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Title: Aerobic oxidation of alcohol by model complexes relevant to metal site galactose oxidase: role of copper(I) intermediate, evidence for the generation of end-on copper(II)–OOH species and catalytic promiscuity for oxidation of benzyl alcohol, catechol and o-aminophenol
Authors: Dhara A.K.
Kumar K.
Kumari S.
Singh, Udai Pratap
Ghosh, Kaushik
Published in: Transition Metal Chemistry
Abstract: Tridentate ligands having meridional NNO donor centres were designed and synthesized mimicking the copper coordination in the metal site of galactose oxidase enzyme. Mononuclear copper complexes [Cu(L )Cl] (1) (L H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L )Cl] (2) (L H = (E)-4-methyl-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L )Cl] (3) (L H = (E)-1-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)naphthalen-2-ol), [Cu(L )Cl] (4) (L H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), [Cu(L )Cl] (5) (L H = (E)-2-((2-phenyl-2-(pyridin-2-yl)hydrazono)methyl)phenol), and [Cu(L )Cl] (6) (L H = (E)-2,4-di-tert-butyl-6-(((pyridin-2-ylmethyl)imino)methyl)phenol) were synthesized and characterized. Molecular structure of complex 3 was determined by single crystal X-ray crystallography. Phenoxyl radical complexes were generated in solution via chemical oxidation using ceric ammonium nitrate (CAN), and the radical complexes were characterized by UV–Vis–NIR spectrophotometer. DFT calculations were performed at B3LYP level to optimize the ground-state molecular geometry of the complexes. To understand the electronic properties and absorption spectra of the complexes, TD-DFT calculations were executed for phenoxyl radical complexes considering triplet as well as singlet spin states. Alcohol oxidation was examined utilizing complexes 1–6 as catalyst, and importance of stabilization of Cu(I) intermediate was scrutinized and generation of Cu(II)–OOH was examined. Catalytic promiscuity for catechol oxidase and phenoxazinone synthase activity by complexes (1–5) was investigated. Theoretical calculations and ESI–MS spectral studies were performed during oxidation chemistry of benzyl alcohol, catechol and o-amino phenol to support the proposed mechanism.
Citation: Transition Metal Chemistry(2020), 45(3): 159-172
Issue Date: 2020
Publisher: Springer
Keywords: Catalytic oxidation
Crystal structure
Density functional theory
Electronic properties
Ground state
Molecular structure
Nitrogen compounds
Reaction intermediates
Single crystals
Spectroscopic analysis
Synthesis (ch
ISSN: 3404285
Author Scopus IDs: 57060128000
Author Affiliations: Dhara, A.K., Indian Institute of Technology, Roorkee, Roorkee, Uttrakhand 247667, India
Kumar, K., Indian Institute of Technology, Roorkee, Roorkee, Uttrakhand 247667, India
Kumari, S., Indian Institute of Technology, Roorkee, Roorkee, Uttrakhand 2
Funding Details: Council of Scientific and Industrial Research, India, CSIR University Grants Committee, UGC SR/S1/IC-47/2012.KG is thankful to SERB-DST(SR/S1/IC-47/2012 dated Oct 2013), New Delhi, India, for financial assistance. AKD, KK are thankful to UGC and SK is thankful to CSIR for financial assistance. We are thankful to Central Instrumental Facility, IIT, Roorkee.
Corresponding Author: Ghosh, K.; Indian Institute of Technology, India; email:
Appears in Collections:Journal Publications [CY]

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