title: Complexes of copper(II) with 3-(ortho-substituted phenylhydrazo)pentane-2,4-diones: syntheses, properties and catalytic activity for cyclohexane oxidation.
abstract: Reactions of copper(II) with 3-phenylhydrazopentane-2,4-diones X-2-C(6)H(4)-NHN=C{C(=O)CH(3)}(2) bearing a substituent in the ortho-position [X = OH (H(2)L(1)) 1, AsO(3)H(2) (H(3)L(2)) 2, Cl (HL(3)) 3, SO(3)H (H(2)L(4)) 4, COOCH(3) (HL(5)) 5, COOH (H(2)L(6)) 6, NO(2) (HL(7)) 7 or H (HL(8)) 8] lead to a variety of complexes including the monomeric [CuL(4)(H(2)O)(2)]·H(2)O 10, [CuL(4)(H(2)O)(2)] 11 and [Cu(HL(4))(2)(H(2)O)(4)] 12, the dimeric [Cu(2)(H(2)O)(2)(μ-HL(2))(2)] 9 and the polymeric [Cu(μ-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(H(2)O)(4){NCNC(NH(2))(2)}(2)](HL(4))(2)·6H(2)O 14 and the heteroligand polymer [Cu(μ-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, (1)H and (13)C 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))(H(2)O)]·H(2)O, [Cu(L(1))(H(2)O)(2)]·H(2)O and [Cu(L(4))(H(2)O)(2)]·H(2)O 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 H(2)O(2)) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H(2)O (total yields of ca. 20% with TONs up to 566), under mild conditions.
authors.affiliation: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, TU Lisbon, Av., Rovisco Pais, 1049-001, Lisbon, Portugal.
authors.forename: Maximilian N
authors.initials: MN
authors.lastname: Kopylovich
authors.forename: Andreia C C
authors.initials: AC
authors.lastname: Nunes
authors.forename: Kamran T
authors.initials: KT
authors.lastname: Mahmudov
authors.forename: Matti
authors.initials: M
authors.lastname: Haukka
authors.forename: Tatiana C O
authors.initials: TC
authors.lastname: Mac Leod
authors.forename: Luísa M D R S
authors.initials: LM
authors.lastname: Martins
authors.forename: Maxim L
authors.initials: ML
authors.lastname: Kuznetsov
authors.forename: Armando J L
authors.initials: AJ
authors.lastname: Pombeiro