Phenyl anions

Rossi and Bunnett64 studied the chemical reductive cleavage of diphenyl sulfoxide, diphenyl sulfone and methyl phenyl sulfone under the action of potassium metal in liquid ammonia in the presence of acetone. The enolate ion is used to trap phenyl radicals formed eventually during the process, in order to determine whether one or two electrons are required for the mechanism of cleavage (Scheme 7). In all the runs, phenyl anion is... 

Scheme 3.37 describes gas-phase generation of m-benzyne anion (the distonic anion-biradical) from m-bis(trimethylsilyl) benzene (Wenthold et al. 1994, 1996 Wenthold and Squires 1998). The same anion-biradical is formed from isophthalic acid under the same conditions (Reed et al. 2000). Particularly, the reaction of m-bis(trimethylsilyl) benzene with fluoride ion, followed by treatment of the formed trimethylsilyl phenyl anion with fluorine in helium, produces the anion-biradical mentioned. The latter is transformed into the corresponding nitro benzoate anion through the addition of CO2 and NO2 (Scheme 3.37). 

Pinson and Saveant 1978, Swartz and Stenzel 1984). On electrochemical initiation (Hg cathode), 4-bromobenzophenone gives rise to 4-(phenylthio)benzophenone in the 80% yield, whereas bromoben-zene yields diphenyldisulfide with the yield of only 10% and unsubstituted benzene with the yield of more than 95%. In the bromobenzene case, this means that the substitution is a minor reaction, whereas the main ronte is ordinary debromination. According to Swartz and Stenzel (1984), the substrate anion-radicals are initially formed in the preelectrode space. Stability of these anion-radicals are different. The less stable anion-radicals of bromobenzene do not have enough time to go into the catholyte pool. They give rise to the phenyl radicals in the vicinity of the cathode. The phenyl radicals are instantly reduced into the phenyl anions. They tear protons from the solvent and yield benzene. 

Swartz and Stenzel (1984) proposed an approach to widen the applicability of the cathode initiation of the nucleophilic substitution, by using a catalyst to facilitate one-electron transfer. Thus, in the presence of PhCN, the cathode-initiated reaction between PhBr and Bu4NSPh leads to diphe-nydisulfide in such a manner that the yield increases from 10 to 70%. Benzonitrile captures an electron and diffuses into the pool where it meets bromobenzene. The latter is converted into the anion-radical. The next reaction consists of the generation of the phenyl radical, with the elimination of the bromide ion. Since generation of the phenyl radical takes place far from the electrode, this radical is attacked with the anion of thiophenol faster than it is reduced to the phenyl anion. As a result, instead of debromination, substitution develops in its chain variant. In other words, the problem is to choose a catalyst such that it would be reduced more easily than a substrate. Of course, the catalyst anion-radical should not decay spontaneously in a solution. 

The anion then reacts with CO2 to form PhC02 (reaction 19). In this case, the role of the Pd complex is simply to reduce the overpotential associated with the reduction of bromobenzene to form the phenyl anion. These two different mechanisms for these closely related complexes indicate that it is difficult to predict precise reaction pathways. However, both complexes effectively carboxy-late PhBr. 

Electrochemical studies in nonaqueous media [59] indicate that phenyl-r-butyl nitrone is not electroactive between +1.5 and -2.4 V vs. SCE. Studies of the reduction of phenyldiazonium salts in the presence of the nitrone gave EPR spectra of the phenyl adduct. However, even here, a two-electron reduction may give the phenyl anion, which can add to the nitrone to give phenyl-f-butyl hydroxylamine, which can be reoxidized to the nitroxide. Chemical tests were used to show that the phenyl radical, rather than the anion, was produced. 

Sieburth and Somers82 studied the product ratio of metallation of t-butyl-lV-phenyhnethyl-V-trimethylsilylmethyl carbamate 68 (equation 26). This ratio reflects the relative abilities of an a-phenyl and a-trimethylsilyl group to stabilize an adjacent carbanion. It was found that metallation a to silicon (70) was slightly favoured kinetically, but at equilibrium the a-phenyl anion 69 was strongly favoured. 

An interesting compound is (N-phenyloctaethylporphyrinato) phenyl-ruthenium(II) (entry 10) in which an agostic hydrogen of the N-phenyl group completes the heavily distored octahedral coordination sphere of the Ru(II) ion. The Ru ion protrudes by 14 pm towards the axial phenyl anion. 

Delocalization of the negative charge by resonance is not possible in the anion of benzene. The pair of unshared electrons in phenyl anion is in an sp2 hybrid orbital that does not interact with the 7r system. 

The reaction of phenyllithium with [(Tj5-C5H5)Mn(CO)2N2] is unique (305) [Eq. (27)]. It has been proposed that the phenyl anion attacks the a-nitrogen atom, and subsequent protonation of the /3-nitrogen gives the diazene product. 

The SASAPOS protocol has been applied to a small variety of pentafluoro benzene derivatives C6F5-E [E = -C(0)H, —C(N—Ph) H, — PCI2/—P(L+)2, —H] yielding the ion clusters C6(L+)s-E (F3CS03-)5.15 The reaction conditions required to observe a heteropolar C-C or C-P disconnection, with a highly stabilized pentakisonio-substituted phenyl anion (10) as the key intermediate have been specified. 

Another application of hyperbranched polymers as supports for catalysts is their use as backbones for the covalent attachment of organometallic fragments. NCN-pincer complexes (NCN-pincer = 2,6-bis[(dimethylamino)-methyl] phenyl anion) are attractive building blocks for catalytic reactions [20,21], Covalent introduction of the transition-metal complexes can also be of interest for visualization and imaging of dendritic polymers by transmission electron microscopy (TEM). 

Phenylcalcium iodide and pyridine give 2-phenylpyridine and either 2,5- (119) or 2,6-diphenylpyridine, depending on conditions.264 Scheme V was tentatively proposed to account for the results. Phenylation of 2-phenylpyridine by phenylcalcium iodide gave only the 2,6-isomer. As was appreciated by the authors,264 the replacement of a hydride ion at C-5 by a phenyl anion is a controversial stage and seems, at first sight, mechanistically improbable. If the nitrogen atom is assumed to form a relatively stable complex with the calcium atom,... 

This is a direct SN2 displacement of a bromide anion by a phenyl anion. Please note that the negative charge of the phenyl anion is accompanied by a magnesium bromide complex. This class of organic salt is known as a Grignard reagent and is characterized by the presence of magnesium and a halide such as chloride, bromide, or iodide. 

Tetraphenyl tellurium provided a phenyl anion in reactions with triphenyl boron, dichloromethane, chloroform, and benzaldehyde2. 

Fig. 2 (a) shows the absorption spectra observed in CMS films following pulse radiolysis. There is no evidence of formation of excimer, triplet, or phenyl anion as observed in pulse radiolysis of polystyrene film (14) suggesting that these transient species or their precursors are scavenged by the chloromethyl group. Instead, absorption spectra with double peaks around 320 nm due to a substituted benzyl type polymer radical and the complex of phenyl rings and chlorine atoms are observed. 

The observed side-reactions can be also due to the presence of the phenyl anion as a by-product in the synthesis of the phospholyl anions De Lauzon has shown that a stoichiometric amount of AICI3 could selectively destroy phenyllithium without reacting with phospholyllithium (unpublished results)... 

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