Behaviour of [PdH(dppe)2]X (X=CF3SO3-, SbF6-, BF4-) as proton or hydride donor: relevance to catalysis |
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Authors: | Aresta Michele Dibenedetto Angela Pápai Imre Schubert Gábor Macchioni Alceo Zuccaccia Daniele |
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Affiliation: | Department of Chemistry, University of Bari, and CIRCC via Celso Ulpiani 27, 70126 Bari, Italy. aresta@metea.uniba.it |
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Abstract: | The synthesis, characterization and properties of [PdH(dppe)(2)](+)CF(3)SO(3) (-).0.125 THF (1; dppe=1,2-bis(diphenylphosphanyl)ethane) and its SbF(6) (-) (1') and BF(4) (-) (1") analogues, the missing members of the [MH(dppe)(2)](+)X(-) (M=Ni, Pd, Pt) family, are described. The Pd hydrides are not stable in solution and can react as proton or hydride donors with formation of dihydrogen, [Pd(dppe)(2)](2+) and [Pd(dppe)(2)]. Complexes 1-1" react with carbocations and carbanions by transferring a hydride and a proton, respectively. Such H(-) or H(+) transfer occurs also towards unsaturated compounds, for example, hydrogenation of a C=C double bond. Accordingly, 1 can hydrogenate methyl acrylate to methyl propionate. Complex 1" is an effective (hourly turnover frequency=16) and very selective (100 %) catalyst for the hydrogenation of cyclohexen-2-one to cyclohexanone with dihydrogen under mild conditions. Density functional calculations coupled with a dielectric continuum model were carried out to compute the energetics of the hydride/proton transfer reactions, which were used to rationalize some of the experimental findings. Theory provides strong support for the thermodynamic and kinetic viability of a tetracoordinate Pd complex as an intermediate in the reactions. |
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Keywords: | density functional calculations homogeneous catalysis hydride ligands hydrogenation palladium |
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