Cp*Ir^III-Catalyzed Oxidative Coupling of Benzoic Acids with Alkynes

Cp*Ir­(III) complexes have been shown
to catalyze the oxidative
coupling of benzoic acids with alkynes in methanol at 60 °C to
form a variety of isocoumarins. The use of AgOAc as an oxidant was
required to facilitate significant product formation. Alkyl alkynes
were shown to be more reactive substrates than aryl alkynes, and a
number of functional groups were tolerated on benzoic acid. Combined
mechanistic and computational studies (BP86) revealed that (1) C–H
activation occurs via an acetate-assisted mechanism; (2) C–H
activation is not turnover limiting; and (3) the oxidant oxidizes
the reduced form of the catalyst via an Ir­(I)–Ir­(II)–Ir­(III)
sequence.