Phospholes, radicals from

Anion-radicals were obtained by alkali-metal reduction of phospholes in ether solvents.602 Sodium and potassium gave radicals rapidly whereas lithium failed. The radicals persisted several days at — 80° but decomposed above - 30°. The persistence of the radicals and their relatively large phosphorus hyperfine splitting, e.g., 186, by comparison with anion-radicals from phosphines, were interpreted in terms of aromatic character.602 The results obtained here contrast with results obtained earlier for 187 where phenyl cleavage and small phosphine-like phosphorus splittings had been observed for the products of attempted anion-radical formation.603 Chemiluminescence on oxidation of the anion-radical of 1,2,5-triphenylphosphole has been reported.604... 

Possible mechanisms for these reactions are depicted in Scheme 2. Both rely on the expulsion of a phenyl group from a transient phosphole radical such as XLVII or IL. 

Phosphole radicals are known to be more readily made and more stable than analogous phosphine radicals . This is probably due to the delocalization of the unpaired electron over the ring. On the other hand, complexes such as XLVIII are isolated from the reaction mixture and their mass spectra contain a medium-intensity peak corresponding to the final phosphaferrocene however, their thermolysis in the pure state does not produce phosphaferrocenes in detectable amounts. Phenyl-substituted phosphaferrocenes are always among the by-products of the synthesis of phosphaferrocenes. No satisfactory explanation of this fact (the formation of phenyl substituted phosphaferrocene by radical arylation as initially proposed is not very likely since ferrocene cannot be arylated in this way could be found until the very recent discovery that, at around... 

Irradiation of 2,3-diphenyl-2//-azitine in the presence of Cgo fullerene leads to the formation of mono- and ohgo adducts (98,99). A monoadduct, l,9-(3,4-dihydro-2,5-diphenyl-2//-pytTolo)fullerene-60 was isolated and characterized. Mechanistic studies showed that under conditions of direct irradiation it was formed by a classic nitrile yhde cycloaddition but in the presence of 1,4-napthalenedicarbonitrile (DCA) it resulted from reaction of the radical cation intermediate 108. Cycloaddition reactions have also been carried out with diaza-phospholes and diazaarsoles (100) to give adducts of the type 189 (A=As,P) and with cyanogen to give 190 and with atyldiazocyanides where addition to both the azo moiety and the cyano group were observed (101). 

The formation of radical-anion intermediates from the reaction of phospholes with alkali metals has been demonstrated by e.s.r. spectroscopy. -... 

The only application of this technique in phosphole chemistry has been in the detection of radical intermediates in the cleavage of P-substituents with alkali metals at — 80°C. Radical anions at phosphorus were formed as the initial products from l-methyl-2,5-diphenylphosphole, 1,2,5-triphenylphosphole, and pentaphenylphosphole. The P nucleus exhibited strong coupling with the electron <71T5705>. Radical anions were also detected in the reaction of 1,2,5-triphenylphosphole oxide and pentaphenylphosphole oxide with alkali metals <71CC782>. 

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