1,721,229 research outputs found
Deactivation of Ru-benzylidene Grubbs catalysts active in olefin metathesis
No full textIn this work, we explore the reactivity induced by coordination of a CO molecule trans to the Ru-benzylidene bond of a prototype Ru-olefin metathesis catalyst bearing a N-heterocyclic carbene (NHC) ligand. DFT calculations indicate that CO binding to the Ru center promotes a cascade of reactions with very low-energy barriers that lead to the final crystallographically characterized product, in which the original benzylidene group has attacked the proximal aromatic ring of the ligand leading to a cycloheptatriene ring through a Buchner ring expansion. In conclusion, the overall mechanism is best described as a carbene insertion into a C-C bond of the aromatic N-substituent of the NHC ligand, forming a cyclopropane ring. This cyclopropanation step is followed by a Buchner ring expansion reaction, leading to the experimentally observed product presenting a cycloheptatriene ring
Exploring the mechanism of Grignard metathesis polymerization of 3-alkylthiophenes
No full textIn this study we have investigated computationally the mechanism of polymerization of 2,5-dibromo 3-butylthiophene via the GRIM method, with the focus on the origin of the head to tail (HT) selectivity. To this end, first the Grignard reagent underwent oxidative addition to the monomer to afford the 2-bromo5-chloromagnesio-3-butylthiophene (intermediate I1) or the 2-chloromagnesio 5-bromo-3-butylthiophene (intermediate I2) regioisomers. Then intermediates I1 and I2 were polymerized catalytically to a series of regiospecific poly-3-butyithiophenes using the commonly used Ni(dppp)Cl-2 [dppp: 1,3-bis(diphenylphosphino) propane] and Pd(dppp)Cl-2 catalysts. Due to the asymmetric nature of I1 and I2 that act as the active monomeric species, 6 coupling modes may occur. The whole energy profile of all modes has been studied by considering a three-stage mechanism, including coordination, transmetalation, and reductive elimination, to compare quantitatively the ability of so-called catalysts in selective coupling of desired isomers to produce regioregular poly-3-butylthiophene. Finally, to quantify the steric role of the dppp in regioselectivity, analysis of the buried volume in terms of steric maps was performed
Nitrite to nitric oxide interconversion by heme Fe-II complex assisted by [Cu-I(tmpa)](+)
No full textThe present computational study complements the recent experimental efforts by Karlin and coworkers to describe the interconversion of nitrite to nitric oxide by means of an iron porphyrin complex together with a Cu chemical system, i.e., the iron(II) complex (F8TPP)Fe-II [F8TPP = tetrakis(2,6-difluorophenyl)porphyrinate(2-)] and a preformed copper(II)-nitrito complex [(tmpa)Cu-II(NO2)][B(C6F5)(4)] [tmpa = tris(2-pyridylmethyl)amine], being the latter an oxidized species of [(tmpa)Cu-I(MeCN)](+). By DFT calculations, we unravel how the reduction of nitrite to nitric oxide takes place through a mu-oxo heme-Fe-III-O-Cu-II complex, following a mimetic path as in the cytochrome c oxidase. Mayer bond order (MBO) and energy decomposition analyses are used to analyze the bonding strength of such nitro derivatives to either copper or iron
Exploring the reactivity of ru-based metathesis catalysts with a π-acid ligand trans to the Ru-ylidene bond
No full textComparison of different ruthenium-alkylidene bonds in the activation step with N-heterocyclic carbene Ru-catalysts for olefins metathesis
No full textOn the use of chemical bonding descriptors in machine learning
No full textThis review explores recent advances in machine learning in chemistry, emphasizing mechanistic understanding, performance optimization, and emerging design strategies. Key developments include novel synthesis routes, computational screening, hybrid experimental–theoretical approaches, and in-situ characterization. The review highlights how these innovations improve efficiency, selectivity, and scalability while uncovering fundamental structure-activity relationships. Special attention is given to integrating predictive modeling and high-throughput experimentation, which accelerates discovery cycles and enables rational design. Comparative discussions of different methodologies reveal synergies between traditional approaches and data-driven tools. Despite remarkable progress, translating laboratory results into practical applications remains a central challenge. The review concludes by outlining open questions, methodological gaps, and future research directions aimed at developing robust, cost-effective, and environmentally sustainable solutionsA.P. is a Serra Húnter Fellow and thanks the Spanish Ministerio de Ciencia e Innovación for project PID2024-155989NB-I00 and the Generalitat de Catalunya for project 2021SGR623. M.G. thanks for being funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - 217133147/SFB1073, project C03Open Access funding provided thanks to the CRUE-CSIC agreement with Elsevie
