Synthesis and Characterization of a RuPt‐Based Photo‐Hydrogen‐Evolving Molecular Device Tethered to a Single Viologen Acceptor

Abstract

A dinuclear RuIIPtII complex tethered to a methyl viologen (MV2+) unit {RuPt‐MV2+; [RuII(bpy)2{phen‐bpy(MV2+)}PtIICl2]4+, bpy = 2,2′‐bipyridine, phen = 5‐amino‐1,10‐phenanthroline} has been synthesized to investigate the effect of tethering a single pendant MV2+ acceptor on its photo‐hydrogen‐evolving (PHE) activity. Upon photoirradiation of RuPt‐MV2+ in the presence of EDTA as a sacrificial electron donor, the one‐electron‐reduced species of RuPt‐MV2+ {i.e., [RuII(bpy)2{phen‐bpy(MV+·)}PtIICl2]3+} is generated as a major photoproduct by intramolecular electron transfer (IET) from the 3MLCT excited state of the [RuII(bpy)2(phen)]2+ unit to the MV2+ unit, followed by subsequent reduction of the [RuIII(bpy)2(phen)]3+ unit by EDTA. Although RuPt‐MV2+ shows PHE activity in the presence of EDTA, the estimated turnover number (0.4) is smaller than that for the parent RuIIPtII system, which has no MV2+ tether. The relatively small driving force (0.08 eV) for the IET from the 3MLCT excited state of the [RuII(bpy)2(phen)]2+ unit to the PtIICl2(bpy) unit, which leads to the H2 formation, has been judged to be the major cause of the exceptionally low PHE activity observed for the present system.