Vanadium(ivandv) complexes of pyrazolone based ligands: Synthesis, structural characterization and catalytic applications

Abstract

The ONO donor ligands obtained from the condensation of 4-benzoyl-3-methyl-1-phenyl-2-pyrazoline-5-one (Hbp) with benzoylhydrazide (Hbp-bhz I), furoylhydrazide (Hbp-fah II), nicotinoylhydrazide (Hbp-nah III) and isonicotinoylhydrazide (Hbp-inh IV), upon treatment with [VO(acac)], lead to the formation of [VO(bp-bhz)(HO)] 1, [VO(bp-fah)(HO)] 2, [VO(bp-nah)(HO)] 3 and [VO(bp-inh)(HO)] 4, respectively. At neutral pH the in situ generated aqueous K[HVO] reacts with ligands I and II, forming potassium salts, K(HO)[VO(bp-bhz)] 5 and K(HO)[VO(bp-fah)] 6, while ligands III and IV give neutral complexes, [VO(Hbp-nah)] 9 and [VO(Hbp-inh)] 10, respectively. Acidification of aqueous solutions of 5 and 6 with HCl also gives neutral complexes [VO(Hbp-bhz)] 7 and [VO(Hbp-fah)] 8, respectively. Complexes 1-4, upon slow aerial oxidation in methanol, convert into monooxidovanadium(v) complexes, [VO(bp-bhz)(OMe)] 11, [VO(bp-fah)(OMe)] 12, [VO(bp-nah)(OMe)] 13 and [VO(bp-inh)(OMe)] 14, respectively. All complexes were characterized by various spectroscopic techniques like FT-IR, UV-visible, EPR (for complexes 1-4) and NMR (H, C andV), elemental analysis, thermogravimetry and single crystal X-ray diffraction (for complexes 5-10 and 12). In the solid state, all complexes characterized by X-ray diffraction show the metal ion 5-coordinated in a distorted square pyramidal geometry. Complexes 11-14 were tested as catalysts for the one-pot three-component (ethylacetoacetate, benzaldehyde and ammonium acetate) dynamic covalent assembly, via Hantzsch reaction, using hydrogen peroxide as oxidant in solution and under solvent-free conditions. The complexes are also active catalysts for the oxidation of tetralin to tetralone with HO as oxidant. The influence of the amounts of catalyst and oxidant, and solvent, temperature and time on the catalyzed reactions was investigated.

Bis{cis‐[MoO2]} Complexes of 4,6‐Diacetyl Resorcinol Bis(hydrazone)and Their Catalytic Application for the Three Components Dynamic Covalent Assembly via Hantzsch Reaction

“…The electron withdrawing chloro‐ and nitro‐ derivatives of benzaldehyde show considerably poor conversion (70 and 72 %, respectively) while electron donating derivatives i. e. methoxy, methyl, t‐butyl and OH group on benzaldehyde give better (92‐98 %) conversion, however, selectively ratio of hydropyridine and pyridine obtained is nearly same in all cases. These results are comparable to the one reported recently using vanadium complexes as catalyst precursors . Catalytic activity reported here also compares very well with catalyst V 2 O 5 /H 2 O 2 which gives 96 % conversion at room temperature with 96 % selectivity towards pyridine derivative in MeCN and with VOCl 3 which gives 97 % conversion with 97% selectivity towards pyridine derivative in CH 2 Cl 2 .…”

“…Recently we have explored the catalytic activity of mononuclear dioxidomolybdenum(VI) and dioxidovanadium(V) complexes towards three components (methyl acetoacetate/ethyl acetoacetate, benzaldehyde and ammonium acetate) one pot Hantzsch reaction ,. In the present investigation, we present the isolation of binuclear complexes having cis ‐bis[Mo VI O 2 ] 2+ core with binucleating ligands derived from 4,6‐diacetyl resorcinol (Scheme ) and after their full characterization, explore their catalytic activity for the three components (ethyl acetoacetate, benzaldehyde and ammonium acetate) one pot Hantzsch reaction.…”

“…Synthesis of DHPs via Hantzsch reaction and their aromitization have also attracted attention of researchers and various catalysts have been explored such as L‐proline, S‐valine, Yb(OTf) 3 , I 2 , TBAHS, HOAc, Et 3 N, DBU, pyridine, trimethyl silyl iodide, ionic liquids, in situ generated HCl, K 7 [PW 11 CoO 40 ], ceric ammonium nitrate, p‐toluene sulfonic acid‐sodium dodecyl sulphate, boronic acid etc. Metal complexes e. g. cobalt silica grafted complexes, MoOCl 4 , Schiff base complexes of manganese, molybdenum and vanadium have also been used as catalysts in the presence of mild oxidant like H 2 O 2 for aromatization.…”

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

“…In MeOH complex 4 shows two overlapped peaks at –546.5 and –547.75 ppm, while 8 in DMSO shows two peaks with ratios of 1:4 at –534.0 and –547.3 ppm, respectively. These chemical shifts are upfield from the ones found for the 4‐benzoyl‐3‐methyl‐1‐phenyl‐2‐pyrazoline‐5‐one vanadium complexes, implying that the electronic density in the metal center is lower in this case, which is in agreement with the involvement of the phenolate donor.…”

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

“…Compounds 1 and 2 are mononuclear having penta‐coordinated molecular structures with distorted square pyramidal geometry. The axial sites of the pyramid are occupied by one of the oxide atoms of the dioxide moiety [V(1)‐O(2), 1.616(2) Å, in 1 and 1.6091(14) Å in 2 ], like in other similar compounds . The V=O bonds are very similar and characteristic of oxido‐type O atoms with strong π bonding.…”