Mechanistic Insights of a Selective C-H Alkylation of Alkenes by a Ru–based Catalyst and Alcohols
No full textDensity functional theory calculations have been used to investigate the reaction mechanism for [(C6H6)(PCy3)(CO)RuH]+ (1; Cy, cyclohexyl) mediated alkylation of indene substrate using ethanol as solvent. According to Yi et al. [Science 2011, 333, 1613] the plausible reaction mechanism involves a cationic Rualkenyl species, which is initially formed from 1 with two equivalents of the olefin substrate via the vinylic C H activation and an alkane elimination step. Once the active catalytic species is achieved the oxidative addition step is faced. The latter step together with the next C C bond formation might display the upper barrier of the catalytic cycle. Having these experimental insights at hand, we investigated in detail the whole reaction pathway using several computational DFT approaches including alternative pathways, higher in energyA.P. thanks the Spanish MINECO for a project CTQ2014-59832-JI
Tuning the steric hindrance of alkylamines: a predictive model of steric editing of planar amines
No full textAmines are one of the most prevalent functional groups in chemistry. Perhaps even more importantly, amines represent one of the most ubiquitous moieties within the realm of bioactive natural products and life-saving pharmaceuticals. The archetypal geometrical property of amines is their sp3 hybridization with the lone pair of nitrogen occupying the apex of the pyramid. Herein, we present a blueprint for quantifying the properties of extremely sterically hindered alkylamines. These amines reach planarity around the nitrogen atom due to the excessive steric hindrance, which results in a conformational re-modeling of the amine moiety. Crucially, the steric properties of amines are characterized by the %VBur index, which we show is a general predictive parameter for evaluating the properties of sterically hindered amines. Computational studies on the acidic nature and the reactivity of organometallic Au and Pd complexes are outlined. Density functional theory calculations permit for predictive catalysis, ordering the mapping of extremely hindered tertiary amines by employing artificial intelligence via machine learning. Overall, the study outlines the correlation between the unusual geometry and the key thermodynamic and kinetic properties of extremely hindered alkylamines. The steric hindrance, as quantified by %VBur, is the crucial factor influencing the observed trends and the space required to accommodate sterically hindered tertiary amines.Amines are one of the most prevalent functional groups in chemistry
Structural and energetic characterization of the emissive RNA alphabet based on the isothiazolo[4,3-: D] pyrimidine heterocycle core
No full textWe present theoretical characterization of fluorescent non-natural nucleobases, tzA, tzG, tzC, and tzU, derived from the isothiazolo[4,3-d]pyrimidine heterocycle. Consistent with the experimental evidence, our calculations show that the non-natural bases have minimal impact on the geometry and stability of the classical Watson-Crick base pairs, allowing them to accurately mimic natural bases in a RNA duplex, in terms of H-bonding. In contrast, our calculations indicate that H-bonded base pairs involving the Hoogsteen edge are destabilized relative to their natural counterparts. Analysis of the photophysical properties of the non-natural bases allowed us to correlate their absorption/emission peaks to the strong impact of the modification on the energy of the lowest unoccupied molecular orbital, LUMO, which is stabilized by roughly 1.0-1.2 eV relative to the natural analogues, while the highest occupied molecular orbital, HOMO, is not substantially affected. As a result, the HOMO-LUMO gap is reduced from 5.3-5.5 eV in the natural bases to 4.0-4.4 eV in the modified ones, with a consequent bathochromic shift in the absorption and emission spectraThe research reported in this publication was supported by funding from King Abdullah University of Science and Technology (KAUST). For computer time, this research used the resources of the Supercomputing Laboratory at King Abdullah University of Science & Technology (KAUST) in Thuwal, Saudi Arabia, project K1017. A. P. thanks the Spanish MINECO for a project CTQ2014-59832-JI
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