Disproportionation Equilibrium of a μ‐Oxodiiron(III) Complex Giving Rise to C−H Activation Reactivity: Structural Snapshot of a Unique Oxoiron(IV) Adduct. Issue 32 (3rd July 2019)

• Record Type: Journal Article
• Authors: Cordes (née Kupper), Claudia; Morganti, Massimiliano; Klawitter, Iris; Schremmer, Claudia; Dechert, Sebastian; Meyer, Franc
• Is Part Of: Angewandte Chemie international edition. Volume 58:Issue 32(2019)
• Page Start: 10855
• Page End: 10858
• Publication Date: 2019-07-03
• Subjects: C−H activation -- iron -- iron–oxo complexes -- kinetics -- N-heterocyclic carbene ligands; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.201900683
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: μ‐Oxodiiron(III) species are air‐stable and unreactive products of autoxidation processes of monomeric heme and non‐heme iron(II) complexes. Now, the organometallic [(L NHC )Fe III ‐(μ‐O)‐Fe III (L NHC )] 4+ complex 1 (L NHC is a macrocyclic tetracarbene) is shown to be reactive in C−H activation without addition of further oxidants. Studying the oxidation of dihydroanthracene, it was found that 1 thermally disproportionates in MeCN solution into its oxoiron(IV) (2 ) and iron(II) components; the former is the active species in the observed oxidation processes. Possible cleavage scenarios for 1 are shown by scrambling experiments and structural characterization of an unprecedented adduct of 1 and oxoiron(IV) complex 2 . Kinetic analysis gave an equilibrium constant for the disproportionation of 1, which is very small ( K eq =7.5±2.5×10 −8 m ). Increasing K eq might by a useful strategy for circumventing the formation of dead‐end μ‐oxodiiron(III) products during Fe‐based homogeneous oxidation catalysis. Abstract : Scrambling experiments and kinetic analyses indicate thermal disproportionation of a tetracarbene‐ligated μ‐oxodiiron(III) complex in solution, enabling C−H activation by the resulting oxoiron(IV) intermediate. Structural characterization of a unique adduct between the oxoiron(IV) and μ‐oxodiiron(III) species provides a snapshot of the scrambling process.