Organolithium reagents hydrocarbon formation

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. 

Most simple organolithium reagents can also be prepared by reaction of the appropriate halide with lithium metal. The simple alkyllithium reagents exist mainly as hexamers in hydrocarbon solvents. In ethers the evidence indicates that tetramers are dominant. The tetramers, in turn, are solvated with ether molecules. Certain highly hindered alkyllithiums have been observed to be more reactive than simpler alkyl systems. This has been attributed to steric hindrance, which prevents the formation of the tetramer. Higher reactivity is generally associated with the less-aggregated species. ... 

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