Synthesis, characterization and molecular structure of oxo and phenylimido rhenium(V) complexes of 1-phenyl-2-(diisopropylphosphino)-ethanone

Abstract New rhenium-oxo and phenylimido complexes were synthetized and isolated by reaction of 1-phenyl-2-(diisopropylphosphino)ethanone on ReOX 3 (PPh 3 ) 2 (X=Cl, Br, I), ReO(OEt)Cl 2 (PPh 3 ) 2 and Re(NPh)Cl 3 (PPh 3 ) 2 in basic media (NEt 3 ). In these complexes the ligand bonds mainly as monoanionic enolato chelating agent. The reactions are solvent dependent. The disubstituted ReOX(PO) 2 compounds ( 1 – 7 ) adopt a ‘twisted’ octahedral structure with a mixture of cis -PP and trans -PP configurations in toluene, thus indicating that in this case the stability gap between the two diastereoisomers is small. In ethanol, only the ‘twisted’ cis -PP conformers ReOCl(PO) 2 ( 1 ) and ReO(OEt)(PO) 2 ( 7 ) were observed. The ethoxo-oxo complex ReO(OEt)(PO) 2 ( 7 ) resulting from the stereoselective substitution of the halide by the ethoxo group is the unique species isolated when X=Br and I. The reaction with Re(NPh)Cl 3 (PPh 3 ) 2 was less selective and, in ethanol, excess of ligand was needed to get trans -PP-Re(NPh)Cl(PO) 2 ( 8 ) as unique species. A mixture of ( 8 ), of the monosubstituted Re(NPh)Cl 2 (PPh 3 )(PO) ( 9 ) and of Re(NPh)Cl 2 (PCO)(PO) ( 10 ) was observed in toluene with and without base. All these data emphasize the influence of the basicity and steric hindrance of the phosphinoenolato ligand on the rhenium complexes formation.