Radical anion of anthracene

Disilabicyclo[2.2.2]octa-2,5-dienes, prepared by the interaction of the radical anion of anthracene, naphthalene or biphenyl with 1,2-dichlorotetra-methyldisilane were found to undergo thermal decomposition472). 

The competition between ET and 5n2 processes in the reaction between radical anions of various aromatic compounds, e.g. anthracene, pyrene, (E)-stilbene, and m- and / -cyanotoluene, and substrates such as RHal (where R = Me, Et, Bu, 2-Bu, neopentyl, and 1-adamantyl) or various methanesulfonates has been studied in DMF as solvent. The reaction mechanism could be characterized electrochemically in many of the systems indicated above. The presence of an 5n2 component is related not only to the steric requirements of the substrate, but also to the magnitude of the driving force for the ET process. 

One of the great advantages in studying the catalytic activity of organic solids is that sometimes the heterogeneous reaction may be compared with reactions of the same molecule in solution, by which special solid state effects can be eliminated. An example of this is the study of hydrogen adsorption by anion radicals and di-anions of anthracene in tetrahydrofuran-solution. The following mechanisms have been proposed 43 ... 

A radical anion of an aromatic hydrocarbon was implicated as early as 1866, when Berthelot obtained a black dipotassium salt from naphthalene and potassium [41]. This reaction must have proceeded via the naphthalene radical anion as a more or less fleeting intermediate. Again, Schlenk and co-workers captured the essence of such an intermediate. In the case of anthracene they noticed the existence of two different species, a purple dianion and a blue transient species with a banded spectrum [42]. They identified this intermediate as a monosodium addition product which contains trivalent carbon . Further details were revealed only with the advent of electron paramagnetic resonance spectroscopy. 

Spontaneous localization of charge in a 7i-system with extended Ti-conjuga-tion can occur not only as a consequence of steric hindrance, but also as a result of the topology [41]. Thus, the dianion of dibenzotetracene 20 localizes the excess charge in the anthracene subunit [42, 43], and the radical anion of 1,3-distyrylbenzene (21) has the unpaired electron localized on one stilbene unit [44], although there is no significant steric inhibition of resonance. The immediate conclusion is, and this will be reconsidered in Sect. 3.2, that the electron-transfer behavior of a structurally related poly-meta-phenylenevinylene (22) should be closely related to that of the small model compound 21. 

Photoinduced electron transfer between amines and aromatic hydrocarbons occurs to generate radical cations of amines and radical anions of aromatic hydrocarbons. Pac and Sakurai reported the photoaddition of N,N-dimethylaniline to anthracene via photoinduced electron transfer [60]. In benzene, the 4n + 4n) photocyclodimer of anthracene is produced as a sole isolable product, although an emission due to the exciplex formed from anthracene and JV,N-dimethylaniline is observed. In acetonitrile, the addition of dimethylaniline to anthracene occurs via their radical ions to give 9,10- dihydro-9-(4 -dimethylaminophenyl)anthracene as the major product. However, the photoamination on anthracene takes place even in benzene when iV-methylani-line is used as an electron donor. Sugimoto and his coworkers reported the intramolecular photoaddition of anilines to aromatic hydrocarbons to give cyclic amino compounds (Scheme 16) [61-63]. 

In a study of the reaetion between alkyl halides and the electrogenerated naphthalene radical anion, Sease and Reed [297] observed that only alkyl chlorides, such as 1-chloro-hexane and 6-chloro-l-hexene, are catalytically reduced 1-chlorohexane gives only n-hex-ane, whereas 6-chloro-l-hexene affords methylcyclopentane and 1-hexene. In an earlier paper [296], the reactions of 1-bromo- and 1-chlorobutane with the electrogenerated radical anions of rmn -stilbene and anthracene in DMSO were examined. Britton and Fry [298] elucidated the kinetics of the electron-transfer reaction between 1-chlorooctane and the phenanthrene radieal anion in DMF. 

Why are the absorption spectra of the radical cation and anion of anthracene nearly identical [End of Section 4.7]... 

The reduction of l,2-di-terf-butyl-l,2-dicyclohexyl-l,2-dichlorodisilane with excess lithium yields the radical anion of l,2-di-tert-butyl-l,2-dicyclohexyldisilene (g = 2.0033, flSi=49.8 G), with equivalent silicon atoms and a half-life of about 12 h49. The intermediacy of the disilene in the reduction process was supported by a trapping experiment with anthracene. The ESR spectrum of the less severely hindered tetracyclohexyldisilene radical anion was not observed under otherwise identical conditions. 

The donor-acceptor pairs investigated were pyrene-anthrace, pyrene-9, 10-dimethylanthracene and m-terphenyl-p-terphenyl. The radical anions of these compounds may be observed at the appropriate optical absorption bands, the maxima of which are as follows m-terphenyl, 7400 A., a broad weak band p-terphenyl, 8770 A. pyrene, 4900 A. anthracene, 7200 A. and 9,10-dimethylanthracene, 7300 A. For most of the systems we have studied in this and earlier work (1, 2, 3) these absorption bands have been known (4, 6, 8) from work on solutions in which the radical anions are stable. In the systems involving pyrenide anion as donor the decay of the donor anion and the formation of the acceptor could be observed simultaneously since their absorption bands do not overlap extensively. 

The disproportionation [reaction (19)] of lithium salts of radical anions of naphthalene, anthracene, tetracene, perylene, and pyrene in Et20 and of sodium tetracenide in has been investigated. The magnitudes of the... 

Therefore, one can conclude that for the less exothermic reduction by sodium anthracene,eq. 1 is a one-step radical formation. For radical anions of higher reduction potential, the possibility for the species, RXt, must still be considered. 

The opposite is true for naphthalene where the radical anion is faster than the anion in reaction with primary chloride. The difference arises from disparate reactivity of the respective radical anions and shows the danger in extrapolating from one radical anion-anion pair to another. Another point of interest is the much greater reactivity of naphthalene radical anion ys. anthracene, which suggests alternate mechanisms for the electron transfer step, again raising the possibility for the existence of RX7 for the naphthalene system. 

---