Heterobimetallic Gold/Ruthenium Complexes Synthesized via Post-functionalization and Applied in Dual Photoredox Gold Catalysis

Abstract

The synthesis of heterobimetallic AuI/RuII complexes of the general formula syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)2}][PF6]2 is reported. The ditopic bridging ligand L1∩L2 refers to a P,N hybrid ligand composed of phosphine and bipyridine substructures, which was obtained via a post-functionalization strategy based on Diels-Alder reaction between a phosphole and a maleimide moiety. It was found that the stereochemistry at the phosphorus atom of the resulting 7-phosphanorbornene backbone can be controlled by executing the metal coordination and the cycloaddition reaction in a different order. All precursors, as well as the mono- and multimetallic complexes, were isolated and fully characterized by various spectroscopic methods such as NMR, IR, and UV-vis spectroscopy as well as cyclic voltammetry. Photophysical measurements show efficient phosphorescence for the investigated monometallic complex anti-[(L1∩L2){Ru(bpy)2}][PF6]2 and the bimetallic analogue syn-[{AuCl}(L1∩L2){Ru(bpy)2}][PF6]2, thus indicating a small influence of the {AuCl} fragment on the photoluminescence properties. The heterobimetallic AuI/RuII complexes syn- and anti-[{AuCl}(L1∩L2){Ru(bpy)2}][PF6]2 are both active catalysts in the P-arylation of aryldiazonium salts promoted by visible light with H-phosphonate affording arylphosphonates in yields of up to 91 %. Both dinuclear complexes outperform their monometallic counterparts.