped with Ph,SnCI.
2RLi + SnCI, ~ 'R,Sn' + 2LiCI
'R,Sn' + RLi ~ R,SnLi
3Ph,SnLi + SnCI, ----> (Ph,Sn),SnLi
l'h 1 Snl'l
_______, (Ph ,Sn) 4 Sn
m.p. 280 (dec.)
The strengths of M-M bonds decrease down Group IV. so it is not surprising
that organoderivatives which contain lead-lead bonds are rather unstable.
When lead(II) chloride is treated with methylmagnesium iodide, the first product
is probably polymeric dimethyllead, but this disproportionates first into lead and
hexamethyldilead and finally on warming into lead and PbMe 4 •
PbCI 2
MeMgl
'Me,Pb'
6'Me,Pb' -----> 2Pb + 2Me,Pb-PbMe, ----> 3Me 4 Pb + .3Pb
4. 7 Divalent organic compounds of the elements of Group IV
The elements of Group IV form oxides and halides in two formal oxidation states,
+ 2 and + 4. The + 2 compounds of carbon and silicon (except for CO) are only
short lived species which are unstable to dimerization (CX,) or to disproportionation
or polymerization (SiO, SiX,). For ali the other elements representatives of
both oxidation states can be isolated. The + 2 state becomes increasingly
favoured relative to the + 4 state down the group.
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