Radicals phosphorus-centred

Marque S, Tordo P (2005) Reactivity of Phosphorus Centred Radicals. 250 43-76... 

When the charge-transfer complex between hexamethylbenzene (123) and oxygen is irradiated (313nm) in methanol, a methoxymethyl derivative and pentamethylanisole are formed. These are not the products obtained when singlet oxygen attacks (123) see structure (62). Finally in this section, an example of substitution in benzene by a phosphorus-centred radical is seen in the formation of O-ethyl diphenylphosphinate (124) as one of the products of photolysis of O-ethyl 5-propyl phenylphosphonotli o e in benzene. ... 

A new route to phosphaalkenes is provided by treatment of dichloro-phenylphosphine with two equivalents of carbonyl-functional carbenes, resulting in a two-electron reduction of the phosphorus centre coupled with carbene oxidation. A range of amido-functional phosphaalkenes, e.g., (112), (alternatively viewed as carbene-phosphinidene adducts), was prepared using this approach, followed by full spectroscopic and structural characterisation. A related diamino-functional phosphaalkene has also been described and its coordination chemistry studied. Among other new phosphaalkene systems reported is a series of phosphaalkene-phospholes, e.g., (113), the monoanionic phos-phaalkenyl-phosphido ligand (114), alkali metal salts of the phosphaalkene radical anion (115), ° and new 1,3-diphosphacyclobutadiene... 

We have also examined the addition of phosphorus-centred radicals to acetylenes. Thus, treatment of dimethylphosphite (2 mmol) with di-r /7-butyl peroxalate (1 mmol) and the aminoxyl 1 (2.1 mmol) in phenylacetylene (100 mmol) at 60"C for 70 mins, gave the expected addition product 27 (85%) as well as 28 (15%). The structure of 27 was confirmed by O... 

The radical trapping technique can be used to study the initiation step in polymerisation where the initiating species is a phosphorus-centred radical. Addition of phosphorus-centred radicals to alkenes was found to be competitive with direct trapping by the aminoxyl. 

In later sections, heterolytic reactions at trigonal carbon centres, and at phosphorus, and reactions of radicals will be treated. 

The physical aspects underlying the reactivity of P-centred radicals are essential in order to benefit from the full potential offered by phosphorus-containing compounds. Hydrogen atom transfers (HATs), halogen atom abstractions, cyclisations and additions are the tool box of the widely applied free radical chemistry to date. Several authors have determined key rate constants through various physical methods, including time-resolved ESR spectroscopy and flash photolysis.3... 

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