Dehydrogenation of (Di)amine-Boranes by Highly Active Scandocene Alkyl Catalysts

摘要

The scandocene alkyl complexes (C5Me5)(2)ScR (I, R = CH(SiMe3)(2); 5, R = CH2SiMe3) were found to be highly active catalysts for the dehydrogenation of dimethylamine borane (DMAB), exhibiting turnover frequencies up to 100 min(-1) ambient temperature. The beta-B-agostic scandium amidoborane intermediate 6 was isolated from a stoichiometric reaction of complex 5 with DMAB. In contrast, treatment of complex 5 with sterically bulky diisopropylamine-borane led to isolation of the aminoborane-coordinated scandocene hydride 7 via a complete beta-H elimination. Scandium amidoborane complex 6 showed scandium hydride like reactivity toward dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMAP), affording DCC insertion product 8 and DMAP ortho-borylation product 9, respectively. In addition, complexes 1 and 5 also showed remarkably high activity for the catalyzed dehydrogenative cyclization of diamine-boranes to give N-heterocyclic boranes.