Halides phosphines

A range of mechanisms is possible for the acidolysis of phosphorus amides, depending on the nucleophilicity of the departing amine. A recent study of phosphinic amides (160) in acidic media demonstrated that, when R2 is aryl, the presence of an o-Me group reduced the hydrolysis rate significantly, and also that the mechanism appears to be of an associative type.128 The phosphinic halides (161 X = Cl or F R = Me) are more reactive, probably for steric reasons, than the corresponding halides (161 R = Bu1) in 5 n2(P) solvolyses with aqueous acetone and with alkali. In the case of the t-butyl compounds, the fluoride is more reactive to OH- than is the chloride.129... 

A variety of behaviour is observed in the reactions of [Na(THF)4][cyclo-P5 Bu4] with phosphine halide complexes of the nickel triad." Of particular interest is the formation of the complex Ni(cyclo-P5 Bu3)(PEt3)2 in which the... 

Secondary phosphines can be prepared by three main routes. The first method, reduction of a phosphinous halide, R2PCI with UAIH4 (Scheme 12) requires an efficient synthesis of the starting phosphorus halide, as both the starting material and the product may be difficult to purify. 

Phosphinous halides can be prepared from secondary phosphine oxides and phosphorus trichloride. The starting secondary phosphine oxides are easy to handle and can be prepared by treating readily available diethyl or dibutylphos-phite with an organometallic reagent.33... 

Biphosphines may be formed by several methods involving the treatment of phosphinous halides with either electropositive metals or organomercury compounds. An additional intriguing approach involves the reaction of metal organophosphides (see Section 3.2) with 1,2-dibromoethane to form the phosphorus-phosphorus bond and extrude ethylene (equation 17). 

In 1991 Farina carried out a detailed study on the effect of ligands on the reaction between vinyltributyltin and several halides and triflates [77], His conclusion was that the best ligand for this type of reaction was tris(2-furyl)phosphine. Halides (particularly iodides) and triflates are indeed the most frequently used leaving groups, although Roth and Sapino showed that fluorosulfonates can also be used [78] their catalyst was palladium(II) acetate. A look at the catalyst (or to be exact precatalyst) and cocatalyst combinations, together with solvent variations, which have been used in the papers cited above will make it clear that there is in fact no ideal system, but that each reaction will basically require optimization. 

Furtliermore, we could show that the reaction is not limited to perfluoroalkyl iodides. When methyl or ethyl halides were passed through a mixture of red phosphorus and copper at around 350 °C mainly phosphorus dihalides were produced. The phosphinous halide is formed in small amount along with some phosphines. With methyl bromide, e.g., the reaction product is composed of 80-90% CH3PBr2, 2-3% (Cf j-PBr and 7-14% (CH3)2PBr3. 

The mechanism of the alkylation of white phosphorus in the presence of a phosphorus trihalide is probably the same as without PX3. However, the phosphinous halides formed react with the phosphorus trihalide with the formation of phosphonus dihalides. The back reaction, i.e., formation of R2PX and PX3... 

Since the basic properties increase with the number of alkyl substituents, phosphinous halides are more readily alkylated than P or PX3. Catalysis by these compounds may therefore be expressed by ... 

If no phosphorus trihalide is present the reaction should stop at the phosphinous halide stage or go even further to give tertiary phosplunes. The preparation of phosphinous halides has been claimed... 

A study has been made of the kinetics of epoxidation of allylphosphinates and of the addition of C-benzoyl-iV-phenylnitrone to vinyl- and allyl-phosphonates. Boron trifluoride stabilizes phosphorus(v) thiocyanates, preventing their isomerization to isothiocyanates. Cleavage of the phosphinothioic methanesulphonic anhydride (97) with aluminium halides yields the phosphinic halide with retained chirality. ... 

As pointed out above, nucleophiles such as sulfides, alcohols, amines, phosphines, halides, and halide ions readily attack sulfur radical cations forming S.-.S, S.-.O, S.-.N, S.-.P, and S.-.X species. Generation of Me2S , under pulse radiolysis conditions, by the reaction of Me2SO with H- in aqueous HC104 permitted the... 

---