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A series of nickel(0) complexes, 3, 4, and 5, containing unsaturated 15-memberedazamacrocyclicligands have been synthesized. Structural characterization of thecomplexes is based on NMR spectroscopy, X-ray diffraction analysis,and differential scanning calorimetry. In addition, the catalyticactivity of the complexes in the Suzuki–Miyaura cross-couplingof arylboronic acids and aryl halides has been tested. [ABSTRACT FROM AUTHOR]

Molecular structures featuring one or two triolefinic 15-membered azamacrocycles (1 and 6) as well as their homo- and heterobimetallic complexes of palladium(0) and platinum(0) (3, 4, and 7) have been synthesized from biphenyl-4,4'-disulfonyl chloride. The strategy employed allows easy preparation of heterobimetallic complexes in a controlled manner. Pulsed-Field Gradients Spin-Echo (PFGSE) NMR techniques together with different mass spectrometry techniques can provide highly useful information about the structure of these polynuclear complexes. [ABSTRACT FROM AUTHOR]

Rhodium complexes of N-heterocyclic carbenes (NHC) [RhCl(cod)(NHC)], [cod = 1,5-cyclooctadiene, NHC = 1,3-diisopropylimidazolin-2-ylidene, and NHC = 1,3-dimesitylimidazolin-2-ylidene] are tested for intra- and partially intramolecular [2+2+2]-cycloaddition reactions demonstrating their effectiveness in this kind of process. This is the first use of a rhodium-NHC complex in a [2+2+2]-cycloaddition reaction of three alkynes. ESI-MS has been used to detect oxidative addition intermediates using rhodium NHC as the catalytic system. [ABSTRACT FROM AUTHOR]

A stepwise preparation of a series of nitrogen-containing 25-membered pentaolefinic macrocycles is presented. The corresponding arenesulfonamides and trans-1,4-dibromo-2-butene served as precursors for the synthesis. [ABSTRACT FROM AUTHOR]

Predictive catalysis was applied to the reaction of pyridinium 1,4‐zwitterionic thiolates with a copper carbene. Theoretical calculations were first performed to determine the suitability of their annulation reaction and to make predictions about the performance of different copper salts, diazo species, and pyridinium derivatives. With calculations in hand, the experimental conditions were optimized, the scope of the reaction was assessed, and the precision of the predictions was evaluated. Yields up to 90% were obtained for the synthesis of indolizine scaffolds in the reactivity of pyridinium 1,4‐zwitterionic thiolates with a metal carbene. [ABSTRACT FROM AUTHOR]

The trapping of the elusive vinylogous position of a vinyl carbene with an aliphatic C(sp3)−H bond has been achieved for the first time during a silver‐catalyzed carbene/alkyne metathesis (CAM) process. A Tpx‐containing silver complex first promotes the generation of a donor‐acceptor silver carbene which triggers CAM, generating a subsequent donor‐donor vinyl silver carbene species, which then undergoes a selective vinylogous C(sp3)−H bond insertion, leading to the synthesis of a new family of benzoazepines. Density functional theory (DFT) calculations unveil the reaction mechanism, which allows proposing that the C−H bond insertion reaction takes place in a stepwise manner, with the hydrogen shift being the rate determining step. [ABSTRACT FROM AUTHOR]

An interesting reaction for the synthesis of aromatic carbo- and heterocycles is the transition-metal catalyzed [2 + 2 + 2] cycloaddition reaction. In this elegant and atom-efficient process three C-C or C-X (X = N, O, S...) bonds are formed in a single synthetic process. The [2 + 2 + 2] cycloaddition is catalyzed by a variety of organometallic complexes, including more than 15 different metals. In this work, we carry out computational studies of the reaction mechanism between two acetylenes and a nitrile to form substituted pyridines catalyzed by the Wilkinson complex. Our results show that initial oxidative addition between the two acetylene molecules is the rate-determining step. Oxidative addition between two acetylenes is more favorable than between acetylene and nitrile moieties. Our results are in agreement with the experimental finding that the formation of pyridines in some cases requires the use of an excess of nitrile. Nitriles with electron withdrawing substituents favor the incorporation of nitrile in the insertion process and improve the ratio of pyridine vs. benzene. [ABSTRACT FROM AUTHOR]

Abstract: The combination of cationic rhodium(I) complexes with N-phosphino tert-butylsulfinamides (PNSO) ligands is efficient for catalytic intra- and intermolecular [2+2+2] cycloaddition reactions. PNSO ligands are a new class of chiral bidentate ligands, which have the characteristic of combining the easily accessible sulfur chirality with the coordinating capacity of phosphorous. Cycloaddition of open-chained and macrocyclic E-enediynes with these chiral complexes have proved to be highly efficient in terms of yields, giving moderate enantiomeric excesses of the corresponding cyclohexadiene derivatives. In addition Rh(I)/PNSO complexes catalyzed the intermolecular cycloaddition of diynes with monoalkynes in mild reaction conditions and short reaction times. [ABSTRACT FROM AUTHOR]

