Functionalized Alkyllithium Compounds

Anionic polymerizations initiated with alkyllithium compounds enable us to prepare homopolymers as well as copolymers from diene and vinylaromatic monomers. These polymerization systems are unique in that they have precise control over such polymer properties as composition, microstructure, molecular weight, molecular weight distribution, choice of functional end groups and even copolymer monomer sequence distribution. Attempts have been made in this paper to survey these salient features with respect to their chemistry and commercial applications. 

Fig. 5.37. ort/io-Selective electrophilic functionalization of aromatic compounds via a substituent-controlled lithia-tion. As alkyllithium compounds are oligomers (cf. Section 10.1) the presentation of the adduct B of the aromatic compound and sec-butyllithium as monomeric is likely to simplify the actual situation. Regarding the degree of oligomerization in the alkyllithium substructure, the structure of the adduct D of the aromatic compound and sec-butyllithium is the correct one. It contains one molecule Me2N-CH2-CH2-NMe2 (tetra-methylethylendiamine,... 

Keywords oiganosilane, benzylsilane, alkyllithium compound, stereochemistry, density functional calculation... 

The reaction is usually fast and is tolerant of most types of functional substituent, such as epoxy groups or unprotected carbonyl groups a variety of solvents can be used, most commonly THF at low temperature. Generally, when tin and hydrogen are present as competing electrophilic centres, alkyllithium compounds give transmetallation, whereas lithium diisopropylamide gives deprotonation (equation 22-2).7... 

This is one of the many examples where it is preferable to use Grignard reagents over alkyllithium compounds for the alkylation of the heteroatom-functionalized Cp and related halide complexes, because of the risk of possible side-reactions with lithium alkyls. 

The functionalization of PSLi with GPTMS was also performed in the presence of lithium alkoxides, specifically, lithium 2,3-dimethyl-3-pentoxide. It is known that lithium alkoxides cross-associate with alkyllithium compounds in solution. The cross-association would be expected to... 

The reaction of polymeric organolithium compounds with thiir-anes is reported to be a viable route for the preparation of thiol-functionalized polymers. However, until recently the mechanism of this reaction had not been elucidated, that is, whether this proceeds via a sulfur extmsion reaction (path (a) in Scheme 11) or via a ring-opening reaction (path (b) in Scheme 11). For simple alkyllithium compounds, the sulfur extmsion pathway has been shown to be operative. 

Lithiation ortho to functional groups of arenes followed by trapping with electrophiles is an appealing synthetic methodology. The directed ortho metalation (DoM) is the reaction of an alkyllithium compound with an arene bearing a direct metalation group (DMG) that leads to an ori/jo-lithiated intermediate. The abiHty of DMGs to effect the ortho metalation process... 

Solvation of the organolithium polymeric species, with possibly some disruption of the polymers to less-associated species, leads to adducts which may function as a source of carbanions in this sense the adducts behave as bases in furnishing a nucleophilic moiety. It is important to realize, however, that such basic behavior can occur only in the presence of a basic solvent, or it requires a strong Lewis add. Examples of the latter situation are found in the reaction of alkyllithium compounds vrith other organometals, as described in the following section. 

Reaction scheme (it) is more likely than (i) on energy grounds. The dimer is probably an important species present in ether or triethylamine solutions of n-alkyllithium compounds, and might therefore reasonably be expected to function as a reactive intermediate in hydrocarbon solution. Rather complex kinetics should follow from scheme ( ), because various concurrent equilibria between alkyllithium species (e.g., between tetramer and hexamer, tetramer and tetramer, etc.) would be in effect. 

The number of possible structural devices increases as functionality gets further from the anionic center in functionalized organolithium compounds. So, d-func-tionalized organolithium compounds can be classified according to the hybridization of the carbon atom bonded to the lithium in alkyllithium compounds (XXI and XXII), allylic and benzylic derivatives (XXIII-XXV) and alkenyl (XXVI-XXVIII) and alkynyl systems (XXK). 

The alkyllithium-initiated, anionic polymerization of vinyl and diene monomers can often be performed without the incursion of spontaneous termination or chain transfer reactions (1). The non-terminating nature of these reactions has provided methods for the synthesis of polymers with predictable molecular weights and narrow molecular weight distributions (2). In addition, these polymerizations generate polymer chains with stable, carbanionic chain ends which, in principle, can be converted into a diverse array of functional end groups using the rich and varied chemistry of organolithium compounds (3). 

In the group of van Koten, dilithiated precursors for the peripheral functionalization of carbosilane dendrimers were generated by deprotonation of compounds 32, 34a and 34b using f-butyllithium. The reaction was effected in n-pentane at room temperature, using the appropriate amount of the alkyllithium base. Dilithiated compounds 33, 35a and 35b were almost quantitatively obtained, the para positions of the aromatic ring systems... 

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