Oxo-rhenium(V) mixed-ligand complexes with bidentate functionalized phosphines and tridentate Schiff base ligands

A series of monooxo-rhenium(V) mixed-ligand complexes containing bidentate functionalized phosphines and tridentate Schiff base (SB) ligands have been synthesized via ligand-exchange reactions starting from labile Re(V) precursors. A convenient route of synthesis is provided by the isolation of intermediate species such as [Re(O)(Ln)Cl3]− (1–3), (Ln=bidentate phosphino-phenolato or phosphino-carboxylato ligands). Subsequent addition of the relevant SB affords neutral mixed-ligand complexes of general formula [Re(O)(Ln)(SBm)] (1–3m). By reversing the addition of the two ligands, i.e. SB first followed by functionalized phosphine, the resulting mixed-ligand species do not change formulation. Conventional spectroscopic techniques and the single-crystal X-ray structure determination of the two representative compounds ([Re(O)(L1)(SBa)] (1a) and [Re(O)(L1)(SBb)] (1b)) reveal a distorted octahedral geometry around the rhenium center, with the phosphino-phenolato oxygen located trans to the oxo group and the equatorial sites filled by the SB donors and the phosphine phosphorus. It is worth noting that technetium chemistry works quite differently under the same reaction conditions. In fact, no intermediate species of the type [Tc(O)(Ln)Cl3]− can be isolated with [Tc(O)Cl(L1)2] and reduced [Tc(Ln)3] being the major compounds.