Phosphorus Anions

Denmark, S.E. and Miller, PC., Asymmetric [2,3]-Wittig rearrangements with chiral, phosphorus anion-stabilizing groups, Tetrahedron Lett., 37, 6631, 1995. 

The extremely low solubility of lead phosphate in water (about 6 x 10 15m) again suggests potentiometric analysis. Selig57,59 determined micro amounts of phosphate by precipitation with lead perchlorate in aqueous medium. The sample was buffered at pH 8.25-8.75 and a lead-selective electrode was used to establish the end-point. The detection limit is about 10 pg of phosphorus. Anions which form insoluble lead salts, such as molybdate, tungstate or chromate, interfere with the procedure. Similar direct potentiometric titrations of phosphate by precipitation as insoluble salts of lanthanum(III), copper(II) or cadmium(II) are suggested, the corresponding ion-selective electrodes being used to detect the end-point. 

Hellwinkel discovered another valuable synthesis of a phosphole derivative, namely the action of dilithiobiphenyl (95) on P(0Ph)30 and PC1S to give (98). This can be transformed into the cation (99) by HI. Most interestingly, when treated with Nal this cation gives the hexacoordinate phosphorus anion (100) as well as the tetracoordinate cation (99 Scheme 15) (65CB576). 

Finally, an interesting nine-membered 107r 1-phenylphosphonin derivative (137) deserves mention. It is, however, too highly substituted to be used to study delocalization of the 10 it- electrons (equation (83)) (70JCS(C)386). A similar system (139) was obtained when Hellwinkel thermolyzed the lithium salts, e.g. (138b), of the hexavalent phosphorus anion for 10 min at 270 °C (equation (84)) (65CB576). 

Hexacoordinate phosphorus anions such as (202), analogues of the well-known and stable anion PF6- but with only carbon bonded to phosphorus, were first synthesized by Hellwinkel from 2,2 -dilithiobiphenyl and PCls in ether (65CB576), or from the spirophosphonium cation (99) and 2,2 -dilithiobiphenyl (201 Scheme 36). 

On the other hand, evidence against an intermediate hypervalent tetracoordinated phosphorus anion in nucleophilic substitutions at phosphorus in tertiary phosphines was put forward by Kyba the fact that the substitution reaction 3 occurs with complete inversion of configuration at phosphorus was interpreted to mean that it proceeds without even one pseudorotation of 9, which makes the passage through such an intermediate unlikely ( ). 

Based upon observations made for the CD30-/(CH30)3P system, the tetracoordinate phosphorus anion would be an intermediate rather than a transition state. Finally, it must be noted that an attack on one of the carbon atoms of trimethyl phosphite via an SN2 mechanism can only become competitive with the nucleophilic attack on the phosphorus centre, if displacement of methoxide by the latter is sufficiently endothermic (Anderson et al., 1984). 

Reaction of organoantimony halides with phosphorus anions... 

Various studies of transesterification of phosphorous esters have been reported. The hexaco-ordinate phosphorus anion (78) has been prepared ... 

By Bifluoride Ion. Trifluoromethyldifluorophosphine and bis-trifluoromethyl fiuorophosphine are oxidized to hexacoordinate phosphorus anions [(CF3) PF5 H] when heated with potassium bifluoride 235). The reactions occur even more readily in the presence of acetonitrile at room temperature. 

Table 25.2.2 BDEs in Phosphorus-Anion Clusters/Complexes ...

Because of the solubility of alkali metals in NH3 (1), some alkali metal phosphides have been prepared from NH3(1). Reactions in solvents, either by using compounds containing polyanions or, in the course of suitable syntheses, from compounds starting with isolated phosphorus anions or from... 

An alternative approach that avoids many of the difficulties of the Abramov reaction uses a trivalent phosphorus component with at least one acidic site on phosphorus. The Pudovik reaction uses a base for the removal of the acidic proton and facilitates attack by the electron-rich phosphorus anionic site on the carbonyl carbon. A variety of bases have been used for this purpose, as have phosphorus reagents with differing numbers of acidic sites on the phosphorus component. High yields of adducts are possible under very mild conditions using this approach (equation 31). The... 

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