Abstract
The controlled hydrogenolysis of Me
x
SnR
4 −
x
(0 ≤
x
≤ 4; R = methyl,
n
-butyl,
tert
-butyl, neopentyl, cyclohexyl) onto Rh/SiO
2
is followed by quantitative and qualitative analysis of evolved gases. Only MeH and RH are detected in the evolved gases. There is hydrogenolysis of the Sn-C bonds without any C-C bond hydrogenolysis, leading to formation of grafted organometallic fragments. Using various organotin compounds, Me
x
SnR
4 −
x
, it has been possible to determine the regioselectivity of the hydrogenolysis of the Sn-C bonds. The initial selectivity is inversely proportional to the steric bulk of the alkyl group:
t
Bu < Np < Bu. The formation of a five-coordinate tetraalkyl tin on the surface, Rh-SnMe
x
R
4 −
x
(symmetry
D
3
h
), in which the bulkiest group,
e.g.
, R, is away from the surface could explain these results. This surface five-coordinate tin species could eliminate an alkyl group, generally a methyl group, thus decreasing the steric bulk around the tin, into the equatorial plane of
D
3
h
,
via
a concerted hydrogen transfer-elimination mechanism to give Rh-SnMe
x
− 1
R
4 −
x
. Then, in the successive steps of the hydrogenolysis, the bulkiest group, R, would be eliminated.
Grafted organometallic fragments were obtained by stepwise hydrogenolysis of Me
x
SnR
4 −
x
(0 ≤
x
≤ 4; R = methyl,
n
-butyl,
tert
-butyl, neopentyl, cyclohexyl) onto Rh/SiO
2
. It is demonstrated that the steric hindrance of the alkyl groups governs the regiselectivity of the hydrogenolysis.