Catalytic C-H bond amination from high-spin iron imido complexes

Dipyrromethene ligand scaffolds were synthesized bearing large aryl (2,4,6-Ph(3)C(6)H(2), abbreviated Ar) or alkyl ((t)Bu, adamantyl) flanking groups to afford three new disubstituted ligands ((R)L, 1,9-R(2)-5-mesityldipyrromethene, R=aryl, alkyl). While high-spin (S=2), four-coordinate iron complexes of the type ((R)L)FeCl(solv) were obtained with the alkyl-substituted ligand varieties (for R=(t)Bu, Ad and solv=THF, OEt(2)), use of the sterically encumbered aryl-substituted ligand precluded binding of solvent and cleanly afforded a high-spin (S=2), three-coordinate complex of the type ((Ar)L)FeCl. Reaction of ((Ad)L)FeCl(OEt(2)) with alkyl azides resulted in the catalytic amination of C-H bonds or olefin aziridination at room temperature. Using a 5% catalyst loading, 12 turnovers were obtained for the amination of toluene as a substrate, while greater than 85% of alkyl azide was converted to the corresponding aziridine employing styrene as a substrate. A primary kinetic isotope effect of 12.8(5) was obtained for the reaction of ((Ad)L)FeCl(OEt(2)) with adamantyl azide in an equimolar toluene/toluene-d(8) mixture, consistent with the amination proceeding through a hydrogen atom abstraction, radical rebound type mechanism. Reaction of p-(t)BuC(6)H(4)N(3) with ((Ar)L)FeCl permitted isolation of a high-spin (S=2) iron complex featuring a terminal imido ligand, ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))), as determined by (1)H NMR, X-ray crystallography, and (57)Fe Mo?ssbauer spectroscopy. The measured Fe-N(imide) bond distance (1.768(2) ?) is the longest reported for Fe(imido) complexes in any geometry or spin state, and the disruption of the bond metrics within the imido aryl substituent suggests delocalization of a radical throughout the aryl ring. Zero-field (57)Fe Mo?ssbauer parameters obtained for ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) suggest a Fe(III) formulation and are nearly identical with those observed for a structurally similar, high-spin Fe(III) complex bearing the same dipyrromethene framework. Theoretical analyses of ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) suggest a formulation for this reactive species to be a high-spin Fe(III) center antiferromagnetically coupled to an imido-based radical (J = -673 cm(-1)). The terminal imido complex was effective for delivering the nitrene moiety to both C-H bond substrates (42% yield) as well as styrene (76% yield). Furthermore, a primary kinetic isotope effect of 24(3) was obtained for the reaction of ((Ar)L)FeCl(N(p-(t)BuC(6)H(4))) with an equimolar toluene/toluene-d(8) mixture, consistent with the values obtained in the catalytic reaction. This commonality suggests the isolated high-spin Fe(III) imido radical is a viable intermediate in the catalytic reaction pathway. Given the breadth of iron imido complexes spanning several oxidation states (Fe(II)-Fe(V)) and several spin states (S=0→(3)/(2)), we propose the unusual electronic structure of the described high-spin iron imido complexes contributes to the observed catalytic reactivity.     

Chemical composition of the essential oil of Cachrys libanotis from Algeria

The essential oil of aerial parts of Cachrys libanotis L. (Apiaceae) from east Algeria was extracted by hydrodistillation and analyzed by GC-FID and GC-MS. Thirty-one compounds were identified, the main components being germacrene-D (18.0%), gamma-terpinene (6.4%), p-cymene (5.5%), caryophyllene oxide (5.1%), and limonene (5.1%).     

A Preparatively Simple Access to Homochiral Heterocyclic α-Hydroxy Acids and their Derivatives

 The synthesis of homochiral heterocyclic α-hydroxy acids starting from (S)- and (R)-malic acid using hexafluoroacetone as protecting and activating agent is described. The new compounds are useful building blocks for peptide and depsipeptide modification.     

