In-Depth Study on Chloride Abstractions from (NHC)Ir(COD)Cl Complexes

While attempting to prepare a series of cationic NHC-Ir complexes of general formula [(NHC)Ir(COD)]+ via the silver salt metathesis reaction of its precursor (NHC)Ir(COD)Cl in dichloromethane, we unexpectedly synthesized [(μ-Cl){(2,7-SICyNap)Ir(COD)}·{Ag(OTf)}], a chloride-bridged Ir–Ag adduct. This result led us to investigate the chloride abstraction from the (NHC)Ir(COD)Cl system in detail. We show how the outcome of this ubiquitous reaction is dependent on a fine balance between the nucleophilicity of the weakly coordinating anion (WCA) and the polarity/coordinating ability of the reaction medium. A frequently encountered alternative to using silver salts is also presented and compared. The experimental difference in the reactivities of cationic catalysts in a representative intramolecular hydroamination reaction shows how a cationic Ir–Ag adduct can fail to deliver the reaction product through what appears to be a stabilization of the catalytically inactive iridium–silver intermediate by the educt.