For example, the structurally complex eight membered rings can be constructed via [4+4]-cycloaddition (Scheme 17).

Scheme 17

Compared to the [4+4]-cycloaddition, the [4+2] is stereospecific and effective at low temperature (Scheme 18).

11.9.4 Carbonylation

Ni catalyzes the addition of carbon monoxide to alkenes and alkynes in presence of water or MeOH to give carboxylic acid or ester, respectively, which are very useful processes in organic synthesis (Scheme 19).

Scheme 19

 

11.9.5 Alkene/Alkyne Oligomerization Reactions

In the presence of catalysts, alkynes and alkenes can react itself or with many other organic and inorganic compounds. Nickel catalysts are found wide applications for this purpose. For example, Reppe synthesis of cyclic polymerization of acetylene gives cyclooctatetraene, which represents a true milestone in transition-metal-catalysis (Scheme 20).

Scheme 20

The formation of organonickel compounds have been revealed by a carefully designed experiment (Scheme 21).

Scheme 21