Click-Derived Triazoles and Triazolylidenes of Manganese for Electrocatalytic Reduction of CO2

Abstract

A series of new fac-[Mn(L)(CO)3Br] complexes where L is a bidentate chelating ligand containing mixed mesoionic triazolylidene-pyridine (MIC^py, 1), triazolylidene-triazole (MIC^trz, 2), and triazole-pyridine (trz^py, 3) ligands have been prepared and fully characterized, including the single crystal X-ray diffraction studies of 1 and 2. The abilities of 1–3 and complex fac-[Mn(MIC^MIC)(CO)3Br] (4) to catalyze the electroreduction of CO2 has been assessed for the first time. It was found that all complexes displayed a current increase under CO2 atmosphere, being 3 and 4 the most active complexes. Complex 3, bearing a N^N-based ligand exhibited a good efficiency and an excellent selectivity for reducing CO2 to CO in the presence of 1.0 M of water, at low overpotential. Interestingly, complex 4 containing the strongly electron donating di-imidazolylidene ligand exhibited comparable activity to 3, when the experiments were performed in neat acetonitrile at slightly higher overpotential (−1.86 vs. −2.14 V).

A Mesoionic Carbene–Pyridine Bidentate Ligand That Improves Stability in Electrocatalytic CO2 Reduction by a Molecular Manganese Catalyst

“…The primary difference in these two systems is not the catalytic activity but rather the photophysical properties, which suggested to us that a N MIC-py bidentate ligand could be well-suited to garner improvements in the long-term stability of the analogous Mn complex under catalytic conditions. Notably, the C MIC-py ligand reported by Royo and co-workers made by coupling py to 5-C in the MIC fragment yielded [Mn­( C MIC-py)­CO 3 Br] (Figure E), which appears less active for CO 2 electroreduction compared to the analogous complex containing bpy originally reported by Deronzier and co-workers . Taken together, the bpy, C MIC-py, and N MIC-py bonding motifs implicate perturbation in the frontier orbitals of these complexes.…”

“…Structural motifs of tricarbonyl Group 7 electrocatalysts based on pyridyl ligand fragment(s): (A) body of work since 1984 (Re) and 2011 (Mn); (B) [Mn­(NHC-py)­CO 3 Br] reported by Agarwal and co-workers; , (C) body of work since 2017 reported by Sarkar and co-workers (Re) and Royo and co-workers (Mn); (D) [Re­( N MIC-py)­CO 3 Cl] reported by Sarkar and co-workers; (E) [Mn­( C MIC-py)­CO 3 Br] reported by Royo and co-workers; (F) [Mn­( N MIC-py)­CO 3 Br] ( 1 ) reported here.…”

N‐Heterocyclic and Mesoionic Carbenes of Manganese and Rhenium in Catalysis

“… [37] The presence of the bulky mesityl groups allowed the isolation of a one‐electron reduced intermediate [Mn(bis‐NHC Mes )(CO) 3 ] 0 , which was crystallographically characterized. In addition, the impact of the presence of mesoionic triazolylidene ligands in the CO 2 electroreduction activity of Mn tricarbonyl complexes was recently explored by our group [38] . Complex 21 a (Scheme 13) bearing a di‐triazolylidene ligand displayed a FE of 70 % for the selective production of CO, without any detectable traces of H 2 .…”

“…In addition, the impact of the presence of mesoionic triazolylidene ligands in the CO 2 electroreduction activity of Mn tricarbonyl complexes was recently explored by our group. [38] Complex 21 a (Scheme 13) bearing a di-triazolylidene ligand displayed a FE of 70 % for the selective production of CO, without any detectable traces of H 2 . At the end of the bulk electrolysis experiments, a TOF CO value of 4 h À 1 was obtained, that is significantly lower than that obtained with the Mn-bis-NHC complex 5 a (14 h À 1 ).…”

“…At the end of the bulk electrolysis experiments, a TOF CO value of 4 h À 1 was obtained, that is significantly lower than that obtained with the Mn-bis-NHC complex 5 a (14 h À 1 ). [38] At the moment, it is unclear if the lower activity of 21 a compared to 5 a is due to the introduction of the triazolylidene ligand or is a consequence of the higher rigidity of the ditriazolylidene ligand compared to the bis-NHC that contains a À CH 2 -bridge.…”