Photochemical CO2-reduction catalyzed by mono- and dinuclear phenanthroline-extended tetramesityl porphyrin complexes.

We here present a comprehensive study on the light-induced catalytic CO2 reduction employing a number of mono- and dinuclear complexes with a phenanthroline-extended tetramesityl porphyrin ligand (). A stepwise synthesis of heterodinuclear complexes is possible because the phenanthroline moiety of the ligand can selectively coordinate a second metal center, e.g. Ru(tbbpy)2(2+) fragment, while any other metal can reside in the porphyrin cavity. We expanded our former studies to cobalt and iron compounds and synthesized the complexes , and , . Thorough catalytic investigation on the light-driven CO2 reduction of all compounds (M = 2H, Cu, Pd, Co, FeCl) was performed in a DMF solution in the presence of triethylamine (TEA) as a sacrificial electron donor. A very surprising wavelength dependence of the catalytic performance was observed. Turnover numbers (TONs) of CO were quantified and showed that redox active metals (i.e.M = Co and FeCl) in the porphyrin cavity caused the highest catalytic activity. After 24 hours of illumination with light λ > 305 nm reached a TONCO of 11.4 with our experimental setup without showing much decomposition. This value is twice as high as the TONCO determined for CoTPP (5.8) under the same conditions, which represented the most active porphyrinic system so far for photocatalytic CO2 reduction.