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Vanadium(V) and Molybdenum(VI) Complexes Containing ONO Tridentate Schiff Bases and Their Application as Catalysts for Oxidative Bromination of Phenols
Author(s) -
Maurya Mannar R.,
Jangra Nancy,
Avecilla Fernando,
Ribeiro Nádia,
Correia Isabel
Publication year - 2019
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201903678
Subject(s) - dhap , chemistry , medicinal chemistry , hydrazide , nuclear chemistry , stereochemistry , organic chemistry , enzyme
Condensation of 2,4‐dihydroxyacetophenone with isonicotinoyl hydrazide and nicotinoyl hydrazide in an equimolar ratio in methanol results in the formation of two stable ONO donor ligands, H 2 dhap‐inh ( I ) and H 2 dhap‐nah ( II ), respectively. These ligands react with [V IV O(acac) 2 ] (Hacac=acetylacetone) in 1:1 molar ratio to give the corresponding neutral dioxidovanadium(V) complexes, [V V O 2 (Hdhap‐inh)] ( 1 ) and [V V O 2 (Hdhap‐nah)] ( 2 ), after overnight aerial oxidation in the presence of K 2 CO 3 . In the absence of K 2 CO 3 , they result in (μ‐O){bisoxidovanadium(V)} complexes, [{V V O(dhap‐inh)} 2 (μ‐O)] ( 3 ) and [{V V O(dhap‐nah)} 2 (μ‐O)] ( 4 ). Treatment of neutral dioxidovanadium(V) complexes, 1 and 2 , with H 2 O 2 yields oxidoperoxidovanadium(V) complexes K[V V O(O 2 )(dhap‐inh)(H 2 O)] ( 5 ) and K[V V O(O 2 )(dhap‐nah)(H 2 O)] ( 6 ). The ligands also react with [Mo VI O 2 (acac) 2 ] in 1:1 molar ratio to form [Mo VI O 2 (dhap‐inh)] n ( 7 ) and [Mo VI O 2 (dhap‐nah)] n ( 8 ). The reaction of oxidoperoxidomolybdenum(VI) species, generated in situ by the reaction of MoO 3 with H 2 O 2 with ligands I and II , gives the oxidoperoxidomolybdenum(VI) complexes, [Mo VI O(O 2 )(dhap‐inh)(MeOH)] ( 9 ) and [Mo VI O(O 2 )(dhap‐nah)(MeOH)] ( 10 ), respectively. All synthesized complexes are characterized by elemental analysis, thermogravimetric, electrochemical, spectroscopic (IR, UV–Vis, 1 H, 13 C and 51 V NMR) and single crystal X‐ray diffraction (for 1 , 2 and 8 ). Complexes are explored as catalysts for the oxidative bromination of phenol, a model oxidative halogenation reaction, in the presence of HClO 4 and KBr, using 30% H 2 O 2 as oxidant. Under optimized reaction conditions, the product selectivity follows the order: 4‐bromophenol>2‐bromophenol, both for molybdenum and vanadium complexes. Products characterized by GC analysis showed very good conversion of phenol.