Alkoxy-1,3,5-triazapentadien(e/ato) Copper(II) Complexes: Template Formation and Applications for the Preparation of Pyrimidines and as Catalysts for Oxidation of Alcohols to Carbonyl Products

Authors

  • Dr. Maximilian N. Kopylovich,

    Corresponding author
    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
    • Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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  • Dr. Yauhen Yu. Karabach,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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  • Dr.  M. Fátima C. Guedes da Silva,

    Corresponding author
    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
    2. Universidade Lusófona de Humanidades e Tecnologias, Campo Grande 376, 1749-024 Lisbon (Portugal)
    • Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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  • Dr. Paweł J. Figiel,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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  • Dr. Jamal Lasri,

    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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  • Prof. Dr. Armando J. L. Pombeiro

    Corresponding author
    1. Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
    • Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049–001 Lisbon (Portugal), Fax: (+351) 218464455
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Abstract

Template combination of copper acetate (Cu(AcO)2⋅H2O) with sodium dicyanamide (NaN(C≡N)2, 2 equiv) or cyanoguanidine (N≡CNHC(=NH)NH2, 2 equiv) and an alcohol ROH (used also as solvent) leads to the neutral copper(II)–(2,4-alkoxy-1,3,5-triazapentadienato) complexes [Cu{NH[DOUBLE BOND]C(OR)NC(OR)[DOUBLE BOND]NH}2] (R=Me (1), Et (2), nPr (3), iPr (4), CH2CH2OCH3 (5)) or cationic copper(II)–(2-alkoxy-4-amino-1,3,5-triazapentadiene) complexes [Cu{NH[DOUBLE BOND]C(OR)NHC(NH2)[DOUBLE BOND]NH}2](AcO)2 (R=Me (6), Et (7), nPr (8), nBu (9), CH2CH2OCH3 (10)), respectively. Several intermediates of this reaction were isolated and a pathway was proposed. The deprotonation of 610 with NaOH allows their transformation to the corresponding neutral triazapentadienates [Cu{NH[DOUBLE BOND]C(OR)NC(NH2)[DOUBLE BOND]NH}2] 1115. Reaction of 11, 12 or 15 with acetyl acetone (MeC([DOUBLE BOND]O)CH2C([DOUBLE BOND]O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NCNHC([DOUBLE BOND]NH)OR, whereas the same treatment of the cationic complexes 6, 7 or 10 allows the corresponding metal-free triazapentadiene salts {NH2C(OR)[DOUBLE BOND]NC(NH2)[DOUBLE BOND]NH2}(OAc) to be isolated. The alkoxy-1,3,5-triazapentadiene/ato copper(II) complexes have been applied as efficient catalysts for the TEMPO radical-mediated mild aerobic oxidation of alcohols to the corresponding aldehydes (molar yields of aldehydes of up to 100 % with >99 % selectivity) and for the solvent-free microwave-assisted synthesis of ketones from secondary alcohols with tert-butylhydroperoxide as oxidant (yields of up to 97 %, turnover numbers of up to 485 and turnover frequencies of up to 1170 h−1).

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