Phosphination, free-radical

Other known types of radical include phosphobetaine free radicals R3P+-CR2, phosphobetaine cation radicals, R3P-CR2 phosphine free radicals R2P-CR2 and other species snch as (R0)2P(0)0 and (R0)2P(S)S in which the nnpaired electron is not sitnated on the P atom. Examples of other radicals of this kind are (13.213). Deep bine (13.213c), based on sp carbon atoms, is stable for several minntes [38]. 

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. 

The addition of phosphines to fiuoroolefins is of free radical nature [6, 7, (equations 2-5)... 

The decomposition of di- e -butyl peroxide in the presence of diethyl phosphite and an aromatic substrate leads to free-radical phosphination, Eqs. (43) and (44). 

The reaction given here has been described before as a general reaction,2 and there can be a wide variety of alkyl, aryl, and halo substituents on the diene and phosphorus. Dibromophosphines are appreciably more reactive than dichlorophosphincs. If a free-radical catalyst is used instead of an inhibitor, the copolymers can be made in good yield.3 The 1,4-addition of dichloro-phosphines to 1,3-dienes is of theoretical interest because of its analogy to the well-known 1,4-addition of sulfur dioxide to 1,3-dienes. 

The strained hydrocarbon [1,1,1] propellane is of special interest because of the thermodynamic and kinetic ease of addition of free radicals (R ) to it. The resulting R-substituted [ 1.1.1]pent-1-yl radicals (Eq. 3, Scheme 26) have attracted attention because of their highly pyramidal structure and consequent potentially increased reactivity. R-substituted [1.1.1]pent-1-yl radicals have a propensity to bond to three-coordinate phosphorus that is greater than that of a primary alkyl radical and similar to that of phenyl radicals. They can add irreversibly to phosphines or alkylphosphinites to afford new alkylphosphonites or alkylphosphonates via radical chain processes (Scheme 26) [63]. The high propensity of a R-substituted [1.1.1] pent-1-yl radical to react with three-coordinate phosphorus molecules reflects its highly pyramidal structure, which is accompanied by the increased s-character of its SOMO orbital and the strength of the P-C bond in the intermediate phosphoranyl radical. 

Reactions and Properties of Phosphonic and Phosphinic Acids and their Derivatives.-A free radical mechanism has been proposed to account for the cleavage of the phosphorus-carbon bond in the alkylphosphonic acids (155) by E coli to give a mixture of alkane (methane only, from methylphosphonic acid) and terminal alkene. 

Saturated ketones and aldehydes have been reduced to alcohols using Co2(CO)8-phosphine (P) mixtures at high H2 pressures, probably via the coordinatively unsaturated species HCo(CO)2P (187). A reassessment of experimental data on hydrogenation of aromatics (A) catalyzed by Co2(CO)8 under hydroformylation conditions has led to the suggestion that free radicals rather than organocobalt complexes are involved (188), e.g.,... 

A reaction of red phosphorus with arylhalides (chlorobenzene) in phosphorus trichloride and in the presence of a variety of catalysts has been reported to provide moderate yields of the aryldichloro-phosphine.38 No reaction occurs in the absence of the catalysts, and a free radical mechanism is presumed to be involved. 

The preparation in good yield of (3-mercaptoethylphosphines has been accomplished by the free radical-induced addition of primary and secondary phosphines across the olefinic linkage of 2-(vinylthio)tetrahydropyran.446 The target materials were isolated by hydrolysis of the intermediate substituted thiotetrahydropyran. 

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. 

Tin-free radical reduction by an organophosphite [17] and phosphinic acid can also be initiated by Et3B/02. Radical cyclizations using phosphinic acid neutralized with sodium carbonate and Et3B/02 as a radical initiator... 

In contrast to the free-radical polymerizations, there have been relatively few studies on transition metal catalysed polymerization reactions in water. This is largely due to the fact that the early transition metal catalysts used commercially for the polymerization of olefins tend to be very water-sensitive. However, with the development of late transition metal catalysts for olefin polymerizations, water is beginning to be exploited as a medium for this type of polymerization reaction. For example, cationic Pd(II)-bisphosphine complexes have been found to be active catalysts for olefin-CO copolymerization [21]. Solubility of the catalyst in water is achieved by using a sulfonated phosphine ligand (Figure 10.5) as described in Chapter 5. 

Free-radical-catalysed additions have also been reported, and provide a genuine alternative to the more familiar base-catalysed addition routes. Thus the secondary diphosphine (28) readily adds to diphenylvinylphosphine in the presence of AIBN to give (29).25 Similarly, addition of di(pentafluorophenyl)phosphine to diphenylvinylphosphine affords26 the diphosphine (30). Sequential addition of silanes and secondary phosphines to terminal aco-dienes under the influence of u.v. light affords the silylalkylphosphines (31), which may be anchored via silicon to the surface of inorganic oxides and used as polymeric catalysts.27... 

Tris(trimethylsilyl)silane reacts with phosphine sulfides and phosphine selen-ides under free radical conditions to give the corresponding phosphines or, after treatment with BH3-THF, the corresponding phosphine-borane complex in good to excellent yields (Reaction 4.45) [82]. Stereochemical studies on P-chiral phosphine sulphides showed that these reductions proceed with retention of configuration. An example is given in Reaction (4.46). 

The addition of phosphine to olefins provides today a generally applicable method for the syntheses of organophosphines. Stiles, Rust and Vaughan were the first to study the reaction systematically. It is catalysed by organic peroxides such as, for example, di-t-butyl peroxide, by a, a -azobis-isobutyro-nitrile by other free radical sources or by exposing the reaction mixture to UV- or X-radiation. The PHj radicals, produced according to Eq. (77), react further with olefins thus producing PH2 radicals continually. 

Polyhaloalkyl compounds such as CCI4 and the trichloroacetate 920 undergo addition to alkenes with catalysis by Pd(OAc>2 and tri(o-tolyl)phosphine in the presence of The reaction is explained by a free radical mechanism,... 

Photoinitiators [INITIATORS - FREE-RADICAL INITIATORS] (Voll4) hexafluoroantamonatesas [FLUORINE COMPOUNDS, INORGANIC - ANTIMONY] (Vol 11) phosphine-based [PHOSPHINE AND ITS DERIVATIVES] (Vol 18) polymethines [POLYMETHINE DYES] (Vol 19)... 

A large number of Group VIII metal-dioxygen complexes catalyze the oxidation of phosphine to phosphine oxide or isocyanides to isocyanates by molecular oxygen.6,12,56,140,141 146,184 However, their use as catalysts for the oxidation of alkenes generally leads to the same products as those obtained from free radical chain autoxidations.184,196-198... 

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