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

Two homologous complexes of the type [(NHC)Au-I-Ar], in which the aryl substituent was either phenyl or pentafluorphenyl, were prepared. Treatment of [(IPr)(AuC6F5)-C-I] with PhICl2 leads directly to the expected Au-III oxidation addition product [(IPr)-Au-III(Cl)(2)C6F5]. This complex is thermally stable but undergoes photochemical reductive elimination to deliver [(IPr)(AuCl)-Cl-I] and C6F5Cl. In contrast, the reaction of [(IPr)(AuPh)-Ph-I] with PhICl2 does not deliver an isolable Au-III oxidation addition product but rather leads directly to the formation of [(IPr)(AuCl)-Cl-I] and PhCl, presumably via a [(IPr)Au-III(Cl)(2)Ph] intermediate. These related reactivity pathways are rationalized on the basis of the electronic structures of the two [(NHC)Au-I-Ar] complexes.