Stereospecific coupling of 1,2-disubstituted vinyl group

Recent developments in catalysis at the atomic level are described. The use of transition metal halides which form intermediate metal n-complexes can promote both the catalytic and stoichiometric coupling of aryl Grignard reagents, the stereospecific coupling of 1,2 disubstituted vinyl groups and the double coupling of ethylene to dimers of butadiene. 

Stereospecific coupling of 1,2-disubstituted vinyl groups is attained by reaction of a vinyl Grignard with CrClg, CoClj, PdClj, and NiBrz catalysts (50, 51). The stereospecificity of the products appears to result from the selective configuration of the transition metal halide (Fig. 20). 

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