Substitution anionic

Searching for donoracceptor-substituted anions as well as related cations derived from cyclopentadiene, the azafulvalene 32 was synthesized by condensation of the potassium salt of the pushpull-substituted cyclopentadiene with 3-methyl-2-methylsulfanyl-benzothiazolium tetrafluoroborate (85AG996) (Scheme 9). 

The preparation of cyclopentadienes with up to four trimethylsilyl groups can be performed easily on a large scale starting with monomeric cyclopentadiene by repeated metalation with n-butyllithium and treating the resulting anion with chlorotrimethylsilane [84], Any complication caused by formation of regioisomers does not occur, since all trimethylsilyl-substituted cyclopentadienes are fluxional by virtue of proto- and silatropic shifts [85], Upon deprotonation with n-butyllithium the thermodynamically most favorable anion is formed selectively (Eqs. 20, 21). Thus, metalation of bis(trimethylsilyl)cyclopentadiene 74, which exists preferentially as the 5,5-isomer, selectively affords the 1,3-substituted anion 75. Similarly, tris(trimethylsilyl)cyclopentadiene 76, which is found to be mainly as the 2,5,5-isomer, affords the 1,2,4-substituted anion 77. 

In accordance with the electropositive nature of the bridgehead atoms, all di(pyridyl) substituted anions behave like amides with the electron density accumulated at the ring nitrogen atoms rather than carbanions, phosphides or arsenides. The divalent bridging atoms (N, P, As) in the related complexes should in principle be able to coordinate either one or even two further Lewis acidic metals to form heterobimetallic derivatives. According to the mesomeric structures, (Scheme 7), it can act as a 2e- or even a 4e-donor. However, theoretical calculations, supported by experiments, have shown that while in the amides (E = N) the amido nitrogen does function as... 

A family of tricoordinated persilyl substituted anions of the heavier group 14 elements (RaSOaE (R = alkyl E = Si, Ge, Sn) was synthesized in recent years. Sekiguchi and co-workers employed the straightforward one-electron rednction of the corresponding radicals (r-Bu2MeSi)aE 43-45 with metallic Li or K to form anionic derivatives (r-Bu2MeSi)aE ]VI (E = Si, Ge, Sn M = Li, K) 58 M (Scheme 2.55). ... 

The Peterson olefination reaction involves the addition of an a-silyl substituted anion to an aldehyde or a ketone followed by the elimination of silylcarbinol either under acidic (awP -elimination) or basic (syn-elimination) conditions to furnish olefins178. Thus, Peterson olefination, just like Wittig and related reactions, is a method for regioselective conversion of a carbonyl compound to an olefin. Dienes and polyenes can be generated when the Peterson reaction is conducted using either an ,/l-unsaturated carbonyl compound or unsaturated silyl derivatives as reaction partners (Table 20)179. 

The C-H bond in CBnHi2 and related anions can be metallated by butyllithium and then converted into C-substituted anions with aldehydes, alkyl halides, Ph3SiCl, and Ph2PCl.322-329 C-halogenated (F,Cl,Br, or I) derivatives are made from the C-copper derivative with (PhS02)2NF or the corresponding N-halosuccinimide.330 The l-Me-2,3>4,5,6,7,8,9,10,ll>12-Fu-CBii- anion is made from the reaction of the corresponding Fn anion with... 

Electroreductive coupling of ketones with silyl-substituted olefins promotes interesting reactions that are useful for organic synthesis. For example, coupKng of ketones with trimethylvinylsilanes affords /I-trimethylsilyl alcohols, which are easily transformed to the corresponding olefins (Scheme 40). This reaction is interesting from the synthetic point of view since vinylsilane behaves as the equivalent to a /I-trimethylsilyl group-substituted anion [77, 83]. 

Example Even a moderate voltage drop between nozzle and skimmer can cause the elimination of weakly bonded substituents such as CO2 in case of carbon dioxide-protected deprotonated A-heterocycles. In particular SnMes-substituted anions such as 2-(trismethylstannyl)pyrrole-A-carbamate exhibit variations in the [A-C02]7A ratio of up to a factor of 30 (Eig. 11.10). [76]... 

The field of R3C lithium organic structures is wide and we wiU concentrate on those with alkyl-, aryl- and silyl-substituted anions. Heteroatom-snbstitnted lithinm organics will just be mentioned briefly. 

The use of lithionaphthalene and lithio 8-methylnaphthalene as functionally substituted anionic initiators is very disappointing (21, 22). The deactivation of living polyanions onto a-bromonaphthalene or bromo-8-methylnaphthalene is another unsatisfactory approach due to metal halogen interconversion (eqs 9, 10) (23). 

