Reactions of Nickel(0)-Olefin Pincer Complexes with Terminal Alkynes: Cooperative C-H Bond Activation and Alkyne Coupling

Abstract

Metal-ligand cooperation can facilitate the activation of chemical bonds, opening reaction pathways of interest for catalyst development. In this context, olefins occupying the central position of a diphosphine pincer ligand (PC═CP) are emerging as reversible H atom acceptors, e.g., for H2 activation. Here, we report on the reactivity of nickel complexes of PC═CP ligands with a terminal alkyne, for which two competing pathways are observed. First, cooperative and reversible C-H bond activation generates a Ni(II) alkyl/alkynyl complex as the kinetic product. Second, in the absence of a bulky substituent on the olefin, two alkyne molecules are incorporated in the ligand structure to form a conjugated triene bound to Ni(0). The mechanisms of these processes are studied by density functional theory calculations supported by experimental observations.