Butadiene, reaction with lithium alkyls

The kinetics and mechanistic details of the lithium alkyl-initiated anionic polymerization of styrene and diene monomers in hydrocarbon solvents have been the subject of numerous investigations [15]. Some of the first investigations revealed that the propagation reaction was first order in monomer, as might be expected, but followed a fractional order in the lithium alkyl [16]. Most investigators have observed a 0.5 order for the polymerization of styrene. Values have been quoted for the polymerization of butadiene and isoprene ranging from about 0.17 to 0.5, with 0.25 being the most commonly quoted value for both monomers. There is some evidence that the order in lithium for diene polymerization... 

Additionally, if the initiation reaction is more rapid an the chain propagation, a very narrow molecular weight distribution, MJM = 1 (Poisson distribution), is obtained. Typically living character is shown by the anionic polymerization of butadiene and isoprene with the lithium alkyls [77, 78], but it has been found also in butadiene polymerization with allylneodymium compounds [49] and Ziegler-Natta catalysts containing titanium iodide [77]. On the other hand, the chain growth can be terminated by a chain transfer reaction with the monomer via /0-hydride elimination, as has already been mentioned above for the allylcobalt complex-catalyzed 1,2-polymerization of butadiene. 

Lithium dialkylamide having bulky alkyl groups, such as isopropyl groups, exhibits unique behavior in polymerization reactions of isoprene and divinylbenzene. It was previously reported by us that lithium dialkylamide underwent a stereospecific addition reaction with butadiene in the presence of an appropriate amount of dialkylamine in cyclohexane as solvent (1, 2). For instance, on reacting with butadiene, lithium diethylamide gave the sole adduct, 1-diethylamino-cis-butene-2, in a 98-997o purity. In the absence of free amine, on the other hand, no reaction took place under the same experimental conditions (50°C... 

In the stannole series, the reactions could be explained by the extraordinary reactivity of the exocyclic tin-carbon bonds with regard to lithium reagents. Thus, the reaction of 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadiene with 1,1 -dialkyl-2,3,4,5-tetraphenylstannole leads to alkyl-tin bond cleavage-cyclization by the dilithium reagent33 (equation 61). 

It has been shown by - C-NMR spectroscopy that the reaction of alkyl lithium species with butadiene to form the substituted butenyl compounds gives a mixture of the anti and the syn isomers, with the latter being the more stable one [43] for the polybutadienyl- and polyisoprenyllithium compounds in hydrocarbons a dimeric association has been proved [41, 44]. 

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