Cobalt Complexes with Pyrazole Ligands as Catalyst Precursors for the Peroxidative Oxidation of Cyclohexane: X‐ray Absorption Spectroscopy Studies and Biological Applications. Issue 4 (30th January 2014)

• Record Type: Journal Article
• Authors: F. S. Silva, Telma; M. D. R. S. Martins, Luísa; Guedes da Silva, M. Fátima C.; Kuznetsov, Maxim L.; Fernandes, Alexandra R.; Silva, Ana; Pan, Chun‐Jern; Lee, Jyh‐Fu; Hwang, Bing‐Joe; J. L. Pombeiro, Armando
• Is Part Of: Chemistry, an Asian journal. Volume 9:Issue 4(2014:Apr.)
• Page Start: 1132
• Page End: 1143
• Publication Date: 2014-01-30
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1002/asia.201301331
• Languages: English
• ISSNs: 1861-4728

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>[CoCl(μ‐Cl)(Hpz<sup>Ph</sup>)<sub>3</sub>]<sub>2</sub> (<bold>1</bold>) and [CoCl<sub>2</sub>(Hpz<sup>Ph</sup>)<sub>4</sub>] (<bold>2</bold>) were obtained by reaction of CoCl<sub>2</sub> with HC(pz<sup>Ph</sup>)<sub>3</sub> and Hpz<sup>Ph</sup>, respectively (Hpz<sup>Ph</sup>=3‐phenylpyrazole). The compounds were isolated as air‐stable solids and fully characterized by IR and far‐IR spectroscopy, MS(ESI+/−), elemental analysis, cyclic voltammetry (CV), controlled potential electrolysis, and single‐crystal X‐ray diffraction. Electrochemical studies showed that <bold>1</bold> and <bold>2</bold> undergo single‐electron irreversible Co<sup>II</sup>→Co<sup>III</sup> oxidations and Co<sup>II</sup>→Co<sup>I</sup> reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex <bold>1</bold>, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of <bold>1</bold> and <bold>2</bold> were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of <bold>1</bold> and <bold>2</bold> (that before structural relaxation) affects mostly the chloride and pyrazolyl ligands, whereas adiabatic oxidation (that after the geometry relaxation) and reduction are mostly metal centered. Compounds <bold>1</bold> and <bold>2</bold> and, for comparative purposes, other related scorpionate and pyrazole cobalt complexes, exhibit catalytic activity for the peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions (room temperature, aqueous H<sub>2</sub>O<sub>2</sub>). In situ X‐ray absorption spectroscopy studies indicated that the species derived from complexes <bold>1</bold> and <bold>2</bold> during the oxidation of cyclohexane (i.e., Ox‐<bold>1</bold> and Ox‐<bold>2</bold>, respectively) are analogous and contain a Co<sup>III</sup> site. Complex <bold>2</bold> showed low in vitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.</p> </abstract>