Novel six-co-ordinate oxorhenium complexes with ligands containing PN2 andPNO donor atom sets: syntheses and structural characterization

Reactions of [(Bu4N)-Bu-n][Re(O)Cl-4] 1 with an excess of the recently desc ribed heterofunctionalized phosphane ligands 2-(diphenylphosphanyl)-N-(2-hy droxyethyl)benzamide (H2PNO) and N-(2-aminoethyl)-2-(diphenylphosphanyl)ben zamide (HPN2), in refluxing methanol, afforded the six-co-ordinated monooxo rhenium(V) complexes [Re(O)(kappa(3)-PNO)(kappa(2)-H2PNO)]Cl 5 and [Re(O)(k appa(3)-PN2)(OMe)Cl] 6, respectively. Ligand exchange between H2PNO and [Re (O)Cl-3(PPh3)(2)] 2 in the presence of NaOAc has led to the six-co-ordinate d monooxorhenium(V) complex [Re(O)(kappa(3)-PNO)(kappa(2)-DPPBA)] 7 (HDPPBA =2-(diphenylphosphanyl)benzoic acid). The characterization of the compounds involved IR, H-1 and P-31 NMR spectroscopy and X-ray crystallographic anal ysis. The overall geometry around the metal is best described as a distorte d octahedron: the co-ordination is defined by an oxo group, a tridentate di anionic PNO, and a bidentate co-ligand, which is the neutral H2PNO in the f irst case 5, and monoanionic DPPBA in the case of 7. In both these complexe s the equatorial plane is defined by the phosphorus, nitrogen and oxygen at oms of the dianionic PNO ligand and by a phosphorus atom of the co-ligand. The axial positions are occupied by the oxo group and by an oxygen atom of the co-ligand. In complex 6 the axial position is defined along the O=Re-OM e bond, three equatorial positions being occupied by the PN2 ligand, wherea s the fourth position is occupied by a chloride atom.