Ring-opening metathesis polymerization with vanadium(V) alkylidenes: Survey of initiators, density-functional theory calculations, and functional group tolerance

Ring-opening metathesis polymerization (ROMP) with vanadium(V) alkylidene initiators bearing diverse ligand sets is presented, along with analyses of factors governing the activity and kinetics for each. The first DFT calculations on ROMP with vanadium are executed and show that non-covalent interactions between supporting ligands and the alkylidene have drastic effects on rates of initiation and propaga-tion, specifically with both stabilizing and destabilizing interactions occurring in transition states. This allows for rationalization of the kinetics inferred from the molar mass distributions. Furthermore, we demonstrate that the metallocyclobutane forms in a manner quite distinct from group 6 analogues. NMR experiments empirically support the computational findings and allow for important insights for future initiator design. Termination of growing polymer chains is shown to not play any role in the observed broad molar mass distributions, which has been assumed but not proven experimentally until now, and for the first time with vanadium the syn-alkylidenes are shown experimentally to be less reactive than their anti-counterparts, analogous to group 6 alkylidenes. Functional group tolerance, which has yet to be investigated in ROMP with vanadium-based initiators, is also explored for each class of initiators. In general, the more electron poor chlorido ligated complexes were less tolerant to functional groups.Published by Elsevier B.V.