Carbonylation of methane, alkenes and alkynes

Oxidative carbonylation of methane to acetic acid is one of the pursued ways to solve the fundamental problem of direct methane utilization. Partly aqueous systems with RhCl3-HCl-KI catalyst mixture were applied with some success for this purpose. However, the reaction proceeds faster in acetic acid as solvent, containing only a small percentage of water [34], 

The alkylruthenium species obtained in eq. 5.1 is very stable in water, neither the addition of strong acids nor boiling for several hours lead to its decomposition. In aqueous solution it exists as a monomeric cation, however, it was isolated in solid state and characterized by X-ray crystallography as a dimer [ Ru(C2H5)(C0)2(H20)2 2]2+. The stability of this ruthenium alkyl is attributed to the stabilization effect of strong hydrogen bonds which could be detected in the crystal structure and are postulated also in its aqueous solutions. Finally, elimination of propionic acid from the acyl could be induced by raising the temperature this reaction closes the catalytic cycle  

The rate of the overall catalytic reaction is not very high, TOF =15.4 h 1 at 140 °C, 4 bar CO, 30 bar ethene, 0.01 M [Ru] and 0.1 M CF3S03H. Infrared spectroscopic studies revealed no change in the concentration of the acylruthenium species during the reaction which suggests that the rate 

The importance of this study is given by the fact the carbonylation is mn in water with no need for co-solvents, furthermore the catalyst precursor and the intermediates do not contain other ligands than the constituents of the final product (C2H4, CO and H20). Besides, all elementary steps of the catalytic cycle were studied separately, and all intermediate complexes were characterized unambiguously either in isolated form by X-ray crystallography or/and in solution by NMR techniques. 

Insertion of ethene into the Pd-H bond provides the ethyl complexes [Pd(Et)(TPPTS)3] and tra j-[Pd(Et)(TPPTS)2] which take up CO and yield trans-[ d C(CO)Et (TPPTS)2]. These complexes were all characterized by NMR techniques in separate reactions. Again, elimination of propionic acid from the acylpalladium intermediate (eq. 5.6) was found rate-determining  

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