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)(kappa O-1, kappa(NL1a)-L-2] (3) and [Cu(H2O)(kappa O-1, kappa(NL1b)-L-3)] (4), tetranuclear [Cu-4(1 kappa O-1, kappa N-2:2 kappa(OL2a)-L-1) 3-(1 kappa O-1, kappa N-2: 2 kappa(OL2a)-L-2)] (5), [Cu-2(H2O)(1 kappa O-1, kappa N-2: 2 kappa(OL2c)-L-1)-(1 kappa O-1,1 kappa N-2: 2 kappa O-1,2 kappa N-1-L-2c)](2) (6) and [Cu2(H2O)(2)(kappa O-1, kappa(NL1dd)-L-2)-(1-1 kappa O-1, kappa N-2: 2 kappa(OL1dd)-L-1)(mu-H2O)](2)center dot 2H(2)O (7 center dot 2H(2)O), as well as polymeric [Cu(H2O)(kappa O-1,1 kappa N-2: 2 kappa(NL1c)-L-1)](n) (8) and [Cu(NH2C2H5)(kappa O-1,1 kappa N-2: 2 kappa(NL2a)-L-1)](n) (9). The ligands 2-SO3H-C6H4(NH) N=C{(CN)[C(NH2)-(=NCH2CH2H2)]} (H2L1b, 10), 2-CO2H-C6H4(NH) N={C(CN)[C(OCH3)-(=NH)]} (H2L2a, 11) and 2-SO3H-C6H4-(NH) N=C{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-)-C6H4-N=NC(-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)(mu-H2O)(2)}-(HL1d)](n) (14) to [Cu(H2O)(6)]-[HL1d](2)center dot 2H(2)O (15) and [{CuNa(H2O)(kappa N-1,1 kappa O-2: 2 kappa(OL1d)-L-1)(2)} K-0.5(mu-O)(2)](n)center dot 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%.