Gold nanoparticle–antibody conjugates for specific extraction and subsequent analysis by liquid chromatography–tandem mass spectrometry of malondialdehyde-modified low density lipoprotein as biomarker for cardiovascular risk

Oxidized low-density lipoproteins (OxLDLs) like malondialdehyde-modified low-density lipoprotein (MDA-LDL) play a major role in atherosclerosis and have been proposed as useful biomarkers for oxidative stress. In this study, gold-nanoparticles (GNPs) were functionalized via distinct chemistries with anti-MDA-LDL antibodies (Abs) for selective recognition and capture of MDA-LDL from biological matrices. The study focused on optimization of binding affinities and saturation capacities of the antiMDA-LDL-Ab-GNP bioconjugate by exploring distinct random and oriented immobilization approaches, such as (i) direct adsorptive attachment of Abs on the GNP surface, (ii) covalent bonding by amide coupling of Abs to carboxy-terminated-pegylated GNPs, (iii) oriented immobilization via oxidized carbohydrate moiety of the Ab on hydrazide-derivatized GNPs and (iv) cysteine-tagged protein A (cProtA)-bonded GNPs. Depending on immobilization chemistry, up to 3 antibodies per GNP could be immobilized as determined by ELISA. The highest binding capacity was achieved with the GNP-cProtA-Ab bioconjugate which yielded a saturation capacity of 2.24 ± 0.04 μg mL⁻¹ GNP suspension for MDA-LDL with an affinity K_d of 5.25 ± 0.11 × 10⁻¹⁰ M. The GNP-cProtA-antiMDA-LDL bioconjugate revealed high specificity for MDA-LDL over copper(II)-oxidized LDL as well as native human LDL. This clearly demonstrates the usefulness of the new GNP-Ab bioconjugates for specific extraction of MDA-LDL from plasma samples as biomarkers of oxidative stress. Their combination as specific immunoextraction nanomaterials with analysis by LC–MS/MS allows sensitive and selective detection of MDA-LDL in complex samples.     

Access to New Endoperoxide Derivatives by Electrochemical Oxidation of Substituted 3‐Azabicyclo[4.1.0]hept‐4‐enes

A series of substituted 3‐azabicyclo[4.1.0]hept‐4‐ene derivatives were prepared and analysed by cyclic voltammetry. Preparative aerobic electrochemical oxidation reactions were then carried out. Three original endoperoxides were isolated, characterised and subjected to antimalarial and cytotoxicity activity assays.     

Formation of an Imino‐Stabilized Cyclic Tin(II) Cation from an Amino(imino)stannylene

The novel amino(imino)stannylene 1 was prepared by conversion of HNIPr (NIPr=bis(2,6‐diisopropylphenyl)imidazolin‐2‐imino) with one equivalent of Lappert’s tin reagent (Sn[N(SiMe₃)₂]₂). Treatment of 1 with DMAP (4‐dimethylaminopyridine) yields its Lewis acid–base adduct 2 . The reaction of 1 with one equivalent of trimethylsilyl azide results in replacement of the amino group at the tin center by an N₃ substituent with concomitant elimination of N(SiMe₃)₃ to afford dimeric [N₃SnNIPr]₂ ( 3 ). Remarkably, the reaction of 1 with B(C₆F₅)₃ produces the novel tin(II) monocation 4 ⁺[MeB(C₆F₅)₃]^? comprising a four‐membered stannacycle through methyl‐abstraction from the trimethylsilyl group.     

Surface and bulk morphology of cold-crystallized poly(ethylene terephthalate)

The morphology/habit of crystals of cold-crystallized poly(ethylene terephthalate) (PET) has been evaluated using scanning and transmission electron microscopy and using atomic force microscopy. The combination of different preparation and analysis techniques allowed assessing the structure at the nanometer scale of films of PET at both the surface and the bulk. It is found that crystals formed on heating the amorphous glass to a temperature higher than the glass transition temperature are of lamellar shape in the bulk and almost isometric habit at the surface. This finding is explained by different rates of nucleation/crystallization in the bulk and at the surface, being supported by the observation of nanometer-scale surface heterogeneities after quenching PET to ambient temperature before crystallization was initiated by heating.     

Analysenmethoden zum Nachweis und zur Bestimmung verschiedener organischer S?uren

Ohne Zusammenfassung     

Tetracyanoquinodimethane Reduction by Complexed Guanidinyl‐Functionalized Aromatic Compounds

In this work, we report on the reduction of tetracyanoquinodimethane (TCNQ) with dicationic complexes of guanidinyl‐functionalized aromatic (GFA) electron donors. In contrast to reduction with free GFAs, milder reduction conditions were achieved, and this led to semiconducting materials with extended TCNQ π stacking. The charge on the TCNQ units was estimated from the structural data obtained by single‐crystal X‐ray diffraction analysis and from IR spectroscopic data. The electrical conductivity was studied and the activation energy of the semiconducting materials was estimated from the temperature dependence of the conductivity.