Thermal versus Photochemical Reductive Elimination of Aryl Chlorides from NHC–Gold Complexes

Two homologous complexes of the type [(NHC)­AuI–Ar], in which the aryl substituent was either phenyl or pentafluorophenyl, were prepared. Treatment of [(IPr)­AuIC6F5] with PhICl2 leads directly to the expected AuIII oxidation addition product [(IPr)­AuIII(Cl)2C6F5]. This complex is thermally stable but undergoes photochemical reductive elimination to deliver [(IPr)­AuICl] and C6F5Cl. In contrast, the reaction of [(IPr)­AuIPh] with PhICl2 does not deliver an isolable AuIII oxidation addition product but rather leads directly to the formation of [(IPr)­AuICl] and PhCl, presumably via a [(IPr)­AuIII(Cl)2Ph] intermediate. These related reactivity pathways are rationalized on the basis of the electronic structures of the two [(NHC)­AuI–Ar] complexes.