Electrochemical Properties and CO₂-Reduction Ability of m-Terphenyl Isocyanide Supported Manganese Tricarbonyl Complexes

Abstract

To circumvent complications with redox-active ligands commonly encountered in the study of manganese electrocatalysts for CO reduction, we have studied the electrochemistry of the manganese mixed carbonyl/isocyanide complexes XMn(CO)(CNAr) (X = counteranion), to evaluate the pairing effects of the counteranion and their influence over the potential necessary for metal-based reduction. The complexes described herein have been shown to act as functional analogues to the known homoleptic carbonyl manganese complexes [Mn(CO)] (n = 1-, 0, 1+). The m-terphenyl isocyanide ligand CNAr improves the kinetic stability of the resulting mixed carbonyl/isocyanide systems, such that conversion among all three oxidation states is easily effected by chemical reagents. Here, we have utilized an electrochemical study to fully understand the redox chemistry of this system and its ability to facilitate CO reduction and to provide comparison to known manganese-based CO electrocatalysts. Two complexes, BrMn(CO)(CNAr) and [Mn(THF)(CO)(CNAr)]OTf, have been studied using infrared spectroelectrochemistry (IR-SEC) to spectroscopically characterize the redox states of these complexes during the course of electrochemical reactions. A striking difference in the necessary potential leading to the first one-electron reduction has been found for the halide and triflate species, respectively. Complete selectivity for the formation of CO and CO is observed in the reactivity of [Mn(CO)(CNAr)] with CO, which is deduced via the trapping and incorporation of liberated CO into the zerovalent species Mn(CO)(CNAr) to form the dimers Mn(CO)(CNAr) and Mn(CO)(CNAr).

Photoinduced electron transfer from rylenediimide radical anions and dianions to Re(bpy)(CO)3 using red and near-infrared light

“…23 Second, Kubiak and co-workers recently reported a Mn-based CO 2 reduction catalyst that contains only redox-innocent isocyanide ligands that do not dissociate during catalysis. 24 These two reports suggest that attaching a reduced RDI chromophore to either the redox-active bpy ligand or directly the Re center holds promise, and consequently it is valuable to understand the effect that these different attachment motifs have on the electron transfer behavior of the complex.…”

Terminal Iron Carbyne Complexes Derived from Arrested CO2 Reductive Disproportionation

“…[1][2][3][4][5][6][7][8][9][10][11] In contrast to other CO 2 reduction processes that produce CO as feedstock, [12,13] reductive disproportionation is unique in that CO 2 itself serves as the ultimate oxygen atom acceptor en route to the production of inorganic carbonate. [1][2][3][4][5][6][7][8][9][10][11] In contrast to other CO 2 reduction processes that produce CO as feedstock, [12,13] reductive disproportionation is unique in that CO 2 itself serves as the ultimate oxygen atom acceptor en route to the production of inorganic carbonate.…”

“…[1][2][3][4][5][6][7][8][9][10][11] In contrast to other CO 2 reduction processes that produce CO as feedstock, [12,13] reductive disproportionation is unique in that CO 2 itself serves as the ultimate oxygen atom acceptor en route to the production of inorganic carbonate. [2][3][4][7][8][9][10][11] Of these complexes,h ighly reduced Group 6a nd 8m etal carbonyl dianions have been established as the most operationally simple CO 2 reductive disproportionation archetypes as they produce discrete alkali or alkaline-earth metal carbonates and av olatile,n eutral transition-metal carbonyl complex upon addition of two equivalents of CO 2 . [2][3][4][7][8][9][10][11] Of these complexes,h ighly reduced Group 6a nd 8m etal carbonyl dianions have been established as the most operationally simple CO 2 reductive disproportionation archetypes as they produce discrete alkali or alkaline-earth metal carbonates and av olatile,n eutral transition-metal carbonyl complex upon addition of two equivalents of CO 2 .…”

“…Carbon dioxide reductive disproportionation to carbon monoxide and carbonate (CO and [CO 3 ] 2À )h as long been investigated as ap otentially useful synthetic CO 2 fixation process. [1][2][3][4][5][6][7][8][9][10][11] In contrast to other CO 2 reduction processes that produce CO as feedstock, [12,13] reductive disproportionation is unique in that CO 2 itself serves as the ultimate oxygen atom acceptor en route to the production of inorganic carbonate. [7,10,11] Many electron-rich transition-metal complexes, especially those that can readily function as two-electron reductants,have been shown to mediate stoichiometric and/or catalytic CO 2 reductive disproportionation.…”

“…[7,10,11] Many electron-rich transition-metal complexes, especially those that can readily function as two-electron reductants,have been shown to mediate stoichiometric and/or catalytic CO 2 reductive disproportionation. [2][3][4][7][8][9][10][11] Of these complexes,h ighly reduced Group 6a nd 8m etal carbonyl dianions have been established as the most operationally simple CO 2 reductive disproportionation archetypes as they produce discrete alkali or alkaline-earth metal carbonates and av olatile,n eutral transition-metal carbonyl complex upon addition of two equivalents of CO 2 . [3,4,7] In such reductive disproportionation schemes,t he reduced carbonyl metalate salts Na 2 [W(CO) 5 ]a nd Na 2 [Fe(CO) 4 ]h ave been extensively examined and have been proposed to share common intermediates with respect to the activated CO 2 unit.…”