• The influence of particle size of Ziegler-Natta (ZN) catalysts on the micro-structure and properties of related polypropylenes. • Experimental mild conditions for the catalyst choice together with excellent catalytic activity. • Catalysts with a larger particle size provided polymers with a lower isotacticity index, and a shorter meso sequence length. • The importance of catalyst/support particle size control during the preparation process in industrial polypropylene plants. This study investigates the influence of particle size of Ziegler-Natta (ZN) catalysts on the micro-structure and properties of related polypropylenes. In this regard, three catalysts were synthesized with different particle sizes (PS) including PS < 25, 25 ≤ PS ≤ 45, and PS > 45 μm, but from the same ingredients. The catalyst characterization involved a wide range of methods including TGA, BET, SEM, EDS, XRD, LPS, and N 2 adsorption-desorption techniques. Next, a series of propylene homopolymers and their copolymers with 1-hexene were prepared using the as-synthesized catalysts, in the presence or absence of H 2 under similar reaction conditions. The synthesized (co)polymers were characterized with DSC, SSA, 13CNMR and TREF techniques. The activity was found to increase with decreasing catalyst particle size in both homo- and copolymerization experiments. Furthermore, a catalyst with a larger particle size provided a polymer with a lower isotacticity index, slightly longer meso sequence length, and higher 1-hexene content of about 10.57 %. This affirms the importance of catalyst/support particle size control during the preparation process in industrial polypropylene plants. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Aryl–heteroaryl and heteroaryl–heteroaryl compounds are obtained through the Suzuki–Miyaura cross-coupling reactions between diazonium salts and potassium trifluoroborates using PdCl2(CH3CN)2 as the catalyst in water and in the absence of any additive, ligand or base. In addition, the same mild catalytic system is effective for the Matsuda–Heck reaction between several monoolefins with aryldiazonium salts. [Copyright &y& Elsevier]

The oxalamide skeleton is a common structural motif in many biologically active molecules. These scaffolds can be synthesized via ruthenium pincer complex-catalyzed acceptorless dehydrogenative coupling of ethylene glycol and amines. In this study, we elucidate the mechanism of this oxalamide synthesis using density functional theory calculations. The rate-determining state is identified as the formation of molecular hydrogen following the oxidation of hydroxyacetamide to oxoacetamide. In predictive catalysis exercises, various modifications to the ruthenium pincer catalyst were investigated to assess their impact on the reactivity.

Photodynamic therapy is an important tool in modern medicine due to its effectiveness, safety, and the ability to provide targeted treatment for a range of diseases. Photodynamic therapy utilizes photosensitizers to generate reactive oxygen species (ROS). Fullerenes can be used as photosensitizers to produce ROS in high quantum yields. Open-cage fullerenes are a subclass of fullerenes characterized by a partially open structure, with one or more openings or apertures. The promising electrochemical properties of open-cage fullerenes motivated us to investigate their use for DNA-cleavage and ROS generation under visible light irradiation through type I electron transfer and type II energy transfer reactions. Our results show that open-cage C 60 fullerenes are more efficient for photoinduced cleavage of DNA and ROS generation via both the type I electron transfer and type II energy transfer pathways than pristine C 60 or a C 60 pyrrolidine derivative without open-cage. The greater efficiency of ROS generation by open-cage C 60 fullerene in type I and type II reactions can be attributed to the increased rate of the initial intersystem crossing process, resulting from larger total reorganization energies, as indicated by computationally calculated relative rates using the Marcus equation, and the lower reduction potential of the open-cage derivative 3, as determined by CV, which facilitates a more efficient generation of the corresponding radical anion (C 60 ˙ - )., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Given its wide variety of applications in the pharmaceutical industry, the synthesis of imidazo[1,2-a]pyridines has been extensively studied since the beginning of the last century. Here, we disclose the mechanism for the synthesis of imidazo[1,2-a]pyridines by means of the Ortoleva-King reaction. We also reveal the reaction pathway leading to the formation of a iodinated byproduct, demonstrating the challenge of preventing the formation of such a byproduct because of the low energy barrier to access it. Moreover, quantum chemistry tools were employed to investigate the mechanism of intramolecular proton transfer in the excited state, and connections with aromaticity were explored., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

The regioselective functionalization of fullerenes holds significant promise for applications in the fields of medicinal chemistry, materials science, and photovoltaics. In this study, we investigate the regioselectivity of the rhodium(I)-catalyzed [2 + 2 + 2] cycloaddition reactions between diynes and C 70 as a novel procedure for generating C 70 bis(fulleroid) derivatives. The aim is to shed light on the regioselectivity of the process through both experimental and computational approaches. In addition, the photooxidation of one of the C-C double bonds in the synthesized bis(fulleroids) affords open-cage C 70 derivatives having a 12-membered ring opening., (Copyright © 2024, Castanyer et al.)

