Potassium fluorenyl derivatives

The first example of group 4 complexes comprising an annulated derivative with a pendant NHC group was reported in 2006 by Downing and Danopoulos (Scheme 14.20) [14,68]. The titanium (III) complex 37 was obtained by reaction of the Ti(IV) bis-amido precursor TiQ2(NMc2)2 with the corresponding potassium fluorenyl NHC salt and proceeded with Ti(IV) to Ti(III) reduction. Dimethyl-functionalized N-heterocyclic carbene complexes of Ti(IV), Ti(III), and Zr(IV) were also prepared by salt metathesis reactions, and the bidentate coordination mode was confirmed by various X-ray diffraction studies (complexes 38) [69]. 

One case of n—5 —n delocalization was demonstrated by Stevenson et al. (2006). The potassinm anion-radical salt of l-(9-methyl-9H-fluoren-9-yl)-4-methyl benzyl is characterized by the delocalization of an nnpaired electron within the fluorenyl moiety only. Its ESR spectrnm completely coincides with the spectrnm of the potassium anion-radical salt of the 9,9-dimethyl fluorene anion-radical in THE However, the cesium anion-radical salt of the fluorenyl methylbenzyl derivative produces the ESR spectrum corresponding to the placement of this cation between the fluorenyl and methylbenzyl moiety. The conditions of n—s—n delocalization appear An unpaired electron spends its time within both fluorenyl and methylbenzyl fragments. The situation is explained in Scheme 3.54. 

The relatively strong Bronsted acidity of cyclopentadienes, indenes, and fluorenes, permits the formation of alkali metal compounds of the conjugate bases of these organic molecules by direct reaction with the metal. The effect of substituents on the rate of formation of 9-R-fiuorenyllithium compounds in THE solution and on the degree of ion pairing in solutions of these species has been determined.Potassium derivatives are commonly prepared by the reaction of the cyclopentadiene with potassium bis(trimethylsilyl)amide. Fluorenyl and indenyl compounds with the heavier alkali metals, Rb and Cs, are also prepared by reaction with the metal bis(trimethylsilyl)amide. The cyclopentadienyl ring in alkali metal compounds can also be coordinated to other metals. ... 

The fluorenyl-ferrocene based NLO-phores have were prepared by condensing 2-bromo-, 2,7-dibromofluorene, and 2-nitrofluorene with ferrocene carboxaldehyde to afford 2a, 3a, and 4, respectively, all in reasonable yidd. For 2-nitrofluorene the base used is potassium tert-butoxide and for the bromofluorenes, lithium diisopropylamide (LDA). Complexes 2a and 3a undergo clean halogen-metal exchange Ity treatment with n-BuLi in tetrahydrofiiran (THF) at -78 °C and are thm converted to their respective carboxaldehyde and tributylstannyl derivatives by... 

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