An open-shell Ir(II)/Ir(IV) redox couple outperforms an Ir(I)/Ir(III) pair in olefin isomerization

Abstract

Open-shell systems based on first-row transition metals and their involvement in various catalytic processes are well explored. By comparison, mononuclear open-shell complexes of precious transition metals remain underdeveloped. This is particularly true for Ir^II complexes, as there is very limited information available regarding their application in catalysis. Here we show that a family of Ir^II metalloradicals, featuring a C₆H₃-2,6-(OP(^tBu)₂)₂ (POCOP) pincer ligand, effectively catalyses olefin isomerization—a key step in alkane metathesis—exhibiting up to 20 times higher activity than their Ir^I counterparts. Computational studies reveal that the Ir^II/Ir^IV redox cycling enables faster kinetics than the traditional Ir^I/Ir^III pathway owing to reduced barriers for the oxidative addition and reductive elimination steps. Thus, this study presents a redox catalyst involving an Ir^II/Ir^IV pair, highlighting the capabilites of precious-metal systems that extend beyond traditional redox cycles. These findings emphasize the need for expanding catalytic design principles, especially for platinum-group metals.