Enhanced catalytic activity towards one-pot hydroxylation of phenol with hydrogen peroxide by nickel(II) complex encompassing 3-formylchromone-S-methylisothiosemicarbazone derivatives

• Published in: Polyhedron Vol. 124; pp. 77 - 85
• Main Authors: Vijayan, Paranthaman, Anitha, Panneerselvam, Rajeshkumar, Mani, Viswanathamurthi, Periasamy, Sugumar, Paramasivam, Ponnuswamy, Mondikalipudur Nanjappagounder
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 09-03-2017
• Subjects: Crystal structure; Hydroxylation of phenol; Ni(II) complex; S-methylisothiosemicarbazone; Template synthesis; Template synthesis; Ni(II) complex; S-methylisothiosemicarbazone; Hydroxylation of phenol; Crystal structure
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2016.12.031

We portrayed the synthesis and characterization of four new nickel(II) complexes encompassing 3-formylchromone-S-methylisothiosemicarbazone ligand. The resulting complexes were scrutinized for their catalytic performances in one-pot hydroxylation of phenol into catechol and hydroquinone in presence of H2O2.
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The new template reaction between 3-formylchromone-S-methylisothiosemicarbazone and substituted 2-hydroxy benzaldehydes in presence of Ni(OAc)2·4H2O salts afforded four new complexes (1–4) with general molecular formula [NiL1–4] (L1=(N1-3-formylchromone)(N2-(2-hydroxybenzylidene)-S-methylisothiosemicarbazone, L2=(N1-3-formylchromone)(N2-(2-hydroxy-1-naphthalene)-S-methylisothiosemicarbazone, L3=(N1-3-formylchromone)(N2-(5-chloro-2-hydroxybenzylidene)-S-methylisothiosemicarbazone, L4=(N1-3-formylchromone)(N2-(2-hydroxy-3-methoxybenzylidene)-S-methylisothiosemicarbazone). The compounds are remarkably stable and were obtained in good yields. Structural elucidation was carried out thoroughly in solid and solution-states by elemental analysis and various spectroscopy techniques (IR, UV–Vis, 1H NMR) as well as ESI-mass spectrometry. The molecular structure of the complex 1 was investigated by single-crystal X-ray diffraction. The analysis showed tetradentate coordination of the complexes 1–4, in which the metal atom adopts a square planar geometry with the ligand coordinating ONNO tetradentate fashion and the complex 1 [NiL1] units are forming dimerized chains through Ni(1)⋯Ni(2) interactions (3.408Å). The new complexes were examined for their catalytic performances in one-pot hydroxylation of phenol in presence of H2O2 into catechol and hydroquinone.