Phosphorane-phosphane

The reactivity of fluoro(organyl)phosphanes depends on the nucleophilicity of phosphorus For mstance the phosphanes may add to the carbonyl carbon to form phosphiniio phosphoranes (equation 36) or may react with acid fluondes to form acyldifhiorophosphoranes [37] (equation 37)... 

Note. Names based on phosphane, rather than phosphine or phosphorane, are used in this document, as recommended in [14]. 

In another approach, 2-(alkylamino)alcohol is employed as starting material for aziridine syntheses with the aid of dihalogenophosphoranes (70BCJ1185). Intramolecular transformation of 3-azidopropyloxirane 73 results in a simultaneous formation of a condensed aziridino[l,2-a]pyrrol-idine system (Scheme 39). The azide group is first transformed into imino-phosphorane 74, the nucleophilic N atom cleaves the oxirane to form betaine 75 [as in the Mitsunobu reaction (81S1)], and the phosphorus is shifted from N to O and then eliminated as phosphane oxide under simultaneous cyclization to bicyclic 76 (89JA7500). 

This variation of the Wittig reaction uses ylides prepared from phosphonates.12 The Horner-Wadsworth-Emmons method has several advantages over the use of phosphoranes. These ylides are more reactive than the corresponding phosphoranes, especially when substituted with an electron withdrawing group. In addition the phosphorus product is a phosphate ester and soluble in water - unlike the Ph3PO product of the Wittig reaction - which makes it easy to separate from the olefin product. Phosphonates are also cheaper than phosphonium salts and can easily be prepared by the Arbuzov reaction from phosphanes and halides. 

With amines, the variety of results is larger. There is no reaction with pyrrole, diphenylamine or N-methylaniline, but with aniline, the equilibrium phosphane + amine aminophosphorane is shifted to the right side (>65%). With propylamine and methyl-amine, only the phosphorane is present. 

Conversion of Bicyclic Phosphoranes into Phosphoranides and Phosphane Adducts with Transition Metal Derivatives... 

Aryl-dichlor-phosphane setzen sich mit Phosphor(V)-chlorid zu Phosphor(V)-chlorid-Addukten der Aryl-tetrachlor-phosphorane um74,75, Alkyl-dichlor-phosphane bilden zu-nachst ebenfalls Alkyl-tetrachlor-phosphorane, die jedoch einer weitergehenden Chlo-rierung in a-Position des Alkyl-Restes unterliegen76. 

Die Umsetzung von Tris-[chlormethyl]-phosphan mit Chlor69 bzw. des entsprechenden Phosphanoxids mit Phosphor(V)-chlorid70 fiihrt unter Spaltung einer P-C-Bindung zum Bis- trichlormethyl trichlor-phosphoran ... 

The majority of the publications in the field of oxidative addition of HFA to tertiary phosphanes deal with the formation and properties of l,3,2-A -dioxaphospholanes 57 (60,61). These compounds are generally stable when the a carbon atoms do not bear hydrogen atoms. Heterocycles with a hydrogen atoms are stable up to about 70°C at this temperature the isomeric phosphetanes are formed. The syntheses of some sterically hindered phosphoranes require drastic conditions. 

On the other hand, tertiary phosphanes react with fiuorinated alkenes to form either vinyl-phosphoranes in the case of perfluorinated alk-l-enes, or ylides when perfluorinated alk-2-enes are used as starting materials. The latter lead to useful building blocks for Wittig-type reactions. 

In lUPAC nomenclature, a phosphane" is normally a derivative of what wc ordinarily call phosphine." PHj. Pentavalent derivatives of the hypothetical PHc (phosphorane) are labeled. Similarly, derivatives of H S would be sulfancs. and the tetravalent and hcxavaicni derivatives would be labeled X- and X. respectively. 

A similar system to the P(V) phosphoranes we have experienced in Tables 6.5 and 6.6 is also available for phosphorus (111) and presented in Table 6.8. The trends are absolutely analogous, with the exception of the different influences of equatorial and axial ligands, as such a distinction does not apply in T -phosphanes. The phosphorus resonances are shifted downfield by AA= 150-200ppm in accord with the difference in coordination numbers on phosphorus. 

At least three names are available for the compound H3P=CH2. These are phosphine methylene, methylene phosphonium ylid and phosphonium methylide moreover, the compound can be classed as a phosphorane The compound PhjP Rj may be called triphenylphosphonium methylide, tri-phenylphosphonium methanide or triphenyl-methylenephosphorane. The pyridine analogue, C5H5P, has been known variously as phosphobenzene, phosphabenzene, phosphorin, and most recently, phosphinine. The term phosphane for (1) in Table 1.4 and its derivatives is the most recent and the most systematic, but it is difficult to see how the more widespread and firmly rooted term phosphine will ever be replaced. In addition, adoption of the term phosphane would put it in line with such little-used terms as carborane for CH4, nitrane for NH3 and oxane for HjO. 

Use as a Reducing Agent. Tris(TMS)phosphine can be used as a reducing agent for the selective removal of the two axial fluorine atoms in difluorotris(perfluoroalkyl)phosphoranes, to give the corresponding tris(perfluoroalkyl)phosphanes. Trimethylsilyl fluoride is produced as an easily removable by-product (eq 23). ... 

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