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Direct amination of C–H or C＝C bonds using unprotected amino groups is very challenging, especially with earth abundant metal ions. Here we show that a bioinspired iron(II) complex catalyses the double amination of its dangling benzyl branch in the presence of hydroxylamine derivatives as the unprotected amine donor and that the replacement of the benzyl branch by a methyl group also allows the aziridination of styrene. [ABSTRACT FROM AUTHOR]

Two new symmetrical and unsymmetrical diiron(III) complexes were synthesized and characterized by X-ray diffraction analysis, mass spectrometry, UV-visible and Mössbauer spectroscopies. They proved to be good catalysts for alkene and alkane oxidation reactions by H2O2 in acetonitrile solution, and interesting effects of both the nature and the symmetry of the complexes were observed on catalysis in the presence of water. [ABSTRACT FROM AUTHOR]

We report a new artificial hydrogenase made by covalent anchoring of the iron Knölker's complex to a xylanase S212C variant. This artificial metalloenzyme was found to be able to catalyze efficiently the transfer hydrogenation of the benchmark substrate trifluoroacetophenone by sodium formate in water, yielding the corresponding secondary alcohol as a racemic. The reaction proceeded more than threefold faster with the XlnS212CK biohybrid than with the Knölker's complex alone. In addition, efficient conversion of trifluoroacetophenone to its corresponding alcohol was reached within 60 H with XlnS212CK, whereas a ≈2.5‐fold lower conversion was observed with Knölker's complex alone as catalyst. Moreover, the data were rationalized with a computational strategy suggesting the key factors of the selectivity. These results suggested that the Knölker's complex was most likely flexible and could experience free rotational reorientation within the active‐site pocket of Xln A, allowing it to access the subsite pocket populated by trifluoroacetophenone. [ABSTRACT FROM AUTHOR]

We demonstrate that the devised incorporation of an alkylamine group into the second coordination sphere of an FeII complex allows to switch its reactivity with H2O2 from the usual formation of FeIII species towards the selective generation of an FeIV‐oxo intermediate. The FeIV‐oxo species was characterized by UV/Vis absorption and Mössbauer spectroscopy. Variable‐temperature kinetic analyses point towards a mechanism in which the heterolytic cleavage of the O−O bond is triggered by a proton transfer from the proximal to the distal oxygen atom in the FeII‐H2O2 complex with the assistance of the pendant amine. DFT studies reveal that this heterolytic cleavage is actually initiated by an homolytic O−O cleavage immediately followed by a proton‐coupled electron transfer (PCET) that leads to the formation of the FeIV‐oxo and release of water through a concerted mechanism. Don't cleave me this way: A novel synthetic iron(II) complex bearing a second sphere intra‐molecular base efficiently forms an iron(IV)‐oxido species in the presence of H2O2 rather than the usual formation of an FeIII species. Mechanistic studies demonstrate an overall heterolytic cleavage of the O−O bond proceeding by a homolytic cleavage with a concerted proton coupled electron transfer (PCET). [ABSTRACT FROM AUTHOR]

Direct incorporation of molecular oxygen into small organic molecules has attracted much attention for the development of new environmentally friendly oxidation processes. In line with this approach, bioinspired systems mimicking enzyme activities are of particular interest since they may perform catalysis in aqueous media. Demonstrated herein is the incorporation of a natural flavin cofactor (FMN) into the specific microenvironment of a water‐soluble polymer which allows the efficient reduction of the FMN by NADH in aqueous solution. Once reduced, this artificial flavoenzyme can then activate molecular dioxygen under aerobic conditions and result in the Baeyer–Villiger reaction at room temperature in water. Keeping it local: Incorporation of flavin cofactors (FMN) within the local hydrophobic microenvironment of a modified polyethyleneimine allows activation of dioxygen in the presence of NADH. This activation results in a successful Baeyer–Villiger reaction at room temperature in water. [ABSTRACT FROM AUTHOR]

