Mixed Phosphoranes

Phosphoranes of the type R3PX2 are produced by the halogenation of alkyl phosphines (6.141) or oxides (6.493). 

Under conditions in which hydrogen chloride can be removed, successive chlorination of the alkyl group may occur with some halophosphines. 

Phosphorus pentachloride adds easily to many alkenes or alkynes to give either chlorinated aliphatic derivatives or the dehydrochlorinated products, alkenyltetrachlorophosphoranes. 

Phosphorus pentachloride reacts with phenol to give triphenoxy di chloro phosphorane (6.496), which may also be obtained by direct chlorination of triphenyl phosphite (6.497), or by Equation 6.487. This compound readily dissociates into a series of anions and cations of general formulae 

Condensation of phosphorus pentachloride with aromatic compounds containing adjacent OH groups, gives spiran-type phosphoranes (6.491, 6.498). Condensation of phosphorus pentafluoride with o-phenylenedioxy bis tri-methylsilane also gives a spiran-type derivative (4.499). 

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A number of preparations of mixed halogenophosphoranes from tervalent phosphorus-fluorine compounds have been reported. For example, acyclic and cyclic fluorine compounds have been converted to phosphoranes, such as (36) and (37), by treatment with chlorine. Similar reactions leading to AA-dialkylaminodichlorodifluorophosphoranes (38) have been described and the stability of (38) to exchange processes commented upon. iVA-Dialkylaminotetraiodophosphoranes (39) have been prepared from AA-dialkylaminodichlorophosphines and lithium iodide, although no detailed physical evidence for the structure of these unusual compounds has yet been reported. The preparation of bis-(A-alkylamino)difluorophosphoranes (4) has been described above (see Section lA). 

Experiments with aspartic acid have shown that only a-aspartic acid dipeptides are formed [123], which is consistent with the transformation of the substrate into a pentacoordinated phosphorane mixed anhydride 17 [24] containing a five-membered ring through a self-activation process. 

Combination of the stabilizing factors of a 2,2 -biphenylylene ligand with those of the phosphahomocubane system was achieved in the form of the mixed-skeleton phosphoranes 103, synthesized according to the foregoing principles 113). A hexa-coordinated structure, however, including the phosphahomocubane system could not be realized here 113>. 

The mixed chloroalkyl phosphoranes, R PC15 behave as Lewis acids, for example,... 

Carbodiimides also insert into Ta—N bonds in a mixed tantalium amido/imido complex. Pentacoordinated phosphoranes, such as 413, react with DCC or diisopropylcarbodi-imide to give hexacoordinate phosphorus amidinates 414 ... 

Reactions between compounds with mixed hydroxyl-amino functionality and P(III) species yield P—H-phosphoranes also ... 

Mixed substituted orthoesters, e.g. (383 equation 180), can be obtained by addition of alcohols to ketene 0,0-acetals. With the aid of phosphoranes containing a ketene O,(7-acetal structure, various orthoesters, e.g. (384) and (385) (Scheme 70) were prepared. " Cyclic orthoesters (386)-(390) (Scheme 71) are formed in cycloaddition reactions of ketene 0,0-acetals with aldehydes, ketones, 7.848 gj.yj cyanides, oxiranes, a-keto esters, o-diketones or ketones (with irradiation), a,3-unsaturated aldehydes and ketones (under pressure or catalyzed by ZnCh), diazoaceto-phenone, 7 diazoacetone and azodicarboxylate. ... 

The formation of acrylonitriles from the reaction of dihalogenomethylene-phosphoranes with aroyl cyanides has now been extended to include the use of aliphatic acyl cyanides, although the conditions need to be closely defined. Perfluoroisocyanates with diphenylmethylenetriphenylphosphorane give the expected keten-imines (28) or their rearrangement products (29). Formylation of both reactive and stable ylides has been achieved using the mixed anhydride of formic and acetic acids. ... 

Phosphoranes failed even in refluxing toluene to undergo Wittig olefination of lactones, unlike other carbonyl compounds. However, under MWI for 90 s, lactone 102 reacted with ethoxycarbonyl methylidene triphenyl phosphorane on mixing a 1 1.2 ratio to give 104 and 105. Similarly, 103 gave 106 and 107 after MWI for 110 s, each as a mixture of isomers in 80-82% yields. The EjZ product ratio was 20/80 for 104 and 105 and 15/85 for 106 and 107 (Scheme 21) (99TL165). 

The mixed phosphonium-iodonium ylides (Section 2.1.10.1), such as the tosylate 796, represent a useful class of reagents that combine in one molecule the synthetic advantages of a phosphonium ylide and an iodonium salt [1091-1100]. Specifically, phosphorane-derived phenyliodonium tosylate 796 reacts with soft nucleophiles, such as iodide, bromide, benzenesulfinate and thiophenolate anions, to form selectively the respective a-functionalized phosphonium ylides 797 (Scheme 3.315), which can be further converted into alkenes (e.g., 798) by the Wittig reaction with aldehydes [1092]. The analogous arsonium-iodonium ylides have a similar reactivity toward nucleophiles [1091, 1094, 1101]. 

The molecular structures of four heteroleptic fluoro-methyl-phosphoranes P(CH3)5 F , = 1,2,3, or 4, are shown in Fig. 15.9. Note that the F atom in the monofluoro derivative occupies an axial position, so do both the F atoms in the difluoro compound. When more F atoms are introduced, they enter equatorial positions. The only member of the series exibiting an axial methyl group is thus the monofluoro compound. Studies of the mixed... 

While some of the parent carbophosphenes (6.2) probably exist as spectroscopic species, only their derivatives have in some cases been characterised. Most numerous of known species are those of type (6.2a) (methylene phosphines, 6.2e) (methylene phosphoranes). Mixed varieties such as (6.2g) have only recently been reported [19],... 

The interchange of groups between different trigonal bipyramids can in some instances take place. Thus on mixing the two phosphoranes indicated, no less than six different species are formed (13.113). As far as is known psendorotation is not involved and the process can be compared with the scrambling which takes place on mixing certain pyramidal or tetrahedral compounds (Chapter 3.2). 

Methyltetraphenoxyphosphorane and the p-nitrophenoxy analog rapidly disproportionate on mixing to give all five possible phosphoranes, CH3P(OPh) (OAr)4 . All disproportionation equilibria have been characteiized along with rate constants for their dissociation to phosphonium salts and for the corresponding associations. 

Halogenotrifluoromethyl-phosphines and -phosphoranes. The synthesis and stereochemistry of fluorophosphoranes RaPFj,-a (R = alkyl or aryl x — 1,2, or 3) have been extensively discussed, but comparatively little information is available on mixed halogenofluorophosphoranes of general formula... 

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