Heterolytic Oxidative Addition of sp2 and sp3 C–H Bonds by Metal–Ligand Cooperation with an Electron-Deficient Cyclopentadienone Iridium Complex

Oxidative addition reactions of C–H bonds that generate metal–carbon-bond-containing reactive intermediates have played essential roles in the field of organometallic chemistry. Herein, we prepared a cyclopentadienone iridium­(I) complex 1 designed for oxidative C–H bond additions. The complex cleaves the various sp2 and sp3 C–H bonds including those in hexane and methane as inferred from their H/D exchange reactions. The hydroxycyclo­pentadienyl­(nitromethyl)­iridium­(III) complex 2 was formed when the complex was treated with nitromethane, which highlights this elementary metal–ligand cooperative C–H bond oxidative addition reaction. Mechanistic investigations suggested the C–H bond cleavage is mediated by polar functional groups in substrates or another iridium complex. We found that ligands that are more electron-deficient lead to more favorable reactions, in sharp contrast to classical metal-centered oxidative additions. This trend is in good agreement with the proposed mechanism, in which C–H bond cleavage is accompanied by two-electron transfer from the metal center to the cyclopentadienone ligand. The complex was further applied to catalytic transfer-dehydrogenation of tetrahydrofuran (THF).