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.