Rhenium and technetium complexes from pentadentate (N3O2) and tetradentate (N2O2) Schiff base ligands

Abstract

The rhenium(V) and technetium(V) complexes: [ReO(apa)], [{ReO(epa)}2O], and [TcOCl(epa)] have been prepared from a potentially pentadentate N3O2 ligand, N,N′-3-azapentane-1,5-diylbis(3-(1-iminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione) (H3apa), or a potentially tetradentate N2O2 ligand, N,N′-ethylene-diylbis(3-(1-iminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione) (H2epa). The N2O2 complexes were synthesized in low yields. There was also evidence indicating that H2ppa, N,N′-propylene-diylbis(3-(1-iminoethyl)-6-methyl-2H-pyran-2,4(3H)-dione), hydrolyzed in the course of coordination, forms a rhenium complex of the bidentate monoprotic (O,O) dehydroacetate (dha−), [Re(dha)Cl2(OPPh3)(PPh3)]•EtOH. The structure of this complex was determined by X-ray crystallography. Crystals of [Re(dha)Cl2(OPPh3)(PPh3)] EtOH (C44H37Cl2O5P2Re•C2H6O) are monoclinic, a = 11.064(2), b = 24.167(2), c = 16.6687(8) Å, β = 98.779(7)°, Z = 4, space group P21/c. The structure was solved by the Patterson method and refined by full-matrix least-squares procedures to R = 0.030 and Rw = 0.025 for 6942 reflections with I ≥ 3σ(F2). Keywords: dehydroacetic acetate based Schiff base ligands, rhenium, technetium, N3O2 Schiff base, N2O2 Schiff base, oxygen transfer.