HYDROGEN ABSTRACTION FROM SILYLAMINES - AN INVESTIGATION OF THE 1,2-MIGRATION OF THE TRIMETHYLSILYL GROUP IN AMINYL RADICALS
HYDROGEN ABSTRACTION FROM SILYLAMINES - AN INVESTIGATION OF THE 1,2-MIGRATION OF THE TRIMETHYLSILYL GROUP IN AMINYL RADICALS
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DOI：
10.1039/p29930002119
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发表时间：
1993-11-01
期刊：
影响因子：
--
通讯作者：
PICARD, JP
中科院分区：
文献类型：
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作者：
HARRIS, JM;WALTON, JC;PICARD, JP
本文用EPR谱研究了叔丁氧基自由基从一系列硅烷基取代胺Me_3SiCHRNHR ′中夺氢的反应。对于每种胺，从亚甲基（或次甲基）和氨基中夺取氢，得到氨基烷基Me3SiC.RNHR '和氨基Me 3SiCHRN. R'的混合物。从氨基中提取的氢的比例小于从亚甲基（次甲基）中提取的氢的比例。氨基自由基不能通过EPR光谱直接检测到，但它们在特定温度以上通过三甲基甲硅烷基从碳到氮的1，2-迁移重排，得到碳中心自由基，CHRNR'SiMe 3，其已被光谱表征。机械证据有利于通过过渡态的三甲基甲硅烷基的分子内迁移，其中硅原子将其价壳层扩展到5，而不是通过消除-再添加路线。速率参数的迁移已估计从重排的自由基浓度的温度发展，并发现是敏感的存在下，在氮末端的空间大基团。
Hydrogen abstraction from a series of silyl-substituted amines, Me3SiCHRNHR', by tert-butoxyl radicals has been examined by EPR spectroscopy. For each amine hydrogen is abstracted from both the methylene (or methine) group and from the amino group to give a mixture of aminoalkyl, Me3SiC.RNHR', and aminyl radicals, Me3SiCHRN.R'. The proportion of hydrogen abstraction from the amino groups is less than from the methylene (methine) groups. The aminyl radicals are not directly detectable by EPR spectroscopy, but they rearrange above a particular temperature by 1,2-migration of the trimethylsilyl group from carbon to nitrogen to give carbon-centred radicals, .CHRNR'SiMe3, which have been spectroscopically characterised. Mechanistic evidence favours an intramolecular migration of the trimethylsilyl group via a transition state in which the silicon atom expands its valence shell to five, rather than via an elimination-readdition route. Rate parameters for the migrations have been estimated from the temperature development of the rearranged radical concentrations and found to be sensitive to the presence of sterically large groups at the nitrogen terminus.