The selective assembly of the 1,4-oxathiin nucleus has been treated as a powerful strategy to access this scaffold present in molecules with very interesting properties. In this study, the chameleon-like reactivity of pyridinium 1,4-zwitterionic thiolates is exploited to assemble the 1,4-oxathiin core through a [3 + 3] annulation. The optimal annulation partner has been found to be the iodonium ylide of the cyclic 1,3-diketones. The developed protocol allows the synthesis of a variety of bicyclic 1,4-oxathiin derivatives under very mild conditions under copper(I) iodide catalysis. Access to benzoannulated 1,4-oxathiins has been achieved through iodine-mediated aromatization of the initially obtained bicyclic compounds.

The stereoselective synthesis of cyclobutanes that possess an array of stereocenters in a contiguous fashion has attracted the wide interest of the synthetic community. Cyclobutanes can be generated from the contraction of pyrrolidines through the formation of 1,4-biradical intermediates. Little else is known about the reaction mechanism of this reaction. Here, we unveil the mechanism for this stereospecific synthesis of cyclobutanes by means of density functional theory (DFT) calculations. The rate-determining step of this transformation corresponds to the release of N 2 from the 1,1-diazene intermediate to form an open-shell singlet 1,4-biradical. The formation of the stereoretentive product is explained by the barrierless collapse of this open-shell singlet 1,4-biradical. The knowledge of the reaction mechanism is used to predict that the methodology could be amenable to the synthesis of [2]-ladderanes and bicyclic cyclobutanes.

The [2 + 2 + 2] cycloaddition of 1,5-bisallenes and alkynes under the catalysis of Rh(I) with hemilabile thioether-functionalized N-heterocyclic carbene ligands is described. This protocol effectively provides an entry to different trans -5,6-fused bicyclic systems with two exocyclic double bonds in the cyclohexene ring. The process is totally chemoselective with the two internal double bonds of the 1,5-bisallenes being involved in the cycloaddition. The complete mechanism of this transformation as well as the preference for the trans -fusion over the cis -fusion has been rationalized by density functional theory calculations. The reaction follows a typical [2 + 2 + 2] cycloaddition mechanism. The oxidative addition takes place between the alkyne and one of the allenes and it is when the second allene is inserted into the rhodacyclopentene that the trans -fusion is generated. Remarkably, the hemilabile character of the sulfur atom in the N-heterocyclic carbene ligand modulates the electron density in key intermediates, facilitating the overall transformation., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The interest in the fusion product of quinoxalinone skeletons and 1,2,3-triazole units has greatly increased in recent years since they are known to be agonists of G-protein-coupled Niacin receptor 109A and inhibitors of the benzodiazepine and adenosine receptors. Here, we unveil the mechanism for the photoredox catalyzed synthesis of those scaffolds by means of DFT calculations. The calculations indicate that the rate determining step of this transformation is the attack of the in situ generated radical intermediate on the CN bond of the quinoxalinone species to form a new C-C bond. Predictive chemistry here reveals that the energy difference is so subtle, and gives the recipe of which substituents, sterically and electronically, can fit to perform the reaction at room temperature.

The synthesis of spiro compounds featuring seven- and six-membered rings in the spirobicyclic motif is successfully achieved through a cascade process encompassing a rhodium(I)-catalyzed cycloisomerization followed by a highly selective Diels-Alder homodimerization. The scope of the reaction is analyzed based on a series of synthetic substrates, and control experiments and DFT calculations led us to justify the exquisite degree of selectivity observed.

[2+2+2] Cycloaddition reaction is a captivating process that assembles six-membered rings from three unsaturations with complete atom economy. Of the multiple transition metals that can be used to catalyze this reaction, rhodium offers many advantages. These include high activity and versatility, but especially the ability to easily tune the reactivity and selectivity by the modification of the ligands around the metal. In this personal account, we summarize our endeavours in the development of efficient and sustainable [2+2+2] cycloaddition reactions to prepare products of interest, develop conditions in which the catalyst can be recovered and reused, and understand the mechanistic details that govern the selectivity of the processes.

The functionalization of fullerenes helps to modulate their electronic and physicochemical properties, generating fullerene derivatives with promising features for practical applications. Herein, DFT is used to explore the attachment of a cyclohexadiene ring to C 60 through a rhodium-catalyzed intermolecular [2+2+2] cycloaddition of C 60 and acetylene. All potential reaction paths are analyzed and it can be concluded that the [2+2+2] cycloaddition of C 60 and two acetylene molecules catalyzed by [RhCl(PPh 3 ) 3 ], yielding a cyclohexadiene ring fused to a [6,6] bond of C 60 , is energetically feasible., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

N-tosyl-linked open-chain yne-ene-yne enediynes 1 and 2 and yne-yne-ene enediynes 3 and 4 have been satisfactorily synthesised. The [2+2+2] cycloaddition process catalysed by the Wilkinson catalyst [RhCl(PPh(3))(3)] was tested with the above-mentioned substrates resulting in the production of high yields of the cycloadducts. Enediynes 1 and 2 gave standard [2+2+2] cycloaddition reactions whereas enediynes 3 and 4 suffered β-hydride elimination followed by reductive elimination of the Wilkinson catalyst to give cycloadducts, which are isomers of those that would be obtained by standard [2+2+2] cycloaddition reactions. The different reactivities of these two types of enediyne have been rationalised by density functional theory calculations., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)