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- A bis(mu-chlorido)-bridged cobalt(II) complex with silyl-containing schiff base as a catalyst precursor in the solvent-free oxidation of cyclohexanePublication . Zaltariov, Mirela-Fernanda; Vieru, Veacheslav; Zalibera, Michal; Cazacu, Maria; Martins, Nuno M. R.; Martins, Luisa; Rapta, Peter; NOVITCHI, Ghenadie; Shova, Sergiu; Pombeiro, Armando; Arion, Vladimir B.A new bis(µ-chlorido)-bridged cobalt(II) complex [Co2(µ-Cl)2(HL2)4][CoCl4] (1), where HL2 is a silyl-containing Schiff base, was synthesised. The structure of this compound was established by X-ray crystallography revealing a zwitterionic form adopted by the organic ligand. The temperature dependence of the magnetic susceptibility and the field dependence of the magnetisation indicate the presence of ferromagnetic interactions between paramagnetic d7 cobalt(II) centres (SCo = 3/2). The exchange coupling parameter J(Co1–Co2) = +7.0 cm–1 extracted from broken-symmetry (BS) DFT calculations agrees well with the value of +8.8 cm–1 determined from the experimental data by fitting them with the Hamiltonian math formula. Electrochemical studies indicate that complex 1 is inefficient as a catalyst in electrochemical reduction of protons. One of the reasons is the low stability of the complex in solution. In contrast, 1 acts as an effective homogeneous (pre)catalyst in the microwave-assisted neat oxidation of cyclohexane with aqueous tBuOOH (TBHP). The possible mechanism of catalytic oxidation and other advantages of using 1 in the oxidation of cycloalkanes are discussed.
- µ-Chlorido-bridged dimanganese(II) complexes of the schiff base derived from [2+2] condensation of 2,6-diformyl-4-methylphenol and 1,3-bis(3-aminopropyl)tetramethyldisiloxane: structure, magnetismo, electrochemical behaviour, and catalytic oxidation of secondary alcoholsPublication . Alexandru, Mihaela; Cazacu, Maria; Arvinte, Adina; Shova, Sergiu; Turta, Constantin; Simionescu, Bogdan C.; Dobrov, Anatolie; Alegria, Elisabete; Martins, Luisa; Pombeiro, Armando; Arion, Vladimir B.The reaction of 2,6-diformyl-4-methylphenol with 1,3-bis(3-aminopropyl)tetramethyldisiloxane in the presence of MnCl2 in a 1:1:2 molar ratio in methanol afforded a dinuclear -chlorido-bridged manganese(II) complex of the macrocyclic [2+2] condensation product (H2L), namely, [Mn2Cl2(H2L)(HL)]Cl center dot 3H(2)O (1). The latter afforded a new compound, namely, [Mn2Cl2(H2L)(2)][MnCl4]center dot 4CH(3)CN center dot 0.5CHCl(3 center dot)0.4H(2)O (2), after recrystallisation from 1:1 CHCl3/CH3CN. The co-existence of the free and complexed azomethine groups, phenolato donors, mu-chlorido bridges, and the disiloxane unit were well evidenced by ESI mass spectrometry and FTIR spectroscopy and confirmed by X-ray crystallography. The magnetic measurements revealed an antiferromagnetic interaction between the two high-spin (S = 5/2, g = 2) manganese(II) ions through the mu-chlorido bridging ligands. The electrochemical behaviour of 1 and 2 has been studied, and details of their redox properties are reported. Both compounds act as catalysts or catalyst precursors in the solvent-free low-power microwave-assisted oxidation of selected secondary alcohols, for example, 1-phenylethanol, cyclohexanol, 2- and 3-octanol, to the corresponding ketones in the absence of solvent. The highest yield of 72% was achieved for 1-phenylethanol by using a maximum of 1% molar ratio of catalyst relative to substrate.