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Browsing by Author "Kopylovich, Maximilian N."

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  • Copper(II) and cobalt(II) tetrazole-saccharinate complexes as effective catalysts for oxidation of secondary alcohols
    Publication . Frija, Luis M. T.; Alegria, Elisabete C. B. A.; Sutradhar, Manas; Cristiano, Maria De Lurdes; Ismael, Amin; Kopylovich, Maximilian N.; Pombeiro, Armando J. L.
    Mononuclear Cu(II) and Co(II) complexes comprising 2-methyltetrazole-saccharinate bidentate N,N-chelating ligand have been synthesized for the first time and tested as homogeneous catalysts for oxidation of secondary alcohols in a solvent-free and microwave assisted protocol using aqueous tertbutyl hydroperoxide (TBHP) as oxidant. The developed catalytic system exhibits broad functional group compatibility, allowing efficient and selective conversion of a variety of secondary alcohols, including allylic ones, into the corresponding ketones. With typical 0.2 mol% content of the catalyst and under 20-50 W microwave irradiation, most reactions are complete within 10 min, presenting TONs up to 5.5 x 10(2) and TOFs up to 1.1 x 10(4)h(-1). No additives and co-oxidants have been used, while TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) acts as inhibitor in most cases. A plausible reaction mechanism involving the new catalytic systems is outlined. (C) 2016 Elsevier B.V. All rights reserved.
    2016-12Journal article Restricted access Show more
  • Organocatalyzed oxidation of benzyl alcohols by a tetrazole-amino-saccharin: A combined experimental and theoretical (DFT) study
    Publication . Frija, Luis M. T.; Kuznetsov, Maxim L.; Rocha, Bruno G. M.; Cabral, Lília; Cristiano, Maria Lurdes Santos; Kopylovich, Maximilian N.; Pombeiro, Armando J. L.
    A new catalytic system for the anaerobic oxidation of benzyl alcohols using a tetrazole-amino-saccharin organocatalyst has been established. In a solvent-free and microwave assisted process comprising aqueous tert-butyl hydroperoxide (TBHP) as oxidant, a variety of benzyl alcohols has been efficiently converted to aldehydes under mild conditions. Most reactions are complete within 30 min and the catalyst exhibits varied functional group compatibility. A catalytic cycle for the oxidation of the alcohols promoted by the tetrazole-amino-saccharin derivative is outlined involving radical species. DFT calculations performed for the oxidation of benzyl alcohol with and without organocatalyst show that the rate limiting step of the whole reaction is the cleavage of the O-O bond in TBHP with the subsequent hydrogen abstraction from the alcohol. The tetrazole-amino-saccharin organocatalyst assists the H-abstraction from benzyl alcohol by the bound HO center dot radical. The simplicity, selectivity and softness of reaction conditions of the studied organocatalytic protocol suggest a great potential for extensive use in synthetic chemistry. (C) 2017 Elsevier B.V. All rights reserved.
    2017-12Journal article Restricted access Show more