Iron Porphyrin-Catalyzed Reduction of CO₂. Photochemical and Radiation Chemical Studies

Abstract

Several iron porphyrins have been reduced by photochemical and radiation chemical methods, in organic solvents and in aqueous solutions, from FeIIIP to FeIIP to FeIP and beyond. In aqueous solutions, the FeIP state is relatively stable for the tetrakis(N-methyl-2-pyridyl)porphyrin at high pH but is shorter lived in neutral and acidic solutions. The FeIP state of tetrakis(N-methyl-3-pyridyl)porphyrin and tetrakis(N-methyl-4-pyridyl)porphyrin are short-lived at any pH. Decay of FeIP is accelerated by H+ and by CO2, probably via reaction with the Fe0P state formed upon disproportionation of FeIP. These reactions may lead to formation of H2 and CO, respectively, and to formation of the chlorin, FeIIPH2, as a side product. The FeIP state is also observed as a stable product in several organic solvents. This is observed by photolysis of iron tetraphenylporphyrin and several of its derivatives (e.g., trimethyl-, dichloro- and pentafluorophenyl), mainly in dimethylformamide and acetonitrile solutions, using triethylamine as a reductive quencher. Further photoreduction in the presence of CO2 results in catalyzed reduction of CO2 to CO and formation of (CO)FeIIP. The yield of free CO increases with time of photolysis and reaches turnover numbers of ∼70 molecules of CO per porphyrin molecule.

Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N–C)(CO)3] complexes

“…To date, only four first-row transition metals have been successfully employed as metal centers in molecular catalysts for the conversion of CO 2 : manganese, [12][13][14][15][16][17][18] iron, [19][20][21][22][23][24][25][26][27][28][29] nickel, [30][31][32][33][34][35][36] and cobalt. [37][38][39][40][41][42][43] All generally yield carbon monoxide as the principal product from CO 2 .…”

Synthesis, spectroscopic and electrochemical investigations of supramolecular nickel(II)tetraazaporphyrin complexes

“…They offer a wide synthetic choice for creating varied molecular architectures and are being used as building blocks for the construction of artificial systems and catalysts for a verity of substrates [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The metalloporphyrins/ tetraazaporphyrins and ruthenium(II) polypyridyls are versatile and robust chromophores possessing strong visible region absorption and reversible redox behavior.…”

Light Harvesting Unsymmetrical Conjugated Dendrimders as Photosynthetic Mimics

“…Such efforts hold tremendous promise for techological advances and provide valuable insight into the photosynthetic process. A variety of photonic devices are possible using the principle of directed energy transfer, including novel photovoltaic (Hagfeldt and Gra¨tzel 2000) and photo-catalytic devices (Gradkowski et al 1997;Steinberg-Yfrach et al 1997) molecular scale information processing devices (Wagner et al 1996;Kuciauskas et al 1998), molecular-based nanomachines (Ashton et al 1998) and molecular-based sensors (Swager 1998;Vo¨gtle et al 2000).…”