Abstract
The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe4(μ-O)4(PTEBIA)4](CF3SO3)4(CH3CN)2] (1a), [Fe2(μ-O)Cl2(PTEBIA)2](CF3SO3)2 (1b), and [Fe2(μ-O)(HCOO)2(PTEBIA)2](ClO4)2 (MeOH) (2) were prepared from the sulfur-containing ligand (2-((2,4-dimethylphenyl)thio)-N,N-bis ((1-methyl-benzimidazol-2-yl)methyl)ethanamine (PTEBIA). The tetrairon complex 1a features four μ-oxido bridges, while in dinuclear 1b, the sulfur moiety of the ligand occupies one of the six coordination sites of each Fe(III) ion with a long Fe-S distance of 2.814(6) Å. In 2, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidation. Complexes 1a and 1b show broad sulfur-to-iron charge transfer bands around 400–430 nm at room temperature, consistent with mononuclear structures featuring Fe-S interactions. In contrast, acetonitrile solutions of 2 display a sulfur-to-iron charge transfer band only at low temperature (228 K) upon addition of H2O2/CH3COOH, with an absorption maximum at 410 nm. Homogeneous oxidative catalytic activity was observed for 1a and 1b using H2O2 as oxidant, but with low product selectivity. High valent iron-oxo intermediates could not be detected by UV-vis spectroscopy or ESI mass spectrometry. Rather, evidence suggest preferential ligand oxidation, in line with the relatively low selectivity and catalytic activity observed in the reactions.
Highlights
The interaction between iron and sulfur in metalloproteins and in biomimetic molecular systems has attracted increased attention in recent years (Beinert et al, 1997; Ohnishi, 1998; Rao and Holm, 2004; Ballmann et al, 2008a; Meyer, 2008; Lill, 2009)
Fe-S interaction in various molecular systems having iron in different formal oxidation states is an interesting field of research
We describe new di- and tetranuclear Fe(III)μ-oxido complexes with the thioether-containing PTEBIA ligand (Castillo et al, 2012), viz [Fe4(μO)4(PTEBIA)4](CF3SO3)4(CH3CN)2] (1a), and [Fe2(μO)Cl2(PTEBIA)2](CF3SO3)2 (1b) (Figure 1)
Summary
The interaction between iron and sulfur in metalloproteins and in biomimetic molecular systems has attracted increased attention in recent years (Beinert et al, 1997; Ohnishi, 1998; Rao and Holm, 2004; Ballmann et al, 2008a; Meyer, 2008; Lill, 2009). Fe(II), there are molecular systems where the sulfur atom has been found to be bonded to high valent (III and IV) iron centers with distorted octahedral geometry (Harrop and Mascharak, 2004; McDonald et al, 2010; Widger et al, 2014). The selective and environmentally benign oxidation of hydrocarbons using affordable and efficient catalysts is another important area of modern synthetic chemistry In this regard, bio-inspired iron chemistry has received increasing attention in recent decades due to the natural iron abundance in the earth crust, and the highly selective catalytic hydrocarbon oxidations of iron-containing oxygenases such as cytochrome
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