Mono- and dinuclear iron complexes of bis(1-methylimidazol-2-yl)ketone (bik): structure, magnetic properties, and catalytic oxidation studies

Autor: Bruijnincx, P.C.A., Buurmans, I.L.C., Huang, Y., Juhász, G., Viciano-Chumillas, M., Quesada, M., Lutz, M., Spek, A.L., Münck, E., Bominaar, E.L., Klein Gebbink, R.J.M., Inorganic Chemistry and Catalysis, Organic Chemistry and Catalysis, Rontgen participation programme, Sub Inorganic Chemistry and Catalysis, Sub Chem Biol & Organic Chem begr 1-6-12, Sub Crystal and Structural Chemistry
Jazyk: angličtina
Rok vydání: 2011
Předmět:
Zdroj: RiuNet. Repositorio Institucional de la Universitat Politécnica de Valéncia
instname
Inorganic Chemistry, 50(19), 9243. American Chemical Society
ISSN: 0020-1669
DOI: 10.1021/ic200332y
Popis: [EN] The newly synthesized dinuclear complex [Fe-2(III)(mu-OH)(2)(bik)(4)](NO3)(4) (1) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe center dot center dot center dot Fe (3.0723(6) angstrom) and Fe-O distances (1.941(2)/1.949(2) angstrom) compared to other unsupported Fe-2(III)(mu-OH)(2) complexes. The bridging hydroxide groups of 1 are strongly hydrogen-bonded to a nitrate anion. The Fe-57 isomer shift (delta = 0.45 mm s(-1)) and quadrupole splitting (Delta E-Q = 0.26 mm s(-1)) obtained from Mossbauer spectroscopy are consistent with the presence of two identical high-spin iron(III) sites. Variable-temperature magnetic susceptibility studies revealed antiferromagnetic exchange (J = 35.9 cm(-1) and H = JS(1).S-2) of the metal ions. The optimized DFT geometry of the cation of 1 in the gas phase agrees well with the crystal structure, but both the Fe center dot center dot center dot Fe and Fe-OH distances are overestimated (3.281 and 2.034 angstrom, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 angstrom) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J. by 35%. Spontaneous reduction of 1 was observed in methanol, yielding a blue [Fe-II(bik)(3)](2+) species. Variable-temperature magnetic susceptibility measurements of [Fe-II(bik)(3)](OTf)(2) (2) revealed spin-crossover behavior. Thermal hysteresis was observed with 2, due to a loss of cocrystallized solvent molecules, as monitored by thermogravimetric analysis. The hysteresis disappears once the solvent is fully depleted by thermal cycling. [Fe-II(bik)(3)](OTf)(2) (2) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C-H bond oxidation was observed with adamantane (3 degrees/2 degrees value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of O-2, and a low retention of configuration in cis-1,2-dimethylcyclohexane oxidation were observed. Stereoselective oxidation of olefins with dihydrogen peroxide yielding epoxides was observed under both limiting oxidant and substrate conditions.
This work was financially supported by the National Research School Combination-Catalysis (P.C.A.B.), the Council for Chemical Sciences of The Netherlands Organization for Scientific Research (CW-NWO) (M.L. and A.L.S.), and the National Institutes of Health Grant EB-001475 (E.M.). Dr. Stefania Tanase-Grecea is kindly acknowledged for her help with the collection of the magnetic measurements. Part of the work was financially supported the EC-RTN "QuEMolNa" (No. MRTN-CT-2003-504880) and the EC Network of Excellence "MAG-MANet" (No. 515767-2).
Databáze: OpenAIRE
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