Evaluation of a trinuclear heteroleptic bis-cyclometalated iridium(III) complex as a photoredox catalyst for visible light-mediated hydrothiolation reactions

Abstract

A trinuclear bis-cyclometalated iridium(III) polypyridyl complex was synthesised and evaluated as a photoredox catalyst for visible light- mediated thiol-ene coupling reactions. Electronic absorption and emission studies revealed that the complex shows a blue-shifted emission spectrum, with a wavelength at 578 nm, relative to the canonical iridium complex, [Ir(ppy)3] (598 nm). The emissions are attributed to the transition from the triplet MLCT excited state (3MLCT) to the ground state. Cyclic voltammetry studies demonstrated that this complex is a promising candidate for the photoredox catalysed reactions, with the trinuclear iridium complex increasing the oxidation potential without sacrificing the reduction ability. The iridium(III) complex was evaluated as a photoredox catalyst in the model hydrothiolation coupling reaction and benchmarked against a trinuclear ruthenium congener. Reactions conducted with the trinuclear iridium polypyridyl complex resulted in the highest NMR yields.