Fluorenide anion

E. Reduction of Halomethyl Phenyl Sulfones and Chloromethyl Phenyl Sulfoxide by Fluorenide Anions... 

Another example of path a of Scheme 1.15 is the anion-radical derived from fluorene. It undergoes a first-order decay to give the conjugate base (the fluorenide anion) and a hydrogen atom (Casson and Tabner 1969) according to Scheme 1.16. 

Just as the one electron reduction of a neutral molecule produces an anion radical, the one electron reduction of an organic anion can yield a dianion radical, assuming that the LUMO of the anion is not too high in energy. Two anions familiar in organic chemistry are the dibenzoylmethide (an enolate of a 6-diketone) [112] and fluorenide anions [113] (Scheme 68). 

Figure 3.10 Correlation of A//het of carbon-carbon bonds with AGet for the trityl cation reacting with substituted fluorenide anions. Energies are in kcal/mol. After Reference 81.

A silaaromatic anion analogous to the fluorenide anion has been prepared recently (equation 146) and found to be stable in solution313. It was characterized by NMR and UV spectroscopy and by trapping reactions with electrophiles. An attempt to prepare a monocyclic derivative of the parent silacyclopentadienide anion in an analogous fashion was not successful313. 

The autoxidations of certain carbanions, such as fluorenide anion, have been demonstrated to proceed via a chain mechanism involving electron transfer (Russell, 1953 Russell et al., 1965, 1968) as shown in Scheme 8. In MejSO... 

The crystals obtained are suitable for X-ray structure analysis V crystallizes in space group P-1 the triclinic unit cell contains four separated ion pairs. As to be seen in the ORTEP plot (Fig. 6.2), the tetrabenzo[a,c,g,i]fluorenide anion is not planar but exhibits a slightly helical distortion due to the steric repulsion of the aromatic ring protons. 

Indene and fluorene (benzo- and dibenzo-cyclopentadiene) also have acidic methylene groups and can be converted into metal indenides and fluorenides respectively. A tetramethylammonium salt of fluorene has also been prepared [47]. It is an orange compound which remains unchanged when kept under nitrogen, and decomposes to give fluorene and 9-methylfluorene when heated in ether. Annelation reduces the acidity of the cyclopentadiene ring, however [48]. This infers reduced stabilisation of the cyclopentadienide anion relative to the... 

The reduced reactivity here of o-methyl thiophenoxide may be ascribed to steric factors. In these and other examples, relatively good correlations with the Hammett and Brpnsted equations may be observed, and it has been noted [57] that when nucleophilic attack is rate limiting, the Brpnsted value is usually in the range 0.5-0.7. Studies of the substitution reactions of halogenonitrobenzenes with nucleophiles, including substituted fluorenide carbanions, such as (12), and phenothiazine nitranions (13) in DMSO solvent [53] indicated that for anions of the same basicity, the nucleophilic reactivity was in the order S >>C >0 >N. The high reactivity of thianions is most likely due to their high polarizability. 

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