Mechanistic Elucidation of Dimer Formation and Strategies for Its Suppression in Electrochemical Reduction of Fac-Mn(bpy)(CO)₃Br

TY - JOUR

T1 - Mechanistic Elucidation of Dimer Formation and Strategies for Its Suppression in Electrochemical Reduction of Fac-Mn(bpy)(CO)3Br

AU - Rønne, Magnus Haugaard

AU - Madsen, Monica Rohde

AU - Skrydstrup, Troels

AU - Pedersen, Steen Uttrup

AU - Daasbjerg, Kim

PY - 2021/6

Y1 - 2021/6

N2 - Development of new catalytic approaches for reduction of small molecules is an aspiring technology to alleviate increasing energy demands without use of fossil fuels. One of the most promising molecular catalysts for reduction of CO 2 is fac-Mn(bpy)(CO) 3Br (bpy=2,2’-bipyridine). In this work, the mechanism of electrochemical reduction of this complex is elucidated using cyclic voltammetry along with digital simulations. It is revealed that the dimer complex, Mn 2(bpy) 2(CO) 6, is not, as often assumed, formed by dimerization of the singly reduced manganese complex, [Mn(bpy)(CO) 3] ., but instead from its reduction to [Mn(bpy)(CO) 3] −, followed by further reaction with Mn(bpy)(CO) 3Br (rate constant=1.75×10 5 M −1 s −1). On the basis of cyclic voltammetry, infrared-spectroelectrochemistry, and 1H NMR spectroscopy, we establish that this parent-child reaction involving Mn(bpy)(CO) 3Br as electrophile can be diverted by adding either acids or iodomethane as substituting electrophiles. This demonstrates that [Mn(bpy)(CO) 3] −, which is the central catalyst for CO 2 reduction, can be formed at less extreme potentials than previously believed by suppressing the parent-child reaction.

AB - Development of new catalytic approaches for reduction of small molecules is an aspiring technology to alleviate increasing energy demands without use of fossil fuels. One of the most promising molecular catalysts for reduction of CO 2 is fac-Mn(bpy)(CO) 3Br (bpy=2,2’-bipyridine). In this work, the mechanism of electrochemical reduction of this complex is elucidated using cyclic voltammetry along with digital simulations. It is revealed that the dimer complex, Mn 2(bpy) 2(CO) 6, is not, as often assumed, formed by dimerization of the singly reduced manganese complex, [Mn(bpy)(CO) 3] ., but instead from its reduction to [Mn(bpy)(CO) 3] −, followed by further reaction with Mn(bpy)(CO) 3Br (rate constant=1.75×10 5 M −1 s −1). On the basis of cyclic voltammetry, infrared-spectroelectrochemistry, and 1H NMR spectroscopy, we establish that this parent-child reaction involving Mn(bpy)(CO) 3Br as electrophile can be diverted by adding either acids or iodomethane as substituting electrophiles. This demonstrates that [Mn(bpy)(CO) 3] −, which is the central catalyst for CO 2 reduction, can be formed at less extreme potentials than previously believed by suppressing the parent-child reaction.

KW - IR spectroscopy

KW - cyclic voltammetry

KW - manganese

KW - molecular electrochemistry

KW - reaction mechanism

KW - ALKYL

KW - CO2 REDUCTION

KW - COMPLEXES

KW - SUBSTITUENTS

KW - DIMERIZATION

KW - ELECTROCATALYSTS

KW - RHENIUM

KW - MANGANESE

KW - HOMOGENEOUS REDOX CATALYSIS

KW - LIGAND

U2 - 10.1002/celc.202100279

DO - 10.1002/celc.202100279

M3 - Journal article

SN - 2196-0216

VL - 8

SP - 2108

EP - 2114

JO - ChemElectroChem

JF - ChemElectroChem

IS - 11

ER -