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.