@article {ISI:000251974000023, title = {An electronic rationale for observed initiation rates in ruthenium-mediated olefin metathesis: charge donation in phosphine and N-heterocyclic carbene ligands.}, journal = {J. Am. Chem. Soc.}, volume = {129}, number = {51}, year = {2007}, month = {dec}, pages = {15774{\textendash}6}, chapter = {15774}, abstract = {Ru K-edge XAS data indicate that second generation ruthenium-based olefin metathesis precatalysts (L = N-heterocyclic carbene) possess a more electron-deficient metal center than in the corresponding first generation species (L = tricyclohexylphosphine). This surprising effect is also observed from DFT calculations and provides a simple rationale for the slow phosphine dissociation kinetics previously noted for second-generation metathesis precatalysts.}, keywords = {ALKENES, Alkenes: chemistry, BOND, carbenes, CATALYSTS, CL, DFT, ELECTRONS, Heterocyclic Compounds, Heterocyclic Compounds: chemistry, HYDROCARBONS, Hydrocarbons: chemistry, KINETICS, LIGANDS, MECHANISM, METHANE, Methane: analogs \& derivatives, Methane: chemistry, MOIETY, NHC LIGANDS, OLEFIN METATHESIS, phosphines, Phosphines: chemistry, RAY-ABSORPTION SPECTROSCOPY, ruthenium, Ruthenium: chemistry, TRANSITION-METAL-COMPLEXES, XAS}, isbn = {0002-7863}, issn = {1520-5126}, doi = {10.1021/ja0747674}, url = {://000251974000023 http://www.ncbi.nlm.nih.gov/pubmed/18047332}, author = {Getty, Kendra and Delgado-Jaime, Mario Ulises and Kennepohl, Pierre} }