Copper(ii) complexes incorporating poly/perfluorinated alkoxyaluminate-type weakly coordinating anions: Syntheses, characterization and catalytic application in stereoselective olefin aziridination

摘要

The synthesis and characterization of a series of cationic copper(ii) complexes of the type [Cu(NCR)_6][Al(OC(CF_3) _2R′)_4]_2 (R = CH_3, Ph; R′ = CF_3, Ph, PhCH_3), incorporating poly/perfluoronated alkoxyaluminates as weakly coordinating anions (WCAs) is presented. Aziridination of various olefins, such as the unreactive olefins e.g. ethylhex-2-enoate and 1-decene, with N-tosyliminophenyliodinane catalyzed by [Cu(NCR)_6][Al(OC(CF_3)2R′) _4]_2 affords very good yields (up to 96%) and high TOFs (up to 5000 h~(-1)) under mild conditions. Using disubstituted olefins as substrates, high stereoselectivities are obtained at room temperature. The to date highest cis:trans ratio (98:2) of the obtained aziridines is achieved for cis-stilbene in good yield (85%) as well as promising TOF (> 2000 h ~(-1)). The investigation of the solvent effect on yield and selectivity reveals that for certain oleophilic substrates (1-decene), less polar solvents, such as dichloromethane are a better choice than acetonitrile, which is commonly considered as the best solvent for olefin aziridination. Accordingly, a mechanism involving a paramagnetic copper nitrene intermediate with both concerted and stepwise pathways is proposed.