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.