Photochemistry and photophysics of a Pd(II) metalloporphyrin: Re(I) tricarbonyl bipyridine molecular dyad and its activity toward the photoreduction of CO2 to CO.

The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2′-bipyridine-4′-carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO)3(Pic)Bpy-PdTPP][PF6]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO)3(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C6H4 group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λex = 520 nm) of [Re(CO)3(Pic)Bpy-PdTPP][PF6] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO)3(Pic)Bpy-PdTPP][PF6] is employed as a photocatalyst for the reduction of CO2 to CO in DMF/NEt3 solution with λex > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)3(Pic)Bpy][PF6] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms af...