Polymerization organolithium reagents

Also, addition of small quantities of Lewis bases such as amines to alkyllithium reagents in hydrocarbons markedly affects reactivity, especially in connection with various anionic polymerization reactions. Findings such as these prompted a number of research groups in the early 1950 s to study in detail the role of Lewis bases in the structures of organolithium compounds (4, 5). In each case it was concluded that coordination complexes form when amines are added to organolithium reagents in hydrocarbons. 

Organolithium reagents are known to add to alkenes. This generates a carbon-carbon bond and a new organolithium species. Addition to styrene generates a benzyllithium species that normally adds to a second molecule of styene and so on to undergo polymerization, although under suitable conditions the benzyllithium... 

Cohen and Liu have examined the yield and selectivity enhancement effects of TMSCl and TMSCl/HMPA on conjugate addition of some stabilized organolithium reagents onto, particularly, easily polymerized a, -unsaturated carbonyl compounds. The authors proposed that the beneficial effect is due to the prevention of 1,2-addition and polymerization of the Q , 8-unsaturated carbonyl compounds. ... 

These observations, added to the fact that addition of polar solvents to polymerization reactions of butadiene initiated by organolithium reagents in hydrocarbon solvents can change the stereochemistry from one of predominantly rtr-1,4 to that of 1,2 and trans-, , suggests that the lithium may form a tt complex with the olefin, and if this is sufficiently strong, orient the monomer prior to the incorporation step. 

Here the driving force is provided by the formation of a carbanion adjacent to a stabilizing group (RjSi— or dithioacetal). Organolithium reagents, however, add to conjugated dienes and hence initiate their polymerization. In hydrocarbon solvents n-butyl lithium and butadiene result in mostly 1,4-addition. The polymer contains a mixture of cis and trans stereochemistry about the double bonds. 

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