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) precu rsors. A convenient route of synthesis is provided by the isolation of inte rmediate species such as [Re(O)(L-n)Cl-3](-) (1-3), (L-n = bidentate phosph ino-phenolato or phosphino-carboxylato ligands). Subsequent addition of the relevant SE affords neutral mixed-ligand complexes of general formula [Re( O)(L-n)(SBm)] (1-3m). By reversing the addition of the two ligands, i.e. SE first followed by functionalized phosphine, the resulting mixed-ligand spe cies do not change formulation. Conventional spectroscopic techniques and t he single-crystal X-ray structure determination of the two representative c ompounds ([Re(O)(L-1)(SBa)] (1a) and [Re(O)(L-1)(SBb)] (1b)) reveal a disto rted octahedral geometry around the rhenium center, with the phosphino-phen olato oxygen located trans to the oxo group and the equatorial sites filled by the SE donors and the phosphine phosphorus. It is worth noting that tec hnetium chemistry works quite differently under the same reaction condition s. In fact, no intermediate species of the type [Tc(O)(L-n)Cl-3](-) can be isolated with [Tc(O)Cl(L-1)(2)] and reduced [Tc(L-n)(3)] being the major co mpounds. (C) 2001 Elsevier Science B.V. All rights reserved.