The complex (Tpy)Ru(Pyo)2(OH2) (1  ) (where Tpy=2,2':6',2'-terpyridine and Pyo=2-pyridonate) has been previously reported as a ketone transfer hydrogenation catalyst that acts through an inner-sphere mechanism. ESI-MS of reaction solutions has shown that the catalytic activity is directly correlated to the formation of loosely bound mixed-valent RuIIRuIII dimers. The bis(terpyridine) bridged dimers (Tpy)Ru(TpyPhTpy)Ru(Pyo)2(OH2)2+ (2  ) and (Bpy)(Cl)Ru(TpyPhTpy)Ru(Pyo)2(OH2)+ (3  ) [where Tpy=2,2':6',2'-terpyridine, Bpy=2,2'-bipyridine, TpyPhTpy=4',4��-(1,4-phenylene)bis(2,2':6',2�-terpyridine), and Pyo=2-pyridonate] have been prepared as stable dimer analogs of complex 1  , and both complexes indeed are effective ketone transfer hydrogenation catalysts. In an effort to optimize catalytic activity and probe the underlying mechanism, ligand substituent effects within complex 3  have been surveyed through in-situ tests. Overall, catalytic rates slow with electron donating substituents on the Bpy ligand and trend slower from electron donating to withdrawing substituents on the Pyo ligands. These trends are consistent with destabilization of discrete RuIIRuIII mixed-valent state intermediates (with the RuIII center being bound by the Pyo ligands). Details of the ligand and dimer syntheses as well as the in-situ catalytic tests will be provided.

Preparation of asymmetric bis(terpyridine) ruthenium dimers: Ligand substituent effects on ketone transfer hydrogenation activity

248th National Meeting (2014)

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