Photoinduced O₂-Dependent Stepwise Oxidative Deglycination of a Nonheme Iron(III) Complex

Abstract

The iron(III) complex [Fe(tpena)] 2+ (tpena = N,N,N′-tris(2-pyridylmethyl)ethylendiamine-N′-acetate) undergoes irreversible O 2 -dependent N-demethylcarboxylation to afford [Fe II (SBPy3)(MeCN)] 2+ (SBPy3 = N,N-bis(2pyridylmethyl)amine-N-ethyl-2-pyridine-2-aldimine), when irradiated with near-UV light. The loss of a mass equivalent to the glycyl group in a process involving consecutive C−C and C−N cleavages is documented by the measurement of the sequential production of CO 2 and formaldehyde, respectively. Time-resolved UV−vis absorption, Mossbauer, EPR, and Raman spectroscopy have allowed the spectroscopic characterization of two iron-based intermediates along the pathway. The first of these, proposed to be a low-spin iron(II)-radical ligand complex, reacts with O 2 in the rate-determining step to produce a putative alkylperoxide complex. DFT calculations suggest that this evolves into an Fe(IV)-oxo species, which can abstract a hydrogen atom from a cis methylene group of the ligand to give the second spectroscopically identified intermediate, a high-spin iron(III)-hydroxide of the product oxidized ligand, [Fe III (OH)(SBPy 3 )] 2+ . Reduction and exchange of the cohydroxo/water ligand produces the crystallographically characterized products [Fe II (SBPy3)(X)] 2+/3+ , X = MeCN, [Zn(tpena)] + .

cis Donor Influence on O–O Bond Lability in Iron(III) Hydroperoxo Complexes: Oxidation Catalysis and Ligand Transformation

“…The abbreviated names are illustrated with the crystallographically characterized iron chlorides [Fe III Cl(Htpena)] 2+ and [Fe II Cl(tpenOH)] + (Scheme 2b). 46,52 Solution 55 The relative concentrations will depend on the concentration of water, with higher water content increasing the concentration of [Fe III 2 O-(Htpena) 2 )] 4+ . Solution-state EPR spectra of [Fe II Cl(tpenOH)]PF 6 dissolved in MeOH shows that samples, which are frozen immediately after dissolution, do not exhibit an EPR signal at 100 K. This is consistent with the iron(II) oxidation state that is present in the solid starting material.…”

Cooperative Co-Activation of Water and Hypochlorite by a Non-Heme Diiron(III) Complex

“…The flexibility in terms of alternative possibilities for the noncoordinated pyridine arm is quite deliberate and supported by the DFT calculations and crystal structures of the metal complexes of tpena. In addition, we have shown that while the mononuclear six coordinated [Fe III (tpena)] 2+ is isolated from acetonitrile, trace water is requisite in solution for its interconversion, via the hemihydrate, between its mer and fac forms . Fast coordination/decoordination of a pyridine on either of the tertiary amines is implicit in this interconversion.…”

Remote Amino Acid Recognition Enables Effective Hydrogen Peroxide Activation at a Manganese Oxidation Catalyst

“…Curiously, in these cases the (S,S)-CR,TIPS Mn forms the optimal combination with the amino acid, suggesting a slightly different arrangement. However, modest yields and ee's were achieved with both N-pivaloyl (14) and N-naphthalenimide (15) lysine derivatives.…”

“…In fact, these complexes either displayed an activity comparable to the model system devoid of the acid or triggered distinct mechanistic pathways, such as peroxide disproportionation [13] and/or ligand degradation. [14] Supramolecular recognition may represent a versatile tool to overcome the synthetic challenges of tuning the second coordination sphere of a catalyst, [5j, 15, 16] and test the validity of this approach (Figure 1C). In particular, catalysts CR M and CR,X M (Figure 2, M=Fe, Mn) bearing two or one 18benzo-crown-6-ether (CR) receptors, respectively, strongly bind protonated primary amines, promoting their selective CÀ H oxidation.…”