Other Reactions of Carbon Monoxide

From the temperature variation of the equilibrium constant, thermodynamic parameters for the reaction were also obtained. The extent of formation of [Mo(CO)5l] was found to be cation-dependent, and while equilibrium constants of 39 and 21 atm L moF were obtained for Bu4P and pyH+, none of the anionic iodide complex was observed for Na. Despite this variation, there seemed to be no correlation between the concentration of [Mo(CO)5l] and the rate of the catalytic carbonylation reaction. It was proposed that [Mo(CO)5] and [Mo(CO)5l] are spectator species, with the catalysis being initiated by [Mo(CO)5]. Based on the in situ spectroscopic results and kinetic data, a catalytic mechanism was suggested, involving radicals formed by inner sphere electron transfer between EtI and [Mo(CO)5]. 

A number of ruthenium-based catalysts for syn-gas reactions have been probed by HP IR spectroscopy. For example, Braca and co-workers observed the presence of [Ru(CO)3l3] , [HRu3(CO)ii] and [HRu(CO)4] in various relative amounts during the reactions of alkenes and alcohols with CO/H2 [90]. The hydrido ruthenium species were found to be active in alkene hydroformylation and hydrogenation of the resulting aldehydes, but were inactive for alcohol carbonylation. By contrast, [Ru(CO)3l3] was active in the carbonylation of alcohols, glycols, ethers and esters and in the hydrogenation of alkenes and oxygenates. 

In the ruthenium catalysed carbonylation of piperidine (60 °C, 10 bar CO) the catalyst precursor, [Ru3(CO)i2] was found to be converted mainly to [Ru(CO)5], although IR absorptions due to other minor species were also observed [94]. A catalytic mechanism was tentatively proposed, which involved [RuCO)4] as the active 

In the [Ru(CO)3(dppe)] catalysed carbonylation of para-nitrotoluene (Eq. (6)) HP IR spectroscopy indicated conversion of the Ru(0) complex into an oxidised species with v(CO) bands at higher frequency [41]. A mechanism involving single-electron-transfer from the nitroaromatic to the Ru complex was proposed. 

An HP IR study of the platinum catalysed carbonylation of methanol to methyl formate, revealed that the catalyst precursor, ds-[Pt(PEt3)2Cl2] is converted into cis-[Pt(PEt3)2(CO)2] along with a cluster species, [Pt3(PEt3)3(CO) ] (n = 3 or 4) [95]. A mechanism involving oxidative addition of methanol to Pt(0) followed by CO insertion into the Pt-OMe bond was suggested. 

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Other reactions of carbon monoxide and carbonate species. Carbon monoxide may be determined by absorption in CuCl and measuring the loss of volrrme. Aqueous [CuCy" reversibly gives compounds such as CuCl-C0-H20. 

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