SILACALIX-[N]-PHOSPHAARENES - MACROCYCLIC LIGANDS BASED ON DICOORDINATE PHOSPHORUS CENTERS

The synthesis of polyphosphinine macrocycles, which consist of a 16-me mbered ring with four phosphorus atoms (P-4) and a 12-membered ring wi th three phosphorus atoms (P-3), is described. Their high coordination ability is demonstrated by the quantitative synthesis of the rhodium and iridium cation complexes of the P-4 macrocycle and by quantitative synthesis of the W(CO)(3) complex of the P-3 compound. Unlike the oth er available macrocyclic ligands bearing oxygen, sulfur, di- or tricoo rdinate nitrogen, and even tricoordinate phosphorus as ligating atoms, which are all essentially a donors, these dicoordinate phosphorus-bas ed macrocycles have strong pi-acceptor properties. Their use can be en visaged for the stabilization of negative oxidation states of transiti on metals or in reductive catalysis.