Phosphaalkene

These phosphaalkenes are extremely reactive, they undergo facile [2 + 4] cycloaddition reactions (equation 39) or reactions with protic acids... 

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]. 

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. 

Potentially, phosphaalkenes can be precursors to phosphinidenes in the same manner that carbenes can be formed from alkenes. This latter metathesis route deserves more attention in light of the recognition that stable carbenes can be in equilibrium with their dimers [11]. However, a discussion on phosphaalkenes is outside the scope of the present survey. 

The reactivity of the Cp (L)Ir=PMes (L=PPh3, CO) phosphinidene complexes is much less diverse than those with Zr. Only the formation of phosphaalkenes has been observed in the reaction with CH2I2 and CHI3 [102]. This reduced reactivity of the Ir complexes as compared to Zr complex 53 has been... 

Abstract Many similarities between the chemistry of carbon and phosphorus in low coordination numbers (i.e.,CN=l or 2) have been established. In particular, the parallel between the molecular chemistry of the P=C bond in phosphaalkenes and the C=C bond in olefins has attracted considerable attention. An emerging area in this field involves expanding the analogy between P=C and C=C bonds to polymer science. This review provides a background to this new area by describing the relevant synthetic methods for P=C bond formation and known phosphorus-carbon analogies in molecular chemistry. Recent advances in the addition polymerization of phosphaalkenes and the synthesis and properties of Tx-con-jugated poly(p-phenylenephosphaalkene)s will be described. 

A brief history of (3p-2p)7i bonds between phosphorus and carbon followed by an introduction to the methods of phosphaalkene synthesis that are pertinent to this review will be provided. The earliest stable compound exhibiting (3p-2p)7x bonding between phosphorus and carbon was the phosphamethine cyanine cation (1) [33]. An isolable substituted phosphabenzene (2) appeared just two years later [34]. The parent phosphabenzene (3) was later reported in 1971 [35]. These were remarkable achievements and, collectively, they played an important role in the downfall of the long held double bond rule . The electronic delocalization of the phosphorus-carbon multiple bond in 1-3, which gives rise to their stability, unfortunately prevented a thorough study of the chemistry and reactivity of the P=C bond. 

Another method that has been used to prepare phosphaalkenes is the phos-pha-Peterson reaction, a phosphorus analog of the Peterson olefination [46-49]. In this reaction a lithium silylphosphide is treated with an aldehyde or ketone to yield the phosphaalkene (9). Analogous reactions can be conducted with bis(trimethylsilyl)phosphines (10) and ketones (11) using a catalytic quantity of anhydrous base (i.e., NaOH, KOH) [50]. Generally, the reactions proceed cleanly and in high yield. Sufficiently bulky substituents must be employed to stabilize the P=C bond and prevent rapid dimerization to 1,3-diphosphetaines. 

Numerous other reactions can be used to access phosphaalkenes. For example, treating the primary phosphine Mes PH2 with CH2CI2 in the presence of KOH gives Mes P=CH2 [54]. In addition, interesting reactions of tantalum-or zirconium-phosphinidenes with aldehydes have afforded phosphaalkenes [55, 56]. The 1,3-hydrogen rearrangement of secondary vinylphosphines to phosphaalkenes has also been used to prepare phosphaalkenes [57,58]. 

This section will provide details of recent efforts to polymerize phosphaalkenes. It will begin with an introduction to the factors that must be considered when attempting to polymerize P=C bonds. In addition, a historical context will be provided since, perhaps ironically, it was so-called polymerization reactions that plagued early efforts to prepare compounds possessing heavier element multiple bonds. Finally, it will close with the first successful polymerization of a P=C bond to give poly(methylenephosphine)s. 

UV-vis spectra of samples of 32 exhibit broad absorbances (Ajnax=328-338 nm) that presumably result from a 71-71" transition. For comparison, model mono- and bis-phosphaalkenes 33 and 34 were also prepared and their UV-vis spectra show broad absorbances at 310 and 314 nm, respectively. As expected, the polymer 32 is red-shifted with respect to these small molecule models. The red-shift is moderate (ca. 20 nm) when compared with the red shift observed with that for trans-PPV versus trans-stilbene (ca. 130 nm). More striking is the... 

This review has shown that the analogy between P=C and C=C bonds can indeed be extended to polymer chemistry. Two of the most common uses for C=C bonds in polymer science have successfully been applied to P=C bonds. In particular, the addition polymerization of phosphaalkenes affords functional poly(methylenephosphine)s the first examples of macromolecules with alternating phosphorus and carbon atoms. The chemical functionality of the phosphine center may lead to applications in areas such as polymer-supported catalysis. In addition, the first n-conjugated phosphorus analogs of poly(p-phenylenevinylene) have been prepared. Comparison of the electronic properties of the polymers with molecular model compounds is consistent with some degree of n-conjugation in the polymer backbone. 

Keywords u-Conjugated systems Phosphorus Phosphaalkenes Phospholes Optoelectronics... 

Bis(trimethylsilyl)phosphines 1681, whose chemistry has been reviewed [5], condense with DMF and eliminate HMDSO 7 to give, e.g., the phosphaalkene 1682 [6]. Bis(trimethylsilyl)phosphines 1681 react with bis(dialkylamino)difluoro-methanes 1683 with elimination of Me3SiF 71 to give the phosphaalkenes 1684 [7, 8], whereas acid chlorides such as Me3CCOCl afford, with elimination of TCS 14, the O-trimethylsilylphosphaalkenes 1685 [9]. Bis(trimethylsilyl)phosphines 1681 condense with CO2 to the phosphacarbamates 1686 [10] whereas CS2 furnishes the methylenephosphanes 1687 [11, 12] (Scheme 11.1). 

Phosphaalkenes R. Appel 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. 157... 

Phosphaalkenes -P=C<, and phosphaimines -P=N- react with 1 to give secondary zirconated aminoalkyl or diamino phosphines, respectively, with P-coordination to the metal fragment (Scheme 8-24) [207]. An unexpected methylene-transfer reaction was observed upon reaction of 1 with Ph3P=CH2 (Scheme 8-24) [208],... 

Photoelectron and X-ray Spectroscopy. - The photoelectron spectrum of the n2 phosphaalkene (50) was similar to that of the corresponding imine. Its first ionisation potential was at 9.69... 

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