Photochemical Reaction of Diruthenium Tetrahydride-Bridged Complexes with Carbon Dioxide: Insertion of CO2 into a Ru–H Bond versus CO Double-Bond Cleavage

Photochemical reactions of diruthenium tetrahydride complexes containing cyclopentadienyls as auxiliary ligands with carbon dioxide were studied for the effective fixation and reduction of CO2. Whereas the reactions of CpsRu­(μ-H)4RuCps (Cps = Cp*, C5Me5; CpEt, C5Me4Et; Cp‡, 1,2,4-C5(tBu)3H2) with CO2 did not proceed under dark and mild conditions, the photochemical reactions under UV (365 nm) irradiation smoothly proceeded to afford two types of products, (i) a μ-formato complex and (ii) a μ-carbonyl-μ-oxo complex, according to the width of the space for the reaction stretching between the two auxiliary cyclopentadienyl ligands.