Racemic NHC–Iridium Complexes with Electron-PoorDiene Ligands and Their Reactivity in the Intramolecular HydroaminationReaction

TFB (tetrafluorobenzobarrelene), TCB (tetrachlorobenzobarrelene), and BB (benzobarrelene) are introduced as alternative diene ligands to COD (1,5-cyclooctadiene) for NHC–iridium complexes of the general formula [(NHC)Ir(diene)Cl]. This new class of compounds was fully characterized, including by X-ray crystallography of appropriate single crystals. The steric requirements of three different NHC ligands as well as the diene ligands were analyzed using the SambVca program. The corresponding cationic and catalytically active [(NHC)Ir(diene)][PF6] complexes were generated via chloride abstraction with AgPF6. Where possible, these species were isolated and fully characterized. The less stable members were freshly made before being tested as catalysts in a prototypical intramolecular hydroamination reaction of an unactivated aminoalkene. A comparison shows how both diene as well as NHC ligands profoundly influence the catalytic activity and point toward future modifications to be made to these catalysts.