Phosphaalkyne

Syntheses, valence isomerizations, and reactions of phosphaalkyne cyclote-tramers 97CB823. 

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]. 

See Regitz M (1991) Phosphaalkynes. In Regitz M, Scherer OJ (eds) Multiple bonds and low coordination in phosphorus chemistry. Thieme,p 58 Niecke E, Radzeck J, Schoeller WW (unpublished results)... 

Phosphinidenes (R-P) differ from other low-coordinate organophosphorus compounds, such as phosphaalkynes (R-C=P), phosphaalkenes (R2C=PR), and phosphaaromatics, in that the phosphorus atom carries only a single a-bonded substituent [7-9]. They relate to carbenes, nitrenes, and silylenes and likewise can exist as singlet and triplet species. The advances that led to stable carbenes [10, 11] and silylenes [12] stimulated an exploration of the chemistry of phosphinidenes. 

As an illustration of the phosphorus-carbon analogy, consider the result of replacing a carbon fragment (CR2) by a phosphorus moiety (PR) in each of the common low-coordinate organic compounds (1C-4C) shown in Fig. 1. For example, the replacement of a single carbon in an alkene (1C) results in a phos-phaalkene (IP). Similarly, the phosphaalkynes (2P) are isolobal relatives of the alkynes (2C), and terminal phosphinidene complexes (3P) can be related to the... 

Phosphaalkynes M. Regitz on Multiple Bonds and Low Coordination in Phosphorus Chemistry . In M. Regitz and O.J. Scherer (Ed.) Houben-Weyl, Methoden der Organi-schen Chemie, G. Thieme, Stuttgart, New York, 1990, p. 58... 

The preparation of phosphaalkynes, which has been reviewed [1, 4], usually implies elimination of trimethylchlorosilane (TCS) 14 or of hexamethyldisiloxane (HMDSO) 7. Thus pyrolysis of the chloro compounds 1722 and 1723 at 750 or 630 °C, respectively, affords the trimethylsilylphosphaacetylene 1724 and TCS 14. 

In the most versatile preparation of phosphaalkynes, acid chlorides such as pivaloyl chloride [27] are reacted either with P(SiMe3)3 1692, with formation of TCS 14, or with (Me3Si)2PLi 1725 [26] to give the phosphides 1726 [28, 29], which eliminate hexamethyldisiloxane (HMDSO) 7 in the presence of catalytic amounts of NaOH [28] either in a solvent or more efficiently without a solvent at 120-200 °C [29, 30] to afford, via 1727, the corresponding phosphaalkynes 1728 and HMDSO 7 [1, 4] (Scheme 11.7). 

The first catalytic dihydroamination of a phosphaalkyne was confirmed when the product diaminophosphine was formed, the complex /ra ,y-[PdCl2 PfPr NII C fBu ) ].255... 

Some cycloaddition reactions of 4 are summarized in Scheme 1. This shows that silylene 4 undergoes reactions with nitriles [14], phosphaalkynes [15], silyl azides [16], diazabutadienes [17], 2,2 -bipyridyl and its derivatives [18, 19], a-ketoimines [19], and pyridine-2-aldimines [19]. 

More recently, [2+3] cycloaddition reaction of the tri-te/t-butylphenylphosphaethyne (25) has been reinvestigated, when in spite of the steric encumbrance of extremely bulky Mes group, the use of trimethylsilylated diazomethane (24) makes its cycloaddition successful, which is followed by SiMe3/H migration yielding bulky [l,2,4]diazaphospholes [33], Phosphaalkyne 25 reacts with 24 in a regioselective manner to form intermediate cycloadduct 26, which undergoes facile aromatization... 

Reaction of lithiated silyl- and diaminophosphino-diazomethanes (30, R = Me3Si, (R 2N)2P) with triphosphenium salt, [((Me2N)3P)2P]+BPh4 to give the respectively substituted [l,2,4]diazaphospholes has also been described to take place via the corresponding phosphaalkynes. Triphosphino substituted [l,2,4]diazaphosphole has been obtained by thermolysis of the phosphino-phosphiranyl-diazomethane via the... 

A potentially useful synthesis of 177-1,2-azaphospholes by the reaction of alkynes with l-aza-2-phospha-4-vanada-2-cyclobutenes generated from R1N=VC13 and phosphaalkynes may be considered as an example of cyclic carbovanadation 4 (Scheme 50). 

By treating the soft iV-heterocyclic carbenel,3,4,5-tetramethylimidazol-2-ylidene 278 with an electron-rich di(isopro-pyl)amino-phosphaalkyne 279, the bicyclic azaphospholene 281 was formed in almost quantative yield via a P-Ccarbene bond formation 280 and C-H insertion (Equation 123) <2001AGE3144>. 

Phosphacarba- f6>-pentaborane [2-/Bu-l,2-PCB3Fl5] 25 was synthesized by gas-phase reaction of phosphaalkyne with tetraborane(lO) (see Figure 11). In the 31P NMR spectrum a signal at —501 ppm was detected for the apical phosphorus atom and confirmed by quantum mechanical calculations.120... 

In 1981, Appel et al. postulated the transient formation of the (diphenyl-phosphino)(trimethylsilyl)carbene 2e to explain the formation of the phos-phaalkene 4e, in the thermolysis of the P-chloromethylene phosphorane 3e.29 At that time, the authors did not recognize the carbene character of 2e and simply named the intermediate a A5-phosphaalkyne. 

Similarly, the (phosphino)(silyl)carbene 2a reacts at -30°C with a slight excess of the tert-butylphosphaalkyne cleanly affording the 2-phosphino-2//-phosphirene 34.53 The reaction leading to 34 is strictly analogous to that observed on reacting the transient dichlorocarbene with the tert-butyl-phosphaalkyne, in which the 2//-phosphirene 36 was obtained.54 The three-membered heterocycle 34 appeared to be rather unstable and rearranged, quantitatively, to afford the lA5,2A3-diphosphete 35 after 3 h at room temperature.55 Once again, these results as a whole indicate that a concerted [1 + 2]-cycloaddition process is involved in the formation of the 2//-phosph-irene 34. 

Trialkoxy complexes of tungsten with terminal phosphido ligands could not yet be isolated. They were postulated to be very reactive intermediates in different transformation reactions, e.g., during the metathesis reaction of [W2(0R)6] with phosphaalkynes [6, 14]. However, we were able to characterize the complex [(t-BuO)3W=P] (3c) by P-NMR spectroscopy by monitoring the metathesis reaction of [W2(Ot-Bu)6] with MesC=P in the tempera-... 

In the first structurally characterized complexes of type A the metal-phosphorus triple bonds are kinetically stabilized by bulky substituents at the amido ligands. Therefore, these compounds reveal exclusively end-on reactivity via the phosphorus lone pair. This reactivity pattern seems also valid for the solution stable alkoxide derivative [(C/0)3Mo=P], for which the reaction potential is under investigation [13]. In contrast, due to their lesser degree of kinetic stabilization by bulky substituents the short-lived alkoxide containing complexes [(R 0)3W=Pj (R =t-Bu (3c), Ph (3d)), generated by the metathesis reaction between the alkoxide-dimer and the phosphaalkyne (cf. Eq. 8), show additionally a high side-on reactivity towards the phos-phaalkynes of the reaction mixture. Thus, there occurs a formal cycloaddition reaction with the phosphaalkynes, and a subsequent 1,3-OR shift yields the formation of four-membered diphospha-metallo-cyclobutane derivatives 6(Eq. 8) [15,31, 37]. 

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