Synthesis and characterisation of oxo- and phenylimido-rhenium(V) complexes containing bidentate phosphinoenolato ligands

摘要

Reacting 1-phenyl-2-(diphenylphosphino)ethanone (P_1 approx OH), 1-tert-butyl-2-(diphenylphosphino)ethanone (P_2 approx OH) and 1-phenyl-2-(diphenylphosphino)propanone (P_3 approx OH) with ReOCl(PPh_3)_2 and Re(NPh)Cl_3(PPh_3)_2 in toluene and ethanol in the presence of NEt_3 yields complexes in which these ligands bind as monoanionic enolato chelating agents. Bromo and iodo analogues are prepared similarly. The reactions are solvent dependent. The disubstituted ReOCl(P approx O)_2 compounds obtained in toluene adopt the 'twisted' cis-(P,P) octahedral structure. With Re(NPh)Cl_3(PPh_3)_2, P_1 approx OH and P_2 approx OH give the corresponding Re(NPh)Cl(P approx O)_2 compounds and the trans-(P,P)-trans-(Cl,Cl) isomer of monosubstituted Re(NPh)Cl_2(PPh_3) (P approx O) as the major products, together with small amounts of 'twisted' trans-P,P)Re(NPh)Cl(P approx O)_2. The monosubstituted complex is the only species isolated with P_3 approx OH. The major structural differences between the two systems is the small stability gap between the cis- and the trans-(P,P) are isolated, resulting from stereoselective substitution of the halide in the 'twisted' cis-(P,P) octahedral complexes.The reactions with Re(NPh)Cl_3(PPh_3)_2 are less selective and give rise to mixtures of complexes.The trans-ethoxo-phenylimido compound Re(NPh)(OEt)(P_1 approx O)_2 is obtained in good yield. A crystallographic study reveals an unexpected 'equatorial' trans-(P,P) structure with the ethoxo ligand trans to the Re = NPh bond. ~1H NMR indicates that the ethoxo ligand acts as an electron reservoir in these complexes, since its protons are strongly deshielded in the cis-oxo-ethoxo species and strongly shielded in the trans-phenylimido-ethoxo complex.