Re(V) complexes with amino acids based on the ‘3+2’ approach

Five cationic complexes containing the [Re(V)O]3+ core have been prepared by substitution on the precursor [ReIO2(PPh3)2]. Complexes with general formula [ReO(dien-H)(aa)]+have been obtained by reaction of the precursor with 1 equiv. of dien (diethylenetriamine) and one equivalent of an amino acid (glycine, alanine, valine, leucine, proline). Complexes have been characterized by UV–Vis and IR spectrophotometry, elemental analyses, 1H NMR spectra, HPLC and conductivity measurements. The molecular structures of [ReO(dien-H)(leu)]I·0.5H2O and [ReO(dien-H)(pro)]ReO4 have been determined by means of single-crystal X-ray analyses. Cations consist of a six-coordinated rhenium atom bonded to two trans-oxo groups, one of the [ReO]3+ core and one from the carboxilate. Four nitrogen atoms make the equatorial plane. Three N belong to the dien ligand and the other one to the amino acid. One of the secondary amine proton of the dien ligand is lost upon coordination. This arrangement corresponds to the so-called ‘3+2’ chelating framework, with the novel NNN/NO atom set. Complexes are not very stable in aqueous solution. However, solutions in MeOH and DMSO are stable enough to be studied by several techniques. The solid state structure seems to be retained in solution.