Abstract
Ti-catalyzed alkyne hydrohydrazination of terminal alkynes using 1,1-disubstituted hydrazines is reported. Here, a variety of bi- or tridentate dianionic diamide or diamidoamine ligated Ti=NNPh(2) catalysts were examined, wherein fast and selective Ti=NNPh(2) catalysts have ligands with a "goldilocks" intermediate level of steric environment. Ti=NNPh(2) catalysts with ligands of high/medium steric bulk showed slower reactivity compared to the optimal catalysts. Catalysis with Ti complexes with sterically less encumbered ligands is extremely slow (requiring 5-14 days to completion). Development of a fast and selective diamidoamine catalyst with flanking N-SiMe(2)Ph groups led to an expansion of the hydrazine scope and a structurally diverse set of hydrazones.