Photocatalytic CO(2) Reductions Catalyzed by meso‐(1,10‐Phenanthrolin‐2‐yl)‐Porphyrins Having a Rhenium(I) Tricarbonyl Complex

We have prepared Zn and free‐base porphyrins appended with a fac‐Re(phen)(CO)(3)Br (where phen is 1,10‐phenanthroline) at the meso position of the porphyrin, and performed photocatalytic CO(2) reduction using porphyrin–Re dyads in the presence of either triethylamine (TEA) or 1,3‐dimethyl‐2‐phenyl‐2,3‐dihydro‐1H‐benzo[d]imidazole (BIH) as an electron donor. The Zn porphyrin dyad showed a high turnover number for CO production compared with the free‐base porphyrin dyad, suggesting that the central Zn ion of porphyrin plays an important role in suppressing electron accumulation on the porphyrin part and achieving high durability of the photocatalytic CO(2) reduction using both TEA and BIH. The effect of acids on the CO(2) reduction was investigated using the Zn porphyrin–Re dyad and BIH. Acetic acid, a relatively strong Brønsted acid, rapidly causes the porphyrin's color to fade upon irradiation and dramatically decreases CO production, whereas proper weak Brønsted acids such as 2,2,2‐trifluoroethanol and phenol enhance the CO(2) reduction.