Boosting photocatalytic efficiency of iridium polypyridyl complex in coupling reaction through the induction of ferrocene: insights into bimetallic catalysis

Abstract

A bimetallic compound [Ir(ppy)₂(fcbpy)]PF₆ (2, ppy = 2-phenylpyridine; fcbpy = 4-ferrocenyl-2,2′-bipyridine) is synthesized, and its molecular structure is established by single crystal XRD. The catalytic activity of 2 is probed in the coupling of α-ketovinylazides with N,N-dimethylanilines in the presence of light. A maximum of 94% yield is obtained within 23.9 minutes in a micro flowreactor with a turnover number and turnover frequency of 940 and 2350 h⁻¹, respectively. A catalyst lacking the ferrocene moiety, [Ir(ppy)₂(bpy)]PF₆, failed to provide any yield even with higher catalyst loading. The redox and photophysical properties of 2 are thoroughly investigated using electrochemistry and different steady-state and time-resolved spectroscopic techniques. Photoluminescence lifetime measurements and femtosecond transient absorption studies revealed the formation of a long-lived excited state in 2 after photoexcitation. Thus, the enhanced catalytic performance through the induction of ferrocene is rationalized based on transiently shelving electrons in the triplet state for a longer period of time, thereby efficiently harnessing them in photocatalysis.