Synthesis, characterization and DFT study of oxorhenium(v) complexes incorporating quinoline based tridentate ligands

Abstract

Two tridentate quinoline based Schiff base ligands HL¹ and HL² were prepared by condensation of salicylaldehyde and 2-hydroxy naphthaldehyde with 8-aminoquinoline, respectively in excellent yield. These ligands react with [ReOCl₃(OPPh₃)(SMe₂)] in a ratio of 1 : 1 in acetone to form mononuclear trans-dichloro oxo complexes of general formula [Re^VO(L)Cl₂]. Here L⁻ is the deprotonated form of 2-((quinolin-8-ylimino) methyl)phenol (HL¹) or 1-[(quinolin-8-ylimino)methyl]naphthalene-2-ol (HL²). The elemental analysis and ESI mass spectroscopic measurements ensure the formation of the desired complexes. The molecular structure of mer-[Re^VO(L¹)Cl₂] was confirmed by single-crystal X-ray diffraction. The complexes were also characterized by different spectroscopic techniques and electrochemical methods. The ground state geometry, NMR and absorption of Re(V) complexes were examined by DFT and TDDFT methods. The natural transition orbital (NTO) and spin density difference map analysis reveal the nature of the excitations. It was also found that the complexes act as a catalyst for oxidation of cis-cyclooctene to the corresponding epoxide by tert-butyl hydroperoxide (TBHP). The NMR and ESI mass spectroscopic analysis ensure the formation of the desired product which was obtained from catalysis.