Herein, we report the synthesis and characterization of two manganese tricarbonyl complexes, MnI(HL)(CO)3Br (
- Award ID(s):
- 2102156
- NSF-PAR ID:
- 10317598
- Date Published:
- Journal Name:
- Chemical Science
- Volume:
- 12
- Issue:
- 28
- ISSN:
- 2041-6520
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract 1 a‐Br ) and MnI(MeL)(CO)3Br (1 b‐Br ) (where HL=2‐(2’‐pyridyl)benzimidazole; MeL=1‐methyl‐2‐(2’‐pyridy)benzimidazole) and assayed their electrocatalytic properties for CO2reduction. A redox‐active pyridine benzimidazole ancillary ligand in complex1 a‐Br displayed unique hydrogen atom transfer ability to facilitate electrocatalytic CO2conversion at a markedly lower reduction potential than that observed for1 b‐Br . Notably, a one‐electron reduction of1 a‐Br yields a structurally characterized H‐bonded binuclear Mn(I) adduct (2 a’ ) rather than the typically observed Mn(0)‐Mn(0) dimer, suggesting a novel method for CO2activation. Combining advanced electrochemical, spectroscopic, and single crystal X‐ray diffraction techniques, we demonstrate the use of an H‐atom responsive ligand may reveal an alternative, low‐energy pathway for CO2activation by an earth‐abundant metal complex catalyst. -
[Mn(bpy)(CO) 3 Br] is recognized as a benchmark electrocatalyst for CO 2 reduction to CO, with the doubly reduced [Mn(bpy)(CO) 3 ] − proposed to be the active species in the catalytic mechanism. The reaction of this intermediate with CO 2 and two protons is expected to produce the tetracarbonyl cation, [Mn(bpy)(CO) 4 ] + , thereby closing the catalytic cycle. However, this species has not been experimentally observed. In this study, [Mn(bpy)(CO) 4 ][SbF 6 ] ( 1 ) was directly synthesized and found to be an efficient electrocatalyst for the reduction of CO 2 to CO in the presence of H 2 O. Complex 1 was characterized using X-ray crystallography as well as IR and UV-Vis spectroscopy. The redox activity of 1 was determined using cyclic voltammetry and compared with that of benchmark manganese complexes, e.g. , [Mn(bpy)(CO) 3 Br] ( 2 ) and [Mn(bpy)(CO) 3 (MeCN)][PF 6 ] ( 3 ). Infrared spectroscopic analyses indicated that CO dissociation occurs after a single-electron reduction of complex 1 , producing a [Mn(bpy)(CO) 3 (MeCN)] + species. Complex 1 was experimentally verified as both a precatalyst and an on-cycle intermediate in homogeneous Mn-based electrocatalytic CO 2 reduction.more » « less
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Abstract A series of twelve second coordination sphere (SCS) functionalized manganese tricarbonyl bipyridyl complexes are investigated for their electrocatalytic CO2reduction properties in acetonitrile. A qualitative and quantitative assessment of the SCS functional groups is discussed with respect to the catalysts’ thermodynamic and kinetic efficiencies, and their product selectivities. In probing a broad scope of functional groups, it is clear that only the aprotic ortho‐arylester SCS is capable of promoting the highly desired low‐overpotential proton‐transfer electron‐transfer (PT‐ET) pathway for selective CO production. The ortho‐phenolic analogues cause an increase in overpotential with a product selectivity favoring H2evolution, consistent with a high‐overpotential pathway via the anionic [Mn−H]−intermediate. Alternative aprotic Lewis base functional groups such as trifluoromethyl, morpholine and acetamide are shown to also be capable of intermediate manganese hydride generation. The tertiary amine substituent, 2‐morpholinophenyl, exhibits a desirable product distribution characteristic of syn‐gas (CO : H2=30 : 48) with an impressive turnover frequency, while the secondary amine group, 2‐acetamidophenyl, induces a notable shift in selectivity with a faradaic yield of 55 % for the formate (HCO2−) product. In addition to their catalytic properties, cyclic voltammetry and infrared spectroelectrochemistry (IR‐SEC) studies are presented to probe pre‐catalyst electronic properties and the two‐electron reduction activation pathway.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1SC01271A
