Dilithium naphthalene

The lithium naphthalene was prepared in THF from lithium metal and a 25 mole % excess of naphthalene to minimize formation of the dilithium naphthalene dianion (18,19). A sample of a,w-dilithiumpolystyrene was quenched with methanol for molecular weight characterization (see Table II). 

The dynamic behavior of various solid organolithium complexes with TMEDA was investigated by variable-temperature and CP/MAS and Li MAS NMR spectroscopies. Detailed analysis of the spectra of the complexes led to proposals of various dynamic processes, such as inversion of the five-membered TMEDA-Li rings and complete rotation of the TMEDA ligands in their complex with the PhLi dimer (81), fast rotation of the ligands in the complex with cyclopentadienyllithium (82) and 180° ring flips in the complex with dilithium naphthalene (83) °. The significance of the structure of lithium naphthalene, dilithium naphthalene and their TMEDA solvation coiMlexes, in the function of naphthalene as catalyst for lithiation reactions, was discussed . ... 

Aromatic radical anions, such as lithium naphthalene or sodium naphthalene, are efficient difunctional initiators (eqs. 6,7) (3,20,64). However, the necessity of using polar solvents for their formation and use limits their utility for diene polymerization, since the unique abiUty of lithium to provide high 1,4-polydiene microstmcture is lost in polar media (1,33,34,57,63,64). Consequentiy, a significant research challenge has been to discover a hydrocarbon-soluble dilithium initiator which would initiate the polymerization of styrene and diene monomers to form monomodal a, CO-dianionic polymers at rates which are faster or comparable to the rates of polymerization, ie, to form narrow molecular weight distribution polymers (61,65,66). 

Chiral modification of diorganomagnesium compounds with the dilithium salt oi (S)-l,l -bi-naphthalene-2,2 -diol gave reagents with the empirical formula 30. Good to excellent enantiose-lectivities were observed in addition reactions of aliphatic and aromatic reagents to aromatic aldehydes30,31, however, the selectivities were not satisfactory with allylic, vinylic and acetylenic reagents. 

This approach frequently leads to the most active metals as the relatively short reduction times at low temperatures leads to reduced sintering of the metal particles and hence higher reactivity. Fujita, et aL(62) have recently shown that lithium naphthalide in tqluepe can be prepared by sonicating lithium, naphthalene, and N, N, N, N-tetramethylethylene-diamine (TMEDA) in toluene. This allows reductions of metal salts in hydrocarbon solvents. This proved to be especially beneficial with cadmium(49). An extension of this approach is to use the solid dilithium salt of the dianion of naphthalene. Use of this reducing agent in a hydrocarbon solvent is essential in the preparation of highly reactive uranium(54). This will be discussed in detail below. 

Treatment of substituted phthalans 1172 with lithium metal in the presence of catalytic quantities of naphthalene leads to reductive cleavage of the arylmethyl carbon-oxygen bond to form a stable dilithium compound 1173, which upon trapping with carbon dioxide furnishes isochroman-3-ones 1174 (Scheme 289) <1996JOC4913>. 

A substantial body of work also exists on the preparation of so-called diinitiators, species that result in the simultaneous growth of a polymer chain from both ends. There are two basic approaches to this. One is to use the metal in the presence of a conjugated aromatic species such as naphthalene to generate a radical anion capable of transferring an electron to the monomer. Under suitable conditions, the resulting monomer radical anions rapidly dimerize to form a dilithium species that goes on to add monomer in a living fashion... 

Polycyclic aromatics that have low reduction potentials are reduced by Li to give dilithium dianions. Among the more difficult to reduce members of this class that can react with Li are biphenyl and naphthalene " . Other substrates that are reduced to dilithium dianions are shown in Fig. 2. In addition, several benzo-, dibenzo-and tribenzoanthracenes and larger polycyclic aromatic compounds are reduced to dilithium dianions . 

So far only derivatives with two (83) and four (84) A-phenyl groups have been described using l,8-bis(phenylamino)naphthalene (82) as their precursor65. In the preparation of 83 it was methylated through its dilithium salt, whereas in the case of 84 it was successively arylated with dehydrobenzene generated from o-bromofluorobenzene and Mg, and then with iodobenzene according to the Ullmann reaction conditions (Scheme 6). 

Pathway 2 is generally chosen in the academic literature. In addition to sodium naphthalene, dilithium compounds are often used [146-150]. The following terminators are described for the third pathway silicon tetrachloride and tintetrachloride dicarbonic acid ester [151], divinylbenzene [152], and polymers formed from divinylbenzene [153] containing numerous vinyl groups yielding star-shaped polymers. Block copolymers of styrene and butadiene or isoprene are synthesized commercially in large ranges. 

C2aH5oLi2N, Ni, (Dilithium trans-1,5,9-cyclododecatriene)nickel bis(N,N,N ,N -tetramethylethylene-diamine), 45B, 928 C2 5H1gBr2Fe03, 1-Bromo-2-(bromomethyl)naphthalene enneacarbonyldi-iron reaction product, 40B, 799 C2 5HieFe03, Iron 7r-complex, 35B, 582... 

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