Role of Electronic and Steric Effects on Ruthenium Catalysts with Bulky NHC Ligands and Relationship with the Z-Selectivity in Olefin Metathesis

Recently, sterically demanding N-heterocyclic cyclometalated ruthenium were reported as efficient Z-selective catalysts for cross-metathesis, showing a different reactivity in the function of the auxiliary ligand and the bulky ligand. To understand the origin of this behavior, we carried out density functional (M06-L) calculations to explore the reaction mechanism and insight from the energetic contributions into the determinant step. We emphasize the differences that occur when the 2,6-diisopropylphenyl (Dipp) and 2,6-diisopentylphenyl (Dipep) are employed. The results show that the barrier energies, ΔG‡, increase when the bulky ligand is greater, using nitrate as an auxiliary ligand, while the opposite behavior is obtained when pivalate is the auxiliary ligand. This tendency has its origin in the low reorganization energy and the less steric hindrance (%Vbur) obtained in catalysts that involve nitrate ligand and Dipep group. Moreover, by scrutinizing the energy decomposition analysis (EDA), it is found that the electronic contributions are also dominant and are not uniquely the steric effects that control the Z-selectivity

Synthesis, spectroscopic characterization and DFT study of dinuclear ruthenium sawhorse-type complexes derived from the reaction of trinuclear aggregates and (Z)-5-arylidenerhodanines

The synthesis of dinuclear ruthenium sawhorse-type complexes [Ru-2(-ArCH:Rhod)(2)(CO)(4)](n) 12a-e and [Ru-2(ArCH:Rhod)(2)(-ArCH:Rhod)(2)(CO)(4)] 13a-e through reaction of [Ru-3(CO)(10)(NCMe)(2)] and [Ru-3(CO)(12)] and the corresponding (Z)-5-arylidenerhodanines (ArCH:Rhod) 10a-e, respectively, are reported. These complexes are arranged in a sawhorse structure in which two bridged (Z)-5-arylidenerhodanines coordinate to the metals using sulfur and nitrogen of the rhodanine ring. A Density Functional Theory method was used to gain insight into the polymerization process by calculating dimerization Gibbs energies (G(dim)). Values between -10.7 and -5.3kcalmol(-1) indicate that dimerization is a spontaneous process. A reaction pathway for formation of the sawhorse compounds [Ru-2(-ArCH:Rhod)(2)(CO)(4)] was calculated and the rate-determining step for the mechanism is coordination of a second (Z)-5-arylidenerhodanine ligand with activation energies between 41.1 and 47.8kcalmol(-1). In order to understand the apparent thermodynamic favorability of the fragmentation step, we calculated the fragmentation energy (E-Frag) for the key intermediate and its energetic contributors, the interaction energy, E-int and the reorganization energy, E-reorg. Low values of E-Frag imply that the fragmentation is thermodynamically facile. Large values of E-int are countered by opposite and large values of E-reorg which indicate that the cleavage of the trimetallic intermediate aggregate is determined by the nature of the ligand and the balance between its interaction with the metal and the extent of structural reorganizationCOLCIENCIAS Universidad del Valle Illinois State University FONDECYT 1140503 1150629 project CONICYT AKA ERNC-001 fellowship "Program for International Mobility of Researchers and Innovators to Events and Short Term Stays" of COLCIENCIA

Insights into the role of D-A-π-A type pro-aromatic organic dyes with thieno[3,4-b]pyrazine as A acceptor group into dye-sensitized solar-cells. A TD-DFT/periodic DFT study

Time-dependent density functional theory (TD-DFT)/periodic DFT calculations were performed to determine the role of pro-aromatic organic D-A-pi-A type dyes (the NL1-NL17 family) with Thieno[3,4-b]pyrazine (Tpy) as A acceptor group into dyesensitized solar-cells (DSSC). This work presents a discussion of the ground and excited states of these dyes along with the aromaticity analysis and the electron injection step using a dye@(TiO2)(72) model. The results suggest that the pro-aromatic behavior increases from the thiophene ring to the pyrazine when an acceptor p-bridge such as phenyl is used. This strong pro-aromaticity is also reflected in the electron injection step, studied using a 3x2 3 layer (TiO2)(72) slab model. The resulting adsorption energies (Delta E-ads and Delta G(ads)) and the electron injection (Delta G(inject)) in the stablest coordination mode, Bid_CN_COOH, indicate that the redox reaction (Dye* -> Dye(+) + e(-)) is stronger and more spon than the adsorption reaction (Dye(+) + TiO2 [+e(-)] -> Dye@TiO2) in the electron injection. In this way, the highest efficiency of NL6 and NL12 is a consequence of the more significant pro-aromatic characteristics and the more spontaneous redox process. Finally, these NL dyes are promising in the molecular engineering of D-A-pi-A metal-free types dyes.Comisión Nacional de Investigación Científica y Tecnológica PAI77180024 Comisión Nacional de Investigación Científica y Tecnológica (CONICYT) CONICYT FONDECYT 1140503 1150629 1180158 317011

