title: Origins of initiation rate differences in ruthenium olefin metathesis catalysts containing chelating benzylidenes.
abstract: A series of second-generation ruthenium olefin metathesis catalysts was investigated using a combination of reaction kinetics, X-ray crystallography, NMR spectroscopy, and DFT calculations in order to determine the relationship between the structure of the chelating o-alkoxybenzylidene and the observed initiation rate. Included in this series were previously reported catalysts containing a variety of benzylidene modifications as well as four new catalysts containing cyclopropoxy, neopentyloxy, 1-adamantyloxy, and 2-adamantyloxy groups. The initiation rates of this series of catalysts were determined using a UV/vis assay. All four new catalysts were observed to be faster-initiating than the corresponding isopropoxy control, and the 2-adamantyloxy catalyst was found to be among the fastest-initiating Hoveyda-type catalysts reported to date. Analysis of the X-ray crystal structures and computed energy-minimized structures of these catalysts revealed no correlation between the Ru-O bond length and Ru-O bond strength. On the other hand, the initiation rate was found to correlate strongly with the computed Ru-O bond strength. This latter finding enables both the rationalization and prediction of catalyst initiation through the calculation of a single thermodynamic parameter in which no assumptions about the mechanism of the initiation step are made.
authors.affiliation: †Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
authors.forename: Keary M
authors.initials: KM
authors.lastname: Engle
authors.affiliation: ‡Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.
authors.forename: Gang
authors.initials: G
authors.lastname: Lu
authors.affiliation: †Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
authors.forename: Shao-Xiong
authors.initials: SX
authors.lastname: Luo
authors.affiliation: †Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Henling
authors.affiliation: †Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
authors.forename: Michael K
authors.initials: MK
authors.lastname: Takase
authors.affiliation: ‡Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, United States.|§Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.affiliation: §Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States.
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
authors.affiliation: †Arnold and Mabel Beckman Laboratories of Chemical Synthesis, California Institute of Technology, Pasadena, California 91125, United States.
authors.forename: Robert H
authors.initials: RH
authors.lastname: Grubbs
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001597:Benzylidene Compounds / Q000737:chemistry*; D002384:Catalysis; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012428:Ruthenium / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D000475:Alkenes; D001597:Benzylidene Compounds; D002614:Chelating Agents; D009942:Organometallic Compounds; D012428:Ruthenium