Phosphorus species

Tnvalent phosphorus species containmg organofluonne groups have been prepared by pyrolysis at 830 C and 0 01 torr of pentafluoroethyltnfluoromethyl-tnmethylstannylphosphanes 138] (equation 38)... 

Phosphine-borane 63a (75% ee) was obtained by reduction of compound (Sp)-62a using LDBB at -60°C and nucleophilic substitution with iodomethane in 72 % yield. The observed loss of optical purity may be ascribed to stereomutation of the generated tricoordinated phosphorus species. Recrystallization afforded (S)-63a in > 99% ee. On the other hand, severe racemization was observed using the same method with (Rp)-62b. An alternative strategy consisted of deborana-tion of (Rp)-62b using ZSl-methylpyrrolidine, methylation with methyl triflate. 

The donor-acceptor formation can be considered by transfer of electrons from the donor to the acceptor. In principle one can assume donor-acceptor interaction from A (donor) to B (acceptor) or alternatively, since B (A) has also occupied (unoccupied) orbitals, the opposite charge transfer, from B to A. Such a view refers to mutual electron transfer and has been commonly estabUshed for the analysis of charge transfer spectra of n-complexes [12]. A classical example for a donor-acceptor complex, 2, involving a cationic phosphorus species has been reported by Parry et al. [13]. It is considered that the triaminophosphines act as donor as well as an acceptor towards the phosphenium cation. While 2 refers to a P-donor, M-donors are in general more common, as for example amines, 3a, pyridines, 3b, or the very nucleophilic dimethylaminopyridine (DMAP) [ 14], 3c. It is even a strong donor towards phosphorus trichloride [15]. 

Phosphinidenes [1] are low-valent organophosphorus compounds that have attracted attention since the early 1980s when they were first discovered [2]. They are known in two classifications, one being the six-electron singly substituted phosphorus species (A) and the other in which the phosphorus atom carries an additional ri -stabifizing group, typically, but not necessarily, a transition metal group (B). Much has been learned about the reactivities of the complexed phos-... 

Intramolecular alkyl transfer is a fundamental problem with this reaction this problem can be addressed with modification in structure of the reagents. Neutral trivalent phosphorus reagents do react with carbonyl compounds at much lower temperatures, but lead to several types of pentacoordinated phosphorus products.190-198 More will be noted about the use of such pentacoordinated phosphorus species for carbon-phosphorus bond formation in Chapter 5. 

Similarly, monobasic forms of other trivalent phosphorus species have been used successfully in such conjugate addition processes, including monoesters of phosphonous acids375 425 426 and secondary phosphine oxides.427-429 The notable exception to the last of these species is the addition of the anion from diphenyl phosphine oxide to unsaturated aldehydes, which appears always to proceed by addition to the carbonyl carbon.427... 

Several reports have been made of the addition of dialkyl phosphites and related monobasic trivalent phosphorus species to alkenes in the presence of an organic peroxide and acetic acid (Equation 3.28).439-441... 

Although transition metal-mediated P-H addition across ordinary alkenes proceeds well only with five-membered cyclic hydrogen phosphonates, addition across the olefinic linkage of a,P-unsaturated compounds occurs readily with a range of phosphorus species and catalytic agents. Of particular note are the reaction systems involving platinum,96-107 palladium,108-115 and the lanthanides.116-122... 

In this chapter, we consider two aspects of carbon-phosphorus bond formation as they relate to pentacoordinated phosphorus species. The first aspect is the preparation of stable phosphorane species — compounds bearing five bonds to phosphorus with at least one of them being a C-P linkage. At present, this is an area of rather specialized interest, but one that has potential for broader applications. 

In line with the known similarity between the chemistry of Si and P, alkynyl phosphorus species undergo a similar rearrangement (Eq. 2.79) [58]. 

V. EQUILIBRIA AMONG DIFFERENTLY COORDINATED PHOSPHORUS SPECIES A. Introduction... 

Clearly the result is not very sensitive to the guess of the initial cell abundance Of course, all of this presumes that other factors do not limit the microbial population growth in this catastrophic incident-type case. Such factors would include difficulties of mass transport of pollutant molecules (e.g., in an oil slick or tar balls) to microorganisms in a water column (e.g., Uraizee et al., 1998). Also other critical substances like 02 or the nutrients such as nitrogen or phosphorus species must be present in sufficient quantities to permit unchecked microbial growth. 

