Triphosphorus macrocycle complexes of divalent group 6 transition metals; Crystal structure of bromotricarbonyl-[1,5,9-tris(isopropyl)-1,5,9-triphosphacyclododecane]molybdenum(II)tetraphenylborate

New triphosphamacrocycle complexes of molybdenum(ii) and tungsten(ll) have been prepared by oxidative addition of halogens to molybdenum and tungsten tricarbonyl complexes of 1,5,9-triphosphacyclododecane and tritertiary phosphine analogues. The behaviour of these macrocycle complexes is similar to that of previously reported examples with monodentate tertiary phosphines and the metal(0) precursors give rise initially to seven-co-ordinate salts containing a [M(CO)(3)X(L)](+) cation (L = tridentate triphosphamacrocycle) with a halide anion which may be exchanged for other counter ions. The seven-co-ordinate complexes are all fluxional in solution and give rise to temperature-variant NMR spectra. At the low-temperature limit an AB(2) pattern was observed in the P-31 NMR spectra of all the new complexes. The salts all convert slowly into the neutral seven-coordinate dicarbonyldihalogeno complexes [M(CO)(2)X(2)(L)] in solution. These are the first examples of metal complexes of the 1,5,9-triphosphacyclododecane family other than the metal(o) tricarbonyl template complexes upon which the macrocyclic ligands were originally made.