NUCLEOPHILE-ASSISTED RACEMISATIONS OF HALOSILANES - KINETIC-STUDIES

被引:14
作者
BASSINDALE, AR
LAU, JCY
TAYLOR, PG
机构
[1] The Chemistry Department, The Open University, Milton Keynes, MK7 6AA, Walton Hall
关键词
SILICON; RACEMIZATION; MECHANISM;
D O I
10.1016/0022-328X(95)05202-Z
中图分类号
O61 [无机化学];
学科分类号
070301 ; 081704 ;
摘要
Kinetic studies have been carried out on the nucleophile-induced racemisation of PhMeCHSiMe(2)X, 2, X = triflate, Br or Cl. Thirteen nucleophiles were studied. The results are interpreted in terms of two competing mechanisms for racemisation: (a) nucleophile attack on a silane-nucleophile complex formed by displacement of the halide by the nucleophile, and (b) halide-halosilane exchange, with inversion of configuration. Solvent effects were examined, and kinetic orders in the nucleophile and in one case for the halosilane were determined. The order in added nucleophile varied between one and two, with strong nucleophiles in 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 consistent 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 involving extracoordinate silicon.
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页码:75 / 82
页数:8
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