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Author Collman, J. P. ♦ Wagenknecht, P. S. ♦ Lewis, N. S.
Sponsorship USDOE
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword HYDROGEN FUEL ♦ CHEMISTRY ♦ RUTHENIUM COMPLEXES ♦ CHEMICAL PREPARATION ♦ CATALYTIC EFFECTS ♦ OSMIUM COMPLEXES ♦ HYDROGEN ♦ CATALYSIS ♦ CHEMICAL REACTION KINETICS ♦ BOND LENGTHS ♦ OXIDATION
Abstract A series of metalloporphyrin hydride complexes of the type K[M(Por)(L)(H)] (M - Ru, Os; Por - OEP, TMP; L = THF, *Im, PPh{sub 3}, pyridine) has been synthesized by stoichiometric protonation of the corresponding K{sub 2}[M(Por)], followed by addition of L. The addition of excess acids to these hydrides resulted in the elimination of dihydrogen. The kinetics showed no evidence for a bimolecular mechanism for this process and suggest simple protonation of the metal-hydride bond followed by dihydrogen loss. One-electron oxidation of the metal hydrides also resulted in dihydrogen formation. The kinetics of the oxidatively induced hydrogen evolution step from K[Ru(OEP)(THF)(H)] were examined and indicate a biomolecular mechanism in which two metal hydrides reductively eliminate one dihydrogen molecule. The rate constant was determined to be 88 {+-} 14 M{sup -1} s{sup -1}. These reaction mechanisms are discussed in the context of designing bimetallic proton reduction catalysts. The metal hydride K[Ru(OEP)(THF)(H)], was also synthesized by heterolytic activation of H{sub 2}. This hydride is a good one-electron reductant (-1.15 V vs FeCp{sub 2}) and is capable of reducing, by hydride transfer, the NAD{sup +} analogue, 1-benzyl-N,N-diethyl-nicotinamide. This nicotinamide reduction by a hydride formed from heterolytic dihydrogen activation is suggested as the mechanism for hydrogenase enzymes. 38 refs., 4 figs., 3 tabs.
ISSN 00027863
Educational Use Research
Learning Resource Type Article
Publisher Date 1992-07-01
Publisher Place United States
Journal Journal of the American Chemical Society
Volume Number 114
Issue Number 14


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