HYDROGEN ABSTRACTION FROM SILYLAMINES - AN INVESTIGATION OF THE 1,2-MIGRATION OF THE TRIMETHYLSILYL GROUP IN AMINYL RADICALS

Hydrogen abstraction from a series of silyl-substituted amines, Me3SiC HRNHR', by tert-butoxyl radicals has been examined by EPR spectroscopy . For each amine hydrogen is abstracted from both the methylene (or me thine) group and from the amino group to give a mixture of aminoalkyl, Me3SiC.RNHR', and aminyl radicals, Me3SiCHRN.R'. The proportion of hy drogen abstraction from the amino groups is less than from the methyle ne (methine) groups. The aminyl radicals are not directly detectable b y EPR spectroscopy, but they rearrange above a particular temperature by 1,2-migration of the trimethylsilyl group from carbon to nitrogen t o give carbon-centred radicals, .CHRNR'SiMe3, which have been spectros copically characterised. Mechanistic evidence favours an intramolecula r migration of the trimethylsilyl group via a transition state in whic h the silicon atom expands its valence shell to five, rather than via an elimination-readdition route. Rate parameters for the migrations ha ve been estimated from the temperature development of the rearranged r adical concentrations and found to be sensitive to the presence of ste rically large groups at the nitrogen terminus.