Fluorenyl lithium

CnHpbo]2- 2[Li(THF)4]+, which is obtained by the reaction of fluorenyl lithium... 

Figure 1. Electrochemical oxidation of fluorenyl lithium (DMSO, LiClOk (0.1 Mj, room temperature, scan rate 50 mV s 1)...

Glusker et al. (16, 17) found a pseudo-termination reaction in polymerization of methyl methacrylate with fluorenyl lithium at — 60° in toluene. The initiation reaction was found to proceed via a Michael... 

The interaction of indenyl- and fluorenyl-lithium and phenyl-sub-stituted plumbic chlorides produces the corresponding phenyl lead derivatives ( ), but attempts to prepare difluorenyl lead and diindenyl lead were not successful. 

The silanorbomenes 1, 2, and 3 can be synthesized according to the literature [1, 2]. Hydrogen chloride cleavage of 3 leads to the silicon chlorinated precursor of 13, which is obtained by a Grignard reaction with naphthyl magnesium bromide in high yield (86 %). Similarly, 15 is available from HCl cleavage of 1 and reaction of the latter with fluorenyl lithium. The silicon-chlorinated silacyclobutanes 7, 8, and 11 are synthesized by [2+2]-cycloaddition of dichloroneopentylsilene with isoprene and dimethylbutadiene, respectively [3],... 

Perhaps more important, however, are the initial studies of Van Beylen and his collaborators on the dynamics of dissociation of carboanionic species studied by the technique of electric field relaxation. With fluorenyl lithium in pure diethyl ether and added traces of tetrahydrofuran the overall rate constant for dissociation displays a negative activation energy, strongly suggesting that dissociation does not occur directly from contact on tight ion pairs, which are present in vast excess, but rather via a small number of solvent-separated species. This is important because under identical conditions loose ion pairs cannot be detected spectroscopically. Similarly, with polystyryl caesium in tetrahydrofuran the results point to the presence of a small concentration of loose ion pairs and seems to support the hypothesis of Lohr and Schulz. 

Commercial products are often unsatisfactory in kinetic studies. Preparation of some commonly used initiators is given elsewhere141. Benzyl sodium is prepared from mercury dibenzyl and metallic sodium123 a similar technique yields barium and strontium salts. Fluorenyl lithium, sodium etc., are conveniently prepared from fluorene and a suitable organo-metallic compound, e.g. 

The classification into the different ion types can be readily followed in the case of fluorenyl lithium. III, or the corresponding fluorenyl sodium. At room temperature, fluorenyl sodium in tetrahydrofuran has only one uv band at 355 nm at temperature below —50° C, there is only one uv band also, but at 373 nm. Between these two temperatures, both bands occur. The relative band heights at each temperature are not influenced by diluting the solution or by addition of NaB(C6Hs)4, which dissociates readily in THF. Dilution should shift the equilibrium, solvated ion pairs = free ions, in the direction of free... 

Therefore the two bands must arise from two different kinds of ion pairs. The equilibrium is set up in the presence of a large excess of solvent very little solvent is required to form solvated ion pairs and the equilibrium is practically independent of the fluorenyl sodium concentration. Since solvation is favored at lower temperatures, the band at 373 nm must result from solvated ion pairs and the band at 355 nm must be due to contact ion pairs. The spectrum of fluorenyl lithium is also only slightly affected by change in solvent (Figure 18-1). Thus, the fluorenyl anion can not be solvated, but the nonabsorbing lithium gegenion is. 

Figure 18.1. Absorbance (previously extinction or optical density) of fluorenyl lithium at 25""C in 3,4-dihydropyran ( ), 3-methyl tetrahydrofuran (---), 2,5-dihydrofuran (—) and hexamethyl cyclotriphos-phazene (—) (after J. Smid).

The ionization of a carbon-metal bond depends on the polarity of solvent as well as on the electronegativity of the metal. If ionization is favored by using a highly polar solvent, the metal ion is prevented from exerting stereocontrol over monomer addition. For example, in a weakly polar solvent such as toluene, 9-fluorenyl-lithium (XLI) converts methyl methacrylate to crystalline isotac-... 

An overcrowded fulvalene derivative 211 based on a truxene core was also prepared by treatment of truxenetrione 212 with fluorenyl lithium and dehydration of the formed alcohol using thionyl chloride (Scheme 6.56) [128]. 

MesSiCl gives substitution product 3.638 and with fluorenyl-lithium, the adduct 3.640 is produced. The successive introduction of substituents can be achieved by a sequence of reactions with electrophiles and nucleophiles. Thus electrophile Ei gives fulvene 3.642, followed by attack by nucleophile Nu to afford adduct 3.643, and again by electrophile Ei to give product 3.644. These reactions can lead to the preparation of a unique series of homogeneous catalysts for olefin polymerization for it is known that the indenyl complexes are often better catalysts for olefin polymerization than cyclopentadienyl analogs (Scheme 3.58) [308,315]. 

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