Sequential Construction Strategy for Rational Design of Luminescent Iridacycles

A convenient and general strategy has been developed to synthesize stable iridapolycycles 5–8. Reaction of arylacetylenes with iridium-hydride complex [IrH­(CO)­Cl­(PPh3)3]­BF4 via nucleophilic addition, oxidative decarbonylation, and C–H bond activation results in the formation of a series of iridacyclopentadiene derivatives, including benzo-iridacyclopentadiene 5, naphtho-iridacyclopentadiene 6, pyreno-iridacyclopentadiene 7, and thieno-iridacyclopentadiene 8. These iridapolycycles display high thermal and air stability yet can be further functionalized via facile ligand substitution reactions. As an example, complex 5 was used as a metallosynthon to react with 2,2′-dipyridyl to give intensely luminescent Ir­(III) complex 9 bearing one C∧C and one N∧N ligands. Density functional theory (DFT) calculations reveal that the lowest unoccupied molecular orbitals (LUMOs) of iridapolycycles 5–8 are located on the phosphonium groups while the highest occupied molecular orbitals (HOMOs) are mainly located on the metal-embedded C∧C frameworks. Our method offers a sequential construction strategy for constructing luminescent iridacycles, which potentially allows facile tuning of the photoluminescence properties by modulating the C∧C and N∧N moieties independently.