Examination of Dianionic Diamide Ligand Structural Effects on Ti-Catalyzed Hydrohydrazination of Terminal Alkynes
Partha Sarathi Karmakar1, Ian A Tonks1
1Department of Chemistry, University of Minnesota-Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States.
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=NNPh2 catalysts were examined, wherein fast and selective Ti=NNPh2 catalysts have ligands with a "goldilocks" intermediate level of steric environment. Ti=NNPh2 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-SiMe2Ph groups led to an expansion of the hydrazine scope and a structurally diverse set of hydrazones.
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