Reactivity phosphinyl radicals

The acyl phosphonates, acyl phosphine oxides and related compounds (e.g. 81. 82) absorb strongly in the near UV (350-400 nm) and generally decompose by rescission in a manner analogous to the benzoin derivatives.381"285 Quantum yields vary from 0.3 to 1.0 depending on structure. The phosphinyl radicals are highly reactive towards unsaturated substrates and appear to have a high specificity for addition v.v abstraction (see 3.4.3.2). 

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... 

The group VB hydrides show trends in reactivity similar to those of group IVB. The N-H bond can be reacted with alkenes only under the influence of catalysts or under forcing conditions. The P-H bond can be added to alkenes (hydrophosphination) in a free radical chain process, or under photolytic conditions. Such reactions proceed in good yield and in an anti-Markovnikov manner. Some typical free radical P-H additions are listed in Table 1 . The addition of phosphinyl radicals is reversible and can lead to... 

The reactivities of the various phosphinyl radicals with monomers have been... 

Phosphine oxides acyl and biacylphosphine oxides are photoinitiators which, if used alone or in combination with other photoinitiators, absorb well into the visible part of the spectrum and are useful to cure highly pigmented systems. Irradiation leads to highly reactive phosphinoyl and phosphinyl radicals generated by a Norrish type-1 cleavage. 

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. 

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