Lithium phenolates

Small amounts of lithium phenolate or dilithium-2,2 biphenyldiolate, whose anodic decomposition starts at about 3.2 V versus Li and thus before anodic decomposition of the borates begins, prevent the anodic decomposition of benzenediolatoborate anions in PC. The behavior of the solution is then determined by the additive. 

Transesterification was not found with ethyl carbonates or lithium phenolates. 

In a later study, substituted lithium phenolates were investigated in different solvents . Here, the lithium phenolates were shown to exist as monomers, dimers and tetramers, depending on the solvent and substitution pattern. It was found that the different aggregates have different QSC ranges, where the QSC is smaller for higher aggregates. It was also noted that the QSC value depends to some extent on the solvent, especially on the type of coordinating atom, i.e. O V5. N in ethers and amines, respectively. 

When determining QSC values of dimeric lithium phenolates in solution, the value has to be corrected for anisotropic rotational diffusion as the complexes have an oblate, non-spherical shape . The Li2A2S2 complex of 2,6-di-f-butylphenolate has a Li QSC value of ca 280 kHz in a number of different solvents. The 2,6-dimethylphenolate system is present as an Li2A2S4 complex in THF and apparently as an L12A2S2 complex in DEE. These complexes have QSC values of 170 and 270 kHz in the two solvents, respectively. 

The QSC value of the lithium phenolate tetramer in THF solution is between 40 and 46 kHz at —67 and +30 °C, respectively. For other tetramers the QSC ranges from 35 to 57 kHz, depending on substitution pattern and solvent. It was observed that the magnitude of the observed QSC values correlates with the Lewis basicity of the solvent. 

Lithium phenolate is present as a mixture of tetramers and hexamers in 1,3-dioxolane solution. Crystallization of lithium phenolate from THF yields an LigAgSg aggregate, as determined by X-ray crystallography, although the predominant aggregate in solution is the tetramer. In the solid state the measured x value is 67 kHz with a r] value of 0.77, which translates to a QSC value of 73 kHz. This agrees with the QSC value of 72 kHz measured for the hexamer in dioxolane solution. 

The following n/m values were obtained for the degrees of association n at molal concentration m, measured in ammonia by cryoscopy. Lithium phenolate (255a, 2.21 0.20/0.1530) is nearly dimeric in ammonia, while in pyridine and dioxolane it is tetrameric, as shown by vapor pressure and NMR measurements. The 2,6-dimethyl homologue (255b)... 

Many other lithium phenolates can be similarly oxidized. Cycloheptatriene and 14c, suspended in ether, give the tropylium-tetrafluoroborate and the phenol of 14c. 

It is only fair when reviewing syntheses to mention unsuccessful reactions so as to outline any shortcomings of a particular reagent, and this has been done throughout this review. Sah et al. have recently reported that reaction of the metallated lithium phenolate (31) with either nitrobenzene or bis(trimethyl-silyl) peroxide gave only starting material, while reaction with trimethyl borate followed by oxidation furnished a complex mixture. 

Isopropylation of toluene by isopropyl halo- and alkyl-sulfonates (equation 54) has been performed by Olah et al. A variety of cattdysts, such as AlCb, AlCb-MeNOa and Nafion-H were employed, and the isomer distribution (o, m, p) in the product was determined. Sartori et al have recently reported an unusual Friedel-Crafts alkylation of lithium phenolates with ethyl pyruvate in the presence of AlCb to afford a-(2-hydroxyphenyl)ethyl lactates (22), which are the precursors of 3-methyl-2,3-dihydrobenzo-furan-3-ols (23 Scheme 6). 

Although phenols can be lithiated at ortho position, the yields are poor. One of the reasons is that lithium phenolates, quite often, precipitate out of the reaction medium. The other one, which is more important, is that, since the lithiation in these cases would actually occur on the phenolate ion and since the ortho hydrogen in the phenolate ion is considerably less acidic, it is not replaced by lithium in any significant yield. 

Finally, hydroxyaryldihydrosilanols (546) are obtainable from lithiated lithium phenolate (545) and dichlorosilane (equation 270)296. 

The generation of organolithium reagents by o-lithiation of alkyl phenyl ethers, dialkylaminobenzenes, and benzyldialkylamines followed by their reaction with halogenophosphines has afforded a range of new substituted arylphosphines, e.g., (10) and the chiral phosphine (11). Directed-lithiation of 1-dimethyl-aminonaphthalene, followed by treatment with chlorodiphenylphosphine, affords a more direct route to the phosphine (4). The diphosphines (12) are formed in the reactions of chlorodiethylphosphine with u-lithio lithium phenolate... 

In chloroform, no phenolate anion of 5 was detected even in the presence of excess piperidine as a base. When crystalline lithium salts were added to this solution, a dramatic color change from yellow to violet took place rapidly, except for nitrate, fluoride, and sulfate. This phenomenon indicates evidently the formation of the lithium phenolate. On the other hand, no tendency of the interaction was observed with any of the other 58 metal salts listed in Fig. 1. 

Li Relaxation times have been used to study complex formation with nitroxides in the aqueous phase, and the interaction of Li with Mn. Dynamic NMR spectroscopy has been used to study equihbria of chelated lithium phenolates. The formation of a stable betaine Hthium salt adduct has... 

The catalytic cycle, as proposed by the authors, is also displayed in Scheme 5.120. The reaction of Uthium enolate 478 with the chiral proton source 476 leads to nonracemic ketone 479 and the lithium salt 480. An irreversible proton transfer then occurs from the achiral proton source ArOH to the lithiated imide. Thus, the chiral proton source 476 is regenerated under release of lithium phenolate, and the catalytic cycle closes. 

---