COORDINATION CHEMISTRY OF UNSATURATED CYCLIC AND ACYCLIC PNS AND PNSELIGANDS

This review is primarily concerned with the synthesis, structure and f luxional behaviour of cyclic and acyclic chalcogen-nitrogen systems co ntaining phosphorus(V) or phosphorus(III). The cyclic Ph(4)P(2)N(4)S(2 )R(-) and Ph(4)P(2)N(4)S(2)(2-) anions (and their selenium analogues) are versatile ligands for both early and late transition metals, Mono- , di-, tri- and tetradentate bonding modes have been established for t he eight-membered P2N4S2 ring in these inorganic heterocycles. Ligatio n occurs through sulphur (or selenium) and/or nitrogen, while the coor dinatively saturated phosphorus(V) centres serve as an informative pro be of fluxional processes. By contrast, coordination occurs exclusivel y through phosphorus in both the cyclic and acyclic phosphorus(III) sy stems. In order to provide a background for the discussion of the coor dination chemistry of hybrid P-N/S-N systems, the review begins with a short account of N-bonded complexes of cyclophosphazenes and S4N4, wh ich is followed by a discussion of metal complexes of the S4N42- diani on. The concluding section of the review describes metal complexes of some related anionic S-N. ligands. In particular, the alkali metal der ivatives of the acyclic [RNS(R')NR''](-) anions and transition metal c omplexes of the cyclic radical PhCN(2)S(2) are discussed.