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We synthesized a sublimable molecular spin crossover Fe(II) complex based on the Schiff base tridentate ligand qsal-NEt2 (5-diethylamino-2-((quinolin-8-ylimino)methyl)phenol). The compound undergoes a transition in temperature with thermally induced excited spin state-trapping (TIESST) for high-temperature sweep rates, which can be suppressed by reducing the sweep rate. The X-ray absorption spectroscopy (XAS) studies on the microcrystalline powder confirm the TIESST effect. The molecules are deposited under ultra-high vacuum on a graphene/SiO2 substrate as a submonolayer. Investigation of the submonolayer by XAS reveals the molecular integrity and shows a spin crossover for the whole temperature range from 350 to 4 K, with residual HS species at low temperature and no TIESST effect. DFT calculations suggest a distribution of energetically similar adsorption configurations on graphene, i.e., with smooth crossover behaviour and the absence of TIESST, consistent with very weak intermolecular interactions and the absence of large molecular islands within the submonolayer. [ABSTRACT FROM AUTHOR]

Despite the paramount importance of the Suzuki–Miyaura coupling (SMC) in academia and industry, and the great promise of iron to offer sustainable catalysis, iron‐catalyzed SMC involving sp3‐hybridized partners is still in its infancy. We herein report the development of a versatile, well‐defined electron‐deficient anilido‐aldimine iron(II) catalyst. This catalyst effectively performed C(sp3)−C(sp2) and C(sp3)−C(sp3) SMC of alkyl halide electrophiles and (hetero)aryl boronic ester and alkyl borane nucleophiles respectively, in the presence of a lithium amide base. These couplings operated under mild reaction conditions and displayed wide functional group compatibility including various medicinally relevant N‐, O‐ and S‐based heterocycles. They also tolerated primary, secondary and tertiary alkyl halides (Br, Cl, I), electron‐neutral, ‐rich and ‐poor boronic esters and primary and secondary alkyl boranes. Our methodology could be directly and efficiently applied to synthesize key intermediates relevant to pharmaceuticals and a potential drug candidate. For C(sp3)−C(sp2) couplings, radical probe experiments militated in favor of a carbon‐centered radical derived from the electrophile. At the same time, reactions run with a pre‐formed activated boron nucleophile coupled to competition experiments supported the involvement of neutral, rather than an anionic, (hetero)aryl boronic ester in the key transmetalation step. [ABSTRACT FROM AUTHOR]

Regioselective C6‐arylation of thieno[3,2‐c]pyrazoles with aryl iodides as coupling partners has been developed. This strategy was performed in the presence of Pd(OAc)2 as catalyst in combination with AgOTf as an oxidant and TFA in dimethylacetamide. In all experiments, only the C6‐arylated thieno[3,2‐c]pyrazole was isolated since its C5‐regioisomer was not observed, indicating the high regioselectivity of this approach. The catalytic system used is compatible with a variety of 3‐functionalized thieno[3,2‐c]pyrazoles and iodoaryl electrophiles, providing access to 3,6‐disubstituted thieno[3,2‐c]pyrazoles in yields ranging from 49% to 94%. [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]

Three new amine/pyridine FeII complexes bearing pentadentate ligand with one, two or three electron enriched 4‐methoxy‐3,5‐dimethylpyridine were used as catalysts for the oxidation of small organic molecules by hydrogen peroxide. The distribution of products formed suggests that these ligands are not enough electron donating to promote the O−O heterolytic cleavage of the oxidant in order to generate selective FeV(O) species. Using acetic acid in the reaction mixtures results in a significant increase of the efficiency of these catalytic systems. Our investigations show that the use of AcOH leads to the protonation/dissociation of a pyridyl moiety and the formation of (N4)FeII(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N4)FeIII(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N4)FeIV(OAc)(O), which are more efficient than the usual (N4)FeIV(O) and (N5)FeIV(O). [ABSTRACT FROM AUTHOR]

