Formation of Alkanes by Aerobic Carbon–Carbon Bond Coupling Reactions Catalyzed by a Phosphovanadomolybdic Acid

The valorization of alkanes is possible via carbon–carbon coupling reactions. A series of dialkyl cobalt complexes [(RCH_2)_2Co^(III)(bpy)_2]ClO_4 (R = H, Me, Et, and Ph) were reacted with the H_5PV_2Mo_(10)O_(40) polyoxometalate as a catalyst, leading to a selective oxidative carbon–carbon bond coupling reaction. The reaction is initiated by electron transfer from [(RCH_2)_2Co^(III)(bpy)_2]^+ to H_5PV^V_2Mo_(10)O_(40) to yield an intermediate [(RCH_2)_2Co^(IV)(bpy)_2]^(2+)–H_5PV^(IV)V^VMo_(10)O_(40), as identified by a combination of EPR and X-ray photoelectron spectroscopy experiments. The reaction is catalytic with O_2 as terminal oxidant representing an aerobic C–C bond coupling reaction

Improving Fatigue Resistance of Dihydropyrene by Encapsulation within a Coordination Cage

Photochromic molecules undergo reversible isomerization upon irradiation with light at different wavelengths, a process that can alter their physical and chemical properties. For instance, dihydropyrene (DHP) is a deep-colored compound that isomerizes to light-brown cyclophanediene (CPD) upon irradiation with visible light. CPD can then isomerize back to DHP upon irradiation with UV light or thermally in the dark. Conversion between DHP and CPD is thought to proceed via a biradical intermediate; bimolecular events involving this unstable intermediate thus result in rapid decomposition and poor cycling performance. Here, we show that the reversible isomerization of DHP can be stabilized upon confinement within a (PdIIL4)-L-6 coordination cage. By protecting this reactive intermediate using the cage, each isomerization reaction proceeds to higher yield, which significantly decreases the fatigue experienced by the system upon repeated photocycling. Although molecular confinement is known to help stabilize reactive species, this effect is not typically employed to protect reactive intermediates and thus improve reaction yields. We envisage that performing reactions under confinement will not only improve the cyclic performance of photochromic molecules, but may also increase the amount of product obtainable from traditionally low-yielding organic reactions

Polymorphism of L-tryptophan

A new polymorph of L‐tryptophan has been prepared by crystallization from the gas phase, with structure determination carried out directly from powder XRD data augmented by periodic DFT‐D calculations. The new polymorph (denoted β) and the previously reported polymorph (denoted α) are both based on alternating hydrophilic and hydrophobic layers, but with substantially different hydrogen‐bonding arrangements. The β polymorph exhibits the energetically favourable L2‐L2 hydrogen‐bonding arrangement, which is unprecedented for amino acids with aromatic side‐chains; the specific molecular conformations adopted in the β polymorph facilitate this hydrogen‐bonding scheme while avoiding steric conflict of the side‐chains

Nuevos datos acerca de los repertorios teatrales en el primer catálogo de «El peregrino en su patria»

En este artículo se muestra cómo los títulos que contienen los repertorios de los autores de comedias presentes en El peregrino en su patria de 1604 están dispuestos según un orden cronológico, aunque con algunos matices y no pocas excepciones. Además, se amplían los repertorios descubiertos por Thornton Wilder y se afina la fecha de composición de varias obras, prestando especial atención a textos que se han perdido, como La perdición de España, La gobernadora, La gran pintora, La bella gitana o La toma de Álora. Finalmente, el presente artículo pretende mostrar de un modo práctico cómo una base de datos digital como el Diccionario biográfico de actores del teatro clásico español (DICAT) puede resultar de gran ayuda a la hora de resolver algunos de los problemas clásicos de la filología en general y del teatro del Siglo de Oro en particular.This paper shows that the plays contained in the repertoire of the autores de comedias which appear in El peregrino en su patria (1604) are organised chronologically, although there are some nuances and exceptions. The article also expands the repertoire discovered by Thornton Wilder and sets the date of composition for some plays, paying special attention to lost texts such as La perdición de España, La gobernadora, La gran pintora, La bella gitana or La toma de Álora. Finally, this paper attempts to show in a practical way that a database such as the Diccionario biográfico de actores del teatro clásico español (DICAT) can be extremely helpful when it comes to dealing with some of the philology's classical problems in general and those of the theatre of the Golden Age in particular

Crystal structure of a new polymorph of (2S,3S)-2-amino-3-methylpentanoic acid

A new polymorph of (2S,3S)-2-amino-3-methylpentanoic acid, l-isoleucine C6H13NO2, crystallizes in the monoclinic space group P21 with four independent molecules in the asymmetric unit. The molecules are zwitterions. In the crystal, N—H...O hydrogen bonds link two pairs of independent molecules and their symmetry-related counterparts to form two types of layers stacked in an anti-parallel manner parallel to (001). The hydrophobic aliphatic isopropyl groups protrude from these layers

Formal oxidative addition of a C-H bond by a 16e iridium(I) complex involves metal-ligand cooperativity

The first example of oxidative addition of a C–H bond to a square planar d8-Iridium complex, without any external additive, such as an acid, is described. Our mechanistic investigations show that metal–ligand cooperation through aromatization–dearomatization of the lutidine backbone is involved in this process, and that the actual C–H activation step occurs through an Ir(III) intermediate

Controlled selectivity through reversible inhibition of the catalyst: Stereodivergent semihydrogenation of alkynes

Catalytic semihydrogenation of internal alkynes using H2 is an attractive atom-economical route to various alkenes, and its stereocontrol has received widespread attention, both in homogeneous and heterogeneous catalysis. Herein, a novel strategy is introduced, whereby a poisoning catalytic thiol is employed as a reversible inhibitor of a ruthenium catalyst, resulting in the first controllable H2-based semihydrogenation of internal alkynes. Both (E)- and (Z)-alkenes were obtained efficiently and highly-selectively, under very mild conditions, using a single homogenous acridine-based ruthenium catalyst. Mechanistic studies indicate that the (Z)-alkene is the reaction intermediate leading to the (E)-alkene, and that addition of a catalytic amount of bidentate thiol impedes the Z-E isomerization step by forming stable ruthenium thiol(ate) complexes, while still allowing the main hydrogenation reaction to proceed. Thus, the absence or presence of catalytic thiol controls the stereoselectivity of this alkyne semihydrogenation, affording either the (E)-isomer as the final product, or halting the reaction at the (Z)-intermediate. The developed system, which is also applied to the controllable isomerization of a terminal alkene, demonstrates how selective metal catalysis can be achieved by reversible inhibition of the catalyst with a simple auxiliary additive

Formamides as Isocyanate Surrogates: A Mechanistically Driven Approach to the Development of Atom-Efficient, Selective Catalytic Syntheses of Ureas, Carbamates, and Heterocycles

International audienceDespite the hazardous nature of isocyanates, they remain key building blocks in bulk and fine chemical synthesis. By surrogating them with less potent and readily available formamide precursors, we herein demonstrate an alternative, mechanistic approach to selectively access a broad range of ureas, carbamates and heterocycles via a ruthenium-based pincer complex catalyzed acceptorless dehydrogenative coupling reactions. The design of these highly atom-efficient procedures was driven by the identification and characterization of the relevant organometallic complexes, uniquely exhibiting the trapping of an isocyanate intermediate. DFT calculations further contributed to shed light on the remarkably orchestrated chain of catalytic events, involving metal-ligand cooperation