Phosphenium cations reactions

Another approach to a donor adduct of the methylene phosphenium cation is the addition of a phosphonium cation to the phosphaalkyne. The reaction of the protic cation [HPPhal + lCFaSOa] with CjoHuCP produced a white powder which was identified as the P-phosphonio-substituted phosphaalkene [74]. Alternatively to the elimination reaction the phosphaalkynes were protonated. C-protonation of adamantylphosphaacetylene and ferf-butylphosphaacetylene occurred in superacid media under formation of phosphavinyl cations. From these spirocyclic betaines by reaction of l-Ad-C=P (Ad = adamantyl) withB(OTf)3 a phosphavinyl cation could be detected [75]. 

In this progress report we have reviewed the latest developments in the large area of cationic low-coordinated species and their coordination with Lewis donors. It is clear that these species are of a broad interest, in particular for catalysis. In some cases, e. g. the methylene phosphenium cation, the donor adducts also open new routes for synthesis. Regarding the mechanism for the diverse donor-addition reactions, the structural details are only poorly understood and need a better classification. In particular the variation of the Lewis-donor has to be established. Hitherto in most cases iV-donation is studied. It includes amines or pyridines. Obviously the effect of other donors, such as phosphines, thioethers needs to be studied as well. The siliconium cation for which these effects are better known could provide an understanding for further investigations within this field. 

Detailed investigations of the chemical reactivity of the diketiminato-stabilized phosphenium cations like 28 (Scheme 17) are to date rare and include only two reports dealing with the substitution and reduction of P-halogen-derivatives. Thus, reaction of 28 (X=Br) with sodium hydroxide in toluene was reported to proceed with displacement of the halide substituent at phosphorus and conservation of the heterocyclic ring to give a mixture of bromide and triflate salts containing a P-hydroxy-substituted cation, both of which were isolated in small yields [89], The products are remarkable as they represent one of very few examples of a stable phosphinous acid which does not rearrange to the tautomeric secondary phosphine oxide. Potassium reduction of the P-chloro-substituted derivative 34 produced the... 

Phosphines and their derivatives are known to be very useful ligands toward transition metals and a variety of complexes with phosphine as a ligand have been prepared for all kinds of transition metals. If one of the substituents on a coordinating tertiary phosphorus compound is abstracted as an anion, it would form a cationic phosphenium complex. Actually this strategy has been widely used, and halide, hydride, and alkoxide have been abstracted as an anion by an appropriate Lewis acid. An alternative method to prepare cationic phosphenium complexes is a direct reaction of a phosphenium cation with a transition metal complex having appropriate... 

A phosphenium cation reacts with a transition metal complex having an appropriate leaving ligand such as carbonyl, phosphine, and acetonitrile to generate a cationic phosphenium complex [Eqs. (10)-( 14)].2,26-29 This reaction seems to be the simplest method for the preparation of a cationic phosphenium complex. The drawback of this method is that known stable phosphenium cations are limited in number. 

As shown in Eq. (14), W(bpy)(CO)3(MeCN) reacts with the phosphenium cation (17) to give a cationic phosphenium complex (18). The same phosphenium complex (though the counter anion is different) (19) is also prepared in the reaction of the same starting W complex with the corresponding chlorophosphine [Eq. (15)].29 In this reaction, P-Cl heterolytic cleavage spontaneously occurs to form the phosphenium complex. Complex 19 is unstable and is gradually converted into 20 by CP/CO exchange. 

A number of non-routine reactions of halogenophosphines are worthy of note. The first aliphatic phosphenium cation featuring a phosphorus-sulfur bond (17) has been obtained by treatment of the chlorophosphine (18) with aluminium trichloride in dichloromethane solution. A new synthesis of acyclic chiral t-phosphines has been developed which employs selective, sequential alkylation of the chloro(amino) phosphines (19) by Grignard and organolithium reagents. The key intermediates (19) are readily prepared by the... 

The opening of oxazaphospholidine rings (/ p)-122 with tert-butyllithium occurred diastereoselectively with retention of absolute configuration on the phosphorus atom, affording the borane complex of aminophosphine (Rp)-124 [67, 68]. The reaction possibly proceeds via formation of chiral o X -phosphenium cation 126, which was obtained from (Sc)-chlorophosphine 125 and then isolated as borane complex 127 (Scheme 38). 

The phosphenium cation PHJ, with a 6-electron valence shell, is unstable (Chapter 13.4). The PH molecule does not exist at room temperature, but it can be detected spectroscopically in reactions between hydrogen and phosphorus vapour at higher temperatures. 

A.H. Cowley and R. A. Kemp, Synthesis and reaction chemistry of phosphenium cations, Chem. Revs. 85, 267,1985. 

Reaction of bis(dialkyIamino)chlorophosphines with SbClj produces phosphonium cations (7.123a), but with aluminium trichloride at O C, the phosphenium cation, based on a two-coordinated P atom, is formed (7.123b). 

The dimensions of the isopropyl derivative (7.124) indicate that a pjt-pjt bonding system is probably present. Similar 2-coordinated phosphenium cations can be made by reactions such as (7.125) and (7.126). The first stable cation (7.125) was reported in 1972 by Fleming et al. [16]... 

Reactions of P-halogen-NHPs with Lewis acids leading to halide abstraction, or metathetic replacement of the halide by a nucleofugic, noncoordinating anion form by far the most important routes to access phosphenium ions in general [51, 52] and also 1,3,2-diazaphospholenium cations in particular. As Lewis acid assisted P-X... 

IV. Competitive Reactions with Cationic Phosphenium Complex Formation. . 120... 

In the reaction of HBF4 with the neutral complex Cp(CO)2W-[PPh N(SiMe3)2 ] (24) which possesses a planar geometry around the phosphorus, protonation takes place at the metal center to give a cationic phosphenium complex (25) [Eq. (17)].31... 

Although electrophilic character is expected for cationic phosphenium complexes, only a few examples have been reported. Mer-10 readily reacts with Nu- (Me-, OEt-) to generate 29 [Eq. (20)].20 This shows that mer-10 is susceptible to nucleophilic attack at the phosphenium phosphorus. Complex 29 is not obtained in the reaction of the corresponding phosphite complex (30) with Me- or OEt-. 

TMSOTf even in a cationic complex, and (ii) a cationic phosphorus ylide ligand can migrate to a cationic phosphenium ligand. The reaction has been confirmed to take place through intramolecular migration. 

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