Electrochemical Reduction of N₂O with a Molecular Copper Catalyst

Abstract

Deoxygenation of nitrous oxide (N 2 O) has significant environmental implications, as it is not only a potent greenhouse gas but is also the main substance responsible for the depletion of ozone in the stratosphere. This has spurred significant interest in molecular complexes that mediate N 2 O deoxygenation. Natural N 2 O reduction occurs via a Cu cofactor, but there is a notable dearth of synthetic molecular Cu catalysts for this process. In this work, we report a selective molecular Cu catalyst for the electrochemical reduction of N 2 O to N 2 using H 2 O as the proton source. Cyclic voltammograms show that increasing the H 2 O concentration facilitates the deoxygenation of N 2 O, and control experiments with a Zn(II) analogue verify an essential role for Cu. Theory and spectroscopy support metal−ligand cooperative catalysis between Cu(I) and a reduced tetraimidazolyl-substituted radical pyridine ligand (MeIm 4 P 2 Py = 2,6-(bis(bis-2-N-methylimidazolyl)phosphino)pyridine), which can be observed by Electron Paramagnetic Resonance (EPR) spectroscopy. Comparison with biological processes suggests a common theme of supporting electron transfer moieties in enabling Cu-mediated N 2 O reduction.

Open-Cage Copper Complexes Modulate Coordination and Charge Transfer

“…In this case, Cl occupies an equatorial position with an open axial site, with one of the pyridine arms in the PY5 ligand turned away from the Cu­(II) center, to form a five-coordinate Cu­(II) complex with a square pyramidal geometry. Anderson and co-worker recently reported another structurally similar Cu­(II) complex with the pentadentate 2,6-(bis­(bis-2- N -methylimidazolyl)­phosphino)­pyridine ligand, whose absorption spectrum is also similar to that observed here, with two apparent d–d transitions at approximately 600 and 900 nm (maxima and extinction coefficients not reported) . The very similar d–d transitions observed for the structurally similar but different equatorial ligand environments, is surprising.…”

“…Anderson and co-worker recently reported another structurally similar Cu(II) complex with the pentadentate 2,6-(bis(bis-2- N -methylimidazolyl)phosphino)pyridine ligand, whose absorption spectrum is also similar to that observed here, with two apparent d–d transitions at approximately 600 and 900 nm (maxima and extinction coefficients not reported). 29 The very similar d–d transitions observed for the structurally similar but different equatorial ligand environments, is surprising.…”

Boosting a practical Li-CO2 battery through dimerization reaction based on solid redox mediator

“…3a, solid RM(II)-BTC cathode exhibits distinct redox peaks at 2.81 V (E c1 ) and 3.34 V(E a1 ), respectively, indicating that the reversible reduction and oxidation of Cu(II)/Cu(I) may occur in solid RM(II)-BTC 23,35 . The individual redox potentials of active metal centers in complex compounds are influenced by the properties and structure of ligands [36][37][38] . Similarly, in the CO 2 atmosphere, the presence of a reduction peak (2.81 V, E c2 ) at the same position of CV curve indicates that the same reduction process occurs in the solid RM(II)-BTC.…”

Deoxygenation reactions of nitrous oxide assisted by oriented external electric field

“…N 2 O is a chemically stable and kinetically inert molecule [16], its deoxygenation reaction remains difficult, as even thermal decomposition is limited by a high kinetic barrier despite being thermodynamically favorable [14, 17, 18]. According to the previous reports, most of the degradation of N 2 O relied on metal catalysts, such as Mn, Fe, Co, Ni, Cu, Bi, Ru, Re [19–32]. However, those metals exist obvious weaknesses more or less, such as the complicated ligand preparation process, the harsh reaction conditions, rare and expensive, or the low selectivity from the abundant metals [33, 34].…”