Olefin and Acetylene Ligand Exchange

Olefin exchange reactions are particularly related to catalytic reactions involving metal 7r-complexes. One of the first steps in the hydrogenation, isomerization, and polymerization of olefins involves the exchange of a ligand or solvent molecule to form the corresponding metal 7c-complex intermediate. 

The exchange of an ethylene ligand in Zeise s salt was studied by NMR techniques. In contrast to the stability of the salt, the exchange was found to be very fast on the NMR time scale since only one sharp signal is observed when free ethylene and the salt are interacted, equation (6-61). 

TT-f f f-Cyclododecatrienenickel reacts with 3 moles of butadiene at — 40°C, and the cyclododecatriene ligand is replaced by a newly formed linear butadiene-trimer, equation (6-62). When this reaction is carried out in 

7T-Cyclopentadienyl-7c-l,5-cyclo-octadiene cobalt, (tc-C5H5)Co(C8Hi2), undergoes an exchange reaction in the presence of 2 moles of tolane (di-phenylacetylene). This reaction not only involves ligand exchange but also 

Acetylenes often displace one another in metal 7c-complexes, equation (6-65). Electron-withdrawing groups impart stability to these complexes. The effectiveness increases in the order of acetylene alkylacetylene aryl-acetylene j9-nitroaryl-acetylene. 

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