Synthesis of unsymmetrical 1,8-naphthyridine-based ligands for the assembly of tri-and tetra-nuclear copper() complexes

• Published in: New journal of chemistry 2020-10, Vol.44 (39), p.16713-1672
• Main Authors: Bacher, Felix, Isaac, James A, Philouze, Christian, Flot, David, Thibon-Pourret, Aurore, Belle, Catherine
• Format: Article
• Language: English
• Subjects: Acetonitrile; Aminophenol; Binding sites; Chemical Sciences; Complexation; Coordination chemistry; Coordination compounds; Copper; Copper compounds; Crystallography; Ligands; Triethylamine; X ray analysis
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/d0nj02776f

A synthetic route to unsymmetrical 1,8-naphthyridine spacer based ligands is presented. Reaction of a 7-ethyldipyridyl-1,8-naphthyridine-2-carboxaldehyde intermediate with 2-aminophenol or 4,6-di- tert -butyl 2-aminophenol led to the formation of ligands, HL 1 and HL 2 , respectively. Both combined two distinct binding sites: a dipyridyl and an iminophenol site linked through a 1,8-naphthyridine spacer. Treatment of HL 1 with copper( ii ) triflate in the presence of triethylamine/H 2 O in acetonitrile afforded a tetranuclear complex ( 1 tox ·2CH 3 CN). X-ray analysis revealed that the structure is constituted by the association of two identical dinuclear units in which the imine is oxidized to an amide group during the complexation. The coordination capabilities of the corresponding free amide ligands H 2 L 1ox and H 2 L 2ox , prepared by an independent route, were explored using copper( ii ) triflate in the presence of triethylamine/H 2 O. With the amide ligand, H 2 L 1ox , a similar tetranuclear copper complex ( 1 tox ·2DMF) compared to the one isolated after complexation with the imine ligand HL 1 was formed, as evidenced by X-ray diffraction studies. In contrast, H 2 L 2ox , where the amido phenol arm exhibits two additional tert -butyl groups, has allowed the formation of a trinuclear copper complex ( 2 triox ·H 2 O). Exploring copper( ii ) coordination from a new unsymmetrical naphthyridine-based ligand leads to the preparation of tetranuclear and trinuclear complexes. During the complexation, one imine group is oxidized to an amide group.