Phosphine Ligands in the Palladium‐Catalysed Methoxycarbonylation of Ethene: Insights into the Catalytic Cycle through an HP NMR Spectroscopic Study |
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Authors: | Verónica de?la Fuente Dipl‐Chem Mark Waugh Dr Graham?R Eastham Dr Jonathan?A Iggo Dr Sergio Castillón Prof?Dr Carmen Claver Prof?Dr |
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Institution: | 1. Departament de Química Física i Inorgànica, Universitat Rovira i Virgili, C/Marcel?lí Domingo s/n, 43007 Tarragona (Spain), Fax: (+34)?97‐755‐9563;2. Lucite International, Technology Centre, PO Box 90, Wilton, Middlesborough, Cleveland, TS68?JE (UK);3. Department of Chemistry, University of Liverpool, Oxford Street, Liverpool, L69 7ZD (UK);4. Departament de Química Analítica i Orgànica, Universitat Rovira i Virgili, C/Marcel?lí Domingo s/n, 43007 Tarragona (Spain) |
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Abstract: | Novel cis‐1,2‐bis(di‐tert‐butyl‐phosphinomethyl) carbocyclic ligands 6 – 9 have been prepared and the corresponding palladium complexes Pd(O3SCH3)(L‐L)]O3SCH3] (L‐ L=diphosphine) 32 – 35 synthesised and characterised by NMR spectroscopy and X‐ray diffraction. These diphosphine ligands give very active catalysts for the palladium‐catalysed methoxycarbonylation of ethene. The activity varies with the size of the carbocyclic backbone, ligands 7 and 9 , containing four‐ and six‐membered ring backbones giving more active systems. The acid used as co‐catalyst has a strong influence on the activity, with excess trifluoroacetic acid affording the highest conversion, whereas excess methyl sulfonic acid inhibits the catalytic system. An in operando NMR spectroscopic mechanistic study has established the catalytic cycle and resting state of the catalyst under operating reaction conditions. Although the catalysis follows the hydride pathway, the resting state is shown to be the hydride precursor complex Pd(O3SCH3)(L‐ L)]O3SCH3], which demonstrates that an isolable/detectable hydride complex is not a prerequisite for this mechanism. |
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Keywords: | hydroesterification methoxycarbonylation NMR spectroscopy palladium X‐ray diffraction |
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