Polymerization, Oligomerization, and Cyclooligomerization of Alkenes

There is extensive literature on Ziegler-Natta catalysis and the interested reader is referred to the recent review by Fischer et al. (1973), the reviews edited by Ketley (I967), and the summary by Mole and Jeffrey (1972). The following very brief description is intended only to illustrate how the special properties of transition metal-olefin bonds can lead to extremely important C-C bond-forming reactions. 

Ziegler and co-workers (1955) were the first to observe that ethylene could be polymerized at room temperature and low pressure (few atmospheres) in the presence of catalysts of the type TiC /AlEtj. Natta (1955, 1956, 1957) showed that such catalysts could be modified to produce stereoregular polymers of high molecular weight. 

In the reactions of olefins with olefins, different transition metal catalysts can give rise to markedly different products (Heimbach, 1973 Buchholzer a/., 1972 Kricka and Ledwith, 1974). Certain nickel catalysts, for example, normally trimerize butadiene as shown in Eq. (83) (Bogdanovic et al., 1969). These same catalysts, however, in the presence of suitable ligands, will cyclo-dimerize butadiene to give initially divinylcyclobutane (which can be isolated in 40% yield) and finally 1,5-cyclooctadiene in high yield [Eq. (84) (Brenner etal., 1969)]. 

Other nickel catalyst systems can cyclodimerize butadiene to 2-methylene-vinylcyclopentane (Kiji et a ., 1970a, b) or linearly dimerize it to (E,E)-1,3,6-octatriene in high yield [Eq. (85) (Pittman and Smith, 1975)]. 

Similarly, butadiene and ethylene can react together in the presence of naked nickel or nickel-ligand catalytic systems to give c/j,/ra 5-l,5-cyclo-decadiene in yields up to 80% [Eq. (86) (Wilke, 1963 Heimbach and Wilke, 1969)]. Norbornadiene dimerizes or reacts specifically with olefins using Ni(0) (Schrauzer and Glockner, 1964 Schrauzer et al., 1970). 

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