Amination, polymeric organolithium

Adogen 464, coupling reagent, poly(phenylene oxide), 190 Amination, polymeric organolithium compounds, 139-145... 

We have previously reported the results of careful investigations of the solution carbonation (8) and oxidation (9) of polymeric organolithium compounds. These studies have been extended to the investigation of solid-state carbonation reactions and these results are reported herein. In addition, a new method has been developed for the synthesis of telechelic polymers with primary amine end-group... 

Polymeric organolithium compounds exhibit limited stability in ether solvents similar to alkyllithium compounds. Living carbanionic polymers react with ether solvents such as THF in a pseudo-tirst-order decay process and the rate decreases in the order Li > Na > K. For example, a 10 M solution of poly(styryl)lithium in THF at 25 °C exhibited a rate of decay of a few percent per minute, but poly(styryl)cesium was found to be exceptionally stable [96], Metalation and decomposition reactions can also occur in the presence of amines such as TMEDA. 

Because of the problems encountered with the protected benzaldehyde imines undergoing Cannizzaro reactions during functionalization with polymeric organolithium compounds, the corresponding benzophenone imines were investigated (eqn [20]). It was envisioned that this would be a useful primary amine functionalization agent because it does not contain enolizable a-hydrogens nor a proton on the imine carbon that could participate in Cannizzaro-type, hydride-transfer reactions. 

In conclusion, the secondary amine functionalization of polymeric organolithium compounds with the readily available imine, N-benzylidenemethylamine, has been shown to be efficient for both PSLi and PBDLi.No evidence for dimer formation or unfunctionalized polymer was observed. 

Upon the addition of polar agents, such as ethers or amines, the organolithium initiators can produce polybutadienes with vinyl contents up to 100 percent. The vinyl content can be controlled by the ratio of modifier to catalyst and the polymerization temperature, with lower temperatures favoring increased vinyl formation. Even at the high vinyl contents such polymers do not crystallize, because of the atactic nature of the vinyl units. 

A change from an aliphatic or aromatic hydrocarbon solvent (cyclohexane, benzene) to a polar solvent (THF) leads to a large increase in trans-1,4 and 3,4 microstructure (58). Organolithium compounds are highly associated sec-butyllithium in benzene or cyclohexane exists as a tetramer, and -butyllithium as a hexamer (64,65). This association in hydrocarbon solvents results pardy in the slow initiation observed between some organolitbiirms and isoprene (66). At low initiator concentrations, the polymerization rate of isoprene in alkyUithium polymerization is proportional to monomer and alkyUithium concentrations (67). 3,4-Polyisoprenes are obtained by modification of the lithium polymerization with ethers, such as the dialky] ethers of ethylene glycol or tertiary amines (68,69). 

In the alkyllithium initiated polymerizations of vinyl monomers, Lewis bases such as ethers and amines alter the kinetics, stereochemistry, and monomer reactivity ratios for copolymerization. In general, the magnitude of these effects has been directly or indirectly attributed to the extent or nature of the interaction of the Lewis base with the organolithium initiator or with the organolithium chain end of the growing polymer. Unfortunately, all of these observed effects are kinetic in nature, and therefore the observed effects of solvent represent a composite effect on the transition-state versus the ground state as shown below in Eq. (6), where 5 represents the differential... 

Ethylenation of n-butyllithium, phenyllithium, and benzylic lithium compounds does not occur at low temperature and ordinary pressure (9). Under more rigorous conditions, telomerization of ethylene in aromatic hydrocarbons proceeds vigorously in the presence of an organolithium compound and an amine. Although n-butyllithium is introduced initially, rapid transmetalation occurs to the more acidic aromatic hydrocarbon (telogen) which subsequently adds to ethylene (taxogen) and initiates the carbanionic polymerization of ethylene. This polymerization proceeds to modest molecular weight, but it is terminated by transmetalation back to the aromatic hydrocarbon which initiates another chain to complete the catalytic cycle. 

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. 

The Lewis bases, such as ether or amines, are preferably used as a solvent for the reaction shown in eq. (3.9). This is because organolithium compounds have high associative properties and they form the polymeric aggregate (RLi) as described below. These solvents can reduce the associative properties and increase the basicity of lithium atom. For example, -BuLi is a hexamer in hexane, a tetramer... 

The most common Lewis bases used in organolithium-initiated polymerizations are aprotic amines and ethers. More strongly complexing agents include hexamethylphosphoramide, polyglycol dimethyl ethers, cyclic ethers (crown ethers), and dipiperidinoethane (DIPIP)... 

The acceleration of the rates of organolithium reactions resulting from low concentrations of bases such as amines or ethers is very great (54, 60, 72-75), The effect no doubt results from complex formation which labilizes the carbon-lithium bond. Coordination of base also apparently results, as expected, in a more ionic transition state. The stereospecificity of olefin polymerization changes very markedly upon addition of base, and varies with base concentration in a manner which suggests that complex formation is responsible 31, 68, 73). 

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