Radicals phosphorus-centered

Phosphinyl radicals (e.g. 103-107) arc generated by photodecomposition of acyl phosphinates or acyl phosphine oxides (see 3.3.4.LI)282,466 474,473 or by hydrogen abstraction from the appropriate phosphine oxide.467 

The reactivities of the various phosphinyl radicals with monomers have been examined (Table 3. lO).283-465,467-475 Absolute rate constants are high, lying in the range 106-I08 M 1 s 1 and show some solvent dependence. The rate constants are higher in aqueous acetonitrile solvent than in methanol. The high magnitude of the rate constants has been linked to the pyramidal structure of the phosphinyl radicals.46-  

The phosphinyl radicals (103-107) all show nucleophilic character (eg. VAc is substantially less reactive than the acrylic monomers). However, the 

T(7gen abstraction from the appropriate phosphine oxide.  

The reactivities of the various phosphinyl radicals with monomers have been 

With unsaturated phosphoranyl radicals (137) (X = 0 or NH), Davies has recently described the exact opposite results as observed by 

---

The (TMS)3SiH mediated addition of phosphorus-centered radicals to a number of alkenes has been investigated in some detail. Reaction (73) is an example of phosphorous-carbon bond formation using four structurally different phenylseleno derivatives with 3 equiv of (TMSlsSiH and AIBN in refluxing benzene for 2h. Comparative studies on the reaction of the four phosphorus-centered radicals have been obtained. Although the reaction with 1-methylene cyclohexane is efficient with all four derivatives, different selectivity is observed with electron-rich or electron-poor alkenes. 

This chapter surveys the literature published from 1995 to 2003, concerning the reactivity and the chemical applications of the four main families of phosphorus centered radicals, i.e., phosphinyl (L2P )> phosphonyl (L2P =0), phospho-niumyl (L3P ) and related charged species, and phosphoranyl (L4P ) radicals. Due to their specificity, a section is devoted to the generation and properties of persistent and stable phosphorus centered radicals. 

Studies on the formation and reactivity of phosphorus-centered radicals continue to be a versatile source of mechanistic information and reactions in synthetic chemistry. The recent literature devoted to the chemical reactivity of these derivatives is surveyed by S. Marque and P. Tordo in Chap. 2. Various new persistent or stable phosphorus-centered radicals have been described and find applications, for example, as paramagnetic probes. 

Only a few ESR studies of photochemically generated organic phosphorus-centered radicals have been reported, although divalent and tetravalent organophosphinyl radicals are often postulated as intermediates in many photochemical or organophosphorus reactions. Kochi and... 

One of the most important implications of these experiments is the conclusion that, due to the high polarity of the C=0 bond, organoelement a-ketones R3MCOR (M = Ge, Sn) are extraordinary effective radical traps. The electronegative oxygen atom of their carbonyl group could be attacked not only by element-centered radicals R3M (M = Ge, Sn), but also by thiyl radicals SR " and phosphorus-centered radicals. Indeed, the experimental estimates of the absolute reaction rate constants of the element-centered radicals with... 

Ion-beam irradiation (77 K) of DNA hydrated to T = 18 DjO/ nucleotide resulted in a DNA-phosphorus-centered radical. Samples were irradiated with 60 MeV/u, or 100 Mev/u Ar +. The ESR results showed the presence of an axially symmetric spectrum with large phosphorus couplings (Aj = 77.5 mT and = 61.0 mT, = 2.000,= 2.001), from a radical that constituted ca. 0.1% to 0.2% of the total radical concentration. Earlier literature regarding the origin and ESR spectra of such radicals existed and it was concluded that the radical was a phosphoryl radical (ROPOj, Scheme 6), formed from the electron gain path. In DNA, such a radical could result only from P-O bond cleavage at either the C3 or C5 of the deoxyribose sugar... 

O. M. Aagaard, R. A. J. Janssen, B. F. M. de Waal, and H. M. Buck, /. Am. Chem. Soc., 112, 938 (1990). Intermolecular Effects on the Radiogenic Formation of Electron-Capture of Phosphorus-Centered Radicals. A Single-Crystal ESR Study of Diastereomeric Precursors. 

The use of phosphorus-centered radicals in organic chemistry, particularly, syntheses and transformations of heterocycles 05CSR858. 

In a study to learn about the polymerization chemistry of a new class of phosphorus-centered radical initiators, a combination of 3D-NMR techniques was used to study the P-containing chain-end structures of polystyrene. Several of the possible chain-end structures are shown in Figure 15, along with the ID H, and NMR spectra. In the H and NMR spectra, the weak signals from chain-end structures are buried under the much larger signals of the polymer backbone. 

Subvolume E Phosphorus-Centered Radicals, Radicals Centered on Other Heteroatoms, Organic Radical Ions. Part 1. 

This chapter lists phosphorus-centered radicals which contain at least one carbon atom. Carbon-free phosphorus-centered radicals are included in Landolt-Bomstein, New Series, Group II, Vol. 26A1 and phos-phorinyl radicals in Landolt-Bomstein, New Series, Group II, Vol. 26B ( Carbon radicals with conjugated TT-systems ). 

Another phosphorus-centered radical was detected and tentatively assigned to ArPH (P 20.0 mT and H 6.4 mT). 

Assignment to that isomer was done by comparison with the parameters of [C2H602PS2] A Another phosphorus-centered radical Op = 4.78 mT and g = 1.985 was also observed. ... 

---