Phosphorus-carbon analogy

R. Engel, The use of carbon-phosphorus analog compounds in the regulation of biological processes, in Handbook of Organophosphorus Chemistry (Ed. R. Engel), Dekker, New York, 1992, pp. 559-600. 

The carbon-phosphorus analogy has been extended in different areas of organophosphorus chemistry over the last 40 years - some essential steps and consequences have been described very recently [ 13b]. Over the years, it became more and more obvious that this analogy is strengthened if the phosphorus... 

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. 

Methylene trimethylarsorane is a monomer in benzene solution. Study of its H and 13C NMR spectra led to some unexpected conclusions, distinctly different from the findings with the phosphorus analog (80). As shown in Table III, the 5 and J characteristics of the CH2 nuclei are not nearly as different from those of the CH3 groups as are those of CH2 and CH3 in the phosphorus ylide (58). Whereas /(H2C) = 149 of the latter indicates an sp2 carbon (the value for ethylene is 150 Hz), J(H2C) = 131 in the former rather points to an sp3 carbon for the carbanion in (CH3)3-AsCH2. (Methane, 125 Hz CH3 in the ylide, 133 Hz )... 

The concepts of diagonal relationship and isoelectronic families point to a manifold analogy between carbon and phosphorus compounds.Besides P2, the diphosphorus molecule, cyclo-Pj, cyclo-P, and cyc/o-Pg, the all-phosphorus analogs of the carbocyclic n systems CjHs , and... 

Going from a phosphaalkene to a phosphaalkyne, we increase the. r-contribution in the carbon phosphorus multiple bond, and would therefore expect a further down-field shift of the phosphorus resonance. However, a glance at the situation in carbon carbon multiple bond systems in particular, alkenes and alkynes, tells us that C-NMR spectra of these molecules show the carbon resonance of alkynes upheld from that of alkenes. This is usually explained by anisotropic effects associated with the linear rod-shaped structure of alkynes versus the bend structure of alkenes. As the geometries of phosphaalkenes andphosphaalkynes are analogous to alkenes and alkynes, respectively, we can assume that the explanation given for the appearance of the carbon resonance in alkynes upheld from that for alkenes in C-NMR spectra is also applicable for the respective unsaturated phosphoms compounds. 

In complete analogy with procedures noted for the preparation of phosphines (see Section 3.2), carbon-phosphorus bonds may be generated directly from P(V) halide species using organometallic reagents (equation 35). 

Perhaps the most interesting of all the phosphorus analogs of metallocenes is the carbon-free metallocene, [(i7 -P5)2Ti]. This complex, prepared by the reaction of [Ti(naphthalene)2] with P4, contains parallel, eclipsed P5 rings. The P5 ligand in this and other complexes is a weaker donor, but substantially stronger acceptor, than the cyclopen-tadienyl ligand. 

When carbon chain poly(phosphines) act as multidentate ligands they form chelate rings containing carbon, phosphorus and a metal atom. They can be made by reactions analogous to those employed for monodentate derivatives above. In reaction (8.137) a linear complex is first formed, but on raising the temperature a cyclic derivative is obtained. 

Below, a short review of chemical and stereochemical aspects of selected classes of the C P bond-forming reactions, relevant to the synthesis of natural products and their analogs containing carbon phosphorus bonds, is given. As potentially two chiral centers can be formed... 

Addition of Phosphorus Nucleophiles to C=C Bonds Phosphorus nucleophiles, both neutral and anionic, undergo addition to activated carbon—carbon double bonds. Such reactions constitute a phosphorus analogous of the conjugate addition, and they are often referred to as phospha-Michael addition. For hydrophosphonylation of inactivated double bonds, radical conditions are a viable option. In the last 15 years, however, an attractive alternative of a transition-metal-catalyzed hydrophosphonylation has also emerged. ... 

Phospholes and analogs offer a wide variety of coordination modes and reactivity patterns, from the ti E) (E = P, As, Sb, Bi) through ri -dienic to ri -donor function, including numerous and different mixed coordination modes. Electrophilic substitution at the carbon atoms and nucleophilic properties of the phosphorus atom are well documented. In the ri -coordinated species, group V heteroles nearly acquire planarity and features of the ir-delocalized moieties (heterocymantrenes and -ferrocenes). 

We designed less strained analogs of 61a-c by applying the lone pair effects (Sect. 2.1.4) [68]. Substitution of carbons with phosphorus atoms relaxes the strain (Scheme 28). Notably, substitution at the 3- and 4-positions in tricy-clo[2.1.0.0 ]pentane resulted in greater relaxation than substitution at the 2- and 5-positions. 

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. 

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