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

Article abstract of DOI:10.1016/S0020-1693(02)01198-2

New rhenium-oxo and phenylimido complexes were synthetized and isolated by reaction of 1-phenyl-2-(diisopropylphosphino)ethanone on ReOX₃(PPh₃)₂ (X=Cl, Br, I), ReO(OEt)Cl₂(PPh₃)₂ and Re(NPh)Cl₃(PPh₃)₂ in basic media (NEt₃). 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)Cl₃(PPh₃)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)Cl₂(PPh₃)(P-O) (9) and of Re(NPh)Cl₂(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.