Syntheses, characterization, and photo-hydrogen-evolving properties of tris(2,2'-bipyridine)ruthenium(II) derivatives tethered to an H2-evolving (2-phenylpyridinato)platinum(II) unit.

With the aim of developing new molecular devices having higher photo-hydrogen-evolving activity, Pt(ppy)ClX units (ppy = 2-phenylpyridinate, X = Cl(-) or DMSO; DMSO = dimethylsulfoxide) have been employed as an H(2)-evolving site, as the catalytic activity of Pt(ppy)Cl(2) was confirmed to be higher than those of other mononuclear platinum(II) complexes. In the present study, two new heterodinuclear Ru(II)Pt(II) complexes, produced by condensation of Ru(bpy)(2)(5-amino-phen) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline) with Pt(cppy)Cl(2) and Pt(cppy)(DMSO)Cl (cppy = 9-carboxy-phenylpyridinate), respectively, have been prepared and their photo-hydrogen-evolving activities have been evaluated in detail. The ineffectiveness of these systems as photo-hydrogen-evolving molecular devices are interpreted in terms of their negative driving forces for the photoinduced electron transfer from the triplet MLCT excited state of the Ru chromophore to the pi*(ppy) orbital of the catalyst moiety.