Most syntheses of phosphorus amino acid analogues involve the conversion of a nucleophilic, trivalent phosphorus species into a pentavalent adduct. The classical Arbuzov-Michaelis reaction is a well-known transformation that demonstrates this principle.1 In the case of a phosphite diester, the stable form of the reagent is the P-H derivative, depicted in Scheme 2 19 this tautomer is converted into a nucleophilic form by deprotonation or by silylation, which favors the trivalent P—O—Si isomer. 

Nucleophilic phosphorus species are employed in the synthesis of amino acid analogues by condensation with imine derivatives, in parallel with the classical Strecker reaction. A variety of methods are available, depending on the selection of the phosphorus reagents and the imine precursors. 

The most common method for the synthesis of phosphinopeptides is the addition of a nucleophilic, trivalent phosphorus species to a carbon electrophile, including conjugated double bonds, alkylating agents, imines, and carbonyl compounds. By analogy with the phosphite ester additions described above, the nucleophilic form of a phosphinic acid is the trivalent species, generated from the more stable, pentavalent PH derivative by deprotonation or by silylation (cf. Scheme 2). 

Figure 4. Summer averages and winter maxima of phosphorus species soluble reactive P (SRP) (a) and total P (TP) (b). Bars are summer averages shaded, treatment and unshaded, reference. Squares are winter maxima black, treatment and white, reference.

For these reasons, numerous attempts have been made to identify and characterize DOP, but with little success because it is usually present in very low concentrations. Typical values in lake waters range from 5 to 100 xg of P/L in oligotrophic to eutrophic systems. Colorimetric methods have been used extensively to detect and differentiate between soluble reactive phosphorus (SRP) and soluble unreactive phosphorus (SUP) at concentrations as low as 10 xg of P/L (I). SRP is generally considered to consist of only orthophosphate compounds, whereas SUP is composed of all other phosphorus species, primarily organic phosphorus compounds. The sum of SRP and SUP is equal to the total soluble phosphorus (TSP). These methods were used to study the dynamics of bulk phosphorus fractionation between the sediments, suspended particulate matter, the biota, and the dissolved fraction (2). Despite these studies, very little is known regarding the identity and characteristics of the DOP in the hydrosphere. 

As far as the data permit, the dependence of bond energies on the hybridisations of the atoms concerned is allowed for. In the case of F—P, Cl—P and Br—P, the bond energies are based upon data for molecules in which the P atom has (approximately) sp3 hybridisation, e.g. PX3, PX2Y, POX3. These values are inappropriate for PX5 species, or for PX3Y2 etc. The mean bond energies found for, e.g., PF5 are considerably lower than for trivalent phosphorus species. 

Brandes, J. A., Ingall, E., and Paterson, D. (2007). Characterization of minerals and organic phosphorus species in marine sediments using soft X-ray fluorescence spectromicroscopy. Marine Chem. 103, 250-265. 

Shober, A. L., Hesterberg, D. L., Sims, J.T., and Gardner, S. (2006). Characterization of phosphorus species in biosolids and manures using XANES spectroscopy. /. Environ. Qual. 35, 1983-1993. 

Molecular orbital calculations have also provided theoretical justification for these stereoelectronic effects in tetracovalent and pentacovalent phosphorus species (2-7). As has been shown in molecular orbital calculations on the X -P-X2 (X = 0,N) structural fragments, the X.-P bond is strengthened (as indicated by an increase in the Mulliken overlap population) while the P-X3 bond is weakened when the X atom lone pair is app to the P-X3 bond. Thus, in the g,t conformation of dimethyl phosphate (Structure ll the overlap population for the trans P-0 bond is. 017 electron lower than the overlap population for the gauche P-0 bond. As shown for g,t dimethyl phosphate one lone pair (shaded in 1) on the gauche bond oxygen is app to the trans bond, while no lone pairs on the trans bond oxygen are app to the gauche bond. Thus, the weakest X.-P bond has one app lone pair and no lone pairs on X. app to the P=X2 bond. 1... 

Phosphide anions, phosphinyl radicals, and phospheniutn cations are two-coordinate phosphorus species which are related by gain or loss of one electron ... 

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