Synthesis, structures, and catalytic studies of new copper(II) complexes with arene-linked pyrazolyl methane ligands

Abstract

Two new copper complexes, [Cu₂(L1)(dipic)₂(H₂O)₂]⋅2H₂O (1) and [Cu₂(L2)(dipic)₂(H₂O)₂]⋅3H₂O (2) (L1 = 1,4-bis((1H-pyrazol-1-yl)methyl)benzene; L2 = 1,4-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)benzene; and H₂dipic = 2,6-pyridinedicarboxylic acid), were synthesized by the reaction of copper salt, arene-linked pyrazolyl methane ligands, and 2,6-pyridinedicarboxylic acid in 95% C₂H₅OH. They were characterized by elemental analysis, IR, UV–vis, single-crystal X-ray diffraction analysis, X-ray powder diffraction, and thermogravimetric analysis. We explored the application of the copper complexes in bromination reactions; the complexes exhibited bromination catalytic activity in single-pot reaction for the conversion of phenol red into bromophenol blue. A feasible bromination reaction mechanism of copper complexes was proposed.

Graphical abstract

Two new copper complexes, [Cu₂(L1)(dipic)₂(H₂O)₂]⋅2H₂O (1) and [Cu₂(L2)(dipic)₂(H₂O)₂]·3H₂O (2) (L1 = 1,4-bis((1H-pyrazol-1-yl)methyl)benzene; L2 = 1,4-bis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)benzene; and H₂dipic = 2,6-pyridinedicarboxylic acid), have been synthesized. The application of the copper complexes in bromination reaction was explored, and a mechanism was proposed.

Keywords:

• Copper complexes
• Arene-linked pyrazolyl methane
• Hydrogen bond
• Crystal structure
• Oxidative bromination reaction

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the grants of the National Natural Science Foundation of China [grant number 21071071], [grant number 21371086]. Guangxi Key Laboratory of Information Materials, Guilin University of Electronic Technology, PR China (Project No. 1210908-06-K) and State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry, Jilin University, Changchun 130012, PR China [grant number 2013-05] for the financial assistance.