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We report on the synthesis and characterization of three iron(III) phosphasalen complexes, [FeIII(Psalen)(X)] differing in the nature of the counter‐anion/exogenous ligand (X−=Cl−, NO3−, OTf−), as well as the neutral iron(II) analogue, [FeII(Psalen)]. Phosphasalen (Psalen) differs from salen by the presence of iminophosphorane (P=N) functions in place of the imines. All the complexes were characterized by single‐crystal X‐ray diffraction, UV/Vis, EPR, and cyclic voltammetry. The [FeII(Psalen)] complex was shown to remain tetracoordinated even in coordinating solvent but surprisingly exhibits a magnetic moment in line with a FeII high‐spin ground state. For the FeIII complexes, the higher lability of triflate anion compared to nitrate was demonstrated. As they exhibit lower reduction potentials compared to their salen analogues, these complexes were tested for the coupling of 2‐naphthol using O2 from air as oxidant. In order to shed light on this reaction, the interaction between 2‐naphthol and the FeIII(Psalen) complexes was studied by cyclic voltammetry as well as UV/Vis spectroscopy. [ABSTRACT FROM AUTHOR]

Inspired by the sulfur‐rich environment found in active hydrogenase enzymes, a Ni‐based proton reduction catalyst with pentadentate N2S3 ligand was synthesised. When coupled with [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) as photosensitiser and ascorbate as electron donor in a 1:1 mixture of dimethylacetamide and aqueous ascorbic acid/ascorbate buffer, the catalyst showed improved photocatalytic activity compared with a homologous counterpart bearing a tetradentate N2S2 ligand. The mechanistic pathway of photoinduced hydrogen evolution was comprehensively analysed through optical transient absorption and time‐resolved X‐ray absorption spectroscopy, which revealed important electronic and structural changes in the catalytic system during photoirradiation. The NiII catalyst undergoes a photoinduced metal‐centred reduction to form a NiI intermediate with distorted square‐bipyramidal geometry. Further kinetic analyses revealed differences in charge‐separation dynamics between the pentadentate and tetradentate forms. [ABSTRACT FROM AUTHOR]

For the first time, azaoxyallyl cations were used as cycloaddition partners with tropone derivatives to access nitrogen-containing [7,6]-fused bicycles in a metal-free process under mild reaction conditions. DFT computations have been used to shed light on the selectivities observed during the course of the reaction. [ABSTRACT FROM AUTHOR]

We report an efficient and environmentally friendly electrochemical approach to perform the bromo cyclization of tryptophol, tryptamine and tryptophan derivatives. The 3a-bromofuranoindolines and 3a-bromopyrroloindolines obtained are of interest in the total synthesis of natural products. This dearomative procedure relies on the generation of an electrophilic bromine reagent by the electrochemical oxidation of MgBr2. No organic byproducts are generated with this protocol which avoids the use of an additional electrolyte. [ABSTRACT FROM AUTHOR]

We report the preparation and the full characterization of a novel mononuclear trigonal bipyramidal CoII complex [Co(NS3iPr)Br](BPh4) (1) with the tetradentate sulfur‐containing ligand NS3iPr (N(CH2CH2SCH(CH3)2)3). The comparison of its magnetic behaviour with those of two previously reported compounds [Co(NS3iPr)Cl](BPh4) (2) and [Co(NS3tBu)Br](ClO4) (3) (NS3tBu=N(CH2CH2SC(CH3)3)3) with similar structures shows that 1 displays a single‐molecule magnet behaviour with the longest magnetic relaxation time (0.051 s) at T=1.8 K, which is almost thirty times larger than that of 3 (0.0019 s) and more than three times larger than that of 2 (0.015 s), though its effective energy barrier (26 cm−1) is smaller. Compound 1, which contains two crystallographically independent molecules, presents smaller rhombic parameters (E=1.45 and 0.59 cm−1) than 2 (E=2.05 and 1.02 cm−1) and 3 (E=2.00 and 0.80 cm−1) obtained from theoretical calculations. Compounds 2 and 3 have almost the same axial (D) and rhombic (E) parameter values, but present a large difference of their effective energy barrier and magnetic relaxation which may be attributed to the larger volume of BPh4− than ClO4− leading to larger diamagnetic dilution (weaker magnetic dipolar interaction) for 2 than for 3. The combination of these factors leads to a much slower magnetic relaxation for 1 than for the two other compounds. [ABSTRACT FROM AUTHOR]

Herein, we report the preparation of bridged tetrahydrobenzo[b]azepines, which was accomplished through an aza‐Piancatelli cyclization/Michael addition sequence in a one‐pot fashion from readily available precursors. It is noteworthy that a general method to access these scaffolds was hitherto unprecedented. Additionally, the multifaceted aspects of this process have been exemplified through its application to the synthesis of 2‐azabicyclo[3.2.1]octanes and bridged tetrahydrobenzo[b]oxepines, along with post‐derivatizations. [ABSTRACT FROM AUTHOR]

