Template Syntheses of Copper(II) Complexes from Arylhydrazones of Malononitrile and their Catalytic Activity towards Alcohol Oxidations and the Nitroaldol Reaction: Hydrogen Bond-Assisted Ligand Liberation and E/Z Isomerisation

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)2(κO1,κN2 L1a] (3) and [Cu(H2O)(κO1,κN3 L1b)] (4), tetranuclear [Cu4(1 κO1,κN2:2 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)2(κO1,κN2- L1dd)-(1 κO1,κN2:2 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)NC{(CN)[C(NH2)-(NCH2CH2NH2)]} (H2L1b, 10), 2-CO2H-C6H4-(NH)N{C(CN)[C(OCH3)-(NH)]} (H2L2a, 11) and 2-SO3H-C6H4-(NH)NC{C(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−)C6H4NNC(C(NH+)CH2CH2NH)(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]2⋅2 H2O (15) and [{CuNa(H2O)-(κN1,1 κO2:2 κO1 L1d)2}K0.5(μ-O)2]n⋅H2O (16). The synthesized complexes 3–9 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 %.