Abstract
Addition of photochemically-generated trialkylsilyl radicals to alkyl isocyanates to give imidoyl radicals (A) has been studied in cyclopropane solution using e.s.r. spectroscopy. The rate of addition of trimethylsilyl radicals to R13Si˙+ R2NCO [graphic omitted] alkyl isocyanates has been determined relative to that of addition to methyl trifluoroacetate or ethylene and kadd(R1= Me) was found to decrease in the order R2= Me > Et > Pri > But at 164 K. It is proposed that this trend is steric in origin and that the Me3Si group is closer to the N-alkyl group in the transition state for addition than in the product imidoyl radical. The palladium chloride catalysed addition of triethylsilane to n-butyl isocyanate gives the imidate BunNC(H)OSiEt3 rather than the isomeric C-silylamide BunN(H)C(O)SiEt3, as previously reported.
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