4,6‐Diacetyl Resorcinol Based Vanadium(V) Complexes: Reactivity and Catalytic Applications

Abstract

Four ONO donor ligands are isolated from the condensation of 4,6‐diacetyl resorcinol with isonicotinoyl hydrazide (H2dar‐inh, I), nicotinoyl hydrazide (H2dar‐nah, II), benzoyl hydrazide (H2dar‐bhz, III), and 2‐furoyl hydrazide (H2dar‐fah, IV) on refluxing in MeOH. The reaction of in situ generated aqueous K[H2VVO4] with ligands I–IV at neutral pH gives complexes [K(H2O)2][VO2(dar‐inh)] (1), [K(H2O)2][VO2(dar‐nah)] (2), [K(H2O)2][VO2(dar‐bhz)] (3), and [K(H2O)2][VO2(dar‐fah)] (4), respectively. The reaction of [VIVO(acac)2] (acac = acetylacetonato) with these ligands (I–IV) under aerobic conditions in methanol yields oxidomethoxidovanadium(V) complexes [VO(OMe)(MeOH)(dar‐inh)] (5), [VO(OMe)(MeOH)(dar‐nah)] (6), [VO(OMe)(MeOH)(dar‐bhz)] (7), and [VO(OMe)(MeOH)(dar‐fah)] (8). All the isolated complexes are characterized by elemental, thermal, electrochemical, and spectroscopic techniques [FTIR, UV/Vis, NMR (1H, 13C and 51 V NMR)], and single‐crystal X‐ray diffraction analysis (for 1, 6, 7, and 8). X‐ray analysis confirms the coordination of the ligands through Ophenolate, Nazomethine, and Oenolate to the metal center. In the molecular structure of [K(H2O)(EtOH)][VVO2(dar‐inh)] (abbreviated as 1a where one molecule of water is replaced by EtOH), water molecules act as bridges between two K+ ions and the complex shows a dimeric structure due to the presence of electrostatic interactions between V=O oxygen atoms with K+ ions. These complexes are active catalysts for the oxidative bromination of thymol in the presence of KBr, HClO4, and H2O2 and give 2‐bromothymol, 4‐bromothymol, and 2,4‐dibromothymol as major products. Complexes 1–4 were also tested as catalysts for the epoxidation of various alkenes (namely styrene, cyclohexene, cis‐cyclooctene, 1‐hexene, 1‐octene, cyclohexenone, and trans‐stilbene) with H2O2 in the presence of NaHCO3 as promoter, giving the corresponding epoxides selectively.

In vitrocytotoxicity and catalytic evaluation of dioxidovanadium(v) complexes in an azohydrazone ligand environment

“…37 This consequently led to synergistic effects and improved the cytotoxicity of the overall complex. Furthermore, the presence of a naphthyl substituent 13 in the ligand backbone could be attributed to the lower IC 50 39 whereas the antiproliferative potential of 1-3 was also better than or comparable to our previously reported results for vanadium 10 and molybdenum hydrazone 40 complexes against HeLa cells. Nuclear staining assay.…”

“…,5-bis(2-hydroxyphenyl)-1-phenyl-1,2,4-triazole}] (99%), 49 and [K(H 2 O) 2 ][VO 2 L] (H 2 L = ligands derived from 4,6-diacetyl resorcinol and isonicotinoyl hydrazide, nicotinoyl hydrazide, benzoyl hydrazide or 2-furoyl hydrazide) (90-98%), 50 signifying them as efficient catalysts for the oxidative bromination of thymol. Interestingly, 3, which contained a naphthyl substituent in the ligand backbone, showed the highest turnover frequency among the series.…”

“…These changes clearly suggested the formation of oxidoperoxidovanadium(V) species in solution. [48][49][50]53 The reactivities of 2 and 3 are depicted in Fig. S7 and S8 (ESI †), respectively.…”

Vanadium(V) and Molybdenum(VI) Complexes Containing ONO Tridentate Schiff Bases and Their Application as Catalysts for Oxidative Bromination of Phenols

“…Moreover, 1 and 2 are similar to previously reported complexes and show similar chemical shifts . Overall, we can conclude that despite the similarities between ligands I and II , which differ only in the position of the N atom in the heterocycle, their respective complexes show different stability.…”

“…Vanadium complexes Cs(H 2 O)[V V O 2 {3,5‐bis(2‐hydroxyphenyl)‐1‐phenyl‐ 1,2,4‐triazole}] gave 99% conversion, and dioxidovanadium(V) complex [K(H 2 O) 2 ][VO 2 L] (H 2 L=ligands derived from condensation of 4,6‐diacetyl resorcinol and various hydrazides gave 89–98% conversion while dioxidomolybdenum(VI) complexes derived from the condensation of 8‐formyl‐7‐hydroxy‐4‐methylcoumarin with hydrazides gave 94–99% conversion of thymol (a monoterpene phenol) . Polymer anchored Cu(II) complexes, have been reported to give 96% conversion of phenol in 2.5 h along with 100% selectivity of 4‐bromophenol which clearly remarks the importance of newly synthesized vanadium(V) and molybdenum(VI) complexes as efficient catalyst for oxidative bromination reactions.…”