The zinc(II) complexes with ortho-hydroxy substituted arylhydrazo-β-diketonates [Zn(2)(CH(3)OH)(2)(μ-L(1))(2)] (5), [Zn{(CH(3))(2)SO}(H(2)O)(L(2))] (6), [Zn(2)(H(2)O)(2)(μ-L(3))(2)] (7) and [Zn(H(2)O)(2)(L(4))]·H(2)O (8) were synthesized by reaction of a zinc(II) salt with the appropriate hydrazo-β-diketone, HO-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) (H(2)L(1), 1), HO-2-O(2)N-4-C(6)H(3)-NHN=C{C(=O)CH(3)}(2) (H(2)L(2), 2), HO-2-C(6)H(4)-NHN=CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(3), 3) or HO-2-O(2)N-4-C(6)H(3)-NHN=[CC(=O)CH(2)C(CH(3))(2)CH(2)C(=O) (H(2)L(4), 4). They were fully characterized, namely by X-ray diffraction analysis that disclosed the formation of extensive H-bonds leading to 1D chains (5 and 6), 2D layers (7) or 3D networks (8). The thermodynamic parameters of the Zn(II) reaction with H(2)L(2) in solution, as well as of the thermal decomposition of 1-8 were determined. Complexes 5-8 act as diastereoselective catalysts for the nitroaldol (Henry) reaction. The threo/erythro diastereoselectivity of the β-nitroalkanol products ranges from 8:1 to 1:10 with typical yields of 80-99%, depending on the catalyst and substrate used.

Abstract:Reactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C6H4-NHN = C{C(= O)CH3}(2) bearing a substituent in the ortho-position [X = OH (H2L1) 1, AsO3H2 (H3L2) 2, Cl (HL3) 3, SO3H (H2L4) 4, COOCH3 (HL5) 5, COOH (H2L6) 6, NO2 (HL7) 7 or H (HL8) 8] lead to a variety of complexes including the monomeric [CuL4(H2O)(2)]center dot H2O 10, [CuL4(H2O)(2)] 11 and [Cu(HL4)(2)(H2O)(4)] 12, the dimeric [Cu-2(H2O)(2)(mu-HL2)(2)] 9 and the polymeric [Cu(mu-L-6)](n)] 13 ones, often bearing two fused six-membered metallacycles. Complexes 10-12 can interconvert, depending on pH and temperature, whereas the Cu(II) reactions with 4 in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H2O)(4){NCNC(NH2)(2)}(2)](HL4)(2)center dot 6H(2)O 14 and the heteroligand polymer [Cu(mu-L-4)(im)](n) 15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, H-1 and C-13 NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1-8 on the HOMO-LUMO gap and the relative stability of the model compounds [Cu(OH)(L-8)(H2O)]center dot H2O, [Cu(L-1)(H2O)(2)]center dot H2O and [Cu(L-4)(H2O)(2)]center dot H2O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12 and 13 act as catalyst precursors for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H2O (total yields of ca. 20% with TONs up to 566), under mild conditions.

