Synthesis and structural characterization of iron complexes with 2,2,2-tris(1-pyrazolyl)ethanol ligands: Application in the peroxidative oxidation of cyclohexane under mild conditions

resumo

The reactions of FeCl2 center dot 2H(2)O and 2,2,2-tris(1-pyrazolyl) ethanol HOCH2C(pz)(3) (1) (pz = pyrazolyl) afford [Fe{HOCH2C(pz)(3)}(2)][FeCl4]Cl (2), [Fe{HOCH2C(pz)(3)}(2)](2)[Fe2OCl6](Cl)(2)center dot 4H(2)O (3 center dot 4H(2)O), [Fe{HOCH2C(pz)(3)}(2)] [FeCl{HOCH2C(pz)(3)}(H2O)(2)](2)(Cl)(4) (4) or [Fe{HOCH2C(pz)(3)}(2)]Cl-2 (5), depending on the experimental conditions. Compounds 1-5 were isolated as air-stable crystalline solids and fully characterized, including (1-4) by single-crystal X-ray diffraction analyses. The latter technique revealed strong intermolecular H-bonds involving the OH group of the scorpionate 2 and 3 giving rise to 1D chains which, in 3, are further expanded to a 2D network with intercalated infinite and almost plane chains of H-interacting water molecules. In 4, intermolecular pi center dot center dot center dot pi interactions involving the pyrazolyl rings are relevant. Complexes 2-5 display a high solubility in water (S-25 degrees C ca. 10-12 mg mL(-1)), a favourable feature towards their application as catalysts (or catalyst precursors) for the peroxidative oxidation of cyclo-hexane to cyclohexanol and cyclohexanone, with aqueous H2O2/MeCN, at room temperature (TON values up to ca. 385). (C) 2011 Elsevier B. V. All rights reserved.

palavras-chave

COPPER TRIETHANOLAMINE COMPLEXES; ORGANIC MOLECULAR-CRYSTALS; HYDROGEN-PEROXIDE; CATALYTIC-ACTIVITY; WATER CLUSTERS; HYDROCARBON OXYGENATIONS; COORDINATION CHEMISTRY; ALKANE HYDROXYLATION; RHENIUM COMPLEXES; ACID

categoria

Chemistry

autores

Silva, TFS; da Silva, MFG; Mishra, GS; Martins, LMDRS; Pombeiro, AJL

Grupos

agradecimentos

This work has been partially supported by the Fundacao para a Ciencia e a Tecnologia (FCT), Portugal, and its PPCDT (FEDER funded) programme. TFSS is grateful to FCT for a PhD grant (no. SFRH/BD/48087/2008). The authors gratefully acknowledge Dr. Maria Candida Vaz (IST) for the direction of the elemental analysis service, Mr. Indalecio Marques (IST) for running the MS and GC-MS spectra, the Portuguese NMR Network (IST-UTL Centre) for providing access to the NMR facility, the Portuguese MS Network (IST Node) and Dr. Conceicao Oliveira for the ESI measurements.

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