Quantum yield is a direct measure of the overall energy efficiency in photoredox reaction. Knowing the reaction mechanism could offer great insight to optimize this efficiency. We determined the complete photoredox hydroamidation reaction cycle initiated by the proton coupled electron transfer (PCET) between the photoexcited Ir(III) complex and 2-cyclohexen-1-yl(4-bromophenyl)carbamate in the presence of base. With transient absorption spectroscopy, electrochemistry and TD-DFT calculations, we identified all critical intermediate transient species and the productive and non-productive pathways of the catalytic reaction. This allows us to minimize the major non-productive pathway, namely the back electron transfer (BET), by establishing a kinetically competent equilibrium involving the amidyl radical that reduces its back reaction with the Ir(II). This strategy allows us to improve the quantum yield by a factor of ~4. Our results demonstrate that suppressed BET of photoredox catalytic reactions can lead to improved energy efficiency, and hence improved sustainability and cost benefits of photoredox reactions.

Mechanism informed general strategy for optimizing the quantum efficiency of photoredox hydroamidation catalysis

2019 Fall National Meeting

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