Cyclooctadienes palladium catalysis

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

Itami went on to report a new synthesis of [12JCPP based on the shotgun homocoupling of dihalide 56 with bis(cyclooctadiene)nickel(0) in the presence of 2,2 -bipyridyl. This new approach circumvented the synthesis of a boronate and also the need for palladium catalysis, albeit stoichiometric nickel is required (Fig. 27). With these synthetic advantages, Itami was able to synthesize 61, the macrocyclic precursor to [12JCPP on a gram scale. In addition, the authors report that with this synthesis they were able to produce 0.5 g in total of [12JCPP from combined reaction products [36]. 

Toshima [162, 164, 165] has studied a series of PVP protected colloidal bimetallic PtPd catalysts in olefin hydrogenation catalysis. The highest activity for the hydrogenation of 1,3-cyclooctadiene to cyclooctene was observed at a Pd Pt radio of 4 1. On the basis of EXAFS analysis [165] it was concluded that the distribution of the two metals in the particles is nonuniform, and that at the most active composition the colloid particles had a platinum core coated with palladium. A less active 1 1 Pd/Pt catalyst, with the same particle size, apparently had a more uniform distribution of metals, with both platinum and p ladium atoms at the surface. 

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