Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes
Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes
复制标题
通过钳铱络合物活化乙酸甲酯进行逐步无碘化物甲醇羰基化
DOI：
10.1021/jacs.1c05185
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发表时间：
2021
影响因子：
15
通讯作者：
Miller, Alexander J.
中科院分区：
文献类型：
--
作者：
Yoo, Changho;Miller, Alexander J.
碘化物是甲醇羰基化生产醋酸的重要助剂，但也会导致反应器腐蚀和催化剂失活。在此，我们报道了在没有甲基碘或碘盐的情况下，Ir钳形配合物在甲醇羰化合成乙酸甲酯的各个步骤中的中介作用。无碘甲基化是在温和的条件下，通过乙酸甲酯的净C-O氧化加成生成可分离的乙酸甲基锂(III)络合物，由氨基苯亚膦钳形Ir(I)二氮络合物实现的。实验和计算研究为甲基化提供了证据，通过最初的C-H键激活，随后醋酸酯迁移，促进了胺的半衰性。随后在甲醇溶液中CO插入和还原消除生成乙酸甲酯和醋酸。净反应是以乙酸甲酯为促进剂，将甲醇羰化为醋酸，同时将Ir氮络合物转化为Ir羰基络合物。迁移插入和还原消除的动力学研究揭示了溶剂甲醇的基本作用，以及乙酸根和碘离子的不同特征，这些都与未来无碘羰化催化剂的设计有关。
Iodide is an essential promoter in the industrial production of acetic acid via methanol carbonylation, but it also contributes to reactor corrosion and catalyst deactivation. Here we report that iridium pincer complexes mediate the individual steps of methanol carbonylation to methyl acetate in the absence of methyl iodide or iodide salts. Iodide-free methylation is achieved under mild conditions by an aminophenylphosphinite pincer iridium(I) dinitrogen complex through net C–O oxidative addition of methyl acetate to produce an isolable methyliridium(III) acetate complex. Experimental and computational studies provide evidence for methylation via initial C–H bond activation followed by acetate migration, facilitated by amine hemilability. Subsequent CO insertion and reductive elimination in methanol solution produced methyl acetate and acetic acid. The net reaction is methanol carbonylation to acetic acid using methyl acetate as a promoter alongside conversion of an iridium dinitrogen complex to an iridium carbonyl complex. Kinetic studies of migratory insertion and reductive elimination reveal essential roles of the solvent methanol and distinct features of acetate and iodide anions that are relevant to the design of future catalysts for iodide-free carbonylation.