Butadiene rhodium trichloride

Butadiene and ethylene are codimerized with a soluble rhodium-phosphine complex as the catalyst. Very little has been reported on the mechanistic evidence for this reaction. However, a catalytic cycle as shown in Fig. 7.9 involving a rhodium hydride seems likely. Reducing rhodium trichloride with ethanol in the presence of a tertiary phosphine generates the hydride complex 7.32. The 1,4-hydride attack on the coordinated butadiene gives an rf-allyl complex. This is shown by the conversion of 7.33 to 7.34. Ethylene coordination to 7.34 produces 7.35. 

Rhodium trichloride catalyzes the addition of ethylene or propylene to a conjugated diene such as butadiene-1,3, for example 1... 

Rhodium trichloride has been used to catalyze a number of organic reactions. Thus in aqueous emulsions it induces the stereoregular polymerization of butadiene to trans-polybutadiene and it catalyzes the isomerization of various alkenes in ethanolic solutions. 

Selective codimerization of ethene and 1, 3-butadiene is also possible because the diene first forms an f/ -allyl complex with the metal centre (Fig. 12.4). An industrial process along these lines has been developed in the USA by Du Pont. A rhodium catalyst is employed rhodium trichloride in ethanol itself gives 80% selectivity towards the desired product, irflns-1,4-hexadiene, which is used in the manufacture of an ethene-propene-hexadiene synthetic rubber. The diene introduces some double bonds into the polymer chains which are required for vulcanization. 

Treatment of rhodium trichloride or cyclo-octene rhodium chloride dimer with butadiene gives bis-butadiene rhodium(I) chloride for which X-ray studies show the structure 3.30 [79]. 

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