Elucidating the origins of enhanced CO reduction in manganese electrocatalysts bearing pendant hydrogen-bond donors

• Published in: Dalton transactions : an international journal of inorganic chemistry Vol. 48; no. 33; pp. 1273 - 12737
• Main Authors: Tignor, Steven E, Shaw, Travis W, Bocarsly, Andrew B
• Format: Journal Article
• Language: English
• Published: 20.08.2019
• ISSN: 1477-9226; 1477-9234
• DOI: 10.1039/c9dt02060h

Complexes of the general form [Mn(X)(CO) 3 bpy] (X = a variety of monodentate ligands, bpy = 2,2′-bipyridine) have been reported to act as electrocatalysts for the reduction of CO 2 to CO. In this work, a series of phenol and anisole substituted bipyridine ligands were synthesized and ligated to a manganese metal center in order to probe for an intramolecular hydrogen-bonding interaction in the transition state of CO 2 reduction. Ligands without the ability to intramolecularly hydrogen bond displayed decreased catalytic current density compared to those with the ability to hydrogen bond with CO 2 . Electrocatalysis was studied by performing voltammetric and bulk electrolysis experiments under argon or CO 2 environments. Measurements of catalytic rates using hydrogen vs. deuterium for the intramolecular H/D-bonding step show that there is an isotope effect associated with the catalysis. The data presented herein suggest a mechanism involving two subsequent equilibrium isotope effects in combination with a primary kinetic isotope effect. A mechanistic analysis showing the critical importance of an intramolecular hydrogen bond for improved insight and understanding in CO 2 electroreduction.