Cu is known as one of the most promising metallic catalysts for conversion of CO2 to hydrocarbons such as methane, ethylene, and ethanol by electrochemical reduction. The oxide-derived Cu (OD-Cu) moiety has been investigated as a candidate for enhancing the activity for CO2 electrochemical reduction to C2+ products. The reduction process is affected by catalytic grain boundary, local pH, residual oxygen atoms, and other features of the catalysts. In order to understand the detailed mechanism, we performed in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (in situ ATR-SEIRAS) measurements for CO2 reduction using several different Cu electrodes whose oxidation states are controlled. The spectroscopic investigations demonstrate that a copper oxide electrode (Cu2O) has low activity against CO2 reduction on the basis of low-level detection of CO as an intermediate of CO2 reduction. On the other hand, other Cu electrodes possessing an OH layer on the Cu surface (Cu­(OH)2/Cu) and metallic Cu exhibit higher CO2 reduction activity with significantly greater detection of produced CO. When the metallic Cu electrode is used, only one peak (2060 cm–1) assignable to CO bound to the atop site of Cu is observed. However, additional peaks are detected in the range of 1900–2100 cm–1 when the Cu­(OH)2/Cu electrode is used. To understand these findings, the adsorption energy of CO on a Cu­(OH)2/Cu electrode and the CO stretching frequency were evaluated by performing DFT calculations. The adsorption energy is enhanced and the CO stretching frequencies are shifted to lower energy in comparison with those using a metallic Cu electrode. These results indicate that it is predominantly favorable to adsorb some CO molecules near the OH moiety of the Cu­(OH)2/Cu electrode and to induce interactions of CO molecules with each other. This observation is consistent with the results of controlled potential electrolysis (CPE), which generates C2+ products as previously reported. When CPE is carried out in D2O solution, residual and/or adsorbed OD– groups on Cu are detected by ATR-SEIRAS and the surface of the Cu­(OH)2/Cu electrode is confirmed to be metallic Cu, as measured by in situ Raman and XPS. From the ATR-SEIRAS experiments when switching from under CO2 to Ar during the electrochemical reduction, the OH layer is suggested to prevent deactivation of the Cu electrode via formation of the CO layer, which is detected as a bridge-bounded form on the metallic Cu electrode. The above findings indicate that the OH layer provides the advantage of attracting CO molecules closer to each other while reducing them to C2+ products without any degradation during electrolysis.

A novel nickel(II) complex [Ni(L)2 Cl]Cl with a bidentate phosphinopyridyl ligand 6-((diphenylphosphino)methyl)pyridin-2-amine (L) was synthesized as a metal-complex catalyst for hydrogen production from protons. The ligand can stabilize a low Ni oxidation state and has an amine base as a proton transfer site. The X-ray structure analysis revealed a distorted square-pyramidal Ni(II)  complex with two bidentate L ligands in a trans arrangement in the equatorial plane and a chloride anion at the apex. Electrochemical measurements with the Ni(II) complex in MeCN indicate a higher rate of hydrogen production under weak acid conditions using acetic acid as the proton source. The catalytic current increases with the stepwise addition of protons, and the turnover frequency is 8400 s(-1) in 0.1 m [NBu4 ][ClO4 ]/MeCN in the presence of acetic acid (290 equiv) at an overpotential of circa 590 mV.

Reported here is the N 2 cleavage of ao ne-electron oxidation reaction using trans-[Mo(depe) 2 (N 2 ) 2 ]( 1)( depe = Et 2 PCH 2 CH 2 PEt 2 ), which is ac lassical molybdenum(0)-dinitrogen complex supported by two bidentate phosphine ligands. The molybdenum(IV) terminal nitride complex [Mo-(depe) 2 N][BArf 4 ]( 2)( BArf 4 = B(3,5-(CF 3 ) 2 C 6 H 3 ) 4 )i ss ynthesized by the one-electron oxidation of 1 upon addition of amild oxidant, [Cp 2 Fe][BArf 4 ](Cp = C 5 H 5 ), and proceeds by N 2 cleavage from aM o II -N=N-Mo II structure.I naddition, the electrochemical oxidation reaction for 1 also cleaved the N 2 ligand to give 2.The dimeric Mo complex with abridging N 2 is detected by in situ resonance Raman and in situ UV-vis spectroscopies during the electrochemical oxidation reaction for 1.Density-functional theory (DFT) calculations reveal that the unstable monomeric oxidized Mo I species is converted into 2 via the dimeric structure involving az igzag transition state.

Type 1 blue copper proteins uniquely coordinate Cu(2+) in a trigonal planar geometry, formed by three strong equatorial ligands, His, His, and Cys, in the protein. We designed a stable Cu(2+) coordination scaffold composed of a four-stranded α-helical coiled-coil structure. Two His residues and one Cys residue were situated to form the trigonal planar geometry and to coordinate the Cu(2+) in the hydrophobic core of the scaffold. The protein bound Cu(2+), displayed a blue color, and exhibited UV-vis spectra with a maximum of 602-616 nm, arising from the thiolate-Cu(2+) ligand to metal charge transfer, depending on the exogenous axial ligand, Cl(-) or HPO(4)(2-). The protein-Cu(2+) complex also showed unresolved small A(∥) values in the electron paramagnetic resonance (EPR) spectral analysis and a 328 mV (vs normal hydrogen electrode, NHE) redox potential with a fast electron reaction rate. The X-ray absorption spectrum revealed that the Cu(2+) coordination environment was identical to that found in natural type 1 blue copper proteins. The extended X-ray absorption fine structure (EXAFS) analysis of the protein showed two typical Cu-N(His) at around 1.9-2.0 Å, Cu-S(Cys) at 2.3 Å, and a long Cu-Cl at a 2.66 Å, which are also characteristic of the natural type 1 blue copper proteins.