@article {ISI:000254173600010, title = {N-heterocyclic carbene complexes of Rh: reaction with dioxygen without oxidation.}, journal = {J. Am. Chem. Soc.}, volume = {130}, number = {12}, year = {2008}, month = {mar}, pages = {3724{\textendash}5}, abstract = {The reaction of oxygen with rhodium complexes containing N-heterocyclic carbenes was found to give dioxygen complexes with rare square planar geometries and unusually short O-O bond lengths. Analysis of the bonding in these complexes by Rh L-edge X-ray absorption spectroscopy (XAS), Raman spectroscopy, and DFT calculations provides evidence for a bonding model in which singlet oxygen is bound to a Rh(I) d8 metal complex, rather than the more common Rh(III) d6 peroxo species with octahedral geometry and O-O bond lengths in the 1.4-1.5 A range.}, keywords = {chemical, DFT, dioxygen complexes, Heterocyclic Compounds, Heterocyclic Compounds: chemistry, METHANE, Methane: analogs \& derivatives, Methane: chemistry, models, MOLECULAR, molecular structure, ORGANOMETALLIC COMPOUNDS, Organometallic Compounds: chemical synthesis, Organometallic Compounds: chemistry, OXYGEN, Oxygen: chemistry, rhodium, Rhodium: chemistry, SPECTROMETRY, X-Ray Emission, X-Ray Emission: methods, XAS}, issn = {1520-5126}, doi = {10.1021/ja7108213}, url = {http://www.ncbi.nlm.nih.gov/pubmed/18321109}, author = {Praetorius, Jeremy M and Allen, Daryl P and Wang, Ruiyao and Webb, Jonathan D and Grein, Friedrich and Kennepohl, Pierre and Crudden, Cathleen M} } @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} }