PHOTOINDUCED GENERATION OF DIHYDROGEN AND REDUCTION OF CARBON-DIOXIDEUSING TRANSITION-METAL COMPLEXES

Homogeneous and microheterogeneous transition-metal-based systems that generate dihydrogen and/or reduce carbon dioxide upon irradiation wit h visible light are considered. Most of the systems involve polypyridi ne complexes of the d(6) centers cobalt(III), rhodium(III), iridium(II I), ruthenium(II) and rhenium(I). Complexes with diimine ligands serve as photosensitizers and/or catalyst precursors. The corresponding d(8 ) metal centers and d(6) hydrides are important intermediates: bimolec ular reactions of the hydrides or their reactions with H2O/H3O+ are re sponsible for formation of dihydrogen. When carbon dioxide is also pre sent, it may insert into the metal-hydride bond to yield formate. Mech anistic schemes for some dual-acting photoconversion systems that gene rate both dihydrogen and carbon monoxide or formate are considered.