title: Proton-hydride tautomerism in hydrogen evolution catalysis.
abstract: Efficient generation of hydrogen from renewable resources requires development of catalysts that avoid deep wells and high barriers. Information about the energy landscape for H2 production can be obtained by chemical characterization of catalytic intermediates, but few have been observed to date. We have isolated and characterized a key intermediate in 2e(-) + 2H(+) → H2 catalysis. This intermediate, obtained by treatment of Cp*Rh(bpy) (Cp*, η(5)-pentamethylcyclopentadienyl; bpy, κ(2)-2,2'-bipyridyl) with acid, is not a hydride species but rather, bears [η(4)-Cp*H] as a ligand. Delivery of a second proton to this species leads to evolution of H2 and reformation of η(5)-Cp* bound to rhodium(III). With suitable choices of acids and bases, the Cp*Rh(bpy) complex catalyzes facile and reversible interconversion of H(+) and H2.
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Luis M Aguirre
authors.initials: LM
authors.lastname: Quintana
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Samantha I
authors.initials: SI
authors.lastname: Johnson
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Sydney L
authors.initials: SL
authors.lastname: Corona
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Walther
authors.initials: W
authors.lastname: Villatoro
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: William A
authors.initials: WA
authors.lastname: Goddard
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: Michael K
authors.initials: MK
authors.lastname: Takase
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125;
authors.forename: David G
authors.initials: DG
authors.lastname: VanderVelde
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; winklerj@caltech.edu hbgray@caltech.edu blakemore@ku.edu.
authors.forename: Jay R
authors.initials: JR
authors.lastname: Winkler
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; winklerj@caltech.edu hbgray@caltech.edu blakemore@ku.edu.
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
authors.affiliation: Beckman Institute, California Institute of Technology, Pasadena, CA 91125; Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125; Department of Chemistry, University of Kansas, Lawrence, KS 66044 winklerj@caltech.edu hbgray@caltech.edu blakemore@ku.edu.
authors.forename: James D
authors.initials: JD
authors.lastname: Blakemore
keywords: catalysis; hydrogen evolution; pentamethylcyclopentadienyl; proton reduction; rhodium