Mono- and Dinuclear Iron Complexes of Bis(1-methylimidazol-2-yl)ketone (bik): Structure, Magnetic Properties, and Catalytic Oxidation Studies

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• 作者：Pieter C. A. Bruijnincx ; Inge L. C. Buurmans ; Yuxing Huang ; Gergely Juh谩sz ; Marta Viciano-Chumillas ; Manuel Quesada ; Jan Reedijk ; Martin Lutz ; Anthony L. Spek ; Eckard M眉nck ; Emile L. Bominaar ; Robertus J. M. Klein Gebbink
• 刊名：Inorganic Chemistry
• 出版年：2011
• 出版时间：October 3, 2011
• 年：2011
• 卷：50
• 期：19
• 页码：9243-9255
• 全文大小：1089K
• 年卷期：v.50,no.19(October 3, 2011)
• ISSN：1520-510X

文摘

The newly synthesized dinuclear complex [Fe^IIIb>2b>(渭-OH)b>2b>(bik)b>4b>](NOb>3b>)b>4b> (<b>1b>) (bik, bis(1-methylimidazol-2-yl)ketone) shows rather short Fe路路路Fe (3.0723(6) 脜) and Fe鈥揙 distances (1.941(2)/1.949(2) 脜) compared to other unsupported Fe^IIIb>2b>(渭-OH)b>2b> complexes. The bridging hydroxide groups of <b>1b> are strongly hydrogen-bonded to a nitrate anion. The ⁵⁷Fe isomer shift (未 = 0.45 mm s^鈥?) and quadrupole splitting (螖Eb>Qb> = 0.26 mm s^鈥?) obtained from M枚ssbauer 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^鈥? and H = J<b>Sb>b>1b>路<b>Sb>b>2b>) of the metal ions. The optimized DFT geometry of the cation of <b>1b> in the gas phase agrees well with the crystal structure, but both the Fe路路路Fe and Fe鈥揙H distances are overestimated (3.281 and 2.034 脜, respectively). The agreement in these parameters improves dramatically (3.074 and 1.966 脜) when the hydrogen-bonded nitrate groups are included, reducing the value calculated for J by 35%. Spontaneous reduction of <b>1b> was observed in methanol, yielding a blue [Fe^II(bik)b>3b>]²⁺ species. Variable-temperature magnetic susceptibility measurements of [Fe^II(bik)b>3b>](OTf)b>2b> (<b>2b>) revealed spin-crossover behavior. Thermal hysteresis was observed with <b>2b>, 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)b>3b>](OTf)b>2b> (<b>2b>) catalyzes the oxidation of alkanes with t-BuOOH. High selectivity for tertiary C鈥揌 bond oxidation was observed with adamantane (3掳/2掳 value of 29.6); low alcohol/ketone ratios in cyclohexane and ethylbenzene oxidation, a strong dependence of total turnover number on the presence of Ob>2b>, 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.