HOMOGENEOUS CATALYZES OF MIXED-VALENT OCTANUCLEAR PLATINUM COMPLEXES IN PHOTOCHEMICAL HYDROGEN-PRODUCTION FROM WATER

An acetamidate-bridged mixed-valent octanuclear platinum complex, [Pt(2.25+)8 (NH3)16(CH3CONH)8] (NO3)10.4H2O, has been employed as a hydrogen-producing catalyst in a photochemical model system, containing EDTA as a sacrificial electron donor, [Ru(II) (2,2'-bpy)3 as a photosensitizer and methyl viologen as an electron relay. The catalytic activity of the octanuclear compound was higher than those previously reported for the mixed-valent tetranuclear platinum complexes with alpha-pyridonate or alpha-pyrrolidonate bridging ligands, and is also higher than that observed for another mixed-valent octanuclear platinum complex with 2-fluoroacetamidate bridging ligand, [Pt(2.08+)8(NH3)16(CH2FCONH)8](NO3)8.66.4H2O-Photochemical decomposition of the present system, caused by both hydrogenation of methyl viologen and photodecomposition of the catalyst complex, has been studied by means of HPLC. H-1 NMR studies have revealed that cleavage of the acetamidate-bridged Pt(II)6Pt(III)2 octamer into Pt(II)2 and Pt(III)2 dimers takes place rapidly after dissolution in aqueous media. The dinuclear Pt (II), complex seems to be the major species in the solution under the photolysis conditions and would be the active species as the hydrogen-producing catalyst.