Phosphorus redox reactions

Work on phosphorus redox reactions was initiated in my lab on the basis of some enrichment cultures set up by an enthusiastic undergraduate student, Michael Friedrich. He as well as Volker Thiemann and Heike Laue have contributed to the experimental work in our lab on this subject Markus Gobel helped with the drawings for this contribution. My interest in phosphorus biochemistry was aroused by Dr. Ralph S. Wolfe who introduced me to the phenomenon of will-o -the-wisp. He and his colleague. Dr. William Metcalf, maintained my interest in this matter and stimulated my further activities in this held. 

The only structurally characterized derivative of a trisimido organophos-phonate anion is the spirocyclic tellurium(IV) complex (19), which is obtained from the interesting redox reaction between PhPCl2 and [Li2Te(N Bu)3 ] 2 [27]. The phosphorus(V)-centered ligands are generated by imide transfer from tellurium to the phosphorus(III) atoms with concomitant reduction of one-half of the tellurium in the Te(IV) reagent to elemental tellurium [27]. 

Red phosphorus and the chlorite react very exothermally in aqueous suspension above 50°C, and there may be a sudden and near-explosive stage in the redox reaction after an induction period. 

By far the most important redox reaction relative to chemical stability is the reaction between an oxidizable material and oxygen from air. The particle size and any droplets have a large effect on the combustion properties. Some substances react so rapidly in air that ignition occurs spontaneously. These so called pyrophoric compounds (white phosphorus, alkali metals, metal hydrides, some metal catalysts, and fully alkylated metals and nonmetals) must be stored in the absence of air. 

Phosphate is remineralized during the oxidation of organic matter and dissolution of hard parts, such as bones and teeth, that are composed of the minerals hydroxyapatite and fluoroapatite. Unlike the other products of remineralization, pore-water phosphate concentrations are regulated only by mineral solubility, such as through vivianite (iron phosphate) and francolite (carbonate fluoroapatite). Redox reactions are not significant because phosphorus exists nearly entirely in the h-5 oxidation state. 

Veith s group has studied the oxidative addition or redox reaction of a phosphorus(III) I------------------------------------------------------ ---------1, ... 

Reaction of this lO-S-3 [279] tetraazapentalene derivative with [Pd(PPhj) ] or [Rh(PPh3)3)Cl] results in the formal substitution of sulfur by the transition metal accompanied by a redox reaction (see Figure 4.93) [280], The endocyclic sulfur atom is transferred to a PPhj ligand (oxidation of phosphorus to PhjP=S). At the same time the transition metal is oxidis (palladium from 0 to +11 rhodium from +1 to +III), which leaves sulfur to be reduced by four electrons (it is -II in Ph I S and thus must have been +II in the tr-sulfurane starting material). It follows from this electron transfer analysis that the rt-sulfurane is indeed better desaibed as the sulfur complex of a doubly amide functionahsed NHC ligand. 

The phosphorus resonances of the compounds [RPTa(XR )j] in Fig. 7.33 surprise us somewhat, as we would expect the tantalum in these complexes to be in the oxidation state +V rather than +III. The synthesis can be imagined as being between CljTaCXR j and Li PR, and thus between Ta(V) and P(-I). We would expect that given the electronegativities of both phosphorus and tantalum, no intramolecular redox reaction would occur, as that would involve oxidation of phosphorus and reduction of the metal, and therefore the exact opposite to the situation encountered in P(III)/Fe(-II) above. 

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