Low‐Coordinated Iron(II) Siloxide Complexes – Structural Diversity and Reactivity Towards O2 and Oxygen Atom Transfer Reagents

The coordination chemistry of Fe2+ ions in combination with a monodentate siloxide ligand Ph3SiO− (L) was investigated. Using a Fe/L stoichiometry of 1 : 3 the complex [Na(DME)][FeL3], 2, with the iron center in a trigonal ligand environment was isolated and through decreasing the siloxide amount fraction 2 was shown to form via a unique example of a dinuclear complex, where one of the iron ions has a quasi‐trigonal and the other one a tetrahedral coordination sphere, namely [Na(DME)][Fe2L5], 1. If, however, 4 equivalents of L are employed, the tetrasiloxido ferrate(II) anion with a tetrahedral structure is generated, so that the product [Na(DME)]2[FeL4], 3, can be isolated. 2 reacts instantly with O‐atom transfer reagents, also at low temperatures, but no reaction intermediate could be identified. From the product mixture the iron(III) siloxide complex [Na(DME)3][FeL4], 4, could isolated by crystallization as the main product. Likewise, the reaction with dioxygen proceeded rather fast and added substrates did not intercept any intermediate upon its formation. However, in the presence of cyclohexene oxidation products were observed. They correspond to the typical radical‐chain‐derived products of cyclohexene suggesting, that initially a reactive FeOx species is generated that via an H atom ion from cyclohexene triggers its autoxidation. A series of iron(II) silanolate complexes has been accessed in a controlled manner, including a dinuclear complex with a unique structural motif and a rare example of a tri‐coordinated representative. The latter has been tested with regard to its propensity to form reactive intermediates in contact with O atom transfer reagents and O2.