Phosphenium salts

The symmetrical bis(ylidyl)phosphenium chlorides 103, obtained from the reaction of trimethylsilyl ylides 102 with PCI3 are the first phosphenium salts which do not need counterions of low basicity such as AICI4 to be isolated (Scheme 30) [119]. The explanation of their stability lies in the delocalisation of the phosphenium charge in the two phosphonium parts. The reactivity study of these species is reported and for example the phosphenium 103 (R=Ph) adds ortho quinones to the central phosphorus to give the corresponding dioxaphospholenium salts 104 via a [4-1-1] cycloaddition. 

Synthesis of 3-diketiminate stabilized phosphenium salts (R Dipp, C6F3 X=Br, Cl)... 

Scheme 19 Reduction of a P-diketiminate stabilized phosphenium salt...

By analogy with the synthetic method used to prepare the first phosphirenium salts C [18], we initially tried to prepare a diphosphirenium salt of type 2 P by [2+1]-cycloaddition reactions of various phosphenium salts to ferf-butylphos-phaalkyne. However, all our attempts failed (Scheme 5). 

Finally, mention should be made of the ring-chain tautomerism observed in some phosphirenium salts (Scheme 9 and Equation (34)) <90TL819, 93TL1331). In the first case, the existence of the phosphenium salt was demonstrated through its trapping by a conjugated diene. 

Structural analysis of 29 reveals an essentially planar PCPCP skeleton with (E),(E)-conformation. Phosphenium salts 29 are protonated at an ylidic earbon atom with the concomitant re-association of the halide to the central phosphorus atom. They are oxidised at the central phosphorus atom, by halogen or ortho-quinones, giving phosphonium salts, or by elemental sulfur or selenium to... 

Cyclic phosphenium salts also undergo the alkaline hydrolysis... 

A further method for the synthesis of cyclic compounds in the phosphinic acid series, and investigated within the last decade, is the clearly not unrelated cheletropic reaction which takes place between alka-1,3-dienes and phosphenium salts. The latter are based on dicoordinate phosphorus, [R R P ], the commonly encountered counter ion being the tetrachloroaluminate anion. Such salts are obtained in situ through the interaction of AICI3 and a hosphorus(III) chloride R R PCl, for which R = Cl, R = R2N, or R = R =... 

Investigations by Cowley and coworkers and by Soottoo and Baxter have revealed that the reactions between 1,3-dienes and the phosphenium salts 123 (X = NPr 2 or Cl) proceed easily in dichloromethane at 0 °C, to give intermediate cyclic chlorophos-phonium salts (124) (compare structures 97, 119, 120 and 122), several of which were characterized spectroscopically and crystallographically. The highest yields of 124 (X = NPr 2) were achieved when R = R = Me and R = R" = H, and the lowest with the reverse pattern of substitution. The hydrolysis of the salts 124 (X = NR2), using NaOH in aqueous dioxane, yields the cyclic phosphinic amides 125 (X = NR2). 

Weissman and Baxter have also recorded the successful addition of a phosphenium salt to cycloheptatriene the mixture of stereoisomeric aminochlorophosphonium salts (129) then afforded a mixture of phosphinic amides (130) when hydrolysed. 

Interest continues in the development of the chemistry of phosphinidenes and phosphenium salts, and also that of their metal complexes. A molecular orbital study of the... 

NMR spectroscopy." The results show that the interchange process of the rotational isomers follows first-order kinetics with respect to the forward [ki] and reverse [k i) reactions. Activation parameters [ki, k i, ktotai, Eau Ea-i, Ea(totai), AH and AG ), and thermodynamic parameters Ke, Alf, AG° and AS ) were also obtained experimentally. The synthesis and full characterization of the previously unknown, highly-labile, amino-(azido)phosphenium salt [(Me3Si)2N = P-N3][GaCl4] (30), has been reported. ... 

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