Synthesis of an Isostructural Series of Group 6 Complexes Supported by an Alkyne-Based Pincer Ligand

There is longstanding general interest in the organometallic chemistry community in π-complexes of transition metals, including alkynes. This interest lies both in understanding fundamental aspects of alkyne coordination chemistry and in leveraging their reactivity at transition metals for productive alkyne transformations. Herein we report the design and synthesis of an isostructural series of formally zerovalent, group 6 alkyne adducts, with the alkyne incorporated in a bisphosphine pincer ligand (PCCP) and the remaining coordination sites at the metal center bound by carbon monoxide to give (PCCP)M(CO)3 (M = Cr, Mo, W). The stability of these systems allows for thorough structural and spectroscopic comparison of these complexes, with complementary computational studies conducted to examine aspects of the bonding in and electronic structures of these systems. Our analyses revealed little perturbation to carbon monoxide activation descending the column from chromium to molybdenum and tungsten, but with an increase in the activation of the alkyne ligand for the heavier group 6 metals.