4, 6‐Diacetyl Resorcinol Based Vanadium(V) Complexes: Reactivity and Catalytic Applications. Issue 2 (11th January 2019)

• Record Type: Journal Article
• Authors: Maurya, Mannar R.; Jangra, Nancy; Avecilla, Fernando; Correia, Isabel
• Is Part Of: European journal of inorganic chemistry. Issue 2(2019)
• Page Start: 314
• Page End: 329
• Publication Date: 2019-01-11
• Subjects: Vanadium -- Haloperoxidase models -- Structure elucidation -- Homogeneous catalysis -- Oxidative bromination -- Epoxidation of alkenes; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201801243
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Four ONO donor ligands are isolated from the condensation of 4, 6‐diacetyl resorcinol with isonicotinoyl hydrazide (H2 dar‐inh, I ), nicotinoyl hydrazide (H2 dar‐nah, II ), benzoyl hydrazide (H2 dar‐bhz, III ), and 2‐furoyl hydrazide (H2 dar‐fah, IV ) on refluxing in MeOH. The reaction of in situ generated aqueous K[H2 V V O4 ] with ligands I –IV at neutral pH gives complexes [K(H2 O)2 ][VO2 (dar‐inh)] (1 ), [K(H2 O)2 ][VO2 (dar‐nah)] (2 ), [K(H2 O)2 ][VO2 (dar‐bhz)] (3 ), and [K(H2 O)2 ][VO2 (dar‐fah)] (4 ), respectively. 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 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(H2 O)(EtOH)][V V O2 (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 H2 O2 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 H2 O2 in the presence of NaHCO3 as promoter, giving the corresponding epoxides selectively. Abstract : Dioxidovanadium(V) and oxidomethoxido vanadium(V) complexes of dibasic tridentate ligands have been prepared and characterized (some with single‐crystal X‐ray structures). These complexes show potential catalytic activity for the oxidative bromination of thymol as well as oxidation of olefins, thus representing good structural and functional models of the vanadate‐dependent haloperoxidases.