Phosphoranide anions

Compound (13.154) has electronegative influences on both the axial and equatorial positions, and as a result is less stable than (13.153), and exists in equilibrium with a pyramidal form [34]. 

---

Only a few periodonium ions have been isolated and characterized (82JA902). Cyclic periodonium ion (40) is synthesized from periodinane (39) which is obtained by the reaction of bromine with (38). The 10-1-4 species (40) is isovalent and isostructural with sulfurane (41) (74JA3155) and phosphoranide anion (42) (81TH11900). The X-ray crystallographic structure determination of (40) reveals it to have a primarily P-TBP structure with an O—I—O angle of 162.8°. The I—O bond distance is ca. 2.01 A. 

Monocyclic Phosphoranide Anion. The intramolecular oxidative addition of hydroxyalkyl phosphites, which gives P-H phosphoranes, is well known (10). Some P-H phosphoranes are so stable that the open-chain P(III) tautomers cannot be detected spectroscopically or even by attempted H2O2 oxidation (8). Thus, it is surprising to find no evidence for an equilibrium between phosphine alcohol 1 and its closed-ring tautomer phosphorane 2. Phosphine 1 is quaternized by alkyl halides giving phosphonium halides such as 3. These in turn are converted to alkoxyphosphor-anes, such as 4 by NaH (Scheme I). 

Phosphoranide anions 1 - i.e. species based on pentacoordina-ted phosphorus having a lone pair as one of its five substituents -were proposed by Wittig and Maercker as early as 1967, to act as intermediates or transition states in nucleophilic substitutions at tricoordinated phosphorus ( p. Shortly afterwards in 1969, Hellwinkel brought indirect evidence for the formation of phosphoranide 3 in equilibrium with the carbanion 4, since the action of a base on phosphorane 2 gave, after acidic treatment, a mixture of 5 and 6 in proportions that depend on the experimental conditions (i). 

More recently, Munoz et al assigned a signal at +78.4 ppm to the presence of phosphoranide anion 14 in a dynamic equilibrium mixture 5, obtained by treating 13 with trie thylamine or pyridine 06) ... 

Phosphoranide anion 1 is a stable lO-P-4 (7) hypervalent anionic species that could be considered as a transition state for a nucleophilic substitution reaction at a three coordinate phosphine center (2). The stability of 1 (5) can be attributed to several factors. 

Moreover, the formation of the by-product (4b) could be established by the reaction of the intermediate phosphoranide anion with wBuBr, which was produced during the dimetallation process. To avoid this problem, tBuLi was employed instead of wBuLi, giving compound (4) in 35% yield. 

---