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

Abstract

Reactions of [ⁿBu₄N][Re(O)Cl₄] 1 with an excess of the recently described heterofunctionalized phosphane ligands 2-(diphenylphosphanyl)-N-(2-hydroxyethyl)benzamide (H₂PNO) and N-(2-aminoethyl)-2-(diphenylphosphanyl)benzamide (HPN₂), in refluxing methanol, afforded the six-co-ordinated monooxorhenium(V) complexes [Re(O)(κ³-PNO)(κ²-H₂PNO)]Cl 5 and [Re(O)(κ³-PN₂)(OMe)Cl] 6, respectively. Ligand exchange between H₂PNO and [Re(O)Cl₃(PPh₃)₂] 2 in the presence of NaOAc has led to the six-co-ordinated monooxorhenium(V) complex [Re(O)(κ³-PNO)(κ²-DPPBA)] 7 (HDPPBA = 2-(diphenylphosphanyl)benzoic acid). The characterization of the compounds involved IR, ¹H and ³¹P NMR spectroscopy and X-ray crystallographic analysis. The overall geometry around the metal is best described as a distorted octahedron: the co-ordination is defined by an oxo group, a tridentate dianionic PNO, and a bidentate co-ligand, which is the neutral H₂PNO in the first case 5, and monoanionic DPPBA in the case of 7. In both these complexes the equatorial plane is defined by the phosphorus, nitrogen and oxygen atoms 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 ORe–OMe bond, three equatorial positions being occupied by the PN₂ ligand, whereas the fourth position is occupied by a chloride atom.