Chlorophosphonium salts

Hexamethylphosphoramide, (MejN)3P=0, reacts with phosgene to give an interesting chlorophosphonium salt, in a manner similar to the formation of chloroiminium salts (Vilsmeier reagents) cf. Sections 10.2.2.3 and 10.2.7 [1638] ... 

Preparative uses of the reactions of phosphorus pentachloride (78) with simple phosphines have been investigated. Thus tertiary phosphines give mainly the chlorophosphonium salts (79), whilst chlorophosphines give chlorophosphoranes (80 = 1 or 2). An impressive combination of n.m.r. and C1 n.q.r. spectroscopy has revealed that the phosphoranes (80) are molecular in the solid state, and that the phosphoranes (81) and (82) are ionic in the solid state. ... 

Amongst the features of the reaction which have caused concern are the relative roles of chlorophosphonium salt and/or phosphorane intermediates, and the reason(s) for the retention, or otherwise, of 1 mol of HCl within the intermediate species. Russian work had already differentiated between the chlorophosphonium salt and the true tetrachlorophos-phorane when styrene was used as the substrate. A new study of the phosphonylation of styrene and indene has shown that esters of the respective phosphonic acids are obtainable by the alcoholysis of the intermediate(s) from each substrate however, for indene, the esters 184 were obtained only by the use of MeOH, Pr OH or 2-methylpropanol, and EtOH, PrOH, BuOH, pentanol and isopentanol each yield the tetraoxyphosphorane 185. ... 

In outline, the reaction between a phosphorus(III) chloride 462 and an a,)5-unsaturated carboxylic acid 463 might be formulated in a way (Scheme 44) similar to that between the same acids and a phosphorus(III) ester (Scheme 41) a linear dipolar intermediate adduct 464a leads to, or is in equilibrium with, a cyclic chlorophosphonium salt 464b, which, in turn, might be in equilibrium with a pentacoordinate (phosphorane) structure in its tau-... 

Phosphine imine N-diazonium from P-chlorophosphonium salts... 

As noted earlier, triphenylphosphine oxide is typically a by-product of the Appel reaction. A significant amount of this by-product is generated from a classic Appel process, and it has been difficult to remove from the product in some cases. A clever approach to the synthesis entailed the use of catalytic amounts of this by-product to promote the reaction (Scheme 7.27) [44]. The key to this chemistry was the use of oxalyl chloride to generate chlorophosphonium salts that were the active species in the chlorodeoxygenation reaction. The reaction conditions were quite mild, and a host of alcohols were successful converted into alkyl chlorides. 

The key intermediate, a chlorophosphonium salt, is formed by the reaction of triphenylphosphine oxide and oxalyl chloride. After the chlorination of the alcohol, the phosphine oxide is regenerated and the cycle may start again (Scheme 66). ... 

The conversion of the triphenylphosphine oxide by-product of the Wittig- and Appel reactions to chlorophosphonium salt (Scheme 70) by reaction with oxalyl chloride made possible an easy work-up of the reaction mixture, as the insoluble salt could be removed by filtration. The reduction of phosphine oxides to phosphines by (EtO)2MeSiH or PMHS could be catalyzed by Bronsted acids. Scheme 71 shows examples... 

Later it was found that the chlorophosphonium tetrafluoroborates formed by the reaction of the diazonium salts can be reduced to chlorophosphines by magnesium or aluminum. In this way phosphorus trichloride yields aryldichloro-phosphines,348,349 and the latter yield diarylchlorophosphines 349 yields are of the same order as on hydrolytic working up. 

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