The reaction of a cyclic diaminal ligand, obtained from the reaction of N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine, as a secondary diamine, and isophthalaldehyde, with different first-row transition-metal ions, such as FeIII, ZnII, CuII, and CuI, was explored using UV/Vis kinetic studies, and cyclic voltammetry. The 3D structures of the resulting metal complexes were determined by single-crystal X-ray diffraction analysis. We demonstrate that the ring-cleavage reaction of the imidazolidine ligand upon complexation with various metal ions depends on the Lewis acidity of the metal ions, as well as on the coordinative requirements of the metal centers. With a soft acid such as CuI, the diaminal ligand was unmodified and stabilized tricoordinate planar cuprous ions. In contrast, in the presence of harder acids, such as FeIII, ZnII, and CuII, the diaminal ligand undergoes hydrolysis/cleavage to yield complexes of the tetradentate N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine ligand. Interestingly, it was also observed that the ring-cleavage reaction in the presence of FeIII led to the formation of FeII complexes. However, we demonstrate that these two events are independent from each other. [ABSTRACT FROM AUTHOR]

The development of iron catalysts for carbon-heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an FeIIIFeIV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a FeIIIFeIVL. active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self-adaptation of the catalyst to the substrate needs. [ABSTRACT FROM AUTHOR]

We report the use of time-resolved X-ray absorption spectroscopy in the ns–μs time scale to track the light induced two electron transfer processes in a multi-component photocatalytic system, consisting of [Ru(bpy)3]2+/ a diiron(iii,iii) model/triethylamine. EXAFS analysis with DFT calculations confirms the structural configurations of the diiron(iii,iii) and reduced diiron(ii,ii) states. [ABSTRACT FROM AUTHOR]

Metal-catalyzed nitrene transfer reactions arouse intense interest as clean and efficient procedures for amine synthesis. Efficient Rh- and Ru-based catalysts exist but Fe alternatives are actively pursued. However, reactive iron imido species can be very short-lived and getting evidence of their occurrence in efficient nitrene-transfer reactions is an important challenge. We recently reported that a diiron(III,II) complex is a very efficient nitrene-transfer catalyst to various substrates. We describe herein how, by combining desorption electrospray ionization mass spectrometry, quantitative chemical quench experiments, and DFT calculations, we obtained conclusive evidence for the occurrence of an {FeIIIFeIVNTosyl} intermediate that is very active in H-abstraction and nitrene-transfer reactions. DFT calculations revealed a strong radical character of the tosyl nitrogen atom in very low-lying electronic configurations of the FeIV ion which are likely to confer its high reactivity. [ABSTRACT FROM AUTHOR]

Spalten und übertragen: Ein Sensibilisator ‐ Dieisen(III) ‐ Komplex wurde in Gegenwart eines Elektronendonors erst belichtet und dann O2 ausgesetzt. Der Komplex wandelt sich dabei in eine aktive Dieisen(III) ‐ Peroxo ‐ Spezies um, die ein Sauerstoffatom auf ein Substrat übertragen kann (siehe Schema). [ABSTRACT FROM AUTHOR]

The efficient integration of binding, catalysis, and multiple turnovers remains a challenge in building enzyme models. We report that systematic derivatization of polyethylene imine (PEI) with alkyl (C2-C12), benzyl, and guanidinium groups gives rise to catalysts (synzymes') with rate accelerations (kcat/kuncat) of up to 104 for the intramolecular transesterification of 2-hydroxypropyl-p-nitrophenyl phosphate, HPNP, in the absence of metal. The synzymes exhibit saturation kinetics (KM ≈ 250 μM, kcat ≈ 0.5 min-1) and up to 2340 turnovers per polymer molecule. Catalysis can be specifically and competitively inhibited by anionic and hydrophobic small molecules. The efficacy of catalysis is determined by the PEI derivatization pattern. The derivatization reagents exert a synergistic effect, i.e., their combinations increase catalysis by more than the sum of each single modification. The pH--rate profile for kcat/KM is bell shaped with a maximum at pH 7.85 and can be explained as a combination of two effects that both have to be operative for optimal activity: KM increases at high pH due to deprotonation of PEI amines that bind the anionic substrate and kcat decreases as the availability of hydroxide decreases at low pH. Thus, catalysis is based on substrate binding by positively charged amine groups and the presence of hydroxide ion in active sites in an environment that is tuned for efficient catalysis. Inhibition studies suggest that the basis of catalysis and multiple turnovers is differential molecular recognition of the doubly negatively charged transition state (over singly charged ground state and product): this contributes a factor of at least 5--10-fold to catalysis and product release. [ABSTRACT FROM AUTHOR]

Direct amination of C-H or CC bonds using unprotected amino groups is very challenging, especially with earth abundant metal ions. Here we show that a bioinspired iron(II) complex catalyses the double amination of its dangling benzyl branch in the presence of hydroxylamine derivatives as the unprotected amine donor and that the replacement of the benzyl branch by a methyl group also allows the aziridination of styrene.