Results and. Discussion. There are basically two approaches to the preparation of telechelic and semi-telechelic polymers by anionic procedures. One method involves terminating living anionic polymers with suitable electrophiles another technique utilizes functionally substituted anionic initiators. 

The second approach to the synthesis of tele-chelic polymers involves the use of functionally substituted anionic initiators. An example of a functional organolithium initiator is p-lithiophenoxide (40). Unfortunately, p-lithiophenoxide shows low solubility even in polar solvents like THF. It is difficult to control polymer molecular weights with such a heterogeneous initiator (41). Trepka (42) has improved the solubility of D-lithiophenoxide by adding alkyl groups to the ring, nevertheless, only moderate yields of the alkylated initiator have been reported. Hirshfield... 

Fig. 9. The sulfur-substituted anionic 7,8-dicarba-nido-undecaborate( 1 ) ligands.

There are a significant number of strict analogs of M0O4- that contain oxo-analog ligands in place of O while maintaining a tetrahedral or pseudotetrahedral structure about Mo. For example, the treatment of basic solutions of molybdate with sulfide leads successively to thio substituted anions according to Scheme 1. 

The series of para-substituted 2-ary 1-1,3-dithianyl carbanions shown in Table 6 and equation (41) are expected to differ in LUMO energy. The phenoxide-substituted anion (entry 1, Table 6 and equation 41) should have higher LUMO relative to, for example, the simple phenyl-substituted anion (entry 6) and gives a greater preponderance of meta substitution due to stronger orbital control. The smooth correlation of selectivity with reactivity for this series of closely related anions is consistent with a simple two-parameter analysis. Other regioselectivity results, such as those with o-alkylanilines (Table 2 and equation 30) and [(indole)Cr(CO)3] also have been analyzed in terms of orbital control and conformational effects.87,88,93... 

A side-on p,-Tq2 Tq2-peroxo dicopper(II) complex. A very important development in copper-dioxygen chemistry occurred in 1989 with the report by Kitajima et al. [10,108] that another Cu202 species could be prepared and structurally characterized by using copper complexes with a substituted anionic tris(pyrazolyl)borate ligand. This intensely purple compound, Cu[HB(3,5-iPr2pz)3] 2(02) (5), was prepared either by reaction of Cu[HB(3,5-iPr2pz)3] (4) with 02 or by careful addition of aqueous hydrogen peroxide to the p-dihydroxo... 

Scheme 3 briefly summarizes the syntheses of these substituted anions ... 

In cathodic substitution anions are generated from neutral substrates E at the cathode, which react with alkyl halogenides present in the electrolyte to form substitution products E-R according to the scheme (Eq. (105) ) ... 

Fused system" Substitution Anion Formula no. Color (crystals) Ar nax in nm (log e) Solvent Reference... 

In the reaction of 1-naphthoxide ions, a mixture of 2- and 4-aryl-, along with 2,4-diaryl-l-naphthol, is formed. However, substitution occurs only at C4 with the 2-Me-substituted anion (50-70% yields) [1[. On the other hand, 2-naphthoxide ions react with ArX to give substitution only at Cj of the naphthalene ring [32, 33]. The reactivity of the 2-naphthoxide ions allows the synthesis of naphthylpyridines, naphthylquinolines, and naphthylisoquinolines via their coupling reactions with the corresponding halo arenes, in good to excellent yields (50-95%) [33], The photostimulated reaction between 2-naphthoxide ions and l-iodo-2-methoxy-naphthalene was explored in liquid ammonia, as a novel approach to the synthesis of [1,1 ] binaphthalenyl-2,2 -diol (BINOL) derivatives (Scheme 10.23). This procedure has also been applied to the synthesis of BINOL in moderate yield (40%), which represents the first report of an SRN1 reaction in water [34]. 

In polar solvents lithium silylamides dissolve as coordinated monomers, but by using 12-crown-4 a separation of the lithium cation and the nitrogen-substituted anion can be obtained. In nonpolar solvents the lithium silylamides dissolve as dimers, trimers or oligomers. 

These problems are considered within the framework of the cluster model. During simulation the impurity is placed in the substituting anion site. 

In all of the pentadienyl structures determined thus far, some outside perturbations are always present, i.e., there are no structural data thus far pertaining to free, yet electronically simple, pentadienyl anions. There are several polycyano-substituted anions known and despite the strong electronic perturbations brought about by the cyano groups, these species are still likely to be reasonably representative, in a conformational sense, of other... 

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