Redox Processes Involved in the Synthesis and Reactivity of Oxazolinylthiophenolato Complexes of Iron(II)/(III)

The reaction of anhydrous FeCl2 with 2-(4',4'-dimethyloxazolin-2'-yl)thiophenolate (ox-phS(-)) afforded mononuclear [Fe(ox-phS)(2)] (A) and binuclear [{Fe-III(ox-phS)}(2)(mu-S)(2)] (B). In B, iron(III) and S2- resulted from an unexpected redox reaction involving elemental sulfur and the iron(II) starting material. Complexes A and B co-crystallise reproducibly in a 2:1 proportion. An attempt to prepare (oxazolinylthiophenolato)iron(III) from Li(ox-phS) and anhydrous FeCl3 in the presence of N,N,N',N'-tetramethylethane-1,2-diamine (tmen) gave another redox reaction with disulfide D, bis{2-(4 ',4'-di-methyloxazolin-2'-yl)phenyl}disulfide (ox-phS-Sph-ox), and trans-[FeCl2(tmen)(2)] (E) as 1:1 co-crystallised products. Characterisation of all complexes included Mossbauer spectroscopy and single-crystal X-ray diffraction analysis. Quantum mechanical (TDDFT) calculations for A and cyclic voltammetry experiments carried out with A and C helped to distinguish between ligand- and metal-based electronic transitions and redox processes. Results add to the knowledge of the rich redox chemistry of early transition metals with soft S-donor ligands, with possible consequences for catalytic and biochemical transformations.