Probing the origin of degenerate metathesis selectivity via characterization and dynamics of ruthenacyclobutanes containing variable NHCs.

ABSTRACT: The preparation of new phosphonium alkylidene ruthenium metathesis catalysts containing N-heterocyclic carbenes (NHCs) that result in a preference for degenerate metathesis is described. The reaction of the catalysts with ethylene or substrates relevant to ring-closing metathesis (RCM) produced ruthenacyclobutanes that could be characterized by cryogenic NMR spectroscopy. The rate of α/β methylene exchange in ethylene-only ruthenacycles was found to vary widely between ruthenacycles, in some cases being as low as 3.97 s(-1) at -30 °C, suggesting that the NHC plays an important role in degenerative metathesis reactions. Attempts to generate RCM-relevant ruthenacycles resulted in the low-yielding formation of a previously unobserved species, which we assign to be a β-alkyl-substituted ruthen

SUBMITTER: Keitz BK 

PROVIDER: S-EPMC3195404 | biostudies-literature | 2011 Oct

REPOSITORIES: biostudies-literature