Toward photocatalytic CO₂ reduction: Synthesis and photophysical characterization of (4,4′-(X) 2-2,2′-bipyridine)ReI(CO)₃L complexes

Rhenium(I) bipyridine complexes have been shown to be active photo- and electrocatalysts for the reduction of CO₂ to CO. Although several CO₂ containing intermediates have been proposed in these catalytic cycles, detailed photophysical and photochemical information is lacking for many of them, in particular Re-C₁ species (C₁ = COOH, CH₂OH, CH₃, etc.). We report here the synthesis of several potential intermediates in the Re(I) catalyzed reduction of CO₂ using different bipyridine derivatives, as well as the spectroscopic characterization of their ground and excited states in conventional solvents and supercritical CO₂.