Thermodynamic and Ab Initio Design of Multicomponent Alloys Based on (Fe₅₀Mn₃₀Co₁₀Cr₁₀)-xBx (x = 0, 5, 7, 10, and 15 at.%)

Multicomponent alloys have attained general interest in recent years due to their remarkable performance. Non-equiatomic alloys with boron addition as an interstitial element are being studied, exhibiting outstanding mechanical properties. In order to estimate the mechanical behavior of potential alloys, thermodynamic and ab initio calculations were utilized in this work to investigate phase stability and stacking fault energy (SFE) for (Fe50Mn30Co10Cr10)-xBx (x = 0, 5, 7, 10, and 15 at.%) systems. Thermodynamic experiments revealed two structural variations of borides, M2B(C16) with a tetragonal structure and M2B(CB) with an orthorhombic structure. Borides precipitate when boron content increases, and the FCC matrix becomes deficient in Mn and Cr. According to ab initio calculations, the presence of boron in the FCC and HCP structures primarily disrupts the surroundings of the Fe and Mn atoms, resulting in an increased distortion of the crystal lattice. This is related to the antiferromagnetic condition of the alloys. Furthermore, for alloys with a low boron concentration, the stacking fault energy was found to be near 20 mJ/m2 and greater than 50 mJ/m2 when 10 and 15 at.% boron was added. As boron concentrations increase, M2B borides are formed, generating changes in the matrix composition prone to fault-induced phase transitions that could modify and potentially impair mechanical properties

Boron addition in a non-equiatomic Fe50Mn30Co10Cr10 alloy manufactured by laser cladding: microstructure and wear abrasive resistance

A non-equiatomic Fe(50)Mn(30)Co(10)Cr(10 )alloy was prepared by laser cladding, and the effects of boron addition on the microstructure, hardness and abrasive wear-resistance were investigated. Elemental powders were mixed using an attritor mill for 30 h and then applied by laser cladding on a stainless steel 316L substrate. The effect of boron addition (0.1, 0.66 and 5.40 at%) on the alloy microstructure was assessed using optical and electron microscopy, and the phase composition was studied using X-ray diffraction. The laser claddings were exposed to abrasive wear conditions using the dry sand/rubber wheel test. The microstructure of the laser claddings exhibited columnar dendrites formed by two crystalline structures (fcc and hcp) with the same chemical composition. The hcp structure was the result of the partial martensitic transformation of the fcc structure. Boron addition led to the formation of a eutectic phase along the interdendritic regions with a crystalline structure consistent with M2B-type borides (M = Cr, Fe). Hardness and abrasive wear-resistance of the laser claddings were strongly influenced by boron content. When boron content was increased from 0 at% to 5.40 at% the microhardness of the material was from 291 HV to 445 HV. Similarly, the boron content improved the behaviour against abrasive wear due to the increased volume fraction of borides in the microstructure. The high content of the boride phase in the laser cladding with 5.40 at% B allowed reducing the abrasive wear rate by more than 30% when compared with the alloy without boron content.CORFO Chile Innova-10CEII9007 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) FB0809 CSIRO Chile International Centre of Excellence Faculty of Mathematical and Physical Sciences at the University of Chile Mechanical Engineering Department at the University of Chile Fondequip EQM16009

DFT Study on the Relative Stabilities of Substituted Ruthenacyclobutane Intermediates Involved in Olefin Cross-Metathesis Reactions and Their Interconversion Pathways

