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1. Reduction-induced CO dissociation by a [Mn(bpy)(CO) ₄ ][SbF ₆ ] complex and its relevance in electrocatalytic CO ₂ reduction

   https://doi.org/10.1039/c9dt04150h  

   Kuo, Hsin-Ya; Tignor, Steven E.; Lee, Tia S.; Ni, Danrui; Park, James Eujin; Scholes, Gregory D.; Bocarsly, Andrew B. (January 2020, Dalton Transactions)

   [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. 

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2. The Prototypical Transition Metal Carbenes, (CO) ₅ Cr=CH ₂ , (CO) ₄ Fe=CH ₂ , (CO) ₃ Ni=CH ₂ , (CO) ₅ Mo=CH ₂ , (CO) ₄ Ru=CH ₂ , (CO) ₃ Pd=CH ₂ , (CO) ₅ W=CH ₂ , (CO) ₄ Os=CH ₂ , and (CO) ₃ Pt=CH ₂ : Challenge to Experiment

   https://doi.org/10.1021/acs.jpca.8b05394  

   Weidman, Jared D.; Estep, Marissa L.; Schaefer, Henry F. (July 2018, The Journal of Physical Chemistry A)
3. Mechanochemical insertion of cobalt into porphyrinoids using Co ₂ (CO) ₈ as a cobalt source

   https://doi.org/10.1039/D0GC01010C  

   Damunupola, Dinusha; Chaudhri, Nivedita; Atoyebi, Adewole O.; Brückner, Christian (June 2020, Green Chemistry)

   null (Ed.)

   Cobalt porphyrinoids find broad use as catalysts or electrode materials. Traditional solution state cobalt insertion reactions into a free base porphyrinoid to generate the corresponding cobalt complex generally require fairly harsh conditions, involving the heating of the reactants in high-boiling solvents for extended period of times. We report here an alternative method of cobalt insertion: A solvent-free (at least for the insertion step) mechanochemical method using a planetary ball mill with Co 2 (CO) 8 as a cobalt source. The scope and limits of the reaction were investigated with respect to the porphyrinic substrate susceptible to the reaction conditions, the influences of different grinding aids, and bases added. While the mechanochemical method is, like other metal insertion methods into porphyrinoids, not universally suitable for all substrates tested, it is faster, milder, and greener for several others, when compared to established solution-based methods. 

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4. Cobalt-Group 13 Complexes Catalyze CO ₂ Hydrogenation via a Co(−I)/Co(I) Redox Cycle

   https://doi.org/10.1021/acscatal.9b03534  

   Vollmer, Matthew V.; Ye, Jingyun; Linehan, John C.; Graziano, Brendan J.; Preston, Andrew; Wiedner, Eric S.; Lu, Connie C. (January 2020, ACS Catalysis)
5. CO ₂ reduction driven by a pH gradient

   https://doi.org/10.1073/pnas.2002659117  

   Hudson, Reuben; de Graaf, Ruvan; Strandoo Rodin, Mari; Ohno, Aya; Lane, Nick; McGlynn, Shawn E.; Yamada, Yoichi M.; Nakamura, Ryuhei; Barge, Laura M.; Braun, Dieter; et al (September 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   All life on Earth is built of organic molecules, so the primordial sources of reduced carbon remain a major open question in studies of the origin of life. A variant of the alkaline-hydrothermal-vent theory for life’s emergence suggests that organics could have been produced by the reduction of CO 2 via H 2 oxidation, facilitated by geologically sustained pH gradients. The process would be an abiotic analog—and proposed evolutionary predecessor—of the Wood–Ljungdahl acetyl-CoA pathway of modern archaea and bacteria. The first energetic bottleneck of the pathway involves the endergonic reduction of CO 2 with H 2 to formate (HCOO – ), which has proven elusive in mild abiotic settings. Here we show the reduction of CO 2 with H 2 at room temperature under moderate pressures (1.5 bar), driven by microfluidic pH gradients across inorganic Fe(Ni)S precipitates. Isotopic labeling with 13 C confirmed formate production. Separately, deuterium ( 2 H) labeling indicated that electron transfer to CO 2 does not occur via direct hydrogenation with H 2 but instead, freshly deposited Fe(Ni)S precipitates appear to facilitate electron transfer in an electrochemical-cell mechanism with two distinct half-reactions. Decreasing the pH gradient significantly, removing H 2 , or eliminating the precipitate yielded no detectable product. Our work demonstrates the feasibility of spatially separated yet electrically coupled geochemical reactions as drivers of otherwise endergonic processes. Beyond corroborating the ability of early-Earth alkaline hydrothermal systems to couple carbon reduction to hydrogen oxidation through biologically relevant mechanisms, these results may also be of significance for industrial and environmental applications, where other redox reactions could be facilitated using similarly mild approaches. 

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