title: Cobalt catalyzed z-selective hydroboration of terminal alkynes and elucidation of the origin of selectivity.
abstract: A bis(imino)pyridine cobalt-catalyzed hydroboration of terminal alkynes with HBPin (Pin = pinacolate) with high yield and (Z)-selectivity for synthetically valuable vinylboronate esters is described. Deuterium labeling studies, stoichiometric experiments, and isolation of catalytically relevant intermediates support a mechanism involving selective insertion of an alkynylboronate ester into a Co-H bond, a pathway distinct from known precious metal catalysts where metal vinylidene intermediates have been proposed to account for the observed (Z) selectivity. The identity of the imine substituents dictates the relative rates of activation of the cobalt precatalyst with HBPin or the terminal alkyne and, as a consequence, is responsible for the stereochemical outcome of the catalytic reaction.
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Jennifer V
authors.initials: JV
authors.lastname: Obligacion
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Jamie M
authors.initials: JM
authors.lastname: Neely
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Aliza N
authors.initials: AN
authors.lastname: Yazdani
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Iraklis
authors.initials: I
authors.lastname: Pappas
authors.affiliation: Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Chirik