Towards catalytic redox-active iridium polypyridyl complex by in situ photosubstitution

Abstract

In this study, we show that the hydrodehalogenation of reductively inert aryl halides is facilitated by the heteroleptic Ir(III) complex [Ir(dF(CF₃)ppy)₂(dtbbpy)]⁺ (1) in the presence of N-(tert-butoxycarbonyl)-proline and cesium carbonate under irradiation with blue light. We observed in situ modification of 1 to yield intact (Ir-int) and degraded (Ir-deg) complexes. Ir-int complexes are formed through the functionalization of both the C^N and N^N ligands with α-amino radicals, formed via single-electron-oxidation of cesium carboxylate salt (N-Boc-Pro-OCs) derived from N-(tert-butoxycarbonyl)-proline by the photoexcited Ir complex. In this functionalization, electron-withdrawing fluorine atoms on the dF(CF₃)ppy ligands are substituted. The destabilization of the HOMO of the structurally modified Ir-int results in a bathochromic shift of both the excited triplet state absorption and phosphorescence bands when compared to pristine 1. In the presence of excess N-Boc-Pro-OCs, the free Ir-int undergo rapid quenching via excited-state charge-transfer complex formation. The Ir-int˙⁻, after radical ion separation, are responsible for the hydrodehalogenation reaction of aryl halides.