A Bispidine Iron(IV)–Oxo Complex in the Entatic State

Abstract

For a series of Fe(IV) =O complexes with tetra- and pentadentate bispidine ligands, the correlation of their redox potentials with reactivity, involving a variety of substrates for alkane hydroxylation (HAT), alkene epoxidation, and phosphine and thioether oxidation (OAT) are reported. The redox potentials span approximately 350 mV and the reaction rates over 8 orders of magnitude. From the experimental data and in comparison with published studies it emerges that electron transfer and the driving force are of major importance, and this is also supported by the DFT-based computational analysis. The striking difference of reactivity of two isomeric systems with pentadentate bispidines is found to be due to a destabilization of the S=1 ground state of one of the ferryl isomers, and this is supported by the experimentally determined redox potentials and published stability constants with a series of first-row transition metal ions with these two isomeric ligands.

Nonheme Iron‐Oxo‐Catalyzed Methane Formation from Methyl Thioethers: Scope, Mechanism, and Relevance for Natural Systems

“…[7] This reactioni sn either efficient nors elective but, for the environmenta nd therefore for environmental chemistry,i t is of enormous importance.T here is ad ifferencei nt he vital requirements for catalytic processes in living systems, industrial processes,a nd environmentally relevant abiotic reactions. [7] Preliminary mechanistic studies indicated that oxotransferf rom af erryl oxidant to the sulfoxide, obtained by the preceding sulfoxidation of met,i st he key step in producing CH 3 radicals.T hese radicals were trapped and characterizedb y EPR spectroscopy.B ispidine-based ferryl complexes have aw ell-understood oxygenation and oxidation chemistry, [9][10][11][12][13] and are therefore excellent models fort he catalytically active ferryl speciesa nd av aluable tool for the mechanistic evaluation of this interesting reaction. For industrial processes, substrate selectivity is generally not essential and the level of product selectivity is (slightly) less important than in natural systems but catalysts tability is crucial.…”

“…All 13 C/ 12 Ci sotope ratios (d 13 Cv alues) are expressed in the conventional d notation in % vs. VPDB (Vienna PDB standard), defined as Equation (1): The GC-C-IRMS system consisted of ac ryogenic preconcentration unit directly coupled to aH P6 890 n GC (Agilent Te chnologies, Santa Clara, USA), which is connected to aD elta PLUS XL isotope ratio mass spectrometer (ThermoQuest Finnigan, Bremen, Germany) via an oxidation reactor (ceramic tube (Al 2 O 3 ), length 320 mm, 0.5 mm i.d., with oxygen activated Cu/Ni/Pt wires inside, reactor temperature 960 8C) and aG CC ombustion III Interface (ThermoQuest Finnigan).…”

“…Position-specific 13 Cl abeling experiments were conducted with methionine that had as ignificant 13 Ce nrichment of the carbon atom of the thio-methyl group. Preparation of 13 C-enriched 13 CH 3mso was performed by gravimetrically mixing of 13 CH 3 -mso ( 13 CH 3met was oxidized with CH 3 COOOH to 13 CH 3 -mso,S igma-Aldrich, Ta ufkirchen, Germany;I sotec 99 % 13 Ca toms) with unlabeled mso (Sigma-Aldrich, Ta ufkirchen, Germany) at ar atio of 5:95.…”

“…Preparation of 13 C-enriched 13 CH 3mso was performed by gravimetrically mixing of 13 CH 3 -mso ( 13 CH 3met was oxidized with CH 3 COOOH to 13 CH 3 -mso,S igma-Aldrich, Ta ufkirchen, Germany;I sotec 99 % 13 Ca toms) with unlabeled mso (Sigma-Aldrich, Ta ufkirchen, Germany) at ar atio of 5:95. 13 Cg roup when asc and tBuOH, respectively,w ere used for experiments. 13 Cg roup when asc and tBuOH, respectively,w ere used for experiments.…”

“…Ap rominent exception is the oxidation of the Fe II precursor based on L 3 with H 2 O 2 . [31][32][33][34][35] (iv) CH 3 radicals were trappedw ith DMPO( 5,5-dimethyl-pyrroline-N-oxide) and characterized by EPR spectroscopy.S mall amountso fe thane werea lso detected but not quantified (the origin of traces of ethane from met was confimed by 13 Cl abeling). [29] Note however, that in many examples in this area, the ferryl oxidant is not prepared by oxidation using H 2 O 2 .I na ddition, DFT calculations have shown that the ferryl aqua ion is as table species.…”