Jr-allylnickel complexes

Takimoto and Mori reported that the nickel-catalyzed regio- and stereoselective ring-closing car-boxylation of the bis-1,3-diene 81 with dialkylzincs 82 gave the 3-allyl-4-alkenylpyrrolidines 83 in high yields (Scheme 29).108 The reaction proceeds through formation of the cyclic bis-jr-allylnickel complex 84, the insertion of CO2 into a nickel—carbon bond of 84, leading to 85, and the addition of RzZn to 85. 

Elegant applications of this method to the syntheses of large ring (12,14, and 18) compounds and natural products have been reported by Corey and Wat 129>. The last step of the humulene synthesis by Corey and Hamanaka is the following coupling reaction of ally lie dibromide via jr-allylnickel complex formation 13°). 

In contrast to the transition metal catalysts above, nickel complexes have been studied intensely for the polymerization of CHD and its derivatives. jr-Allylnickel-based complexes were employed by Dolgoplosk et al. for CHD polymerization. They used n-alkenylnickel halides, for example, K-metallyl nickel dichloride and it-allyl nickel dibromide, combined with electron acceptors such as chloranil (tetrachloro-/ -quinone) or nickel trichloroacetate. Unfortunately, the true propagating species of the above catalytic systems are not clear, but they were moderately active for CHD polymerization and the polymer obtained appeared to have a predominantly 1,4-linked structure. However, the stereoregularity of the polymer was not very high based on its Tm (270 °C). 

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