Rieske dioxygenases are metalloenzymes capable of achieving cis‐dihydroxylation of aromatics under mild conditions using O2 and a source of electrons. The intermediate responsible for this reactivity is proposed to be a cis‐FeV(O)(OH) moiety. Molecular models allow the generation of a FeIII(OOH) species with H2O2, to yield a FeV(O)(OH) species with tetradentate ligands, or {FeIV(O); OH.} pairs with pentadentate ones. We have designed a new pentadentate ligand, mtL42, bearing a labile triazole, to generate an "in‐between" situation. Two iron complexes, [(mtL42)FeCl](PF6) and [(mtL42)Fe(OTf)2]), were obtained and their reactivity towards aromatic substrates was studied in the presence of H2O2. Spectroscopic and kinetic studies reflect that triazole is bound at the FeII state, but decoordinates in the FeIII(OOH). The resulting [(mtL42)FeIII(OOH)(MeCN)]2+ then lies on a bifurcated decay pathway (end‐on homolytic vs. side‐on heterolytic) depending on the addition of aromatic substrate: in the absence of substrate, it is proposed to follow a side‐on pathway leading to a putative (N4)FeV(O)(OH), while in the presence of aromatics it switches to an end‐on homolytic pathway yielding a {(N5)FeIV(O); OH.} reactive species, through recoordination of triazole. This switch significantly impacts the reaction regioselectivity. [ABSTRACT FROM AUTHOR]

Activation of hydrogen peroxide by FeII salts (Fenton systems) leads to a myriad of oxidizing agents whose nature, FeIVO, or hydroxyl radicals and FeIII species, is dictated by the reaction conditions, in particular the pH value. Using the non heme FeII complex [FeII(L5²)(CH3CN)]2+ (1) (where L5² is the pentadentate ligand N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine) we have observed the simultaneous formation of two reaction intermediates, [FeIV(O)(L5²)]2+ and [FeIII(OOH)(L5²)]2+, in its reaction with excess hydrogen peroxide in the presence of sub-stoichiometric amounts of triethylamine. Kinetic and spectroscopic monitoring of the reaction mixture and of independently prepared [FeIV(O)(L5²)]2+ in the presence of the different constituents of the reaction mixture allows drawing a mechanistic scheme. These two reactive species are formed simultaneously following two independent and competitive pathways. [FeIV(O)(L5²)]2+ is obtained via heterolytic O--O cleavage of the oxidant assisted by the base in a peroxidase-like mechanism whereas [FeIII(OOH)(L5²)]2+ is generated upon homolytic O--O cleavage of hydrogen peroxide. The relative contribution of these two pathways can be tuned by adjusting the amount of base used. [ABSTRACT FROM AUTHOR]

Using light energy and O2 for the direct chemical oxidation of organic substrates is a major challenge. A limitation is the use of sacrificial electron donors to activate O2 by reductive quenching of the photosensitizer, generating undesirable side products. A reversible electron acceptor, methyl viologen, can act as electron shuttle to oxidatively quench the photosensitizer, [Ru(bpy)3]2+, generating the highly oxidized chromophore and the powerful reductant methyl‐viologen radical MV+.. MV+. can then reduce an iron(III) catalyst to the iron(II) form and concomitantly O2 to O2.− in an aqueous medium to generate an active iron(III)‐(hydro)peroxo species. The oxidized photosensitizer is reset to its ground state by oxidizing an alkene substrate to an alkenyl radical cation. Closing the loop, the reaction of the iron reactive intermediate with the substrate or its radical cation leads to the formation of two oxygenated compounds, the diol and the aldehyde following two different pathways. [ABSTRACT FROM AUTHOR]

A trinuclear triphenylene trisemiquinone complex containing paramagnetic NiII is obtained under ambient conditions from the reaction of deprotonated tricatecholate hexahydroxytriphenylene (H6HHTP) with NiII capped with a trispyrazolyl borate tridentate ligand. The magnetic and EPR data are consistent with delocalization of the electronic spin over the three NiII species. The two-electron reduced complex shows an EPR spectrum corresponding to a S = 1/2 species due to a large antiferromagnetic coupling between the radical and only one of the NiII ions highlighting the localization of the electronic spin. No EPR signal is observed for the one- and three-electron reduced species consistent with the closed shell of the bridging ligand. [ABSTRACT FROM AUTHOR]

In the context of developing ecofriendly chemistry, artificial enzymes are now considered as promising tools for synthesis. They are prepared in particular with the aim to catalyze reactions that are rarely, if ever, catalyzed by natural enzymes. We discovered that 1‐aminocyclopropane carboxylic acid oxidase reconstituted with CuII served as an efficient artificial Diels–Alderase. The kinetic parameters of the catalysis of the cycloaddition of cyclopentadiene and 2‐azachalcone were determined (KM=230 μm, kapp=3 h−1), which gave access to reaction conditions that provided quantitative yield and >99 % ee of the (1S,2R,3R,4R) product isomer. This unprecedented performance was rationalized by molecular modeling as only one docking pose of 2‐azachalcone was possible in the active site of the enzyme and this was the one that leads to the (1S,2R,3R,4R) product isomer. [ABSTRACT FROM AUTHOR]

New mononuclear non‐heme FeII complexes derived from a well‐known pentadentate amine/pyridine ligand were synthesized. The new ligand bears an additional OH group on one pyridyl aimed at developing second sphere hydrogen bonds. Two binding modes of the ligand were observed that can be selectively obtained through the choice of the counterion: the OH group develops an intramolecular H‐bond with the 6th exogenous ligand in the classical mode, or an intermolecular one with the unbound triflate counterion in the alternative mode. The complexes were studied by cyclic voltammetry in the reductive activation of O2. The addition of an H‐bond improves the O2 activation potential with a gain of 90 mV in the classical case and 220 mV in the alternative one. The difference is ascribed to the development of stabilizing H‐bonds within the FeIII‐peroxo intermediate with the proximal O atom of peroxo (classical mode) or the distal one (alternative mode). Ultimately, the complex in the alternative mode activates O2 at −0.5 V vs SCE (500 mV gain compared to free O2). We took advantage of this significantly reduced energetic cost to carry out and achieve the electroassisted oxidation of thioanisole by O2 at −0.5 V vs SCE. [ABSTRACT FROM AUTHOR]