Phosphines, radical addition

Commercial phosphine derivatives are produced either by the acid-cataly2ed addition of phosphine to an aldehyde or by free-radical addition to olefins, particulady a-olefins. The reactions usually take place in an autoclave under moderate pressures (<4 MPa (580 psi)) and at temperatures between 60 and 100°C. 

Dilworth, J.R., Griffiths, D.V., Hughes, J.M., and Morton, S., Synthesis of 2-S-(2-tetrahydropyranyl)thioethylphosphines and 2-mercaptoethylphosphines by free radical addition of phosphines to 2-(vinylthio)tetrahydropyran, Phos-ph Sulf, Silic. Relat. Elem., 71, 249, 1992. 

The first amino-phosphines used in AOC for studies of catalyst recovery by aqueous extraction, 59, were prepared by radical addition of PH3 on dialkylallilamines [61]. Similar addition of diphenylphosphine on activated alkenes [33] resulted in formation of a variety of phosphines including also 66. 

Pringle reported that ethyl acrylate also reacts similarly [14]. The radical addition at 70 °C forms a mixture of primary PH2 (CH2CH2COOEt), secondary PH(CH2CH2COOEt)2 and tertiary phosphines. The tertiary phosphine component is not pure P(CH2CH2COOEt)3, but a mixture with telomers. However, Pt complex-catalyzed addition is very clean when PH3 is bubbled through a warmed solution of ethyl acrylate in the presence of 0.002 equiva-... 

The radical addition of PH3 to limonene resulted in the formation of 2-phosphabicyclononane 177 which has been characterized by X-ray crystallographic analysis <2001TL2609>. Phobane is a mixture of the sym- and asym-bicyclic secondary phosphines 178 and 179, formed by the reaction of PH3 with 1,5-dicyclooctadiene. The mixture of phobanes may be separated efficiently by selective protonation of the syn isomer with HC1 <2005ASC1345>. 

The photoaddition of secondary phosphines onto alkenes is one of the straightforward approaches for the synthesis of organophosphorus compounds. An anti-Markovnikov phosphorus-centered free radical addition onto the olefin has been... 

Terao and Kambe showed a dichotomy in the reactivity of nickel complexes (review [102]). While nickel diene complexes reacted primarily via two-electron pathways [34—37], nickel phosphine complexes promote radical addition reactions [103],... 

The system is also present in the bicyclic molecules, which are formed by intramolecular free radical addition of a phosphine to an alkene. The particular product formed depends on the solvent used (85MI1). Compound 30... 

The hydrophosphonylation (addition of dialkyl phosphonates), hydrophos-phinylation (addition of alkyl alkylphosphinates or alkyl phosphinates) and addition of secondary phosphine oxides to unfunctionalized alkenes and alkynes occur under free radical conditions or with transition metal catalysis.10,39 63 90... 

The key step in the synthesis of triazonines with pendant diphenylphosphine arms is the free radical addition of Ph2PH across the alkene double bond (Equation 10) <1996CC1817>. This is accomplished in quantitative yield by photolysis under strictly anaerobic conditions using a mercury lamp. The method was not restricted to allyl substituents longer-arm alkenes react in an identical manner, although more slowly, yielding phosphines with longer alkyl, for example G-5, chains. 

En route to the synthesis of modified ohgonucleotides through radical addition of hypophosphorous substrate 177 to sugar 178, Hubert et al. reported the unforeseen /1-ehmination of a phosphinoyl radical from a phosphinate (Scheme 58) [167]. This example came after a 1,5-H translocation giving a more stabilized oj-oxy radical (from 179), and it demonstrates further that j6-phosphinoyl radicals are prone to undergo elimination (see Scheme 31), even when the substituents are all alkyl groups. 

Primary fluorous phosphines PH2(CH2)raRf8 (n = 2-4) (24) (Scheme 2) were prepared from fluor-ous primary alkyl iodides and Li PI I2-dmc (dme = dimethoxyethane), generated from PH3 and nBuLi, in THF at —45 °C.34 The primary phosphines were isolated either as clear liquids or as a low-melting white solid.34 Subsequent free-radical addition reactions of olefinic fluorous precursors with these primary phosphines afforded unsymmetrical ligands. 

One of the many important differences between phosphorus and nitrogen chemistry is the relative strengths of their bonds to hydrogen. The relatively weak P—H bond means that this functionality can be added across a wide variety of unsaturated molecules (alkenes, alkynes, carbonyls) and hence this represents an excellent method for preparing tertiary phosphines. The addition of P 11 compounds to C=0 and C=N has been described in detail by Gilheany and Mitchell.2 The reaction can be catalyzed by base (potassium hydroxide, butyllithium), acid (HC1, carboxylic acids, sulfonic acids, boron trifluoride), free radical (uv, organic peroxides, AIBN) or metal (simple metal salts, late transition-metal complexes). In some circumstances no catalyst is required at all for P 11 additions to proceed.60... 

Preparation of Phosphines by Addition of P-H to Unsaturated Compounds. -Mechanistic aspects of the addition of P-H bonds to alkenes and alkynes have been reconsidered in the light of new activation methods. In the case of additions of diphenylphosphine, radical and ionic routes are indistinguishable, a duality of mechanism being apparent, the coexistence of the two routes bringing about a competition which depends on conditions. The additions of phosphine to simple alkenes, and bicyclic secondary phosphines, e.g., 9-... 

Alkylation of alkyl methyl- and phenylphosphinates can also be achieved by radical addition to alkenes. Benschop and Platenburg reportedthat addition of menthyl methylphosphinate to cyclohexene and to ethylene, initiated by dibenzoyl peroxide or u.v. light, gave menthyl cyclohexylmethyl-phosphinate and menthyl ethylmethylphosphinate, respectively, with essentially complete inversion of configuration at phosphonis. In contradistinction,... 

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