Photo-Induced Generation of Dihydrogen and Reduction of Carbon Dioxide Using Transition Metal Complexes

Abstract

Homogeneous and microheterogeneous transition-metal-based systems that generate dihydrogen and/or reduce carbon dioxide upon irradiation with visible light are considered. Most of the systems involve polypyridine complexes of the d⁶ centers cobalt(III), rhodium(III), iridium(III), ruthenium(II) and rhenium(I). Complexes with diimine ligands serve as photosensitizers and/or catalyst precursors. The corresponding d⁸ metal centers and d⁶ hydrides are important intermediates: bimolecular reactions of the hydrides or their reactions with H₂O/H₃O⁺ are responsible for formation of dihydrogen. When carbon dioxide is also present, it may insert into the metal-hydride bond to yield formate. Mechanistic schemes for some dual-acting photoconversion systems that generate both dihydrogen and carbon monoxide or formate are considered.

Key Words:

• electron transfer
• photoconversion
• catalysis
• metal complexes
• metal hydrides
• dihydrogen
• carbon dioxide
• carbon monoxide
• formate
• reduction