Mononuclear copper(II) salen‐type Schiff base complexes, CuIIL1–5 [H2L1 to H2L5 = tetradentate N,N,O,O ligands derived from 2‐hydroxybenzaldehyde, 2,4‐dihydroxybenzaldehyde, 3,5‐dibromo‐2‐hydroxybenzaldehyde, 2‐hydroxy‐5‐nitrobenzaldehyde, 5‐chloro‐2‐hydroxybenzaldehyde and 1,3‐bis(3‐aminopropyl)tetramethyldisiloxane, respectively] were prepared in situ in the presence of a copper(II) salt or by direct complexation between a copper(II) salt and a presynthesised Schiff base. The compounds {CuL1, CuL1·0.5Py, CuL2·0.375CH2Cl2, (CuL3)[Cu(4‐Me‐Py)4Cl]Cl·2H2O, CuL4, CuL4·CHCl3 and CuL5, as well as the isolated ligand H2L3} were characterised by elemental analysis, spectroscopic methods (IR, UV/Vis, 1H NMR, EPR) and X‐ray crystallography. The formation of a 12‐membered central chelate ring in these complexes is effected by the tetramethyldisiloxane unit, which separates the aliphatic chains, thus significantly reducing the mechanical strain in such a chelate ring. We dub this a “shoulder yoke effect” by analogy with the load‐spreading ability of such an ancient device. The coordination geometry of copper(II) in CuIIL1–5 can be described as tetrahedrally distorted square‐planar. Maximum tetrahedral distortion of the coordination geometry expressed by the parameter τ4 was observed for CuL1 (0.460), while distortion was minimal for the two crystallographically independent molecules of CuL2 (0.219 and 0.284). The Si–O–Si bond angle varies markedly between 169.75(2)° for CuL1 and 154.2(3)° for CuL4·CHCl3. Charge‐density and DFT calculations on CuL1 indicate high ionic character of the Si–O bonds in the tetramethyldisiloxane fragment. The new copper(II) complexes bearing the disiloxane moiety have been shown to act as catalyst precursors for the aerobic oxidation of benzyl alcohol to benzaldehyde mediated by the TEMPO radical, reaching yields and TONs up to 99 % and 990, respectively, under mild and environmentally friendly conditions (50 °C; MeCN/H2O, 1:1).

A one-pot template condensation of 2-(2-(dicyanomethylene)hydrazinyl)benzenesulfonic acid (H(2)L(1), 1) or 2-(2-(dicyanomethylene)hydrazinyl)benzoic acid (H(2)L(2), 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(H(2)O)(2)(κO(1),κN(2)L(1a)] (3) and [Cu(H(2)O)(κO(1),κN(3)L(1b))] (4), tetranuclear [Cu(4)(1κO(1),κN(2):2κO(1)L(2a))(3)-(1κO(1), κN(2):2κO(2)L(2a))] (5), [Cu(2)(H(2)O)(1κO(1), κN(2):2κO(1)L(2c))-(1κO(1),1κN(2):2κO(1),2 κN(1)- L(2c))](2) (6) and [Cu(2)(H(2)O)(2)(κO(1),κN(2)- L(1dd))-(1κO(1),κN(2):2κO(1)L(1dd))(μ-H(2)O)](2·) 2H(2)O (7·2H(2)O), as well as polymer- ic [Cu(H(2)O)(κO(1),1κN(2):2κN(1)L(1c))](n) (8) and [Cu(NH(2)C(2)H(5))(κO(1),1κN(2):2κN(1)L(2a))](n) (9). The ligands 2-SO(3)H-C(6)H(4)-(NH)N=C{(CN)[C(NH(2))-(=NCH(2)CH(2)NH(2))]} (H(2)L(1b), 10), 2-CO(2)H-C(6)H(4)-(NH)N={C(CN)[C(OCH(3))-(=NH)]} (H(2)L(2a), 11) and 2-SO(3)H-C(6)H(4)-(NH)N=C{C(=O)-(NH(2))}(2) (H(2)L(1dd), 12) were easily liberated upon respective treatment of 4, 5 and 7 with HCl, whereas the formation of cyclic zwitterionic amidine 2-(SO(3)(−))-C(6)H(4)-N=NC(-C=(NH(+))CH(2)CH(2)NH)(=CNHCH(2)CH(2)NH) (13) was observed when 1 was treated with ethylenediamine. The hydrogen bond-induced E/Z isomerization of the (HL(1d))(−) ligand occurs upon conversion of [{Na(H(2)O)(2)(μ-H(2)O)(2)}(HL(1d))](n) (14) to [Cu(H(2)O)(6)][HL(1d)](2)·2H(2)O (15) and [{CuNa(H(2)O)-(κN(1),1κO(2):2κO(1)L(1d))(2)}K(0.5)(μ-O)(2)]n·H(2)O (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%.