Two new symmetrical and unsymmetrical diiron(iii) complexes were synthesized and characterized by X-ray diffraction analysis, mass spectrometry, UV-visible and Mössbauer spectroscopies. They proved to be good catalysts for alkene and alkane oxidation reactions by H2O2 in acetonitrile solution, and interesting effects of both the nature and the symmetry of the complexes were observed on catalysis in the presence of water.

We demonstrate that the devised incorporation of an alkylamine group into the second coordination sphere of an Fe II complex allows to switch its reactivity with H 2 O 2 from the usual formation of Fe III species towards the selective generation of an Fe IV -oxo intermediate. The Fe IV -oxo species was characterized by UV/Vis absorption and Mössbauer spectroscopy. Variable-temperature kinetic analyses point towards a mechanism in which the heterolytic cleavage of the O-O bond is triggered by a proton transfer from the proximal to the distal oxygen atom in the Fe II -H 2 O 2 complex with the assistance of the pendant amine. DFT studies reveal that this heterolytic cleavage is actually initiated by an homolytic O-O cleavage immediately followed by a proton-coupled electron transfer (PCET) that leads to the formation of the Fe IV -oxo and release of water through a concerted mechanism., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Direct incorporation of molecular oxygen into small organic molecules has attracted much attention for the development of new environmentally friendly oxidation processes. In line with this approach, bioinspired systems mimicking enzyme activities are of particular interest since they may perform catalysis in aqueous media. Demonstrated herein is the incorporation of a natural flavin cofactor (FMN) into the specific microenvironment of a water-soluble polymer which allows the efficient reduction of the FMN by NADH in aqueous solution. Once reduced, this artificial flavoenzyme can then activate molecular dioxygen under aerobic conditions and result in the Baeyer-Villiger reaction at room temperature in water., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The development of iron catalysts for carbon-heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an Fe III Fe IV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a Fe III Fe IV L . active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self-adaptation of the catalyst to the substrate needs., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The systematic exploration of the modification of polyethylene imine with guanidinium and octyl groups has led to the identification of a catalyst, CD6, which accelerates the phosphate transfer reaction of HPNP (2-hydroxypropyl-4-nitrophenyl phosphate) in the presence of divalent metals such as Zn(2+), Co(2+), Mg(2+) or Ni(2+). CD6 exhibits saturation kinetics that are described by Michaelis-Menten parameters K(m) ranging from 2.5-8 mM and k(cat) ranging from 0.0014-0.09 s(-1). For Zn(II)-CD6 this corresponds to an overall acceleration k(cat)/k(uncat) of 3.8x10(5) and a catalytic proficiency (k(cat)/K(m))/k(uncat) of 1.5x10(8). Catalysis by Zn(II)-CD6 is specifically inhibited by inorganic phosphate, allowing turnover regulation by product inhibition. This effect stands in contrast to Zn(II)-catalysed transesterification of HPNP in water or by the synzymes Co(II)-CD6 and Ni(II)-CD6, with which no such interference by product is observed. These characteristics render synzyme Zn(II)-CD6 an efficient enzyme model that reflects enzyme-like properties in a wide range of features.

In the presence of hydrogen peroxide, m-chloroperbenzoic acid or an iodosyl arene, the tert-butyl group of the ligand H(L-t-Bu) in the complex [Fe2(L-t-Bu)(mpdp)]2+ is quantitatively hydroxylated to a butanolate terminally bound to one iron in [Fe2(L-t-Bu - H + O)(mpdp)]2+, and mass spectrometry experiments indicate that the reaction proceeds according to different mechanisms.

A non-heme iron complex catalyses the aziridination of various olefins and the amidation of thioanisole in good yields at the expense of an aryl iodinane.