Ortho-Hydroxyphenylhydrazo-β-Diketones: Tautomery, Coordination Ability, and Catalytic Activity of Their Copper(II) Complexes toward Oxidation of Cyclohexane and Benzylic Alcohols

Abstract

New hydrazone o-HO-phenylhydrazo-β-diketones (OHADB), R(1)NHN═CR(2)R(3) [R(1) = HO-2-C(6)H(4), R(2) = R(3) = COMe (H(2)L(1), 1), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(2), 2), R(2) = COMe, R(3) = COOEt (H(2)L(4), 4); R(1) = HO-2-O(2)N-4-C(6)H(3), R(2)R(3) = COCH(2)C(Me)(2)CH(2)CO (H(2)L(3), 3), R(2) = COMe, R(3) = COOEt (H(2)L(5), 5), R(2)R(3) = COMe (H(2)L(6), 6A)], and their Cu(II) complexes [Cu(2)(CH(3)OH)(2)(μ-L(1))(2)] 7, [Cu(2)(H(2)O)(2)(μ-L(2))(2)] 8, [Cu(H(2)O)(L(3))] 9, [Cu(2)(μ-L(4))(2)](n) 10, [Cu(H(2)O)(L(5))] 11, [Cu(2)(H(2)O)(2)(μ-L(6))(2)] 12A and [Cu(H(2)O)(2)(L(6))] 12B were synthesized and fully characterized, namely, by X-ray analysis (4, 5, 7-12B). Reaction of 6A, Cu(NO(3))(2) and ethylenediamine (en) leads, via Schiff-base condensation, to [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}] (13), and reactions of 12A and 12B with en give the Schiff-base polymer [Cu{H(2)NCH(2)CH(2)N═C(Me)C(COMe)═NNC(6)H(3)-2-O-4-NO(2)}](n) 14. The dependence of the OHADB tautomeric equilibria on temperature, electronic properties of functional groups, and solvent polarity was studied. The OHADB from unsymmetrical β-diketones exist in solution as a mixture of enol-azo and hydrazo tautomeric forms, while in the solid state all the free and coordinated OHADB crystallize in the hydrazo form. The relative stabilities of various tautomers were studied by density functional theory (DFT). 7-14 show catalytic activities for peroxidative oxidation (in MeCN/H(2)O) of cyclohexane to cyclohexanol and cyclohexanone, for selective aerobic oxidation of benzyl alcohols to benzaldehydes in aq. solution, mediated by TEMPO radical, under mild conditions and for the MW-assisted solvent-free synthesis of ketones from secondary alcohols with tert-butylhydroperoxide as oxidant.

Water‐Soluble Cobalt(II) and Copper(II) Complexes of 3‐(5‐Chloro‐2‐hydroxy‐3‐sulfophenylhydrazo)pentane‐2,4‐dione as Building Blocks for 3D Supramolecular Networks and Catalysts for TEMPO‐Mediated Aerobic Oxidation of Benzylic Alcohols

“…This is in agreement with the low field chemical shift (δ =14.33 ppm) of the hydrazo NH proton and is also consistent with IR data: the stretching bands ν(C=O) and ν(C=O···H) are at 1677 and 1624 cm -1 , respectively, the latter being shifted on account of the Hbond. [4,5] The ν(OH) and ν(NH) bands at 3400 and 3094 cm -1 also support the existence of the H-bonded hydrazone structure in the solid state. [4,5] X-ray diffraction analyses of analogues of 1, with different substituents, demonstrate that they are stabilized in the hydrazo II rather than in the hydrazo I form.…”

“…[4,5] The ν(OH) and ν(NH) bands at 3400 and 3094 cm -1 also support the existence of the H-bonded hydrazone structure in the solid state. [4,5] X-ray diffraction analyses of analogues of 1, with different substituents, demonstrate that they are stabilized in the hydrazo II rather than in the hydrazo I form. [4] Scheme 1.…”

“…[4,5] X-ray diffraction analyses of analogues of 1, with different substituents, demonstrate that they are stabilized in the hydrazo II rather than in the hydrazo I form. [4] Scheme 1. Synthesis of 2-4.…”

“…Complex 4 acts as catalyst precursor for the aerobic TEMPO-mediated selective oxidation of benzylic alcohols to the corresponding aldehydes in aqueous media. studies [4] have shown that copper(II) complexes with functionalized azo derivatives of β-diketones (ADBs), in particular ortho-hydroxy-substituted ADBs, are significantly active in the aerobic oxidation of benzyl alcohols to aldehydes. Hence, we report our continued preparation of new water-soluble ADB copper(II) and cobalt(II) complexes, which contain sites for possible pH regulation properties, in particular sulfo and amino groups, considered to be good candidates to fulfil these goals.…”

“…[4,5] Ethylenediamine (en) can further participate in this process through template Schiff base condensation or as a protonrich attractor and spacer, allowing the regulation of the size of channels or cavities within the H-bonded assemblies. [6] In addition, the presence of proton acceptor and donor sites within one molecule will result in a pH-tunable arrangement (association), which is interesting for a wide range of applications.…”