Manganese Complexes for Electro‐ and Photocatalytic Transformations

Mechanism of Electrochemical Proton Reduction Catalyzed by a Cobalt Tetraaza Schiff Base Macrocyclic Complex: Ligand Protonation and/or Influence of the Chloro Ligand

“…The contribution of the outer lines increases with increasing acid concentration (inset of Figure 7d), consistent with a change in the speciation. These data indicate that the species with two interacting and equivalent 14 N nuclei predominates under highly acidic conditions, suggesting the coordination of two nitrogen-based axial ligands, which could be CH 3 CN and/or the nitrile of pcyanoanilinium acid (Scheme 1). However, upon the addition of a large excess of p-cyanoaniline (up to 50 mM) to a 1 mM solution of [Co II (CR14)(CH 3 CN) x ] 2+ , no changes are observed on EPR and UV−vis spectra (Figures S9 and S10), indicating that the nitrile of p-cyanoanilinium does not coordinate with the metal center.…”

“…Intense research over the last 15 years has been devoted to the development of efficient molecular catalysts for the electro- and photoinduced reduction of protons into dihydrogen (Hydrogen Evolution Reaction, HER) and the reduction of CO 2 (CO 2 reduction reaction (CO 2 RR)). , Molecular catalysts present the advantages of having tunable redox properties and, for the CO 2 RR, good selectivity. , The most widely employed families of catalysts for the HER based on nonprecious metals are cobaloximes, complexes of cobalt with polypyridine ligands, nickel with pyridine/thiolate or phosphine ligands (DuBois’ catalyst), and diiron carbonyl hydrogenases mimics. − For the CO 2 RR, they mainly rely on iron, cobalt, and nickel complexes with macrocyclic ligands (porphyrin, phthalocyanine, corrole, cyclam) and manganese with bipyridine/carbonyl ligands. , Cobalt complexes with tetra- and pentaaza-macrocyclic ligands, including the pyridyldiimine motif (Scheme ), isolated as early as the 1970s, are also a very promising family of catalysts quite recently exploited for both the electro- and photoinduced HER − and CO 2 RR, − in homogeneous and heterogeneous conditions. ,,− In particular, the tetraaza-macrocyclic Schiff base complex [Co III (CR14)(X) 2 ] n + (CR14 = 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaene), X = Cl ( n = 1) or H 2 O ( n = 3) has received an increasing interest in the recent years as it is now considered as one of the most efficient and stable H 2 -evolving molecular catalysts in fully aqueous solution. − ,− ,, The outstanding performance of this complex has been initially attributed to the stability of its ...…”

“…3−12 For the CO 2 RR, they mainly rely on iron, cobalt, and nickel complexes with macrocyclic ligands (porphyrin, phthalocyanine, corrole, cyclam) and manganese with bipyridine/carbonyl ligands. 13,14 Cobalt complexes with tetra-and pentaaza-macrocyclic ligands, including the pyridyldiimine motif (Scheme 1), isolated as early as the 1970s, 15 are also a very promising family of catalysts quite recently exploited for both the electro-and photoinduced HER 16−31 and CO 2 RR, 32−40 in homogeneous and heteroge-neous conditions. 28,29,41−43 In particular, the tetraaza-macrocyclic Schiff base complex [Co III (CR14)(X) 2 ] n+ (CR14 = 2,12dimethyl-3,7,11,17-tetraazabicyclo [11.3.1]heptadeca-1(17),2,11,13,15-pentaene), X = Cl (n = 1) or H 2 O (n = 3) has received an increasing interest in the recent years as it is now considered as one of the most efficient and stable H 2evolving molecular catalysts in fully aqueous solution.…”

Connecting Biological and Synthetic Approaches for Electrocatalytic CO2 Reduction

“…[16] systems either operating in homogeneous conditions or, more recently, heterogenized onto electrodes. [10,15,[64][65][66][67][68] For heterogenized small molecule catalysts, their size means the distance between the active site and the electrode surface is within tunnelling distance, making electron transfer straightforward. However, the presence of an interface or spacer between the catalyst molecule and the electrode surface can introduce stability and activity limitations originating from catalyst immobilization.…”

Mononuclear manganese complexes as hydrogen evolving catalysts

“…Like iron, manganese is easily available and abundant and shows a benign environmental profile compared to platinum. Mn-complexes reported until now have been mostly studied as catalysts for electro-or photo-catalytic organic oxidations/reductions (C-H hydroxylation; P450-type activity), alkene epoxidation, and CO 2 reduction in homogenous or heterogeneous phases; for reviews see (Fernandez et al, 2022;Sorais, 2022). The complexes designed for these catalytic transformations use porphyrin and corrole derivatives or strong-chelating non-heme pyridylamino ligands, π-acceptors (CO), and pyridine-, diimine-, or N-heterocyclic carbene-based ligands.…”