New fac-[Re(CO)3(OO)(L)] and [Re(CO)2(OO)(L)2] Complexes Bearing Two Natural Food Additives, Maltol and Kojic Acid, as OO Ligands

Abstract

The synthesis and structural characterization of new “2+1” mixed ligand fac-[Re(CO)3(OO)(L)] and Re(CO)2(OO)(L)2 complexes are reported herein. Maltol and kojic acid were chosen as bidentate OO ligands, while imidazole, isocyanocyclohexane or triphenylphosphine were selected as the monodentate ligands. The synthesis of the rhenium complexes was based on the reaction of [NEt4]2[Re(CO)3Br3] with maltol and kojic acid to generate the intermediate aqua complex fac-[Re(CO)3(OO)(H2O)], followed by the replacement of the labile aqua ligand by the monodentate ligand. Structural characterization of all Re complexes was established by NMR and IR spectroscopies, as well as two of them by single-crystal X-ray crystallography, revealing distorted octahedral geometry around the Re center. In the crystal lattice, the complexes form supramolecular networks due to the development of intermolecular interactions of the N-H⋯O, C-H⋯O and C-H⋯π type.