Methane Generation from CO₂ with a Molecular Rhenium Catalyst

Abstract

The atomic-level tunability of molecular structures is a compelling reason to develop homogeneous catalysts for challenging reactions such as the electrochemical reduction of carbon dioxide to valuable C1–C n products. Of particular interest is methane, the largest component of natural gas. Herein, we report a series of three isomeric rhenium tricarbonyl complexes coordinated by the asymmetric diimine ligands 2-(isoquinolin-1-yl)-4,5-dihydrooxazole (quin-1-oxa), 2-(quinolin-2-yl)-4,5-dihydrooxazole (quin-2-oxa), and 2-(isoquinolin-3-yl)-4,5-dihydrooxazole (quin-3-oxa) that catalyze the reduction of CO2 to carbon monoxide and methane, albeit the latter with a low efficiency. To our knowledge, these complexes are the first examples of rhenium­(I) catalysts capable of converting carbon dioxide into methane. Re­(quin-1-oxa)­(CO)3Cl (1), Re­(quin-2-oxa)­(CO)3Cl (2), and Re­(quin-3-oxa)­(CO)3Cl (3) were characterized and studied using a variety of electrochemical and spectroscopic techniques. In bulk electrolysis experiments, the three complexes reduce CO2 to CO and CH4. When the controlled-potential electrolysis experiments are performed at −2.5 V (vs Fc+/0) and in the presence of the Brønsted acid 2,2,2-trifluoroethanol, methane is produced with turnover numbers that range from 1.3 to 1.8. Isotope labeling experiments using 13CO2 atmosphere produce 13CH4 (m/z = 17) confirming that methane originates from CO2 reduction. Theoretical calculations are performed to investigate the mechanistic aspects of the 8e–/8H+ reduction of CO2 to CH4. A ligand-assisted pathway is proposed to be an efficient pathway in the formation of CH4. Delocalization of the electron density on the (iso)­quinoline moiety upon reduction stabilizes the key carbonyl intermediate leading to additional reactivity of this ligand. These results should aid the development of more robust catalytic systems that produce CH4 from CO2.

Investigation of Cyclam Based Re‐Complexes as Potential Electrocatalysts for the CO2Reduction Reaction

“…[23,24] In order to further understand the electrocatalytic CO 2 RR performance of complex 1 a broad variety of modulations of the bpy ligand and furthermore substitutions of bpy for comparable ligand platforms (e. g. pyNHC, pypz, pyiz) were investigated. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] Among the large number of modified rhenium complexes and within the most studied class, the 4,4'substituted bpy rhenium complexes, the t Bu-derivative Re-(bpy-t Bu)(CO) 3 Cl (bpy-t Bu = 4,4'-di-tert-butyl-2,2'-bipyridine) is particularly noteworthy.…”

The role of substituted pyridine Schiff bases as ancillary ligands in the optical properties of a new series of fac-rhenium(i) tricarbonyl complexes: a theoretical view

“…Complexes based on a Re(I) tricarbonyl core with a dinitrogenated ligand (N,N such as 1,10-phenanthroline or 2,2 0 -bipyridine derivatives) in the equatorial position, and halogen or pyridine derivatives as ancillary ligands (X), have been extensively used for diverse applications, including solar cells, 1,2 catalysis, [3][4][5][6][7][8] and more recently, biological applications, [9][10][11][12][13][14][15][16][17] including staining of bacteria, yeasts (walled cells), and proteins separated by SDS-PAGE. 18,19 Photophysical attributes of fac-[Re(I)(CO) 3 (N,N)X] n complexes (where n is 0 or 1+) can be modulated by combining the (N,N) and X ligands.…”

Substituents and Cocatalyst Effect on the Catalytic Response and Overpotential of Re(I) Catalysts for CO2 Reduction

“…To do so, the Re 0 (bpy-R) − –CO 2 intermediates were added to the [Zn­(cyclam)] 2+ in two different binding modes of η 2 -OCO and η 1 -OCO . The local minima optimized geometry of the intermediate with the binding mode of η 2 -OCO rearranged to form the structure with η-OCO binding mode. The switching binding mode indicates that the η 1 -OCO binding is the stable mode in Re 0 (bpy-R) − −CO 2 –[Zn­(cyclam)] 2+ intermediate.…”

“…Despite many efforts to reduce the CO 2 emission into the atmosphere, still the average temperature of the earth is increasing. − The challenging issue associated with utilizing CO 2 is its thermodynamic stability and kinetic inertness due to the highest oxidation state of the carbon (+4) and the linear geometry of CO 2 with a short C–O bond length. − Several studies have been reported to either reduce the existing CO 2 amount with an alternative energy source or converting CO 2 to a useful raw material such as carbon monoxide (CO) or CH 4 . − …”

“…13−15 Carbon monoxide generates the valuable industrial sources; however, finding an active and highly selective electrocatalyst with less energy input requirement still remains challenging. 16,17 To overcome these impediments, this requires a catalyst i.e., (1) robust against decomposition, (2) selective toward producing one product, and (3) displays high electrocatalytic activity at a lower overpotential, where overpotential represents the variation of the potential in which the catalyst shows activity and thermodynamic potential of the desired reaction. 18 Among various studies that have been performed thus far, rhenium catalysts with 2,2′-bipyridine (bpy) or 1,10-phenanthroline (phen) ligands have shown promising results to fulfill those requirements.…”