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The nucleophilic substitution reactions of P[RNC(O)&lR'],CI [R = R' = CH,, (la); C,H,, (1 b); R = CH,, R' = C,H,, ( I c ) ] with Na[Mn(CO),] in tetrahydrofuran at -78 "C result in the synthesisof a new class of four-membered spirobicyclic transition-metal-substituted phosphoranes in which the five-co-ordinated phosphorus is bonded to heteroatoms other than oxygen. These compounds have been characterized by elemental analysis, n.m.r. spectroscopy ('H and ,'P), and thermal analysis.

The iron(III) complex of protoporphyrin IX is the basic component of the active sites of cytochromes P-450 and related mono oxygenases. The axial ligand in cytochromes P-450 is a cysteine thiolate, whereas in peroxidases it is the imidazole of a histidine residue of the protein. During the reaction sequence of peroxidase, the iron(Ill) porphyrin moiety of peroxidase reacts with H 2 02 and other mono oxygen donors to give compound I, which, on further one-electron transformation, leads to the formation of an iron(IV) oxo species, compound II of peroxidase. The formation of iron-oxo intermediates, similar to compound I, have been proposed for cytochromes P-450 catalyzed oxidations, except that the axial thiolate ligand favours the formation of the high-valent iron(V) species. Iron-porphyrins and different mono oxygen donors mimic the different reactions of cytochromes P-450 and other mono oxygenases. The formation of the M-O bonds from different metalloporphyrins and mono oxygen donors has been proposed in the hydroxylation of 1,3-dimethylpyrimidines, the epoxidation of aldrin and related olefins as well as in the oxidation of various sulphur compounds. The formation of M-N and M-C bonds has been proposed during the oxidation of different alkylhydrazines and related compounds. The formation of different intermediates and final products are briefly highlighted in the presentation.

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