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Published April 27, 2011 | Accepted Version + Supplemental Material
Journal Article Open

Characterization and Dynamics of Substituted Ruthenacyclobutanes Relevant to the Olefin Cross-Metathesis Reaction


The reaction of the phosphonium alkylidene [(H_(2)IMes)RuCl2═CHP(Cy)_3)]^(+) BF_(4)^− with propene, 1-butene, and 1-hexene at −45 °C affords various substituted, metathesis-active ruthenacycles. These metallacycles were found to equilibrate over extended reaction times in response to decreases in ethylene concentrations, which favored increased populations of α-monosubstituted and α,α′-disubstituted (both cis and trans) ruthenacycles. On an NMR time scale, rapid chemical exchange was found to preferentially occur between the β-hydrogens of the cis and trans stereoisomers prior to olefin exchange. Exchange on an NMR time scale was also observed between the α- and β-methylene groups of the monosubstituted ruthenacycle (H_(2)IMes)Cl_(2)Ru(CHRCH_(2)CH_(2)) (R = CH_3, CH_(2)CH_3, (CH_2)_)_(3)CH_3). EXSY NMR experiments at −87 °C were used to determine the activation energies for both of these exchange processes. In addition, new methods have been developed for the direct preparation of metathesis-active ruthenacyclobutanes via the protonolysis of dichloro(1,3-bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene)(benzylidene) bis(pyridine)ruthenium(II) and its 3-bromopyridine analogue. Using either trifluoroacetic acid or silica-bound toluenesulfonic acid as the proton source, the ethylene-derived ruthenacyclobutane (H_(2)IMes)Cl_(2)Ru(CH_(2)CH_(2)CH_(2)) was observed in up to 98% yield via NMR at −40 °C. On the basis of these studies, mechanisms accounting for the positional and stereochemical exchange within ruthenacyclobutanes are proposed, as well as the implications of these dynamics toward olefin metathesis catalyst and reaction design are described.

Additional Information

© 2011 American Chemical Society. Published In Issue April 27, 2011; Article ASAP March 31, 2011; Received: January 31, 2011. We wish to thank Mr. Ian Tonks, Mr. Edward C. Weintrob, and Professor John Bercaw for the use of the Schlenk manifold used in the quantitated gas addition experiments. Additional thanks goes to Mr. James Luchi and Dr. Daniel Levin of Norac Pharma for the generous donation of the silica-bound toluenesulfonic acid used in these experiments. Materia Inc. is gratefully acknowledged for the generous donation of catalyst. Professors J. M. O'Connor and Charles Perrin of U.C. San Diego and B. Scott Williams and John Carl Olsen of JSD are acknowledged for invaluable research discussion. Funding for A.G.W. and G.B. was provided by Claremont McKenna, Scripps, and Pitzer Colleges. JSD NMR instrumentation funding was provided by NSF (CHE 0922393); Caltech NMR instrumentation funding was provided by NIH (NIH RR027690). Additional funding for R.H.G. was provided by NIH (5R01GM031332).

Attached Files

Accepted Version - nihms-285377.pdf

Supplemental Material - ja2009746_si_001.pdf


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