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.