Phosphorus-nickel ratio, effect

The homo-Diels-Alder reactions of norbornadiene and quadricyclane with acrylic esters in the presence of nickel catalysts and phosphorus ligands gives, with different kinetics, the same endojexo mixtures of adducts, leading to the conclusion that a common intermediate and stepwise mechanism are involved.A systematic investigation of the effects of several phosphorus ligands on the stereoselectivity of the nickel-catalyzed homo-Diels-Alder reaction of norbornadiene with acrylonitrile shows a clear correlation between ligand bulk and the ratio of exoj endo-Komers ... 

When 1-butene inserts into the growing oligomeric chain there are two possible products a branched and an internal olefin. The product olefin, branched or internal, is determined by the manner in which the butene coordinates to the nickel (Fig. 13). The reason for the interest in the branched/internal ratio is the fact that internal olefins are more desirable than branched ones. Shell s scientists have successfiilly used the RFF to determine both the cis/trans ratio (Fig. 12) and the branched/internal ratio. In addition, workers found that the stereochemistry of butene coordination is determined by steric effects (Fig. 13). In particular, the substituents on phosphorus were found to exert a steric control over the branched/ internal ratio resulting from butene insertion. 

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