[22][23] In the present case, the principle required the preparation of a set of oligomers of an easy-to-use surrogate amino acid, with transformation of all residues present into Aatc(Me) residues in the final step. Keywords: azetidines; late-stage modification; peptides; reductive amination; protected amino acid; oligomers EN azetidines late-stage modification peptides reductive amination protected amino acid oligomers 1787 1790 4 08/29/23 20230915 NES 230915 Graph In the context of a collaborative interdisciplinary program, we were recently given a particular synthetic challenge. Finally, tetramer B 9 b was deprotected as before without incident, but the resulting tetraamine tetrahydrochloride only provided small amounts (<10%) of tetramer B 4 b when subjected to the same reductive amination conditions as above. [29] While the target molecules in our work implicated Aatc(Me) as the constituent amino acid, we took the opportunity to conduct two related experiments on derivative B 6 b (Scheme 3). [Extracted from the article]

trans-3-Benzyloxycarbonylamino-1-methyl-3-(methylcarbamoyl)azetidine-1-oxide was prepared by stereoselective oxidation of the corresponding azetidine precursor. The stable molecule was characterized in a low-polarity solution by IR, 1H-NMR and 13C-NMR, and in the solid state as a co-crystal with water by X-Ray diffraction. The N-oxide function made a strong intramolecular 7-membered ring hydrogen bond with the methyl amide NH in solution and formed an intermolecular H-bond with the carbamate NH in a neighboring molecule in the solid state. [ABSTRACT FROM AUTHOR]

The catalytic properties of an iron complex bearing a pentadentate cross-bridged ligand backbone are reported. With H2O2 as an oxidant, it displays moderate conversions in epoxidation and alkane hydroxylation and satisfactory ones in aromatic hydroxylation. Upon addition of an acid to the reaction medium, a significant enhancement in aromatic and alkene oxidation is observed. Spectroscopic analyses showed that accumulation of the expected FeIII(OOH) intermediate is limited under these conditions, unless an acid is added to the mixture. This is ascribed to the inertness induced by the cross-bridged ligand backbone, which is partly reduced under acidic conditions. [ABSTRACT FROM AUTHOR]

We report a synthetic endeavor towards the highly strained pentacyclic caged framework of the mavacuran alkaloids which culminated with the concise total synthesis of C‐fluorocurine, C‐profluorocurine, C‐mavacurine, normavacurine, 16‐epi‐pleiocarpamine and taberdivarine H. We designed a strategy involving late‐stage construction of the D ring by Michael addition of a vinylic nucleophile to a 2‐indolyl acrylate moiety. While the intramolecular Michael addition did not succeed, we were able to perform a diastereoselective unusual intermolecular 1,4‐addition of a functionalized vinyl lithium reagent to a readily accessible Michael acceptor with the assistance of the piperidine nitrogen atom through the formation of a complex as suggested by DFT computations. Final cyclization was achieved by nucleophilic substitution to form an ammonium intermediate. The first total syntheses of C‐profluorocurine and C‐fluorocurine were finalized by the dihydroxylation of C‐mavacurine and a pinacol rearrangement, respectively. [ABSTRACT FROM AUTHOR]

A stereoselective one‐pot double derivatization of cyclobutene‐1‐carboxylic acid via a mild organic base catalyzed amidation/aza‐Michael addition of benzo[d]oxazol‐2(3H)‐ones has been developed. This unprecedented tandem reaction provides access to novel β‐N‐heterocyclic cyclobutane carboximide derivatives with a trans geometry. The carboximide moiety reacts smoothly with nucleophiles, allowing access to diverse derivatives of trans‐β‐N‐heterocyclic cyclobutanecarboxylic acid, including peptidomimetic structures. [ABSTRACT FROM AUTHOR]

[MoV2 O2S2]2+-based thiosemicarbazone complexes appear as very promising molecules for biological applications due to the intrinsic properties of their components. This paper deals with the synthesis and characterization of six coordination complexes obtained by the reaction of [MoV2 O2S2]2+ clusters with bisthiosemicarbazone ligands that contain flexible or rigid spacers between the two thiosemicarbazone units. Interestingly, structural characterization by single-crystal X-ray diffraction, MALDI-TOF MS technique and NMR spectroscopy revealed that the nuclearity of the complex is controlled by the nature of the spacer between the thiosemicarbazone units. Binuclear complexes, namely [MoV2 O2S2(L1-3)], are isolated with flexible spacers while tetranuclear complexes [(MoV² O2S2)2(L4-6)2] are formed when the bisthiosemicarbazone ligands are built on rigid spacers. [ABSTRACT FROM AUTHOR]

