Ar. Bassindale et al., NUCLEOPHILE-ASSISTED RACEMISATIONS OF HALOSILANES - KINETIC-STUDIES, Journal of organometallic chemistry, 490(1-2), 1995, pp. 75-82
Kinetic studies have been carried out on the nucleophile-induced racem
isation of PhMeCHSiMe(2)X, 2, X = triflate, Br or Cl. Thirteen nucleop
hiles were studied. The results are interpreted in terms of two compet
ing mechanisms for racemisation: (a) nucleophile attack on a silane-nu
cleophile complex formed by displacement of the halide by the nucleoph
ile, and (b) halide-halosilane exchange, with inversion of configurati
on. Solvent effects were examined, and kinetic orders in the nucleophi
le and in one case for the halosilane were determined. The order in ad
ded nucleophile varied between one and two, with strong nucleophiles i
n polar media. Anomalously high orders in nucleophile were observed in
non-polar media and are ascribed to aggregation of the nucleophile. A
kinetic analysis of the competing mechanisms was attempted, and was c
onsistent with the experimental findings. In this particular series of
reactions involving compounds with good leaving groups and relatively
powerful nucleophiles there was no evidence for intermediates involvi
ng extracoordinate silicon.