title: Nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in olefin metathesis: a computational study.
abstract: We used the density functional theory to evaluate the suitability of nitrenium ions and trivalent boron ligands as analogues of N-heterocyclic carbenes in ruthenium-based metathesis catalysts. We demonstrate that these analogues induce only minor structural changes in Hoveyda-Grubbs-like precatalysts, but have major impact on precatalyst initiation. Nitrenium ion-modified precatalysts are characterized by a weak Ru-N bond resulting in a relatively strong Ru-O bond and large free energy barriers for initiation, making them good candidates for efficient latent Ru-based catalysts. On the other hand the trivalent boron ligand, bearing a formal -1 charge, binds strongly to the ruthenium ion, weakening the Ru-O bond and facilitating its dissociation, to promote fast reaction initiation. We show that the calculated bond dissociation energy of the Ru-C/N/B bond may serve as an accurate indicator of the Ru-O bond strength and the rate of metathesis initiation.
authors.affiliation: Centre of New Technologies, University of Warsaw, 02-097 Warszawa, Poland. trzask@cent.uw.edu.pl and Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, 02-093 Warszawa, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Pazio
authors.affiliation: Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, 02-093 Warszawa, Poland.
authors.forename: K
authors.initials: K
authors.lastname: Woźniak
authors.affiliation: Biological and Chemical Research Centre, Department of Chemistry, University of Warsaw, 02-093 Warszawa, Poland.
authors.forename: K
authors.initials: K
authors.lastname: Grela
authors.affiliation: Centre of New Technologies, University of Warsaw, 02-097 Warszawa, Poland. trzask@cent.uw.edu.pl.
authors.forename: B
authors.initials: B
authors.lastname: Trzaskowski