pubs.acs.org/IC Published on Web 01/06/2011 r 2011 American Chemical Society 918 Inorg. Chem. 2011, 50, 918–931 DOI: 10.1021/ic101516k Ortho-Hydroxyphenylhydrazo-β-Diketones: Tautomery, Coordination Ability, and Catalytic Activity of Their Copper(II) Complexes toward Oxidation of Cyclohexane and Benzylic Alcohols Maximilian N. Kopylovich, † Kamran T. Mahmudov, † M. F  atima C. Guedes da Silva, †,‡ Pawe / l J. Figiel, † Yauhen Yu. Karabach, † Maxim L. Kuznetsov, † Konstantin V. Luzyanin, † and Armando J. L. Pombeiro* ,† † Centro de Quı´mica Estrutural, Complexo I, Instituto Superior T ecnico, TU Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal, and ‡ Universidade Lus  ofona de Humanidades e Tecnologias, ULHT Lisbon Av. Campo Grande no. 376, 1749-024, Lisbon, Portugal Received July 28, 2010 New hydrazone o-HO-phenylhydrazo-β-diketones (OHADB),R 1 NHNdCR 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 NdC(Me)C(COMe)dNNC 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 NdC(Me)C(COMe)dNNC 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. Introduction Azoderivatives of β-diketones (ADB, Scheme 1) represent a class of compounds known for a long time but with a surprisingly low impact in coordination chemistry. It was postulated 1,2 that ADB may exist in three tautomeric forms (enol-azo, keto-azo, and hydrazo; see below) allowing their application for the design of functional materials attributed to smart hydrogen bonding, bistate molecular switches, self- assembled layers, liquid crystals, and so forth. 2 However, ex- perimentally it was found that the studied ADB are stabilized in the hydrazo form with formation of a hydrogen bond be- tween the hydrazone =N-NH- moiety and a carbonyl group giving a six-membered cycle (Scheme 1). In contrast to the well- studied chemistry of β-diketones, the number of publications devoted to ADB coordination compounds is very limited, 3 and the structurally characterized complexes are usually simple diligand monomeric chelates. 3a,c Thus, to promote the versatility of coordination of ADB, we decided to focus on a functionalized form, in particular the ortho-hydroxyphenyl *To whom correspondence should be addressed. Fax: (þ351) 218464455. 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