Nickel-Catalyzed Alkyne Cyclotrimerization Assisted by a Hemilabile Acceptor Ligand: A Computational Study

π-coordinating units incorporated in the supporting ligand of an organometallic complex may open up specific reactive pathways. The diphosphine ketone supported nickel complex [(p-tolL1)Ni(BPI)] (p-tol1; p-tolL1 = 2,2′-bis(di-p-tolylphosphino)benzophenone; BPI = benzophenone imine) has previously been shown to act as an active and selective alkyne cyclotrimerization catalyst. Herein, DFT calculations support an adaptive behavior of the ligand throughout the catalytic cycle, several elementary steps being assisted by coordination or decoordination of the C═O moiety. A comparison with related bi- and tridentate phosphine ligands reveals the key role of the hemilabile π-acceptor moiety for the catalytic activity and selectivity of p-tol1 in alkyne cyclotrimerization.