AUTHOR=Das Biswanath , Al-Hunaiti Afnan , Sánchez-Eguía Brenda N. , Zeglio Erica , Demeshko Serhiy , Dechert Sebastian , Braunger Steffen , Haukka Matti , Repo Timo , Castillo Ivan , Nordlander Ebbe 

TITLE=Di- and Tetrairon(III) μ-Oxido Complexes of an N3S-Donor Ligand: Catalyst Precursors for Alkene Oxidations

JOURNAL=Frontiers in Chemistry

VOLUME=7

YEAR=2019

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00097

DOI=10.3389/fchem.2019.00097

ISSN=2296-2646

ABSTRACT=<p>The new di- and tetranuclear Fe(III) μ-oxido complexes [Fe<sub>4</sub>(μ-O)<sub>4</sub>(PTEBIA)<sub>4</sub>](CF<sub>3</sub>SO<sub>3</sub>)<sub>4</sub>(CH<sub>3</sub>CN)<sub>2</sub>] (<bold>1a</bold>), [Fe<sub>2</sub>(μ-O)Cl<sub>2</sub>(PTEBIA)<sub>2</sub>](CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> (<bold>1b</bold>), and [Fe<sub>2</sub>(μ-O)(HCOO)<sub>2</sub>(PTEBIA)<sub>2</sub>](ClO<sub>4</sub>)<sub>2</sub> (MeOH) (<bold>2</bold>) 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 <bold>1a</bold> features four μ-oxido bridges, while in dinuclear <bold>1b</bold>, 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 <bold>2</bold>, two Fe(III) centers are bridged by one oxido and two formate units, the latter likely formed by methanol oxidation. Complexes <bold>1a</bold> and <bold>1b</bold> 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 <bold>2</bold> display a sulfur-to-iron charge transfer band only at low temperature (228 K) upon addition of H<sub>2</sub>O<sub>2</sub>/CH<sub>3</sub>COOH, with an absorption maximum at 410 nm. Homogeneous oxidative catalytic activity was observed for <bold>1a</bold> and <bold>1b</bold> using H<sub>2</sub>O<sub>2</sub> 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.</p>