Phosphorus radical

Radical IV can be considered as a unique phosphorus radical species. Reduction of the parent macrocycle with sodium naphtalenide in THF at room temperature gave a purple solution. The FPR spectrum displayed a signal in a 1 2 1 pattern, with flp(2P)=0.38 mT. DFT calculations on radical IV models indicated a P-P distance of 2.763 A (P - P is3.256 A in the crystal structure of the parent compound and the average value of a single P-P bond is 2.2 A). According to the authors, the small coupling constant arises from the facts that the principal values of the hyperfine tensor are of opposite sign and that the a P P one electron bond results from overlap of two 3p orbitals [88]. 

The mechanistic aspects of aromatic121 and alkene122 radical cation reactions have been reviewed. A second review article covers the structure and properties of hydrocarbon radical cations, as revealed by low-temperature ESR and IR spectroscopy.123 A review of the reactivity of divalent phosphorus radical cations has appeared which discusses ionic and SET processes and their kinetics.124 The structure and reactivity of distonic radical cations have been reviewed, including experimental and calculated heats of formation, structures, reactivity, and mechanisms.122125... 

Recent Developments in the Chemistry of Dicoordinated Phosphorus Radicals and Cations... 

Impressive evidence of such a reaction was provided in Ref. 121, where trivalent phosphoms compound Z3P undergoes single-electron transfer to the photoexcited rhodamine 6C (Rho+ ), generating the corresponding trivalent phosphorus radical cation Z3/J1. However, this cation undergoes the ionic reaction with water in the solvent, which is so fast that electron transfer becomes irreversible ... 

The major psychedelic agent in psilocybian mushrooms is psilocybin— the first indole derivative discovered to contain phosphorus. When ingested, the phosphorus radical is immediately "dephosphorylated by an intestinal enzyme, alkaline phosphatase, into psilocin and phosphoric acid Animal experiments suggest that psilocybin and psilocin appear at similar chemical concentrations at about the same time in various organs. Thus, the phosphorus radical is generally considered "dead weight in terms of psychoactivity. 

Tetravalent phosphorus radicals have the geometry of an incomplete trigonal bipyramid in which the p-orbital on phosphorus containing the unpaired electron can occupy an equatorial or axial position, giving rise to conformational isomers. These can interconvert by bending motions of the substituents, as in Berry pseudorotation (Scheme 21), or by pseudoinversion [223]. Although tetravalent 9-P-4 phosphorus radicals have been studied quite in detail by ab initio theory [224], there are only scant experimental data describing their properties. 

Trifluoromcthyl- and bis(lrifluoromethyl)phosphorus radicals can be added to alkenes under the same conditions. 

A review has recently been published on the subject Phosphorus Radicals . Once again e.s.r. spectroscopy has proved to be an invaluable tool for investigating the kinetics of reactions of phosphorus radicals. Thus the rate constants for the bimolecular reactions of several types of phosphorus radicals, e.g. phosphinyl, phosphonyl, and phosphoranyl radicals, with like species have been determined and shown to be of the same order as, or very close to, the diffusion-controlled limit.These annihilation reactions presumably involve formation of a P—P-bonded dimer. An interesting observation recorded in the paper reporting this work was that t-butoxyl radicals react with (25) to give phosphinyl radicals. 

VIII. THE SILICON-PHOSPHORUS DOUBLE BOND, SILICON-PHOSPHORUS ) COMPOUNDS AND SILYL-PHOSPHORUS RADICALS. 1383... 

The mechanism of the reaction appears to involve an initial attack of the butoxy radical on the P4 tetrahedron followed by addition of the resulting phosphorus radical to the olefin (33). 

Phosphoranyl radicals have been reviewed.An e.s.r. study of a single crystal under X-ray irradiation at low temperatures allowed both stereoisomers (52) and (53) of a phosphoranyl radical to be observed. The parameters showed a small excess Sj spin density in the radial bonds in comparison with the apical bond, which refines the hypothesis that sp d hybridization of phosphorus can be constructed from three radial sp ligands and two pd ligands.Radical ions obtained by the reduction of tertiary phosphines and their chalcogenides have been studied by e.s.r. spectroscopy together with adducts of phosphites with 1,3-dialkyltriazenyl radicals,2,6-di-t-butylphenoxy radicals, and various spin trapped phosphorus radicals. ... 

The mass spectra of a number of heterocyclic compounds have been reported. The fragmentation patterns of thiophosphoryl derivatives of phosphorinanes are sensitive to stereochemistry, thus for the series (95) facile loss of the HS radical is indicative of an axial PS bond. The seven-membered heterocycles (96 Ch = S, Se) undergo a remarkable migration of sulphur or selenium from phosphorus to carbon with ring cleavage. While exocyclic P-C bonds of five-and six-membered heterocycles in the phosphonic class may be readily cleaved with retention of the phosphorus ring system, the seven-membered ring (97) exhibits facile expulsion of a phosphorus radical. ... 

These unsaturated bromo-acids are soluble without decomposition in sodium carbonate solution, but aqueous potassium hydroxide decomposes them, forming benzaldehyde and removing the bromine and phosphorus radicals. The first bromo-acid also gives a small yield of dibenzal acetone, the use of alcoholic potassium hydroxide increasing the yield of unsaturated ketone to 25 per cent. the reaction taking place is probably as follows ... 

Murphy JA, Tripoli R, Khan TA, Mali UW (2005) Novel phosphorus radical-based routes to horsfiline. Org Lett 7 3287-3289... 

Halogen and the phosphorus radical must catch the active radical in the flame field. 

There are literature claims that phosphorus acts not only as a char promoter but also in the vapor phase, leading to a decrease in the effective heat of combustion (EHC). This activity could be either flame inhibition [i.e. incomplete combustion due to scavenging of radicals like H- or HO by phosphorus radicals in the vapor phase) or a change in the pyrolytic gases. If the decrease in the EHC is generally well observed, very few articles provide evidence of flame inhibition. 

Free radicals have been most studied in connection with carbon chemistry, but a number of the possible phosphorus radicals in Table 13.12 are now well authenticated. 

Most phosphorus radicals, like the well-established reactive methyl radical, CH3, are based on a system of seven outer electrons in contrast to the eight outer electrons found in normal phosphorus molecules or ions. The phosphoranyl radical, RjP and the phosphonium radical anion RsP, are exceptional since they have nine outer electrons and no nitrogen analogues. Phosphinidene, PH (Uke nitrene NH) has only six outer electrons. 

W.G. Bentrude, Phosphorus radicals, in J.K. Kochi, PA., Free Radicals, Chapter 22, Wiley, New York, 1973. 

ESR spectroscopy has a very special and important application in the study of phosphorus radicals, which can be detected in very low concentration. ESR can be used for identification and elucidation of mechanisms (Chapter 13.4). 

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