Carbanions fluorenyl

The electron transfer reaction from fluorenyl carbanions adjacent to sulfoxide or sulfone (9) to fluorenone (FIO) has been studied by means of flash photolysis37. For n — 1 as well as n — 2 the transient F10T, M + (contact ion pair) appeared in THF and F10T(free ion)... 

Bordwell and coworkers63 87 have studied the reaction of 9-fluorenyl carbanions (9-RFP) with a series of electron acceptors and in particular a-halosulfones and sulfoxides, in dimethyl sulfoxide solution. The overall reaction is characterized by the formation of the 9,9 -bis-fluorenyl derivative and the reduction of the halogenated acceptor. A family of 9-substituted fluorenyl carbanions covering a basicity range of 9.1 pKa units was used and... 

TABLE 8. Second-order rate constants for reactions of 9-R-fluorenyl carbanions with a-halosulfones and sulfoxides in Me2SO solution at 25 °c63a-87... 

Fluorenyl carbanions 1055, 1065, 1066 Fluoroalkylsulphinyl groups, sigma values of 507-509... 

Fluorenyl carbanions, as initiators, 14 258 (+) -1 -(9-Fluorenyl)ethylchloroformate, chiral derivatizing reagent, 6 76t 9-Fluorenylmethyl chloroformate, molecular formula, 6 29It Fluorescamine, chemiluminescence reagent, 5 850... 

Wong, Konizer, and Smid (42) find by a proton nuclear magnetic resonance technique that in the solvent tetrahydrofuran, dicyclohexyl-18-crown-6 binds the ion pair Na+, F (F = fluorenyl carbanion) more strongly than it does the K+, F ion pair. Although no K values are given they estimate log K to be larger than 10 for the reaction Na+, F + L = Na+, F L (L = dicyclohexyl-18-crown-6 or dimethyldibenzo-18-crown-... 

Background and Possible Intermediates. Accepting the premise of carbanion formation in the basic media, the mode of reaction with molecular oxygen can now be considered. Sprinzak (8) reported that the autoxidation of fluorene in basic media proceeds by direct reaction of the fluorenyl carbanion with oxygen to form initially the hydroperoxide, which decomposes to yield 9-fluorenone, as depicted below. 

Addition of a second crown produces the loose ion pair A, Cr,K, Cr. However, the complexation constant for adding the second crown is 1800 M 1 for the fluorenyl carbanion and only 200 M 1 for the picrate salt. The lower value for picrate may in part be due to less charge delocalization, e.g., the free ion dissociation constant for potassium fluorenyl in TEF is 1.6 x 10 7M (18) as compared to 9.2 x 10 M for potassium picrate (17). The two N02 substituents close to the 0 bond in picrate may also hinder the enlargement of this ionic bond and the insertion of a crown ether molecule because of electronic or sterlc effects. 

Intramolecular triple Ion formation was studied by Collins and Smld using cesium bolaform salts of fluorenyl carbanions (29). The cesium salts of a, oe-bis (9-fluorenyl) polymethylenes (VI, n 2,3,4 and 6), when dissolved In THF,... 

Fluorenyl Carbanions. Salts of fiuorene (pAa = 22.6) (6) are more hindered and less reactive than many other organometallic initiators. These carbanions can be readily formed by reaction with alkali metal derivatives as shown in equation 19 for 9-methylfiuorene (99). Carbanion salts of 9-methylfiuorene are preferable to fiuorene, since the latter generate chain ends which retain reactive, acidic fluorenyl hydrogens which can participate in chain-transfer reactions (100,101). Fluorenyl salts are useful initiators for the polymerization of alkyl methacrylates, epoxide, and thiirane monomers. 

These rearrangement reactions are interpretable in terms of [2.3] sigmatropic shifts of the intermediate ylides. A number of such rearrangements of open-chain systems have been described, involving sulfonium ylides [43] [44] [45], ammonium ylides [46] [57], anions in a-position to oxygen (Wittig rearrangement) [48] [49], and fluorenyl carbanions [50]. 

