Symmetrical Bis-Hydrazone Ligand-Based Binuclear Oxido/Dioxido-Vanadium(IV/V) Complexes: Synthesis, Reactivity, and Catalytic Applications for the Synthesis of Biologically Potent 2-Phenylquinazolin-4-(3H)-ones

Symmetrical bis (hydrazone) -based ligands, H 4 dar (bhz) 2 (I), H 4 dar (fah) 2 (II), H 4 dar (nah) 2 (III), and H 4 dar (inh) 2 (IV) obtained from 4, 6-diacetylresorcinol (H 2 dar) and different hydrazides benzoylhydrazide (Hbhz), isonicotinoylhydrazide (Hinh), nicotinoylhydrazide (Hnah), and 2-furoylhydrazide (Hfah), were used to prepare potassium salts of binuclear cis -V V O 2 + complexes, K (H 2 O) 2 2 (V V O 2) 2 dar (bhz) 2 (1), K (H 2 O) 2 2 (V V O 2) 2 dar (fah) 2 (2), K (H 2 O) 2 2 (V V O 2) 2 dar (nah) 2 (3), and K (H 2 O) 2 2 (V V O 2) 2 dar (inh) 2 (4), and binuclear V IV O 2+ complexes, V IV O (MeOH) 2 dar (bhz) 2 (5), V IV O (MeOH) 2 dar (fah) 2 (6), V IV O (MeOH) 2 dar (nah) 2 (7), and V IV O (MeOH) 2 dar (inh) 2 (8). In the presence of warm MeOH/DMSO (4: 1), 3 changed to K (H 2 O) 2 (V V O 2) 2 Hdar (nah) 2 · DMSO (3a ·DMSO). Single crystal XRD studies of 1 and 3a confirm a binuclear structure along with a distorted square pyramidal geometry of each vanadium center where bisONO (2−) ligands coordinate through phenolate-O, azomethine-N, and enolate-O atoms of each unit. While growing crystals of 6 in EtOH, part of it oxidizes and gives V V O (OEt) 2 dar (fah) 2 (9) along with powdery 6. Complex 9 has a distorted octahedral structure. These complexes were used as catalysts for the synthesis of biologically important 2-phenylquinazolin-4- (3 H) -ones having different aryl aldehydes, and they all show excellent catalytic performance (up to 97% yield) in less reaction time and low temperature, in the presence of 70% aqueous TBHP/30% aqueous H 2 O 2 as a greener oxidant. Generally, these complexes perform better than their mononuclear analogues. Spectroscopy, DFT studies, and isolated intermediates have helped in proposing a suitable reaction mechanism for the catalytic reaction.