A new diMnIII complex, [Mn₂L(OAc)₂(H₂O)](BPh₄)·3H₂O (1), obtained with the unsymmetrical N₃O₃-ligand H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N′-(2-hydroxybenzyl),N′-(benzyl)amino]propan-2-ol, has been prepared and characterized. The unsymmetrical hexadentate ligand L3− leads to coordination dissymmetry (dissimilar donor atoms) around each Mn ion (N₂O₄ and NO₄(solvent), respectively) leaving one labile site on one of the two Mn ions that facilitates interaction of the metal center with H₂O₂, as in Mn catalase. 1 is able to catalyze H₂O₂ disproportionation in acetonitrile, with second-order rate constant kcat = 23.9(2) M⁻¹ s⁻¹. The accessibility of the Mn^II₂ state and the closeness of the two one-electron reduction processes suggest 1 employs Mn^III₂/Mn^II₂ oxidation states for catalysis.

Solar fuels may be generated upon visible light induced catalytic reduction of carbon dioxide. This appealing approach remains highly challenging, especially when earth abundant catalysts, mild conditions, and water as a solvent were used. Employing an iron tetraphenyl porphyrin complex substituted by positively charged trimethylammonio groups at the para position of each phenyl ring and reduction with three electrons by the excited state of an iridium sensitizer (λ > 420 nm) reduce CO₂ to CO and to CH₄ in both acetonitrile and aqueous solutions (acetonitrile/water 3:7 v:v) with good selectivity. Stability of the catalytic system remains a weakness and the reasons were analyzed.

[M^II(qpy)(H₂O)₂]2+ (M = Fe, Co; qpy: 2,2′:6′,2″:6″,2‴-quaterpyridine) complexes efficiently catalyze the electrochemical CO₂-to-CO conversion in acetonitrile solution in the presence of weak Brönsted acids. Upon performing cyclic voltammetry studies, controlled-potential electrolysis, and spectroelectrochemistry (UV–visible and infrared) experiments together with DFT calculations, catalytic mechanisms were deciphered. Catalysis is characterized by high selectivity for CO production (selectivity >95%) in the presence of phenol as proton source. Overpotentials as low as 240 and 140 mV for the Fe and Co complexes, respectively, led to large CO production for several hours. In the former case, the one-electron-reduced species binds to CO₂, and CO evolution is observed after further reduction of the intermediate adduct. A deactivation pathway has been identified, which is due to the formation of a Fe0qpyCO species. With the Co catalyst, no such deactivation occurs, and the doubly reduced complex activates CO₂. High scan rate cyclic voltammetry allows reaching kinetic conditions, leading to scan-rate-independent plateau-shaped voltammograms from which catalytic rate constant was obtained. The molecular catalyst is very active for CO production (turnover a frequency of 3.3 × 10⁴ s^–1 at 0.3 V overpotential), as confirmed by catalytic a Tafel plot showing a comparison with previous catalysts.

The invention of efficient systems for the photocatalytic reduction of CO2 comprising earth-abundant metal catalysts is a promising approach for the production of solar fuels. One bottleneck is to design highly selective and robust molecular complexes able to transform the gas. The Cu(II) quaterpyridine complex [Cu(qpy)]²⁺ (1) is found to be a highly efficient and selective catalyst for visible-light driven CO₂ reduction in CH3CN using [Ru(bpy)₃]²⁺ as photosensitizer, BIH/TEOA as sacrificial reductant. The photocatalytic reaction is greatly enhanced by the presence of H₂O (1–4% v/v), and a TON of >12,400 for CO production can be achieved with 97% selectivity, which is among the highest of molecular 3d CO₂ reduction catalysts. Results from Hg-poisoning and dynamic light scattering (DLS) experiments suggest that this photocatalysis is homogenous. To the best of our knowledge 1 is the first example of molecular Cu-based catalyst for the photoreduction of CO₂.

We have used in situ and operando X-ray absorption spectroscopy at the cobalt K-edge to study the formation of cobalt nanoparticles from a molecular precursor, as well as their structural evolution under hydrogen-evolving electrocatalytic conditions. We show that these particles, which are about 100−150 nm in diameter overall, are made of an uncommon form of amorphous metallic cobalt, the smallest ordered unit being 1 nm clusters of ∼50 cobalt atoms. In aqueous solution, these porous particles are partly oxidized into cobalt(II), a fraction of which remains present as an outer shell during hydrogen evolution electrocatalysis, even at very high cathodic potentials. Our operando measurements show that the activity of the particles is correlated to the oxidized layer thickness, a thinner layer exposing a larger fraction of the active metallic cobalt and leading to a higher activity. These findings expand our current understanding of the solid−liquid interface in hydrogen evolution catalytic species in neutral pH and suggest new directions for the improvement of hydrogen-evolving catalytic systems.

