Homogeneous carbonylation

The use of homogeneous carbonylation reactions for the synthesis of biologically important compounds has been reviewed, covering many methodologies, including direct use of carbon monoxide, and also hydroformylation and alkoxy- and amino-carbonylation, both inter- and intra-molecular.258... 

PdCl2(PPh3)2 catalyzed homogeneous carbonylation of l-(4 -isobutylphenyl) ethanol, in which some of the isomeric linear acid, 4- -Bu-C6H4CH2CH2C02H, is also formed typical yields are 92% of ibuprofen and 6% of the linear acid (see also Section 4.3.1). The carbonylation is performed at 50 bar, 130°C, in an acidic aqueous medium containing chloride ions, a ketone (such as methyl ethyl ketone) as solvent, and at least 10% of water [V. Elango et al., US Patent 4 981 995 (1991)]. A convenient ratio of substrate palladium catalyst is 10 1. A 3.5kt/a plant in Bishop, Texas has been operated by BHC since 1992. The palladium catalyst can be precipitated from the organic phase of the carbonylation reaction and re-used without further treatment. 

Table VI illustrates still another important property of supports vis-a-vis homogeneous carbonyl complexes the ability to inaobilize coordinatively unsaturated sites. It is noteworthy that in solution Fe(C0)3 maintained a slight activity only in the presence of continued irradiation, whereas all measurements on the supported catalysts were made in the dark after photoactivation.

A slurry phase concurrent synthesis of methanol using a potassium meth-oxide/copper chromite mixed catalyst has been developed. This process operates under relatively mild conditions such as temperatures of 100-180°C and pressures of 30-65 atm. The reaction pathway involves a homogeneous carbonylation of methanol to methyl formate followed by the heterogeneous hydrogenolysis of methyl formate to two molecules of methanol, the net result being the reaction of hydrogen with carbon monoxide to give methanol via methyl formate ... 

In view of the vast number of homogeneous carbonylation reactions known it is easy to say that biphasic carbonylations have not yet reached their culmination point. Moreover, the actual importance of other two-phase media, e.g., fluorous biphasic systems [26] (cf. Section 7.2), will lead to further exploitation for carbonylations. 

Homogeneous carbonylation of ethylene to acrolein was investigated in the presence of another early-late bimetallic complex, [AsPh4][Cp 2Zr(,u-S)2Rh(CO)2]J ... 

Halide-promoted heterogeneous catalysts for carbonylation are analogues to homogeneous carbonylation catalyzed by metal carbonyls, that is, the Reppe reaction (11). The first step of the Reppe reaction involves the oxidative addition of alkyl halide promoter to carbonyl metal, for example, Rh(I) complex (Fig. 1). This step is followed by methyl migration, bonding of carbon monoxide to give a coor-dinatively saturated Rh(III) complex, and subsequent decomposition of this complex in the presence of methanol to yield a carbonylated product and regenerate the promoter and the catalyst. 

Liquid-Phase Carbonylation. An incentive for the development of immobilized solid catalysts in liquid-phase carbonylation is to retain the chemical characteristics of the soluble industrial catalysts (6) in the Reppe reaction and reduce the problems of corrosion as well as the separation of catalyst from reaction liquor. Various supporting materials such as active carbon, polymers, zeolites, and amorphous inorganic oxides are used to immobilize homogeneous carbonylation catalysts. 

The activity enhancement by the phosphonate-phosphane complexes 2a and 2b is obvious. The phosphane oxide-phosphane dppe-0, which is known to accelerate the homogeneous carbonylation (28), did not improve the activity of the carbon-supported catalyst. Strongly coordinated chelate ligands like dppe or dppp can even suppress the activity, possibly by blocking coordination sites necessary for carbonylation. 

Platinum. Further comments have been offered concerning the mechanism of PtCl6 -SnCl2 catalysis of homogeneous carbonylation of alkenes. ... 

Pd-catalyzed carbonylation of enol triflates can be successfully applied to the one-carbon elongation on the keto-carbonyl carbon in the total syntheses of various natural products and biologically active derivatives [21-26]. The functionalization of various steroidal skeletons by Pd-catalyzed carbonylations of vinyl iodides/triflates played a relevant role [27]. The strength of the palladium-catalyzed homogeneous carbonylation reaction can be shown by the fact that even the hindered positions 12 of hecogenin derivative 9 can be functionalized to give ester or amide derivative 10 in moderate-to-good yield without any side reaction of the further functionalities (Scheme 9.4) [28]. 

Petz, A., Horvath, J., Tuba, Z., Pinter, Z. and KoDar, L. (2002) Facile synthesis of 17-formyl steroids via palladium-catalyzed homogeneous carbonylation reaction. Steroids, 67, 777-781. 

Homogeneous Carbonylation Reactions in the Synthesis of Compounds of Pharmaceutical Importance... 

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