DOI: 10.1002/ejic.201801243 Full Paper Vanadium Complexes 4,6-Diacetyl Resorcinol Based Vanadium(V) Complexes: Reactivity and Catalytic Applications Mannar R. Maurya,* [a] Nancy Jangra, [a] Fernando Avecilla, [b] and Isabel Correia [c] Abstract: Four ONO donor ligands are isolated from the con- densation of 4,6-diacetyl resorcinol with isonicotinoyl hydrazide (H 2 dar-inh, I), nicotinoyl hydrazide (H 2 dar-nah, II), benzoyl hydrazide (H 2 dar-bhz, III), and 2-furoyl hydrazide (H 2 dar-fah, IV) on refluxing in MeOH. The reaction of in situ generated aque- ous K[H 2 V V O 4 ] with ligands I–IV at neutral pH gives complexes [K(H 2 O) 2 ][VO 2 (dar-inh)] (1), [K(H 2 O) 2 ][VO 2 (dar-nah)] (2), [K(H 2 O) 2 ][VO 2 (dar-bhz)] (3), and [K(H 2 O) 2 ][VO 2 (dar-fah)] (4), re- spectively. The reaction of [V IV O(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 ( 1 H, 13 C and 51 V NMR)], and single-crystal X-ray Introduction A remarkable research growth on mononuclear oxidovana- dium(V) complexes has been observed in recent decades due to interesting discoveries on vanadium bioinorganic chemis- try. [1] Biologically important compounds such as mononuclear oxidovanadium(V) complexes have also served as structural and functional models of vanadate-dependent haloperoxidases. [2,3] These have also been explored as homogeneous catalysts for numerous catalytic transformations [4] such as oxidative bromin- ation, [5] sulfoxidation, [6] epoxidation of olefins, [7] oxidation of alcohols, [8] oxidation of aromatic hydrocarbons/cycloalkanes, [9] hydroamination and oxidative amination, [10] aromatization of 1,4-dihydropyridines, [11] etc. Our research group has been ac- tively engaged in the characterization of structural and func- tional models of haloperoxidases and has made efforts in ex- [a] Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India E-mail: rkmanfcy@iitr.ac.in https://www.iitr.ac.in/CY/rkmanfcy [b] Grupo Xenomar, Centro de Investigacións Científicas Avanzadas (CICA), Departamento de Química, Facultade de Ciencias, Universidade da Coruña, Campus de A Coruña, 15071A Coruña, Spain [c] Centro de Química Estrutural, Instituto Superior Técnico, Universidade Lisboa, 1049-001 Lisboa, Portugal Supporting information and ORCID(s) from the author(s) for this article are available on the WWW under https://doi.org/10.1002/ejic.201801243. Eur. J. Inorg. Chem. 2019, 314–329 © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 314 diffraction analysis (for 1, 6, 7, and 8). X-ray analysis confirms the coordination of the ligands through O phenolate ,N azomethine , and O enolate to the metal center. In the molecular structure of [K(H 2 O)(EtOH)][V V O 2 (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 be- tween V=O oxygen atoms with K + ions. These complexes are active catalysts for the oxidative bromination of thymol in the presence of KBr, HClO 4 , and H 2 O 2 and give 2-bromothymol, 4- bromothymol, and 2,4-dibromothymol as major products. Com- plexes 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 H 2 O 2 in the presence of NaHCO 3 as promoter, giving the corre- sponding epoxides selectively. ploring their catalytic potential towards some of the above transformations. Herein, we report the syntheses and character- ization of dioxidovanadium(V) and oxidomethoxidovana- dium(V) of ligands I–IV derived from 4,6-diacetyl resorcinol and various hydrazides, Scheme 1. Scheme 1. Synthetic scheme used to prepare ligands I, II, III, and IV and their structural formulae. Difunctional 4,6-diacetyl resorcinol and its derivatives have attracted attention due to their biological and particularly phar- maceutical activity. Various hydrazones derived from 4,6-di- acetyl resorcinol and their coordination complexes of nickel(II), cobalt(II), copper(II) and zinc(II) have been investigated against gram-negative (Salmonella Typhi and Escherichia Coli), and gram positive (Bacillus Subtilis and Staphylococcus Aureus) bacteria, as well as antifungal activity against Candida Albicans, Aspergillus Niger and Cladosporium oxy-sporum, with positite results. [12] In copper(II) complexes derived from the products of condensa-