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Keywords:

  • alcohols;
  • copper;
  • isomerization;
  • Lewis acids;
  • oxidation

Abstract

A one-pot template condensation of 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonic acid (H2L1, 1) or 2-(2-(dicyanomethylene)hydrazinyl)benzoic acid (H2L2, 2) with methanol (a), ethylenediamine (b), ethanol (c) or water (d) on copper(II), led to a variety of metal complexes, that is, mononuclear [Cu(H2O)2O1N2 L1a] (3) and [Cu(H2O)(κO1N3 L1b)] (4), tetranuclear [Cu4(1 κO1N2:2 κO1 L2a)3-(1 κO1, κN2:2 κO2 L2a)] (5), [Cu2(H2O)(1 κO1, κN2:2 κO1 L2c)-(1 κO1,1 κN2:2 κO1,2 κN1- L2c)]2 (6) and [Cu2(H2O)2O1N2- L1dd)-(1 κO1N2:2 κO1 L1dd)(μ-H2O)]2 2 H2O (7⋅2 H2O), as well as polymer- ic [Cu(H2O)(κO1,1 κN2:2 κN1 L1c)]n (8) and [Cu(NH2C2H5)(κO1,1 κN2:2 κN1L2a)]n (9). The ligands 2-SO3H-C6H4-(NH)N[DOUBLE BOND]C{(CN)[C(NH2)-([DOUBLE BOND]NCH2CH2NH2)]} (H2L1b, 10), 2-CO2H-C6H4-(NH)N[DOUBLE BOND]{C(CN)[C(OCH3)-([DOUBLE BOND]NH)]} (H2L2a, 11) and 2-SO3H-C6H4-(NH)N[DOUBLE BOND]C{C([DOUBLE BOND]O)-(NH2)}2 (H2L1dd, 12) were easily liberated upon respective treatment of 4, 5 and 7 with HCl, whereas the formation of cyclic zwitterionic amidine 2-(SO3)[BOND]C6H4[BOND]N[DOUBLE BOND]NC([BOND]C[DOUBLE BOND](NH+)CH2CH2NH)([DOUBLE BOND]CNHCH2CH2NH) (13) was observed when 1 was treated with ethylenediamine. The hydrogen bond-induced E/Z isomerization of the (HL1d) ligand occurs upon conversion of [{Na(H2O)2(μ-H2O)2}(HL1d)]n (14) to [Cu(H2O)6][HL1d]22 H2O (15) and [{CuNa(H2O)-(κN1,1 κO2:2 κO1 L1d)2}K0.5(μ-O)2]nH2O (16). The synthesized complexes 39 are catalyst precursors for both the selective oxidation of primary and secondary alcohols (to the corresponding carbonyl compounds) and the following diastereoselective nitroaldol (Henry) reaction, with typical yields of 80–99 %.