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Published May 6, 2015 | Supplemental Material
Journal Article Open

Origins of Initiation Rate Differences in Ruthenium Olefin Metathesis Catalysts Containing Chelating Benzylidenes


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.

Additional Information

© 2015 American Chemical Society. Received: February 5, 2015. Publication Date (Web): April 21, 2015. Dr. Bruce S. Brunschwig is acknowledged for assistance with the UV/vis kinetics experiments, which were carried out at the Molecular Materials Research Center of the Beckman Institute at Caltech. Prof. Jeffrey S. Cannon (Occidental College) and Zachary K. Wickens (Grubbs group, Caltech) are thanked for helpful discussions. The research described herein was supported financially by the ONR (Award N00014-12-1-0596) and the NIH NIGMS (Award F32GM108145; postdoctoral fellowship to K.M.E.). The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology (CHE-0639094). Materia, Inc. is thanked for the generous donation of catalysts 2, 4, S16, and S17 and (E/Z)-1-isopropoxy-4-nitro-2-(prop-1-en-1-yl)benzene (S20). Calculations were performed on supercomputers from the DoD HPCMP Open Research Systems and the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by the NSF.

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Supplemental Material - ja5b01144_si_003.cif

Supplemental Material - ja5b01144_si_004.cif

Supplemental Material - ja5b01144_si_005.cif

Supplemental Material - ja5b01144_si_006.cif


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