Tricarbonylrhenium(i) complexes of highly symmetric hexaazatrinaphthylene ligands (HATN): structural, electrochemical and spectroscopic properties

Abstract

The new mononuclear and dinuclear tricarbonylrhenium(I) complexes [(HATN)Re(CO)₃Cl] (1-Cl) and [(μ-Me₆-HATN)[Re(CO)₃Cl]₂] (2-Cl₂) of highly symmetric ligands HATN and Me₆-HATN were synthesized and structurally characterized. X-Ray crystal structures reveal identical strained aromatic systems and out of the plane fac-Re(CO)₃Cl units for both complexes. The packing geometry in the unit cell of 1 suggests intermolecular π–π association. Infrared spectroelectrochemistry (SEC) experiments confirmed ligand-based reductions. To get more insight into the reduction mechanism the triflate salts, [(HATN)Re(CO)₃](OTf) (1-OTf) and [(μ-Me₆HATN){Re(CO)₃}₂](OTf)₂ (2-OTf₂), were synthesized. Their electrochemical and spectroelectrochemical behavior also exhibits reduction of the aromatic systems. The electronic absorption spectral features of the one electron reduced species were studied by UV-vis-NIR spectroscopy, which shows a broad shoulder at 1500 nm, confirming intra-ligand charge transfer (ILCT). Density functional theory (DFT) calculations on the complexes 1-Cl and 2-Cl₂ for structural optimization show good agreement with experimental bond lengths and bond angles. The spin density plot shows a metal based HOMO and HATN ligand centered LUMO.