The dication (35) is reduced to the cation radical (53) in the reaction with fluorenyllithium, the same was observed with ferrocene <90TL6375>, which indicates that the fluorenyl carbanion acts as a one-electron donor. 

CNDO/INDO estimates of the net atomic charge distribution for the benzyl and fluorenyl carbanions are given in Figures 16 and 17 (25). The electrostatic potential energy distribution at 2.0 A above the mean plane for these distributions of point charges are shown in Figures 18 and 19. The electrostatic model predicts that the lithium atom would be located over the potential energy minima in the two carbanions— that is, on a normal to the fluorenyl plane that intersects the plane just inside the 9 position, and a normal to the mean benzylic plane that intersects the plane about 0.4 A for C(7) on the C(l)—C(7) bond. In fact, the observed position of the lithium atom is about 1.5 A from the pre-... 

Figure 17. CNDO II charge distribution for isolated fluorenyl carbanion (83)...

Figure 18. Potential energy surface at 2.0 A above the plane of the fluorenyl carbanion calculated from the CNDO II atomic charge distribution of Figure 17. Contour lines are drawn at levels of 0.02 eV (83).

To investigate this interaction it is necessary to examine the symmetry of the molecular orbitals that contain substantial contributions from these atomic orbitals. The bond lengths in the carbanions in the structures examined are close to those expected from simple Hiickel bond orders for the isolated carbanion. As noted, the carbanion 7r-orbital contribution to the HOMO of the complex is probably very similar to the HOMO of the free carbanions. The symmetries of the HOMO s of the free benzyl and fluorenyl carbanions and the orientation of the N—Li—N groups with respect to the carbanions are shown in Figures 25 and 26. The N—Li—N group is positioned to permit the appropriate symmetry overlap of the lithium p orbital, which is parallel to the carbanion plane and the appropriate pz orbitals of carbon atoms in the plane. 

The proton chemical shifts for the fluorenyl carbanion (92, 129) are given in Table XII. Both FLi(DME)n in DME and FLi(THF)n in THF exist in solution as solvent-separated ion pairs (130, 131). This is consistent with the observation that the fluorenyl proton chemical shifts are nearly identical in these solvents. The 1 1 dimethoxyethane (DME) adduct in benzene probably has the same structural configuration as the 2 1 quinuclidine adduct (Figure 20) although a rapid equilibrium will... 

Salts of fluorenyl carbanions or of derivatives of diphenyl-methyl carbanions do not initiate polymerisation of styrene but are efficient and clean initiatiors of methyl methacrylate polymerisation. 

The kinetics of the polymerization of styrene initiated by cumyl caesium in dimethoxyethane have been re-investigated and it was concluded that loose ion pairs are kinetically significant. The initiation of the polymerization of ethylene oxide initiated by iluorenyl sodium is not a straigditforward process. When a molecule of ethylene oxide is added to fluorenyl carbanion, the hydrogen atom on the 9-position of the adduct is susceptible to removal by a second fluorenyl... 

Alkylation of (bromomethyl)chlorodimethylsilane by the acetylide anion followed by addition of the thioacetate anion opened a new access to a silyl tethered yne-vinylsulflde precursor that found use in new radical cascades. Unsymmetrical ansa-fluorenyl containing ligands incorporating a CFl2-SiMe2 bridge have been described and result from a dialkylation with fluorenyl carbanions. ... 

D. J. Cram, W. T. Ford, and L. Gosser (1968), Electrophilic substitution and saturated carbon. XXXVIII. Survey of substituent effects on stereochemical fate of fluorenyl carbanions. J. Amer. Chem. Soc. 90, 2598-2606. 

In the cartoon below the resonance structure on the right sacrifices one "cyclopentadienyl anion" to generate the fluorenyl carbanion hence, there should be little net loss in aromatidty. This "no net loss of aromaticity" has recently been exploited by Marder and coworkers in designing NLO-phores with large h3q>erpolarizabilities. ... 

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