Electrocatalysis is a promising tool for utilizing carbon dioxide as a feedstock in the chemical industry. However, controlling the selectivity for different CO2 reduction products remains a major challenge. We report a series of manganese carbonyl complexes with elaborated bipyridine or phenanthroline ligands that can reduce CO2 to either formic acid, if the ligand structure contains strategically positioned tertiary amines, or CO, if the amine groups are absent in the ligand or are placed far from the metal center. The amine-modified complexes are benchmarked to be among the most active catalysts for reducing CO2 to formic acid, with a maximum turnover frequency of up to 5500 s–1 at an overpotential of 630 mV. The conversion even works at overpotentials as low as 300 mV, although through an alternative mechanism. Mechanistically, the formation of a Mn–hydride species aided by in situ protonated amine groups was determined to be a key intermediate by cyclic voltammetry, 1H NMR, DFT calculations, and infrared spectroelectrochemistry.

Carbon dioxide utilization through electrocatalysis is a promising pathway toward a more sustainable future. In this work the electrocatalytic reduction of carbon dioxide by ReI and RuII bipyridine complexes bearing pendant amines (N,N′-(([2,2′-bipyridine]-6,6′-diylbis­(2,1-phenylene))­bis­(methylene))­bis­(N-ethylethanamine) (dEAbpy)) is evaluated. In both cases, the major reduction product is carbon monoxide accompanied by some formic acid, although the yield of the latter never reaches the predominant level known from the corresponding Mn­(dEAbpy)­(CO)3Br complex. This demonstrates the profound effect of the identity of the metal center, in addition to the ligand, for the product distribution. In this work, we report the synthesis procedures and X-ray diffraction studies along with electrochemical and infrared spectroelectrochemical studies of Re­(dEAbpy)­(CO)3Cl and Ru­(dEAbpy)­(CO)2Cl2 to propose a mechanism for the CO2 reduction reaction.

The selective and efficient reduction of carbon dioxide represents a key solution to producing non‐fossil‐fuel‐based feedstocks for the chemical industry, while alleviating the increasing atmospheric concentration of this greenhouse gas. A variety of catalytic methods for the CO2 reduction reaction (CO2RR) have been developed, including hydrogenations and electrochemical or photochemical reductions. For many of the most significant breakthroughs reported in the last decade, we realized that amines or closely related functional groups play a critical role for such transformations, and in several cases, are directly associated with the catalyst as a pendant group. Amines play multiple roles, such as CO2 trapping agents, proton shuttles, electron donors, or facilitators of CO2 reductions through formamide derivatives. In this Viewpoint, we compile some of these recent findings, and discuss their significance in a broader context in an attempt to provide guidelines for the design of new catalysts with enhanced activity and selectivity.

Selective reduction of CO 2 is an efficient solution for producing nonfossil-based chemical feedstocks and simultaneously alleviating the increasing atmospheric concentration of this greenhouse gas. With this aim, molecular electrocatalysts are being extensively studied, although selectivity remains an issue. In this work, a combined experimental−computational study explores how the molecular structure of Mn-based complexes determines the dominant product in the reduction of CO 2 to HCOOH, CO, and H 2 . In contrast to previous Mn(bpy-R)(CO) 3 Br catalysts containing alkyl amines in the vicinity of the Br ligand, here, we report that bpybased macrocycles locking these amines at the side opposite to the Br ligand change the product selectivity from HCOOH to H 2 . Ab initio molecular dynamics simulations of the active species showed that free rotation of the Mn(CO) 3 moiety allows for the approach of the protonated amine to the reactive center yielding a Mn-hydride intermediate, which is the key in the formation of H 2 and HCOOH. Additional studies with DFT methods showed that the macrocyclic moiety hinders the insertion of CO 2 to the metal hydride favoring the formation of H 2 over HCOOH. Further, our results suggest that the minor CO product observed experimentally is formed when CO 2 adds to Mn on the side opposite to the amine ligand before protonation. These results show how product selectivity can be modulated by ligand design in Mn-based catalysts, providing atomistic details that can be leveraged in the development of a fully selective system.

The enantio- and diastereoselective formation of indenes spirofused to highly substituted cyclopropanes is described. The application of a new cinchona alkaloid derived ammonium salt in a phase transfer catalysis setup facilitates high selectivity and excellent yields at low catalyst loadings (0.1-1.0 mol%).