Relevance to cross-coupling reactions catalyzed by transition metal complexes

2 Relevance to cross-coupling reactions catalyzed by transition metal complexes 

The catalytic cycle involves the oxidative addition of aryl halide to Ni(0) precursor, the transmetalation of organomagnesium reagent to the resulting aryl(halogeno)nickel complex giving an aryl(alkyl)nickel(II) intermediate, and 

Diorganonickel-phosphine complexes with trans geometry are more stable than the cis isomer and are isolated as the sole product in common preparative reactions (Eqs. 5.7 and 5.22) [21,96]. 

The cis-trans isomerization of diorganonickel complex via dissociative or associative intermediates was investigated in detail from both experimental and theoretical aspects [98]. All these results suggest that the stable trans diorganonickel intermediate of the cross-coupling reaction may be converted into the reactive cis isomer during the reaction. Further details are not clear at present in the Ni-catalyzed system. 

Pd-catalyzed coupling of aryl or alkenyl halides and triflates with organotin compounds also takes place smoothly to produce the coupling products, which was discovered by Shlle and Kosugi independently and developed by a number of research groups (Eqs. 5.24 and 25) [100-103], 

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