Halide and Alkoxide Elimination

Several examples of p-chloride elimination are shown in Equations 10.24-10.29. Reaction of vinyl chloride with cationic zirconocene-alkyl complexes (Equations 10.24a and 10.24b) forms propylene and the corresponding zirconocene-chloride complex as the initial products. Tlie final products result from polymerization of the propylene by the starting zirconocene-alkyl species, and generation of a dinuclear cationic chloride species from the resulting cationic chloride complex and a zirconocene dichloride by a less-defined pathway. The propylene is formed by the process shown in Equation 10.24b. Insertion of vinyl chloride into the zirconocene methyl, followed by p-chloride elimination from the p-chloroalkyl intermediate generates propylene and a cationic chloride complex. 

Simpler p-halide eliminations occur from late transition metal catalysts for olefin polymerization (Equations 10.25 and 10.26). Reactions of the cationic palladium-alkyl complexes occur in a similar fashion to the reactions of the cationic group 4 complexes, despite the softer nature of these species. In this case, propylene and the metal chloride are formed. Even a neutral nickel-hydrocarbyl complex (the salicaldimine complex in Equation 10.26) undergoes reactions with vinyl chloride that involve insertion followed by P-chloride elimination. 

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