Trinuclear dioxidomolybdenum(vi) complexes derived from benzene-1,3,5-tricarbohydrazide and study of the catalytic activity

Five new tricompartmental ligands, each having three tridentate dibasic ONO sites, have been obtained from the condensation of benzene-1,3,5-tricarbohydrazide (bthz) and 4-formyl-5-pyrazolone H(6)btzh(fp)(3) (I), 4-acetyl-5-pyrazolone H(6)bthz(mp)(3) (II), 4-propionyl-5-pyrazolone H(6)bthz(ep)(3) (III), 4-butyryl-5-pyrazolone H(6)bthz(pp)(3) (IV) and 4-benzoyl-5-pyrazolone H(6)bthz(php)(3) (V). The reaction of I-V with [(MoO2)-O-VI(acac)(2)] (Hacac = acetylacetone) leads to the formation of tris{cis-[MoO2]} complexes [{(MoO2)-O-VI(H2O)}(3)bthz(fp)(3)] (1), [{(MoO2)-O-VI(H2O)}(3)bthz(mp)(3)] (2), [{(MoO2)-O-VI(H2O)}(3)bthz(ep)(3)] (3), [{(MoO2)-O-VI(H2O)}(3)bthz(pp)(3)] (4) and [{(MoO2)-O-VI(H2O)}(3)bthz(php)(3)] (5) having C-3 symmetry. All ligands and complexes are characterized by various techniques: FT-IR spectroscopy, UV/Visible, NMR (H-1 and C-13), elemental analysis and thermal studies. X-Ray diffraction studies of complexes 2-5 confirm their distorted octahedral geometry, where each pocket of ligands coordinates through the enolate oxygen (of pyrazole), enolate oxygen (of hydrazide), and azomethine nitrogen atoms. Catalytic potentials of these complexes were achieved for the (i) oxidation of 2-methylnaphthalene to 2-methyl-1,4-naphthoquinone (vitamin K-3), (ii) oxidation of different olefins, and (iii) oxidative bromination of various phenol derivatives, including thymol. As high as 99% selectivity of 2-methyl-1,4-naphthoquinone has been obtained in high yield, while the selective olefin epoxidation resulted in the corresponding epoxide. The high yield of brominated products catalyzed by these complexes signifies them as useful functional models of vanadium-dependent haloperoxidases.

Automated summary

Five new tricompartmental ligands with three tridentate dibasic ONO sites were synthesized from the condensation of benzene-1,3,5-tricarbohydrazide and 4-formyl-5-pyrazolone derivatives. These ligands formed tris{cis-[MoO2]} complexes with good catalytic potential for oxidation reactions and bromination reactions. The complexes exhibited high selectivity and yield for specific reactions, making them useful functional models of vanadium-dependent haloperoxidases.