Biphenyl cation

Figure 13. Orbital energy-level scheme for the biphenyl anion radical (A) and biphenyl cation radical (C) based on the SCF calculations (59) by the Pople and Longuet-Higgins method. Pairing of MO s is indicated. Thick lines with arrows represent the five lowest transition energies. All entries are given in eV.

Cation-radicals, stabilized in zeolites, are excellent one-electron oxidizers for alkenes. In this bimolecular reaction, only those oxidizable alkenes can give rise to cation-radicals, which are able to penetrate into the zeolite channels. From two dienes, 2,4-hexadiene and cyclooctadiene, only the linear one (with the cylindrical width of 0.44 nm) can reach the biphenyl cation-radical or encounter it in the channel (if the cation-radical migrates from its site toward the donor). The eight-membered ring is too large to penetrate into the Na-ZSM-5 channels. The cyclooctadiene can be confined if the cylindrical width is 0.61 nm, however the width of the channels in Na-ZSM-5 is only 0.55 nm. No cyclooctadiene reaction with the confined biphenyl cation-radical was detected despite the fact that, in solution, one-electron exchange between cyclooctadiene and (biphenyl) proceeds readily (Morkin et al. 2003). 

Hummel and Luthjens [398] formed electron—cation pairs in cyclohexane by pulse radiolysis. With biphenyl added to the solvent, biphenyl cations and anions were formed rapidly on radiolysis as deduced from the optical spectra of the solutions. The optical absorption of these species decreased approximately as t 1/2 during the 500 ns or so after an 11ns pulse of electrons. The much lower mobility of the molecular biphenyl anion (or cation) than the solvated electron, es, (solvent or cation) increases the timescale over which ion recombination occurs. Reaction of the solvated electron with biphenyl (present in a large excess over the ions) produces a biphenyl anion near to the site of the solvated electron localisation. The biphenyl anion can recombine with the solvent cation or a biphenyl cation. From the relative rates of ion-pair reactions (electron-cation, electron—biphenyl cation, cation—biphenyl anion etc.), Hummel and Luthjens deduced that the cation (or hole) in cyclohexane was more mobile than the solvated electron (cf. Sect. 2.2 [352, 353]). 

REACTIONS OF BUTYL CHLORIDE AND BIPHENYL CATION RADICALS WITH... 

At very long separations, for example, transfer to the biphenyl cation radical over 34 A in 1C)2 s, electronic interactions seemed to be propagated by ion states of the solvent (25), although quantum mechanical tunnelling may be important when diffusion is blocked by steric factors or by immobilization of the reagents (26). Perhaps most convincing are Miller and Closs demonstration of intramolecular electron transfer between donor-acceptor pairs separated by a rigid steroid spacer (27, 28). In 1, for example,... 

The molecular ion of C5H5CoN4Ph2 is weak, and the fragment ions [M-N2]+, [M-N3H]+, [M-2NJ+, and [M-2N2-H]+ are also observed in low abundances the base peak of the spectrum corresponds to the biphenyl cation [C6H5—C6H5]+ and the ion C5H5Co+ is observed in relatively low abundance (153). 

The mobile electrons can either neutralize biphenyl cations, giving rise to the RPL which we observe ... 

The second glow peak is reduced when the number of trapped anions is reduced. Therefore, the second glow peak must be ascribed at least partially to the diffusion of biphenyl cations and anions and their mutual neutralization ... 

Pyrido[2,l-/][l,2,4]triazine-5,6,7,8-tetracarboxylic acid, 4,4a-biphenyl-l-p-tolyl-synthesis, 3, 428 Pyridotropylium cations... 

This derivative is readily cleaved by acidic hydrolysis (dil. CF3COOH, CH2CI2, 10 min, quant.). It is cleaved 3000 times faster than the r-BOC derivative because of stabilization of the cation by the biphenyl group. BnSH... 

