7r-allyl complexes of nickel

One other reaction deserves mention. From bis(cyclooctadiene)nickel and butadiene (31), and in the presence of an isocyanide (RNC, R = cyclohexyl, phenyl, tcrt-butyl) two organic oligomeric products are obtained, 1 -acylimino-11 -vinyl-3,7-cycloundecadiene and 1 -acylimino-3,7,11 -cyclo-dodecatriene. In each, one isocyanide has been incorporated. An analogous reaction with carbon monoxide had been reported earlier. The proposed mechanism of these reactions, via a bis-7r-allyl complex of nickel, is probably related to the mechanism described for allylpalladium complexes above. 

To rationalize these experimental results, the authors [91] proposed that the common intermediate is a 7r-allyl complex of nickel 272 that can give rise either to the SN2-type coupled product 273, or the SN2 -type compound 274, depending on the steric demands [Eq. (93)]. 

Nickel-based Ziegler catalysts are very effective for propylene dimerization.The unsupported catalyst is prepared by mixing NiCl2, Et3Al, and butadiene in chlorobenzene to yield a C12 7r-allyl complex of nickel. A phosphine is then added, followed by liquid propylene at 15 atm pressure. A mixture of n-hexenes, 2-methylpentenes, and 2,3-dimethylbutenes in 85-90% yield are produced rapidly at 30-40°C. Apparently this reaction is not reported for a polymer-bound version. This would be of interest since it is observed that the product distribution is quite sensitive to the nature of the phosphine. 

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