Phosphorus-carbon compounds

In this lecture some new routes to phosphorus-carbon compounds with P-C multiple bonds, found in connection with our investigations on reactions of tertiary phosphanes with chlorinated carbon compounds, such as tetrachloromethane, hexachloroethane, phosgene, and isocyanide dichlorides are reported. Furthermore some stereochemical problems concerning this type of compound will be discussed. 

APPEL Phosphorus-Carbon Compounds with piT-p Bonds... 

Structure and bonding in phosphorus-nitrogen and phosphorus-carbon compounds... 

Phosphaalkynes also play a prominent role as dienophiles in Diels-Alder reactions hence the X -phosphinines 13 [23] are formed from cyclic 1,3-dienes such as a-pyrone or cyclopen-tadienones by way of extrusion of CO2 or CO, respectively reactions with anthracene provide an access to the phosphabarrelene series [24]. This type of reaction is also of significance for the construction of phosphorus-carbon cage compounds. The same is true for homo-Diels-Alder reactions which, with 2-phosphabicyclo[2.2.2]octa-2,5-diene as reaction partner, lead to the diphosphatetracyclodecenes 14 [25]. Last but not least, ene reactions with phosphaalkynes as enophiles [25] are also valuable for the construction of polycyclic phosphorus-carbon compounds. The reactions of 9 with 2,3-dimethyl-2-butene (- 15) [26, 27] emphasize this behavior. 

Phosphorus-carbon compounds (natural products with a C-P bond). Many natural products contain phosphorus-oxygen-bonds, espec. metabolites of the primary metabolism. A few only contain the C-p bond, many of those show antibiotic activities. The first natural product of the C-P-type was aminoethylphos-phonic acid (AEP), discovered in 1959. Others, covered in this book are bialaphos, fosfazinomycin, fosfomycin, fosfonochlorin, phosphinothricin, phosphonothrixin and the rhizocticins. For a complete overview, see Ut.. ... 

The reactions described so far can be considered as alkylation, alkenylation, or alkynylation reactions. In principle all polar reactions in syntheses, which produce monofunctional carbon compounds, proceed in the same way a carbanion reacts with an electropositive carbon atom, and the activating groups (e.g. metals, boron, phosphorus) of the carbanion are lost in the work-up procedures. We now turn to reactions, in which the hetero atoms of both the acceptor and donor synthons are kept in a difunctional reaction produa. 

Organophosphorus compounds. Phosphorus-carbon bond fonnation takes place by the reaction of various phosphorus compounds containing a P—H bond with halides or tritlates. Alkylaryl- or alkenylalkylphosphinates are prepared from alkylphosphinate[638]. The optically active isopropyl alkenyl-methylphosphinate 778 is prepared from isopropyl methylphosphinate with retention[639]. The monoaryl and symmetrical and asymmetric diarylphosphi-nates 780, 781, and 782 are prepared by the reaction of the unstable methyl phosphinate 779 with different amounts of aryl iodides. Tnmethyl orthoformate is added to stabilize the methyl phosphinate[640]. 

The Tetrahedral Carbon Atom.—We have thus derived the result that an atom in which only s and p eigenfunctions contribute to bond formation and in which the quantization in polar coordinates is broken can form one, two, three, or four equivalent bonds, which are directed toward the corners of a regular tetrahedron (Fig. 4). This calculation provides the quantum mechanical justification of the chemist s tetrahedral carbon atom, present in diamond and all aliphatic carbon compounds, and for the tetrahedral quadrivalent nitrogen atom, the tetrahedral phosphorus atom, as in phosphonium compounds, the tetrahedral boron atom in B2H6 (involving single-electron bonds), and many other such atoms. 

Just as in the case for the hydrosphere, the atmosphere participates in all of the major biogeochemical cycles (except for phosphorus). In turn, the chemical composition of the atmosphere dictates its physical and optical properties, the latter being of great importance for the heat balance of Earth and its climate. Both major constituents (O2, H2O) and minor ones (CO2, sulfur, nitrogen, and other carbon compounds) are involved in mediating the amounts and characteristics of both incoming solar and outgoing infrared radiation. 

Species 5 (Scheme 8), commonly known as dialkylaminodifluorophosphines, are readily synthesized via the selective cleavage of the phosphorus-carbon bond of difluoro(trichloromethylphosphane) by the action of secondary amines [65,66]. Compounds 5 show selective F/H exchange with LiAlH4/HN(Tr)2 to give the respective PH2 (P-unsubstituted) phosphinous amides [13]. 

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... 

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. 

Because organophosphorus compounds are important in the chemical industry and in biology, many methods have been developed for their synthesis [1]. This chapter reviews the formation of phosphorus-carbon (P-C) bonds by the metal-catalyzed addition of phosphorus-hydrogen (P-H) bonds to unsaturated substrates, such as alkenes, alkynes, aldehydes, and imines. Section 5.2 covers reactions of P(lll) substrates (hydrophosphination), and Section 5.3 describes P(V) chemistry (hydrophosphorylation, hydrophosphinylation, hydrophosphonylation). Scheme 5-1 shows some examples of these catalytic reactions. 

Geometrical parameters provide much more information than simple identification. The phosphorus-carbon distance of 1.686(6) A in this tungsten complex is consistent with there being a double bond, as it is close to those observed in open chain phosphaalkenes. But how much better it would have been if the parent compound could have been studied uncomplexed, so that the strain in this unusual ring system could have been investigated. The geometrical parameters would then have provided very useful information about the likely reactivity of the compound, and information about the changes on... 

Nickel and palladium complexes also catalyze the formation of the carbon-phosphorus bonds in phosphorus(V) and phosphorus(III) compounds. Indeed, this chemistry has become a common way to prepare phosphine ligands by the catalytic formation of phosphine oxides and subsequent reduction, by the formation of phosphine boranes and subsequent decomplexation, or by the formation of phosphines directly. The catalytic formation of both aryl and vinyl carbon phosphorus bonds has been accomplished. 

MATHEY Phosphorus-Carbon Heterocyclic Chemistry The Rise of a New Domain McKILLOP Advanced Problems in Organic Reaction Mechanisms OBRECHT Solid Supported Combinatorial and Parallel Synthesis of Small-Molecular-Weight Compound Libraries... 

Gross, H. and Keitel, I., a-Substituted phosphonates. 58. A direct phosphorylation of 7,7-bisphosphorylated quinonemethide nucleus with trivalent phosphorus-hydrogen compounds via carbon-carbon cleavage, Phosph., Sulf., Silic. Relat. Elem., 62, 35, 1991. 

Reactions with Simple Alkenes and Aromatic Compounds.—A wide range of conditions continues to be used to form phosphorus-carbon bonds between halogeno-phosphines and alkenes or benzene derivatives. A selection of such reactions (Scheme 2) is outlined for the preparation of the compounds (17)—(23).22-26... 

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 chemistry of phosphorus compounds with a delocalized P-C double bond proves to be very versatile. Whereas the physical properties of phosphamethin-cyanines are similar to the corresponding methin- or azamethin-cyanines, their chemical properties are distinguished by the higher reactivity of the phosphorus atom and the phosphorus-carbon double bond. 

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