title: Mechanistic Studies of Single-Step Styrene Production Using a Rhodium(I) Catalyst.
abstract: The direct and single-step conversion of benzene, ethylene, and a Cu(II) oxidant to styrene using the Rh(I) catalyst (FlDAB)Rh(TFA)(η2-C2H4) [FlDAB = N,N'-bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] has been reported to give quantitative yields (with Cu(II) as the limiting reagent) and selectivity combined with turnover numbers >800. This report details mechanistic studies of this catalytic process using a combined experimental and computational approach. Examining catalysis with the complex (FlDAB)Rh(OAc)(η2-C2H4) shows that the reaction rate has a dependence on catalyst concentration between first- and half-order that varies with both temperature and ethylene concentration, a first-order dependence on ethylene concentration with saturation at higher concentrations of ethylene, and a zero-order dependence on the concentration of Cu(II) oxidant. The kinetic isotope effect was found to vary linearly with the order in (FlDAB)Rh(OAc)(η2-C2H4), exhibiting no KIE when [Rh] was in the half-order regime, and a kH/kDvalue of 6.7(6) when [Rh] was in the first-order regime. From these combined experimental and computational studies, competing pathways, which involve all monomeric Rh intermediates and a binuclear Rh intermediate in the other case, are proposed.
authors.affiliation: Department of Chemistry, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: Benjamin A
authors.identifier: 0000-0001-9607-5696
authors.initials: BA
authors.lastname: Vaughan
authors.affiliation: Center for Advanced Scientific Computing and Modeling, Department of Chemistry, University of North Texas , Denton, Texas 76203, United States.
authors.forename: Sarah K
authors.initials: SK
authors.lastname: Khani
authors.affiliation: Center for Advanced Scientific Computing and Modeling, Department of Chemistry, University of North Texas , Denton, Texas 76203, United States.
authors.forename: J Brannon
authors.initials: JB
authors.lastname: Gary
authors.affiliation: Department of Chemical Engineering, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: James D
authors.initials: JD
authors.lastname: Kammert
authors.affiliation: Department of Chemistry, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Webster-Gardiner
authors.affiliation: Department of Chemistry, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: Bradley A
authors.initials: BA
authors.lastname: McKeown
authors.affiliation: Department of Chemical Engineering, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Davis
authors.affiliation: Center for Advanced Scientific Computing and Modeling, Department of Chemistry, University of North Texas , Denton, Texas 76203, United States.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Cundari
authors.affiliation: Department of Chemistry, University of Virginia , Charlottesville, Virginia 22904, United States.
authors.forename: T Brent
authors.identifier: 0000-0001-5714-3887
authors.initials: TB
authors.lastname: Gunnoe