Stable tetranuclear copper cage as efficient heterogeneous catalyst for C−C and C−N bond forming reactions

• Published in: Journal of molecular structure 2023-09, Vol.1288, p.135759, Article 135759
• Main Authors: Xiong, Peng, Zhang, Tong-Wei, Li, Shi-Ming, Xu, Mei-Yu, -Liang, Guang-Ming, Gui, Liu-Cheng, Wang, Xiu-Jian
• Format: Article
• Language: English
• Subjects: Catalyst; Copper cage; Crystal structures; Heterogeneous
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2023.135759

•Two tetranuclear copper cages with tubular type, [Cu4(BMBA)4((CH3)2 N)2(H2O)2] (1) and [Cu4(BMBA)4(Bipy)(H2O)2] (2), were successfully constructed by the reaction of cupric nitrate with dicarboxylic acid ligand.•Interesting, the complex 2 exhibits excellent stability in common organic solvents and aqueous solutions at pH 2–12.•Upon thermal activation of complex 2, its active metal site show Lewis acid character to be an efficient heterogeneous catalyst for CC (Knoevenagel condensation) and CN (Clauson-Kaas) bond forming reactions. Two tetranuclear copper cages with tubular type, [Cu4(BMBA)4((CH3)2N)2(H2O)2] (1) and [Cu4(BMBA)4(Bipy)(H2O)2] (2), were successfully constructed by the reaction of Cu(NO3)2 with dicarboxylic acid 4,4′-[(ethylazanediyl)bis(methylene)]-bis[(1,1′-biphenyl)-2-carboxylic acid] (H2BMBA) under solvothermal conditions. The complexes 1 and 2 exhibit a similar cage structure, formed by four ligands connecting two binuclear copper paddle-wheel secondary building units (SBUs). Interestingly, the complex 2 was obtained by appropriately binding of 4, 4′-bipyridine (Bipy) molecule on the axial positions of two Cu paddle-wheels inside the cage. For this reason, the complex 2 exhibits excellent stability in some common organic solvents at room temperature and aqueous solutions with a pH of 2 to 12. Upon thermal activation of complex 2, the coordinated water molecules can be removed, and its exposed metal active-sites show Lewis acid character, which can be used an efficient heterogeneous catalysis of Knoevenagel condensation (CC) and Clauson-Kaas (CN) reactions.