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

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.