Carbonylation of dimethyl ether on Rh/Cs₂HPW₁₂O₄₀: Solid-state NMR study of the mechanism of reaction in the presence of a methyl iodide promoter

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• 作者：Maxim S. Kazantsev ; Mikhail V. Luzgin ; Galina G. Volkova ; Alexander G. Stepanov ; ^{stepanov@catalysis.ru}
• 关键词：Dimethyl ether ; Carbon monoxide ; Carbonylation ; 12-Tungstophosphoric acid ; Methyl iodide promoter ; Mechanism ; Rh methyl ; Rhodium carbonyls ; 13C solid-state NMR
• 刊名：Journal of Catalysis
• 出版年：2012
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：July, 2012
• 卷：291
• 期：Complete
• 页码：9-16
• 文件大小：590 K

摘要

Using ¹³C solid-state nuclear magnetic resonance, the carbonylation of dimethyl ether (DME) with carbon monoxide has been studied on solid Rh/Cs₂HPW₁₂O₄₀ in the presence of a methyl iodide promoter. The observed decrease in the reaction temperature in comparison with halide-free systems is caused by a change of the reaction mechanism. At first, the activation of the promoter and CO on Rh/Cs₂HPW₁₂O₄₀ produces methyl rhodium carbonyl species. Carbon monoxide is then embedded into the RhCH₃ bond to afford Rh acetyl. Rapid migration of the acetyl group from the Rh center to a Br酶nsted acid site of Rh/Cs₂HPW₁₂O₄₀ gives rise to an acetate group attached to the Keggin unit (Keggin acetate). Br酶nsted acid sites provide dimethyl ether activation with the formation of a surface methoxy group. The latter, through reaction with hydrogen iodide, which is produced at the stage of Rh acetyl-to-Keggin acetate transformation, restores methyl iodide for subsequent carbonylation stages. Methyl acetate formation from a Keggin acetate and DME closes a catalytic cycle.