Concerted proton-electron transfer (CPET) steps are advantageous in catalyst design schemes as a strategy to enhance reaction kinetics. Reductive CPET strategies are of interest towards the reduction of unsaturated substrates, for example with respect to carbonyl functionalities. Our lab has begun to explore electrocatalytic CPET (eCPET) transformations that benefit from a molecular mediator comprised of cobaltocene modified by N,N-dimethylaniline as a Brønsted base, ([CpCoCpNMe2][OTf]). Site isolation of the redox and protonation sites allows for attenuation of hydrogen evolution reaction (HER) and electroreductive cycling of the mediator. Upon cathodic reduction of CoIII to CoII of the protonated form of this species, a homolytically weak N–H bond with a bond dissociation free energy (BDFEN–H) of 39 kcal/mol has been demonstrated to effectively deliver an H-atom to acetophenone to generate pinacol product (1H+/1e-) and to fumarates to generate hydrogenated products (2H+/2e-), while effectively outcompeting background hydrogen evolution reaction (HER) at a comparatively low potential. Building on our mechanistic studies of eCPET with C–O and C–C π-bonds, we sought to develop synthetically more useful chemoselective ketyl-olefin cyclizations. This eCPET approach complements direct electrolysis methods, which typically result in low yields and limited functional group compatibility.

Electroreduction of organic molecules via electrocatalytic concerted proton-electron transfer with a cobaltocene-derived mediator

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.