Elucidating the mechanism of photochemical CO₂ reduction to CO using a cyanide-bridged di-manganese complex

Abstract

The complex, [{[Mn(bpy)(CO)3]2}(μ-CN)]+ (Mn2CN+), has previously been shown to photochemically reduce CO2 to CO.

Mechanistic insights into CO2 conversion to CO using cyano manganese complexes

“…7 is a photochemical transformation, s-MnCN was first synthesized by irradiating MnCN in MeCN in the presence of oxygen, to prevent further reactivity. 36 The solvent was stripped off this reaction and the product was redissolved in thoroughly degassed and dry MeCN. Separate experiments were then carried out on a mixture of s-MnCN and the starting material, MnCN : a dark control, irradiation at 517 nm, and irradiation at 395 nm.…”

“…Recently, we reported on the photochemical transformation of a cyanide-bridged dimer, 38 [bpy(CO) 3 Mn(µ-CN)Mnbpy (CO) 3 ] + , Mn 2 CN + , that is able to transform CO 2 into CO without a photosensitizer. 36,38 These results suggested a further exploration of the effects of cyanide ligation on the photoevolution of Mn(I) tricarbonyl complexes. Herein, the mechanism for the formation of the doubly reduced catalyti-cally active species, [Mn(bpy)(CO) 3 ] − , upon irradiation of MnCN is presented.…”

“…If oxygen is present, then the complex degrades, releasing CO ligands. 36 While axial ligand substitution can alter the rate of photodegradation under room light in the presence of oxygen, 37 it cannot be completely eradicated. This finding highlights the importance of using 13 CO 2 when studying this class of compounds photochemically, since free CO formed by ligand release, must be deconvoluted from CO formed by the reduction of CO 2 .…”

Electrochemical Characterization and CO2 Reduction Reaction of a Family of Pyridazine-Bridged Dinuclear Mn(I) Carbonyl Complexes

“…Mechanistic studies of rhenium-type catalysts have provided evidence for a concentration-dependent formation of dinuclear intermediates during catalysis [ 10 , 11 , 12 , 13 , 14 , 15 ]. However, only few examples have been related to catalysts with a rigid bridging ligand that links two rhenium or two manganese active sites in close proximity with a predictable intermetallic distance and orientation [ 16 , 17 , 18 ] in order to clearly highlight the contribution of the dinuclear pathway [ 19 , 20 ]. Indeed, cofacial dinuclear Re complexes, with a rigid backbone structure that prevents Re-Re bonding (leading to the deactivation of carbon dioxide reduction catalysis), showed a beneficial interaction between the two reaction sites, clearly outperforming non-cofacial or mononuclear complexes at a double concentration.…”

“…On the basis of these results, we recently synthesized a new similar family of dinuclear manganese complexes containing 1,2-diazine as the bridging ligand and halides or chalcogenide as the ancillary ligands (structural determination and a thorough characterization of all the compounds investigated in this work is reported elsewhere) [ 28 ], which has the general formula [Mn 2 (μ-ER) 2 (CO) 6 (μ-pydz)] (pydz = pyridazine; E = O or S; R = methyl or phenyl). In addition to the rhenium counterpart, only two examples of dinuclear Mn complexes with two “Mn(CO) 3 ” moieties connected by only one aromatic nitrogen bridging ligand have been reported to show higher performances [ 16 , 18 ]. It is worth noting that dinuclear manganese complexes (as those reported in this study)—containing not only the aromatic bridging ligand but also two anionic bridging ligands—have been investigated for the efficient CO release [ 29 , 30 , 31 ] and as electrocatalysts for proton reduction [ 32 , 33 , 34 ], but no examples have been reported for CO 2 reduction reaction.…”