Cobalt complexes with pyrazole ligands as catalyst precursors for the peroxidative oxidation of cyclohexane: X-ray absorption spectroscopy studies and biological applications.
[CoCl(μ-Cl)(Hpz(Ph))3]2 (1) and [CoCl2(Hpz(Ph))4] (2) were obtained by reaction of CoCl2 with HC(pz(Ph))3 and Hpz(Ph), respectively (Hpz(Ph)=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 1 and 2 undergo single-electron irreversible Co(II)→Co(III) oxidations and Co(II)→Co(I) reductions at potentials measured by CV, which also allowed, in the case of dinuclear complex 1, the detection of electronic communication between the Co centers through the chloride bridging ligands. The electrochemical behavior of models of 1 and 2 were also investigated by density functional theory (DFT) methods, which indicated that the vertical oxidation of 1 and 2 (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 1 and 2 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 H2O2). In situ X-ray absorption spectroscopy studies indicated that the species derived from complexes 1 and 2 during the oxidation of cyclohexane (i.e., Ox-1 and Ox-2, respectively) are analogous and contain a Co(III) site. Complex 2 showed low in vitro cytotoxicity toward the HCT116 colorectal carcinoma and MCF7 breast adenocarcinoma cell lines.
Centro de Química Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal), Fax: (+351) 218464455.
Telma F S
TF
Silva
Luísa M D R S
LM
Martins
M Fátima C
MF
Guedes da Silva
Maxim L
ML
Kuznetsov
Alexandra R
AR
Fernandes
Ana
A
Silva
Chun-Jern
CJ
Pan
Jyh-Fu
JF
Lee
Bing-Joe
BJ
Hwang
Armando J L
AJ
Pombeiro
D002384:Catalysis; D002470:Cell Survival / Q000187:drug effects; D003035:Cobalt / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry* / Q000633:toxicity; D018360:Crystallography, X-Ray; D003510:Cyclohexanes / Q000737:chemistry*; D055664:Electrochemical Techniques; D045325:HCT116 Cells; D006801:Humans; D008024:Ligands; D061986:MCF-7 Cells; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D011720:Pyrazoles / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy
D056831:Coordination Complexes; D003510:Cyclohexanes; D008024:Ligands; D011720:Pyrazoles; D003035:Cobalt; C031280:pyrazole; C506365:Cyclohexane
X-ray absorption spectroscopy; cobalt; cyclic voltammetry; cyclohexane oxidation; in vitro cytotoxicity; pyrazole based ligands