Novel vanadium(iii) complexes with rigid phenylpolycarboxylate ligands: synthesis, structures and application in C–H bond activation

Abstract

Two novel vanadium(III) complexes: V(dipic)(Hbdc)(H₂O)₂ (1) and [V₂(dipic)₂(H₂btec)(H₂O)₄]·2H₂O (2) (H₂dipic = 2,6-pyridinedicarboxylic acid, H₂bdc = 1,3-benzene-dicarboxylic acid, H₄btec = 1,2,4,5-benzenetetracarboxylic acid) are synthesized by the reaction of V₂(SO₄)₃, 2,6-pyridinedicarboxylic acid and 1,3-benzene-dicarboxylic acid (for 1) or 1,2,4,5-benzenetetracarboxylic acid (for 2) under hydrothermal condition at 120 °C for 3 days. They were characterized by elemental analysis, IR, UV-Vis, single crystal X-ray diffraction analysis and thermogravimetric analyses (TG). Structural analyses show that the vanadium atoms in the complexes 1 and 2 are both in a pentagonal-bipyramidal coordination environment with the NO6 donor set, and there is intermolecular hydrogen bonding in each complex. Research results found that the complexes exhibited bromination catalytic activity in the single-pot reaction of the conversion of phenol red to bromophenol blue in the mixed solution of H₂O–DMF at the constant temperature of 30 ± 0.5 °C with pH = 5.8, and catalytic C–H bond cleavage activity for the peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cyclohexanol and cyclohexanone (the maximum total turnover number is 395) under the mild conditions.