Two Allogons of an O2‐activating Bis(disiloxido)ferrate(II) Accessible Selectively just by Variation of the Crystallization Temperature

Abstract

AbstractDeprotonation of O(iPr2SiOH)2 (iPrLH2) with LiOtBu followed by reaction with FeCl2 in THF led to the complex [iPrL2Fe][Li(THF)2]2, 2, which represents a structural and spectroscopic model of the α‐Fe sites of Fe/ZSM‐5. Reaction with O2 in THF solution proceeds rather fast and is complete within 200 ms; an intermediate O2 adduct could not be identified by stopped‐flow methods. Cooling blue solutions of 2 to −80 °C led to the growth of blue crystals of 2⋅THF, the analysis of which by XRD revealed a FeO4 core that is somewhat distorted from planarity towards a tetrahedral structure. By contrast, cooling such solutions to −30 °C led to pink crystals of an allogon featuring a perfectly square planar FeO4 entity. Hence, 2 represents a unique case where two different structural isomers (allogons) can be crystallized from the same solvent selectively, controlled by the temperature. DFT calculations were performed to understand this finding.