title: Heterometallic Co(III)4Fe(III)2 Schiff base complex: structure, electron paramagnetic resonance, and alkane oxidation catalytic activity.
abstract: The heterometallic complex [Co(4)Fe(2)OSae(8)]·4DMF·H(2)O (1) was synthesized by one-pot reaction of cobalt powder with iron chloride in a dimethylformamide solution of salicylidene-2-ethanolamine (H(2)Sae) and characterized by single crystal X-ray diffraction analysis, magnetic measurements, high frequency electron paramagnetic resonance (HF-EPR), and Mössbauer spectroscopies. The exchange coupling in the Fe(III)-Fe(III) pair is of antiferromagnetic behavior with J/hc = -190 cm(-1). The HF-EPR spectra reveal an unusual pattern with a hardly detectable triplet signal of the Fe(III) dimer. The magnitude of D (ca. 13.9 cm(-1)) was found to be much larger than in related dimers. The catalytic investigations disclosed an outstanding activity of 1 toward oxidation of cycloalkanes with hydrogen peroxide, under mild conditions. The most efficient system showed a turnover number (TON) of 3.57 × 10(3) with the concomitant overall yield of 26% for cyclohexane, and 2.28 × 10(3)/46%, respectively, for cyclooctane. A remarkable turnover frequency (TOF) of 1.12 × 10(4) h(-1) (the highest initial rate W(0) = 3.5 × 10(-4) M s(-1)) was achieved in oxidation of cyclohexane. Kinetic experiments and selectivity parameters led to the conclusion that hydroxyl radicals are active (attacking C-H bonds) species. Kinetic and electrospray ionization mass spectrometry (ESI-MS) data allowed us to assume that the trinuclear heterometallic particle [Co(2)Fe(Sae)(4)](+), originated from 1 in solution, could be responsible for efficient generation of hydroxyl radicals from hydrogen peroxide.
authors.affiliation: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal.
authors.forename: Dmytro S
authors.initials: DS
authors.lastname: Nesterov
authors.forename: Eduard N
authors.initials: EN
authors.lastname: Chygorin
authors.forename: Volodymyr N
authors.initials: VN
authors.lastname: Kokozay
authors.forename: Volodymyr V
authors.initials: VV
authors.lastname: Bon
authors.forename: Roman
authors.initials: R
authors.lastname: Boča
authors.forename: Yuriy N
authors.initials: YN
authors.lastname: Kozlov
authors.forename: Lidia S
authors.initials: LS
authors.lastname: Shul'pina
authors.forename: Julia
authors.initials: J
authors.lastname: Jezierska
authors.forename: Andrew
authors.initials: A
authors.lastname: Ozarowski
authors.forename: Armando J L
authors.initials: AJ
authors.lastname: Pombeiro
authors.forename: Georgiy B
authors.initials: GB
authors.lastname: Shul'pin