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Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis

Stewart, Ian C. and Benitez, Diego and O'Leary, Daniel J. and Tkatchouk, Ekaterina and Day, Michael W. and Goddard, William A., III and Grubbs, Robert H. (2009) Conformations of N-Heterocyclic Carbene Ligands in Ruthenium Complexes Relevant to Olefin Metathesis. Journal of the American Chemical Society, 131 (5). pp. 1931-1938. ISSN 0002-7863. PMCID PMC2638209.

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The structure of ruthenium-based olefin metathesis catalyst 3 and model π-complex 5 in solution and in the solid state are reported. The N-tolyl ligands, due to their lower symmetry than the traditional N-mesityl substituents, complicate this analysis, but ultimately provide explanation for the enhanced reactivity of 3 relative to standard catalyst 2. The tilt of the N-tolyl ring provides additional space near the ruthenium center, which is consistent with the enhanced reactivity of 3 toward sterically demanding substrates. Due to this tilt, the more sterically accessible face bears the two methyl substituents of the N-aryl rings. These experimental studies are supported by computational studies of these complexes by DFT. The experimental data provides a means to validate the accuracy of the B3LYP and M06 functionals. B3LYP provides geometries that match X-ray crystal structural data more closely, though it leads to slightly less (0.5 kcal mol^(−1)) accuracy than M06 most likely because it underestimates attractive noncovalent interactions.

Item Type:Article
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URLURL TypeDescription CentralArticle
Goddard, William A., III0000-0003-0097-5716
Grubbs, Robert H.0000-0002-0057-7817
Additional Information:© 2009 American Chemical Society. Received October 6, 2008. Publication Date (Web): January 15, 2009. The NIH (F32GM078734 and K99GM084302 to I.C.S., 5RO1GM31332 to R.H.G.), the NSF (NIRT(CTS-0608889) to D.B., E.T., W.A.G., CHE-0410425 to R.H.G.) and Pomona College Chemistry Department (to D.J.O.) for generous financial support. Larry Henling for X-ray crystallography assistance. Computational facilities were funded by grants from ARO-DURIP and ONR-DURIP. D.B. and E.T. thank Dr. Vyacheslav Bryantsev for help with NWChem and Professor Donald G. Truhlar for helpful discussions. NWChem Version 5.1, as developed and distributed by Pacific Northwest National Laboratory, P. O. Box 999, Richland, Washington 99352, and funded by the U.S. Department of Energy, was used to obtain some of these results. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology, CHE-0639094. Supporting Information: Details of NMR experiments and computational data; complete ref 18a. This material is available free of charge via the Internet at
Funding AgencyGrant Number
NIH Postdoctoral FellowshipF32GM078734
Army Research Office (ARO)UNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Department of Energy (DOE)UNSPECIFIED
Issue or Number:5
PubMed Central ID:PMC2638209
Record Number:CaltechAUTHORS:20090828-134843119
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:15419
Deposited By: George Porter
Deposited On:09 Sep 2009 22:30
Last Modified:03 Oct 2019 00:57

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