Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes,Journal of the American Chemical Society

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Stepwise Iodide-Free Methanol Carbonylation via Methyl Acetate Activation by Pincer Iridium Complexes
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2021-08-04 , DOI: 10.1021/jacs.1c05185
Changho Yoo _{1,

2} , Alexander J M Miller ₁

Affiliation

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.

中文翻译：

通过钳形铱配合物活化乙酸甲酯的逐步无碘甲醇羰基化

碘化物是甲醇羰基化工业生产乙酸的重要促进剂，但它也会导致反应器腐蚀和催化剂失活。在这里我们报告，在没有甲基碘或碘盐的情况下，铱钳复合物介导了甲醇羰基化到乙酸甲酯的各个步骤。无碘甲基化是在温和条件下通过氨基苯基亚膦酸盐钳形铱（I）二氮络合物通过乙酸甲酯的净 C-O 氧化加成产生可分离的乙酸甲基铱（III）络合物实现的。实验和计算研究提供了通过初始 C-H 键激活随后乙酸迁移以及胺半化促进甲基化的证据。随后在甲醇溶液中插入 CO 和还原消除产生乙酸甲酯和乙酸。净反应是使用乙酸甲酯作为促进剂将甲醇羰基化为乙酸，同时将铱二氮络合物转化为羰基铱络合物。迁移插入和还原消除的动力学研究揭示了溶剂甲醇的重要作用以及乙酸根和碘根阴离子的独特特征，这些特征与未来无碘羰基化催化剂的设计有关。

更新日期：2021-08-19

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