Photosensitized, energy transfer-mediated organometallic catalysis through electronically excited nickel(II)

Abstract

Transition metal catalysis has traditionally relied on organometallic complexes that can cycle through a series of groundstate oxidn. levels to achieve a series of discrete yet fundamental fragment- coupling steps. The viability of excited- state organometallic catalysis via direct photoexcitation has been demonstrated extensively over the past 100 years. Although the utility of triplet sensitization by energy transfer has long been known as a powerful activation mode in org. photochem., it is surprising to recognize that photosensitization mechanisms to access excited- state organometallic catalysts have lagged far behind. Here, we demonstrate excited- state organometallic catalysis via such an activation pathway: Energy transfer from an iridium sensitizer produces an excited- state nickel complex that couples aryl halides with carboxylic acids. Detailed mechanistic studies confirm the role of photosensitization via energy transfer.