Importance of Ligand Exchange in the Modulation of Molecular Catalysis: Mechanism of the Electrochemical Reduction of Nitrous Oxide with Rhenium Bipyridyl Carbonyl Complexes - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue ACS Catalysis Année : 2023

Importance of Ligand Exchange in the Modulation of Molecular Catalysis: Mechanism of the Electrochemical Reduction of Nitrous Oxide with Rhenium Bipyridyl Carbonyl Complexes

Résumé

Molecular catalysis of electrochemical reactions involving transition-metal complexes as catalysts requires getting a free metal coordination site to bind the substrate. It implies that the generation of a strong coordinating ligand as a product or coproduct of the reaction might be detrimental for an efficient catalysis because it can bind the metal center and block or slow down the catalytic process. This self-modulation phenomenon is revealed and illustrated via a thorough spectro-electrochemical investigation of the mechanism of the electrochemical reduction of nitrous oxide with rhenium bipyridyl triscarbonyl complexes [Re(bpy)(CO) 3 X] n+ (X = CH 3 CN, Cl − , n = 0 or 1) as a catalyst. We show that the bi-reduced [Re 0 (bpy •−)(CO) 3 ] − , electrogenerated from [Re(bpy)-(CO) 3 X] n+ , readily reacts with N 2 O and produces the hydroxo complex [Re I (bpy)(CO) 3 (OH)]. Because hydroxide, a product of the reaction, is a stronger coordinating ligand than acetonitrile or chloride, catalysis does not occur significantly at a potential where [Re 0 (bpy •−)(CO) 3 ] − is generated from [Re(bpy)(CO) 3 X] n+. Substantial catalysis is only triggered at a potential corresponding to the second reduction of [Re I (bpy)(CO) 3 (OH)]. Nonetheless, we show that a slower innersphere reduction of N 2 O by the monoreduced [Re I (bpy •−)(CO) 3 X] (n−1)+ (X = CH 3 CN, Cl −) occurs due to the lability of acetonitrile and chloride in these species. Because hydroxide is less labile and cannot be displaced to create an open coordination position for N 2 O, only an even slower outersphere reduction of N 2 O by the mono-reduced [Re I (bpy •−)(CO) 3 (OH)] − takes place. However, we finally show that an excess of free chloride is able to displace hydroxide and then open the way for a faster innersphere process. This remarkable example emphasizes the critical role of ligand exchange in modulating molecular catalysis of electrochemical reactions with transition-metal complexes as catalysts, a likely general phenomenon.
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hal-04300895 , version 1 (22-11-2023)

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Paternité - Pas d'utilisation commerciale - Pas de modification

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Rana Deeba, Sylvie Chardon-Noblat, Cyrille Costentin. Importance of Ligand Exchange in the Modulation of Molecular Catalysis: Mechanism of the Electrochemical Reduction of Nitrous Oxide with Rhenium Bipyridyl Carbonyl Complexes. ACS Catalysis, 2023, 13 (12), pp.8262-8272. ⟨10.1021/acscatal.3c01495⟩. ⟨hal-04300895⟩
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