Zirconium complexes stabilized by amine-bridged bis(phenolato) ligands as precatalysts for intermolecular hydroamination reactions

Abstract

A series of zirconium complexes bearing amine-bridged bis(phenolato) ligands of different steric and electronic properties have been synthesized, and their activities in catalyzing intermolecular hydroamination reactions have been studied and compared. In general, hexacoordinate zirconium dibenzyl complexes 1–4 stabilized by [ONNO]- or [ONOO]-type ligands were found to be less active than pentacoordinate complexes 5 and 7 that carry [ONO]-type ligands, which clearly imply that amine-bridged bis(phenolato) ligands play crucial roles in influencing catalytic activities. Complex 5 showed good activities and regioselectivities in catalysing reactions of various primary amines and alkynes. Moreover, reactions of challenging substrates, including secondary amines, internal alkynes, and hydrazines, were achieved with in situ generated cationic species from complex 5 and [Ph₃C][B(C₆F₅)₄].