Hydrophosphination of Aromatic Alkenes and α,β‐Unsaturated Compounds Using Cobalt Phenoxyimine Complex and Isolation of Double‐Insertion Products

A cobalt complex bearing a tridentate phenoxyimine ligand has been found to be a suitable precatalyst for the hydrophosphination of both aromatic and activated alkenes, such as vinylarenes, vinylketones, acrylates, and acrylonitrile, with diphenylphosphine to selectively afford the β‐addition (anti‐Markovnikov) product. An efficient conversion was achieved by exposing the precatalyst solution to air prior to the higher temperature reaction of phosphine and alkene. When the amount of alkene increased, double‐insertion products were obtained as byproducts, which had been known for α,β‐unsaturated compounds but never for vinylarenes.