Heterometallic Co^III₄Fe^III₂Schiff 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.

New Trends in Oxidative Functionalization of Carbon–Hydrogen Bonds: A Review

“…[160]. In oxidation of cyclohexane into cyclohexyl hydroperoxide under the action of H 2 O 2 , this compounds exhibits a very high TON of 3570, which is the highest value ever observed for an iron-containing catalyst.…”

“…In oxidation of cyclohexane into cyclohexyl hydroperoxide under the action of H 2 O 2 , this compounds exhibits a very high TON of 3570, which is the highest value ever observed for an iron-containing catalyst. It has been indicated [160] via mass spectral and comprehensive kinetic studies that hexanuclear 2 dissociates when dissolved in CH 3 CN to form a trinuclear particle [Co 2 Fe(L 4 ) 4 ] + . This particle, observed in concentrated (1ˆ10´4 M) solutions of 2, is the catalytically active species responsible for the fast reaction rates greater than 3ˆ10 4 M¨s´1 (maximum turnover frequency TOF = 11,200 h´1 = 3.1 s´1).…”

“…[160]) by the competitive interaction of hydroxyl radicals both with cyclohexane and acetonitrile. The following kinetic scheme describes the dependence of W 0 on [cyclohexane] 0 with the plateau:…”

MAGNETOSTRUCTURAL J-CORRELATIONS IN Fe(III) COMPLEXES – A REVISION

“…4. The problematic datapoint is marked by a cross and excluded from the correlation: Having some more datapoints at the disposal from recent structural and magnetic investigations (NESTEROV et al, 2012;CHYGORIN et al, 2012;NESTEROVA et al, 2013), the original dataset has been enlarged and subjected the linear regression (Fig. 5).…”

Topological insights in polynuclear Ni/Na coordination clusters derived from a schiff base ligand

“…These entities are of great interest for their aesthetically beautiful structures [2][3][4], unexpected transformations [5][6][7] and potential applications in magnetism [8][9][10], luminescence [11][12][13][14][15], catalysis [16][17][18], etc. Paramagnetic transition metal CCs are of intense interest and have attracted a vast amount of attention since the discovery that some CCs behave as single-molecule magnets (SMMs) [19][20][21].…”