Examination of Dianionic Diamide Ligand Structural Effects on Ti-Catalyzed Hydrohydrazination of Terminal Alkynes

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═NNPh₂catalysts were examined, wherein fast and selective Ti═NNPh₂catalysts have ligands with a “goldilocks” intermediate level of the steric environment. Ti═NNPh₂catalysts with ligands of high/medium steric bulk showed slower reactivity compared to that of 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-SiMe₂Ph groups led to an expansion of the hydrazine scope and a structurally diverse set of hydrazones.