Photocatalytic CO₂ Reduction with Manganese Complexes Bearing a κ²-PN Ligand: Breaking the α-Diimine Hold on Group 7 Catalysts and Switching Selectivity

Abstract

The fundamental challenge of reducing CO2 into more valuable energy-containing compounds depends on revealing new catalysts for this process. By removal of the long-standing limitation of α-diimine ligation, which is dominant in photocatalytic complexes in this area, new visible-light, CO2-reducing photocatalysts based on Mn and Re supported by κ2-PN phosphinoaminopyridine ligands were identified. These catalysts, [M­{κ2-(Ph2P)­NH­(NC5H4)}­(CO)3Br], displayed excellent product selectivity and, by a change of only the metal center, gave a dramatic product switch from CO with M = Mn to HCO2H with M = Re. The catalyst systems were explored with variation of the ligand, electron donor, solvent, and photosensitizer. The products were definitively traced using 13CO2 as a substrate. Both complexes quenched the excited-state photosensitizer Ru­(bpy)3 2+*, suggesting oxidative quenching as a potential entry into the catalytic cycle.

(1,2-Azole)bis(bipyridyl)ruthenium(II) Complexes: Electrochemistry, Luminescent Properties, And Electro- And Photocatalysts for CO2 Reduction

“…The determination of the amount of formic acid was accomplished using 1 H NMR spectroscopy. 66 The results, which are compiled in Table 2, show that the catalysts are selective toward the reduction of CO 2 over that of protons. Two products were formed from CO 2 , formic acid and CO; the former product was produced at higher yields than the latter.…”

“…The gaseous products, H 2 and CO, were then analyzed by sampling the headspace of the electrolysis cell using gas chromatography. The determination of the amount of formic acid was accomplished using 1 H NMR spectroscopy . The results, which are compiled in Table , show that the catalysts are selective toward the reduction of CO 2 over that of protons.…”

“…The carrier gas used was helium. The determination of the amount of formic acid was accomplished using 1 H NMR spectroscopy by a previously reported method . Briefly, a calibration curve for formic acid was prepared using an internal standard of dimethyl sulfone in a solvent of D 2 O to quantify the amount of formic acid in the bulk electrolysis samples.…”

“…The determination of the amount of formic acid was accomplished using 1 H NMR spectroscopy by a previously reported method. 66 Briefly, a calibration curve for formic acid was prepared using an internal standard of dimethyl sulfone in a solvent of D 2 O to quantify the amount of formic acid in the bulk electrolysis samples. Thereafter, 150 μL of the bulk electrolysis sample was extracted and subsequently mixed with 600 μL of dimethyl sulfone in a solvent of D 2 O.…”

Dual Photocatalytic Roles of Light: Charge Separation at the Band Gap and Heat via Localized Surface Plasmon Resonance To Convert CO2 into CO over Silver–Zirconium Oxide

“…Numerous studies have investigated photocatalytic CO 2 fuel conversion to initiate a carbon-neutral cycle, which includes the use of solar fuel in contrast to the irreversible consumption of fossil fuels. , However, pitfalls exist in these previous investigations that mistake methane and/or C-containing products converted from catalyst impurities as products converted from CO 2 . ,− Therefore, finding an effective photocatalyst to convert CO 2 (standard formation enthalpy = −393.5 kJ mol –1 ) using only sustainable energy while confirming labeled 13 CO 2 conversion, not adventitious C, is essential. ,,− …”