A set of representative pulvinic acids were synthesised using a bioinspired strategy. Terphenyl‐quinones (polyporic acid scaffold) were prepared via sequential Suzuki‐Miyaura couplings allowing access to unsymmetrically substituted derivatives in a one‐pot protocol. Subjected to the action of acetic anhydride and DMSO, quinones were converted into bis‐lactone intermediates. Methanolysis and deprotection achieved the total syntheses of the corresponding pulvinic acids. Following this general strategy, symmetrical pulvinic, atromentic, variegatic acids and unsymmetrical congener pinastric, iso‐pinastric, xerocomic and iso‐xerocomic acids were prepared in fair yields. Fluorescence properties were observed for the bis‐lactone intermediates and, as a complement to this synthetic work, optical properties were measured, and fluorescence quantum yields were determined for the bis‐lactone pigments. [ABSTRACT FROM AUTHOR]

Solid‐State Vibrational Circular Dichroism (VCD) can be used to determine the absolute structure of chiral crystals, but its interpretation remains a challenge in modern spectroscopy. In this work, we investigate the effect of a twofold screw axis on the solid‐state VCD spectrum in a combined experimental and theoretical analysis of P21 crystals of (S)‐(+)‐1‐indanol. Even though the space group is achiral, a single proper symmetry operation has an important impact on the VCD spectrum, which reflects the supramolecular chirality of the crystal. Distinguishing between contributions originating from molecular chirality and from chiral crystal packing, we find that while IR absorption hardly depends on the symmetry of the space group, the situation is different for VCD, where completely new non‐local patterns emerge. Understanding the two underlying mechanisms, namely gauge transport and direct coupling, will help to use VCD to distinguish polymorphic forms. [ABSTRACT FROM AUTHOR]

Seven dimeric metallacrowns (MC) based on Ln[12‐MCM(III)N(shi)‐4], where LnIII=Dy, Ho, Yb, or Y, MIII=Mn or Ga, and shi3− is salicylhydroximate, have been synthesized and characterized by single‐crystal X‐ray diffraction, and for the dysprosium‐manganese dimers, the magnetic properties have been measured. In each dimer two Ln[12‐MCM(III)N(shi)‐4] units are linked by four bridging dicarboxylate anions (isophthalate, trimesate, dinicotinate, or 2,2′‐dithiodibenzoate). Three different countercations (sodium, gallium(III), or pyridinium) were used to maintain charge balance of the dimer. While pyridinium does not bind to the dimer, the choice of the dicarboxylate dictates where the countercations Na+ or GaIII bind. With isophthalate and trimesate, the sodium ion binds to the central MC cavity opposite of the LnIII, and with dinicotinate the sodium or gallium(III) ions bind to the pyridyl nitrogen of the dinicotinate. All three Dy2Mn8 dimers exhibit an out‐of‐phase magnetic susceptibility signal consistent with a shallow barrier to magnetization relaxation. [ABSTRACT FROM AUTHOR]

A broadly applicable diastereo‐ and enantioselective inverse‐electron‐demand Diels–Alder reaction of 2‐pyrones and acyclic enol ethers is reported herein. Using a copper(II)‐BOX catalytic system, bridged bicyclic lactones are obtained in very high yields (up to 99 % yield) and enantioselectivities (up to 99 % ee) from diversely substituted 2‐pyrones and acyclic enol ethers. Mechanistic experiments as well as DFT calculations indicate the occurrence of a stepwise mechanism. The synthetic potential of the bridged bicyclic lactones is showcased by the enantioselective synthesis of polyfunctional cyclohexenes and cyclohexadienes, as well as a carbasugar unit. [ABSTRACT FROM AUTHOR]

We report two new FeIII complexes [L1FeIII(H2O)](OTf)2 and [L2FeIII(OTf)], obtained by replacing pyridines by phenolates in a known non‐heme aminopyridine iron complex. While the original, starting aminopyridine [(L52)FeII(MeCN)](PF6) complex is stable in air, the potentials of the new FeIII/II couples decrease to the point that [L2FeII] spontaneously reduces O2 to superoxide. We used it as an O2 activator in an electrochemical setup, as its presence allows to generate superoxide at a much more accessible potential (>500 mV gain). Our aim was to achieve substrate oxidation via the reductive activation of O2. While L2FeIII(OTf) proved to be a good O2 activator but a poor oxidation system, its association with another complex (TPEN)FeII(PF6)2 generates a complementary tandem couple for electro‐assisted oxidation of substrates, working at a very accessible potential: upon reduction, L2FeIII(OTf) activates O2 to superoxide and transfers it to (TPEN)FeII(PF6)2 leading in fine to the oxidation of thioanisole. [ABSTRACT FROM AUTHOR]