An iron-substituted tetraphenyl porphyrin bearing positively chargedtrimethylammonio groups at the para position of each phenyl ring catalyzes the photoinduced conversion of CO₂.This complexiswater soluble and acts as amolecular catalyst to selectivelyreduce CO₂ into CO under visible-light irradiation in aqueous solutions (acetonitrile/water=1:9 v/v) with the assistance of purpurin, a simple organic photosensitizer. CO is produced with acatalytic selectivity of 95% and turnover number up to 120, illustrating the possibility of photocatalyzing the reduction of CO₂ in aqueous solutionbyusing visible light, a simple organic sensitizer coupled to an amine as a sacrificial electron donor,and an earth-abundant metal-based molecular catalyst.

The mechanism of the Ullmann-type reaction between potassium thioacetate (KSAc) and iodobenzene (PhI) catalyzed by CuI associated with 1,10-phenanthroline (phen) as a ligand was explored experimentally and computationally. The study on C−S bond formation was investigated by UV−visible spectrophotometry, cyclic voltammetry, mass spec- trometry, and products assessment from radical probes. The results indicate that under experimental conditions the catalytically active species is [Cu(phen)(SAc)] regardless of the copper source. An examination of the aryl halide activation mechanism using radical probes was undertaken. No evidence of the presence of radical species was found during the reaction process, which is consistent with an oxidative addition cross-coupling pathway. The different reaction pathways leading to the experimentally observed reaction products were studied by DFT calculation. The oxidative addition−reductive elimination mechanism via an unstable CuIII intermediate is energetically more feasible than other possible mechanisms such as single electron transfer, halogen atom transfer, and σ-bond methatesis.

in principle reduce fossil fuel consumption and climate-changing CO₂ emissions. One strategy aims for electrochemical conversions powered by electricity from renewable sources, but photochemical approaches driven by sunlight are also conceivable. A considerable challenge in both approaches is the development of efficient and selective catalysts, ideally based on cheap and Earth-abundant elements rather than expensive precious metals. Of the molecular photo- and electrocatalysts reported, only a few catalysts are stable and selective for CO₂ reduction; moreover, these catalysts produce primarily CO or HCOOH, and catalysts capable of generating even low to moderate yields of highly reduced hydrocarbons remain rare. Here we show that an iron tetraphenylporphyrin complex functionalized with trimethylammonio groups, which is the most efficient and selective molecular electro- catalyst for converting CO₂ to CO known, can also catalyse the eight-electron reduction of CO₂ to methane upon visible light irradiation at ambient temperature and pressure. We find that the catalytic system, operated in an acetonitrile solution containing a photosensitizer and sacrificial electron donor, operates stably over several days. CO is the main product of the direct CO₂ photoreduction reaction, but a twopot procedure that first reduces CO2 and then reduces CO generates methane with a selectivity of up to 82 per cent and a quantum yield (light-to-product efficiency) of 0.18 per cent. However, we anticipate that the operating principles of our system may aid the development of other molecular catalysts for the production of solar fuels from CO₂ under mild conditions.

Molecular catalysis of electrochemical reactions currently attracts a lot of attention, notably concerning the transformation of small molecules in response to issues raised by modern energy challenges. This review summarizes recent advances in the mechanism analysis of multi-electrons–multi-steps processes involved in homogenous molecular catalysis of such electrochemical reactions. It also describes strategies for a rational catalyst benchmarking, through the establishment of “catalytic Tafel plots”. We show that careful analysis of through-structure and through-space substituent effects within a given family of catalyst is a powerful tool for intelligent design of new catalysts. Challenges raised by the “heterogenization” of molecular catalysts are discussed in the final section.

The electrochemical behavior of fac‐[Mn(pdbpy)(CO)₃Br] (pdbpy=4‐phenyl‐6‐(phenyl‐2,6‐diol)‐2,2′‐bipyridine) (1) in acetonitrile under Ar, and its catalytic performances for CO₂ reduction with added water, 2,2,2‐trifluoroethanol (TFE), and phenol are discussed in detail. Preparative‐scale electrolysis experiments, carried out at −1.5 V versus the standard calomel electrode (SCE) in CO₂‐saturated acetonitrile, reveal that the process selectivity is extremely sensitive to the acid strength, producing CO and formate in different faradaic yields. A detailed spectroelectrochemical (IR and UV/Vis) study under Ar and CO2 atmospheres shows that 1 undergoes fast solvolysis; however, dimer formation in acetonitrile is suppressed, resulting in an atypical reduction mechanism in comparison with other reported MnI catalysts. Spectroscopic evidence of Mn hydride formation supports the existence of different electrocatalytic CO₂ reduction pathways. Furthermore, a comparative investigation performed on the new fac‐[Mn(ptbpy)(CO)₃Br] (ptbpy=4‐phenyl‐6‐(phenyl‐3,4,5‐triol)‐2,2′‐bipyridine) catalyst (2), bearing a bipyridyl derivative with OH groups in different positions to those in 1, provides complementary information about the role that the local proton source plays during the electrochemical reduction of CO₂.