Carbon-to-phosphorus bond

The breaking of carbon-to-phosphorus bonds is by itself not a useful reaction in homogeneous catalysis. It is an undesirable side-reaction that occurs in systems containing transition metals and phosphine ligands and that leads to deactivation of the catalysts. Two reaction pathways can be distinguished, oxidative addition and nucleophilic attack at the co-ordinated phosphorus atom (Figure 2.35). 

While breaking of the carbon-to-phosphorus bond is a nuisance in catalysis with organometallic complexes, the breaking of carbon-to-nitrogen and -to-sulfur bonds is a desired reaction in the oil industry. Hydrodenitrification (HDN) and hydrodesulfurisation (HDS) are carried out on a large scale in order to remove nitrogen and sulfur from the fuel feedstocks. 

As a second step in the reaction, following co-ordination, most authors propose an oxidative addition of the C-S fragments to the transition metal, similar to the reaction found for carbon-to-phosphorus bond breaking. Since the C-S bond is rather weak it is easy to break and indeed several model reactions can be found in the literature. 

Coenzyme A (CoA) has recently emerged as an important coenzyme in the transfer of acyl groups for a variety of biosynthetic reactions leading to the formation of carbon-to-carbon, carbon-to-nitrogen, and carbon-to-phosphorus bonds. 

Ylides are neutral compounds characterized by internally compensating ionic centers, a carbanionic group and a neighboring onium unit, typically localized at phosphorus, arsenic, or sulfur, Ylidic carbanions are strong nucleophiles and show a high affinity for most metals in their various oxidation states. This can be exemplified by the reactions of a simple phosphorus ylide, like trimethylphos-phonium methylide (trimethylmethylenephosphorane), that are now known to lead to organometallic compounds with exceptionally stable carbon-to-metal bonds. 

B. Hybridization Modifications to Phosphorus-bonded Carbon Atoms. . 567... 

P, and S. The applicability of gj and gr constants defined from substituent effects at carbon to substituents bonded to phosphorus has been clearly demonstrated by the work of Charton and Charton (51-53). These authors have examined the correlation of ionization potentials of Z Z W and Z Z Z W, where W is O, S, and N (54). The results in this case are not sufficient to establish the applicability of gj and Gr constants as the O, S, and N were both skeletal groups and active sites. We have therefore examined the correlation of pAT<,s of acids of the type 4-ZW where W is NH, O, S, and SO2, with Equations 88 and 129 in the case of NH, O, and S and Equations 88 and 103 in the case of SO2. The data used in the correlations are presented in Table 46. In the case of W = NH, very much better correlation is obtained with the gr constants (sets 5Am and 5Bm, Table 44) than with the gr values (sets 5A and 5B, Table 44). The results show that the gj and gr constants are indeed applicable to substituent effects at nitrogen. The case in which W = O presents a new problem. When correlations with Gj and gr or gr are carried out the partial correlation coefficients of gj on Gr or gr constants (revalues) show that the gj and gr or gr constants are linear in each other. This situation results from the small number of points and the limited types of Z groups available. To overcome this difficulty we may make use of composite substituent constants. Rearranging Equation 91 we obtain... 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Dialkylphosphinous acids react with perfiuoroalkenes under free radical conditions to form carbon-phosphorus bonds [10] (equation 7)... 

The most common cause of chirality is the presence of four different substituents bonded to a tetrahedral atom, but that atom doesn t necessarily have to be carbon. Nitrogen, phosphorus, and sulfur are all commonly encountered in organic molecules, and all can be chirality centers. We know, for instance, that trivalent nitrogen is tetrahedral, with its lone pair of electrons acting as the fourth "substituent" (Section 1.10). Is trivalent nitrogen chiral Does a compound such as ethylmethylamine exist as a pair of enantiomers ... 

The Arbusov reaction is one of the best known methods for creating a carbon-phosphorus bond. In its simplest form (Michaelis-Arbusov) an alkyl halide reacts with a trialkyl phosphite to an alkanephosphonic acid diester as shown in Eq. (29) ... 

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. 

The phosphonium salt (116) gave the phosphorane (117) with phenyl-lithium although it has hydrogen atoms attached to carbon bonded to phosphorus. ... 

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. 

The rule in carbon-13 NMR is that sp2-hybridized carbons (carbonyl, aromatic, olefinic) absorb at lowest field, followed by sp-hybridized (acetylenic, nitrile) and sp3 (aliphatic). A first glance leads us to believe we have seven signals, but we must remember that the methine carbon is directly bonded to phosphorus, so that we shall expect a relatively large C-P coupling. The other C-P couplings will probably be very much smaller. 

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. 

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