An “On-Demand”, Selective Dehydrogenative Borylation or Hydroboration of Terminal Alkynes Using Zn2+-based Catalyst

Abstract

An air-stable dicationic Zn2+ complex (1) in a tripod-type ligand with non-bound phosphorus base and three pyridinyl “arms” (TPPh) was synthesized. Remarkably, while 2 mol% of 1 at room temperature selectively catalyzed dehydrogenative borylation of terminal alkynes with HBPin, a lower loading of 1 (0.5 mol%) at 90 °C selectively promoted hydroboration reaction of the same alkynes skipping the dehydrogenative borylation step. The mode of action of 1 was proposed based on experimental observations as well as the mechanism of dehydrogenative borylation was studied by DFT computations.