J. Grodkowski et al., IRON PORPHYRIN-CATALYZED REDUCTION OF CO2 - PHOTOCHEMICAL AND RADIATION-CHEMICAL STUDIES, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 101(3), 1997, pp. 248-254
Several iron porphyrins have been reduced by photochemical anal radiat
ion chemical methods, in organic solvents and in aqueous solutions, fr
om (FeP)-P-III to Fe-II to (FeP)-P-I and beyond, In aqueous solutions,
the (FeP)-P-I state is relatively stable for the tetrakis(N-methyl-2-
pyridyl)porphyrin at high pH but is shorter lived in neutral and acidi
c solutions. The (FeP)-P-I state of tetrakis(N-methyl-3-pyridyl)porphy
rin and tetrakis(N-methyl-4-pyridyl)porphyrin are short-lived at any p
H. Decay of (FeP)-P-I is accelerated by H+ and by CO2, probably via re
action with the (FeP)-P-0 state formed upon disproportionation of (FeP
)-P-I. These reactions may lend to formation of H-2 and CO, respective
ly, and to formation of the chlorin, (FePH2)-P-II, as a side product,
The (FeP)-P-I state is also observed as a stable product in several or
ganic solvents. This is observed by photolysis of iron tetraphenylporp
hyrin and several of its derivatives (e.g., trimethyl-, dichloro- and
pentafluorophenyl), mainly in dimethylformamide and acetonitrile solut
ions, using triethylamine as a reductive quencher, Further photoreduct
ion in the presence of CO2 results in catalyzed reduction of CO2 to CO
and formation of (CO)-(FeP)-P-II. The yield of free CO increases with
time of photolysis and reaches turnover numbers of similar to 70 mole
cules of CO per porphyrin molecule.