Radical Chemistry of Photoexcitable Borates

Abstract

Chemical reactions based on photoexcitation of molecules allow unusual modes that are not available via thermal pathways. Recent photoredox catalysis enable generation of carbon-centered radicals under mild conditions, which previously required harsh conditions. However, the redox process of the catalyst must be involved in the design of the catalytic pathways. As a result, photo-redox reactions undergo multi-step energy and electron transfer, often leading to loss of reaction efficiency. In this context, we have designed and developed boron-ate complexes that can be directly excited under visible-light irradiation. The excited alkyl boron-ate complexes produce alkyl radicals, accompanied by cleavage of carbon-boron bonds. Due to their ability of high single-electron reduction, the radical process proceeds without the photoredox catalysts. This property has been used to develop a new type of photocaged molecule that enables caging/uncaging on carbon.