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

Organo-halides of Group IV
Apart from the fluorides, organosilicon halides do not normally form isolable
adducts with Lewis bases. They are. however. very susceptible to nucleophilic
substitution. Ali are rapidly hydrolysed (p. 112 ). ln contrast Me ,Sir is almost
inert to hydrolysis and alcoholysis under neutra! conditions. This is because ofthe
high energy of the Si-F bond (E(Si-F) > E(Si-0) but E(Si-Cl) <
E(Si-0)) so that the equilibrium.
Me,SiF + RCJH~Me,SiOR + HF
!ies to the left. If HF is removed by base or by cakium ions. for example. the
reaction proceeds to completion.
While tetraorganotin compounds themselves show no Lewis acidity, the
halides R"SnX 4 _" form stable complexes with neutra! and anionic donors. RSnX 3
and R 2 SnX 2 , like SnX 4 • generally give l :2 adducts RSnX,L 2 or R 2 SnX 2 1 2 with
monodentate ligands, in which the tin atom is octahedrally coordinated. R,SnX,
however. normally forms l: l complexes R,SnXL which have trigonal
bipyramidal structures. In polar, donor solvents. these complexes may ionize;
R 3 SnXL might, for example, give R,SnL + and x- ions.
The planar Me,Sn arrangement which is adopted in solid Me,SnF is also
present in the pyridine complex Me,SnClpy. Similar complexes are formed by
Ph,PO and by Me 2 SO. If chlorine is replaced by more poorly coordinating anions
such as BPh;. cationic complexes, [Me,Sn1 2 ] +BPh_;(L = e.g. H 2 0. Me 2 SO). can be
prepared (Fig. 4. 3 ).
Cis and trans geometrica! isomers have been observed for the adducts
R 2 SnX 2 1 3 • The R 2 Sn grouping is usually linear.
Similar complexes ha ve been obtained from organolead halides. although so far
in fewer numbers.
L
Me-Sn'
~ _...-Me
I'Me
CL
L=Ph3 PCHCOMe,
PY
+
CL
1 _-Me
Me-s 1
<,
CL Me
J
R=Me, L=Me 2SO
R=Ph, L=py or L2=bipy
R=Me
L = pyridine -N-oxide
Fig. 4.3 Structures of some complexes of organotin halides with Lewis bases.
105