DFT (M06-L) calculations have been used to determine the relative stabilities of the metallacyclobutane intermediates arising from the cross-metathesis reactions of terminal olefins as well as to get insights into the origin of the nondetection of the α,β-substituted species. For that, we discuss the structures, NMR signatures, stabilities with respect to separated reactants, and experimentally proposed interconversion pathways of all potential metallacyclobutane intermediates arising from propene and styrene homocoupling. For the case of propene, the unsubstituted and mono- and disubstituted metallacycles are lower in Gibbs energy than the separated reactants under the NMR experimental conditions. Moreover, for the same number of substituents, regardless of their nature, the metallacycles presenting substituents at the C_α carbons are always lower in energy than those presenting substituents at C_β, the energy difference being between 1.7 and 8.8 kcal mol^–1. The computed energy barriers associated with the olefin and carbene rotation processes, two of the experimentally proposed pathways for the metallacycle interconversion, are low and are in excellent agreement with the values previously determined through NMR studies. Cycloaddition and cycloreversion energy barriers are also low, and in fact, there is not a significant difference between the barrier heights of the processes leading to observed or nonobserved intermediates. Therefore, the nondetection of metallacyclobutane intermediates with substituents in C_β seems to arise from their lower stability in comparison with the isomers with substituents in C_α, which makes their detection not feasible under thermodynamic equilibrium conditions. That is, for cross-metathesis processes involving small terminal alkenes and activated carbenes, the nature of the observed metallacycles is based on thermodynamic control. The preference of having the substituents in C_α is attributed to the formation of stronger M–C and C–C bonds during the cycloaddition when the substituents are in an α position due to higher charge transfer from the original alkene fragment to the metal carbene

DFT Study on the Relative Stabilities of Substituted Ruthenacyclobutane Intermediates Involved in Olefin Cross-Metathesis Reactions and Their Interconversion Pathways

DFT (M06-L) calculations have been used to determine the relative stabilities of the metallacyclobutane intermediates arising from the cross-metathesis reactions of terminal olefins as well as to get insights into the origin of the nondetection of the α,β-substituted species. For that, we discuss the structures, NMR signatures, stabilities with respect to separated reactants, and experimentally proposed interconversion pathways of all potential metallacyclobutane intermediates arising from propene and styrene homocoupling. For the case of propene, the unsubstituted and mono- and disubstituted metallacycles are lower in Gibbs energy than the separated reactants under the NMR experimental conditions. Moreover, for the same number of substituents, regardless of their nature, the metallacycles presenting substituents at the C_α carbons are always lower in energy than those presenting substituents at C_β, the energy difference being between 1.7 and 8.8 kcal mol^–1. The computed energy barriers associated with the olefin and carbene rotation processes, two of the experimentally proposed pathways for the metallacycle interconversion, are low and are in excellent agreement with the values previously determined through NMR studies. Cycloaddition and cycloreversion energy barriers are also low, and in fact, there is not a significant difference between the barrier heights of the processes leading to observed or nonobserved intermediates. Therefore, the nondetection of metallacyclobutane intermediates with substituents in C_β seems to arise from their lower stability in comparison with the isomers with substituents in C_α, which makes their detection not feasible under thermodynamic equilibrium conditions. That is, for cross-metathesis processes involving small terminal alkenes and activated carbenes, the nature of the observed metallacycles is based on thermodynamic control. The preference of having the substituents in C_α is attributed to the formation of stronger M–C and C–C bonds during the cycloaddition when the substituents are in an α position due to higher charge transfer from the original alkene fragment to the metal carbene

Autoimmune pancreatitis in patients with inflammatory bowel disease - a real-world multicentre collaborative ECCO CONFER study

Autoimmune pancreatitis (AIP) is rarely associated with inflammatory bowel disease (IBD). Long-term outcomes of AIP and IBD in patients with AIP-IBD coexistence and predictors of complicated AIP course are scarcely known. An ECCO COllaborative Network For Exceptionally Rare case reports project (ECCO-CONFER) collected cases of AIP diagnosed in patients with IBD. Complicated AIP was defined as a composite of endocrine and/or exocrine pancreatic insufficiency, and/or pancreatic cancer. We explored factors associated with complicated AIP in IBD. We included 96 patients (53% males, 79% ulcerative colitis, 72% type 2 AIP, age at AIP diagnosis 35±16 years). The majority of Crohn's disease (CD) cases (78%) had colonic/ileocolonic involvement. In 59%, IBD preceded AIP diagnosis, whereas 18% were diagnosed simultaneously. Advanced therapy to control IBD was used in 61% and 17% underwent IBD-related surgery. 82% of patients were treated with steroids for AIP, the majority of which (91%) responded to a single course of treatment. During a mean follow-up of 7 years, AIP complications occurred in 25/96 (26%) individuals. In a multivariate model, younger age at AIP diagnosis (OR=1.05, P=0.008), family history of IBD (OR=0.1, P=0.03) and CD diagnosis (OR=0.2, P=0.04) were associated with uncomplicated AIP course. No IBD or AIP-related deaths occurred. In this large international cohort of patients with concomitant AIP-IBD, most patients have type 2 AIP and colonic IBD. AIP course is relatively benign and long-term outcomes are favourable, however, one-quarter develop pancreatic complications. Age, familial history of IBD and CD may predict uncomplicated AIP course