Cp*IrIII-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.

研究表明，五甲基环戊二烯基铱(III)配合物（Cp*Ir(III)）可在60 ℃的甲醇溶剂中催化苯甲酸与炔烃的氧化偶联反应，生成多种异香豆素类产物。该反应需以乙酸银（AgOAc）作为氧化剂，方可实现可观的产物生成量。实验证实，烷基炔烃的反应活性优于芳基炔烃，且苯甲酸底物可兼容多种官能团。结合机理与计算研究（BP86）结果显示：(1) 碳氢键活化（C–H activation）通过乙酸根辅助的机制进行；(2) 碳氢键活化并非该催化循环的周转限速步骤；(3) 氧化剂通过Ir(I)–Ir(II)–Ir(III)的氧化还原序列，对催化剂的还原态进行氧化。