(ORTHO-PHENYLENEDIIMIDO)DITUNGSTEN AND (PARA-PHENYLENEDIIMIDO)DITUNGSTEN COMPLEXES

The preparations of a series of dinuclear complexes of W(VI), W(V), and W(IV), bridged by either omicron- or p-phenylenediimido ligands, are described. The insoluble (and presumably polymeric) d0-d0 systems, omicron- and p-[Cl4W = NC6H4N = WCl4], are obtained in high yield from the reactions of either omicron- or p-Me3SiNHC6H4NHSiMe3 with 2 equiv of WCl6 in CH2Cl2 solution at room temperature. Upon treatment with tetrahydrofuran, these systems produce the soluble 16-electron complexes omicron- and p-[(THF)Cl4W = NC6H4N = WCl4(THF)]. It is proposed that the THF ligands occupy sites trans to the organoimido ligands in these systems. The THF ligands in the para-disubstituted complex are readily displaced by chloride ions upon treatment with [PPN]Cl to afford the decachloro dianion [PPN]2[Cl5 W = NC6H4N = WCl5]. The ortho- and para-disubstituted THF derivatives each undergo facile reduction in solution in the presence of tertiary phosphines L to produce the W(V)-W(V) (d1-d1) systems omicron- and p-[L2Cl3W = NC6H4N = WCl3L2]. ESR spectra are consistent with the adoption of the mer-trichloro, trans-bis(phosphine) geometry for these complexes. Preliminary studies of the magnetic properties of these d1-d1 systems throughout the temperature range 5-300 K have revealed antiferromagnetic behavior in p-[L2Cl3W = NC6H4N = WCl3L2] (L = Et2PhP) and in omicron-[L2Cl3W = NC6H4N = WCl3L2] (L = Me3P). When these W(V)-W(V) systems are treated with sodium amalgam in the presence of additional phosphine, diamagnetic W(IV)-W(IV) (d2-d2) systems are obtained in high yield. In the case of para-disubstituted system, the product has the stoichiometry [L3Cl2W = NC6H4N = WCl2L3] (L = Et2PhP), and NMR studies suggest the adoption of the cis-dichloro, mer-tris(phosphine) geometry. In the case of the ortho-disubstituted system, the stoichiometry of the product obtained appears to depend on the steric bulk of the phosphine ligand employed. Use of the compact Me3P species allows coordination of three phosphines per W atom, and the product obtained is of the form [L3Cl2W = NC6H4N = W = Cl2L3]; a cis-dichloro, mer-tris(phosphine) geometry is again indicated by NMR studies. In the case of the bulkier Et2PhP ligand, the product incorporates only two phosphines per W atom and is of the form [L2Cl2W = NC6H4N = WCl2L2]; the observed equivalence of the phosphine ligands in this species can be accommodated by a structure derived from either a square-based pyramid or a trigonal bipyramid.