Recently developed trifluoromethylatmg agents capable of transferring the trifluoromethyl group as a cation to strongly nucleophilic compounds such as carbanions and sulfur and phosphorus nucleophiles are prepared from o-biphenyl trifluoromethyl sulfoxide [164] and are shown in equation 141... 

Obtain the energy of each cation that might be generated by electrophilic addition of Br to biphenyl (biphenyl+Br+). Which one is most stable Are there others of comparable stability Examine the structure of the most stable cation(s), and draw all of the resonance contributors needed to describe this ion(s). Predict the product(s) of biphenyl bromination. Will the reaction be highly selective, moderately selective or unselective ... 

Heteroaromatic diazonium salts can also be used for Gomberg-Bachmann aryla-tions. Fukata et al. (1973) refluxed 3,5-dimethyl-4-diazopyrazole (10.27) in benzene and obtained 3,5-dimethyl-4-phenylpyrazole (10.28, 36%), biphenyl (10.29, 17%), 3,5-dimethylpyrazole (10.30, 12%), and pyrazolo[4,3-c]pyrazole (10.31, 15%). In nitrobenzene the three isomeric 3,5-dimethyl-4-(nitrophenyl)-pyrazoles were formed in the ratio o m p = 10 3 3. In the opinion of Fukata et al. this ratio and the course of the reaction indicate a homolytic process. The present author thinks that the data do not exclude a competitive heterolytic reaction with the pyrazolyl cation, because equal amounts of substitution of nitrobenzene in the 3- and 4-positions are not typical for a homolytic aromatic substitution. 

The complexes precipitate immediately on mixing 1 1 complexes (n = 1) are prepared from arenes such as benzene, biphenyl, naphthalene, acenaphthalene, fluorene, phenanthrene, anthracene and m-dinitrobenzene. These complexes contain a complex Hg(I) cation with the arene v coordinated to one Hg as in III ... 

Stimulated by extensive research activities on donor/acceptor substituted stilbenes, Mullen and Klarner have reported a donor/acceptor substituted poly(4,4 -biphenyl-diylvinylene) derivative (85) in which the NR2 donor and CN acceptor substituents are located on the vinylene unit [111]. The synthesis is based on a C-C-coupling reaction of in situ generated carbanion functions with a (pseudo)cation function, followed by a subsequent elimination of MeSH with formation of the olefinic double bond. 

Corke CT, NJ Bunce, A-L Beaumont, RL Merrick (1979) Diazonium cations as intermediates in the microbial transformations of chloroanilines to chlorinated biphenyls, azo compounds and triazenes. J Agric Eood Chem 27 644-646. 

In a similar approach, Demuth and coworkers used PET and employed 1,4-dicyano-tetramethylbenzene (DCTMB) and l,l -biphenyl (BP) to form radical cations as 5-11 from tetraenes as 5-10. 

The present method is successful with a wide variety of ketones (see Table). Cyclic ketones (entries 1-4, 8) produce benzoannelated products in excellent overall yields. There is no need to purify the intermediate both the nucleophilic addition of methallylmagnesium chloride and the aromatic cyclization take place cleanly. Acyclic ketones (entries 5-7) also provide high yields of benzoannelated product. Aromatic ketones are particularly interesting substrates for this reaction since they provide substituted biphenyls, which are potentially useful materials for liquid crystal synthesis and whose preparation through classical methodology is often not straightforward. The conditions for the cationic cyclization step can be modified to accommodate acid-sensitive functionality. For example, cyclization of 3 to 4, the latter a precursor for 3-methyl-8,14-dehydromorphinan, was accomplished in 77% yield by treatment of 3 at... 

Hydroamination of olefins has received considerable attention this year as a route to functionalized piperidines and spiropiperidines, particularly in regard to the investigation of new catalysts. In the synthesis of spiro-piperidines, two new mild and more general intramolecular hydroamination protocols were developed this year. One protocol uses a cationic gold-phosphine complex (Au[P(fBu)2(o-biphenyl)]Cl) as the catalyst... 

---