Bonding types in phosphorus-carbon compounds

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..  

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. 

In addition to the very many procedures available for the preparation of aminoalkyl-phosphonic and -phosphinic acids through phosphorus-carbon bond formation, many of which have just been summarized, the same acids have been obtained through a multitude of procedures which consist in the modification of compounds in which the essential carbon skeleton, and in particular the phosphorus-carbon bond, is already in existence. In the following account, the various types of otherwise functionalized phosphonic and phosphinic acids are considered in the order in which they have so far been listed in this and in the previous chapter. 

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. 

In principle, the three main approaches to the synthesis of phosphonic and phosphinic acid derivatives consist in (i) the generation of phosphorus-carbon bonds in the presence of other functional groups at phosphorus which, themselves, very often act to block the formation of a second (or third) phosphorus-carbon bond (ii) modifications in the phosphonic or phosphinic carbon moieties or (iii) modifications, at phosphorus in tetra-coordinate compounds which already possess phosphorus-carbon bonds reactions of this last type are considered in Chapter 6. 

By far the most important type of reaction displayed by halophosphines is nucleophilic substitution. This is pivotal to the preparation of many other three-coordinate compounds containing either solely P—C, P—O, P—N bonds, or mixed combinations. These reactions are often exothermic and frequently carried out at low temperatures. For the synthesis of phosphorus(III) compounds containing a P—O or P—N bond it is often necessary to add a base (triethylamine or pyridine are frequently used) to capture the hydrogen halide eliminated from these condensation reactions. In the case of P—C bond formation, a variety of routes are possible using various carbon-derived nucleophiles. 

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