1,720,973 research outputs found
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
Mechanism of CO2 Fixation by IrI–X Bonds (X = OH, OR, N, C)
No full textDensity functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the IrI complex [Ir(cod)(IiPr)(OH)] (1; cod = 1,5-cyclooctadiene;
IiPr = 1,3-diisopropylimidazol-2-ylidene) and its derivatives. For 1, our results suggest that CO2 insertion is the rate-limiting step rather than the dimerization step. Additionally, in agreement with the experimental results, our results show that CO2 insertion into the Ir–OR1 (R1 = H, methyl, and phenyl) and Ir–N bonds is kinetically facile, and the calculated activation energies span a range of only 12.0–23.0 kcal/mol. Substantially higher values (35.0–50.0 kcal/mol) are reported for analogous Ir–C bond
Mechanism of Intramolecular Rhodium- and Palladium-Catalyzed Alkene Alkoxyfunctionalizations
No full textDensity functional theory calculations have been used to investigate the reaction mechanism for the [Rh]-catalyzed intramolecular alkoxyacylation ([Rh] = [RhI(dppp)+] (dppp, 1,3-bis(diphenylphosphino)propane) and [Pd]/BPh3 dual catalytic system assisted intramolecular alkoxycyanation ([Pd] = Pd-Xantphos) using acylated and cyanated 2-allylphenol derivatives as substrates, respectively. Our results substantially confirm the proposed mechanism for both [Rh]- and [Pd]/ BPh3-mediated alkoxyfunctionalizations, offering a detailed geometrical and energetical understanding of all the elementary steps. Furthermore, for the [Rh]-mediated alkoxyacylation, our observations support the hypothesis that the quinoline group of the substrate is crucial to stabilize the acyl metal complex and prevent further decarbonylation. For [Pd]/BPh3-catalyzed alkoxycyanation, our findings clarify how the Lewis acid BPh3 cocatalyst accelerates the only slow step of the reaction, corresponding to the oxidative addition of the cyanate O-CN bond to the Pd centeA.P. thanks the Spanish MINECO for project CTQ2014-59832-JIN and the European Commission for a Career Integration Grant (CIG09-GA-2011-293900
Catalytic role of nickel in the decarbonylative addition of phthalimides to alkynes
No full textDensity functional theory calculations have been used to investigate the catalytic role of nickel(0) in the decarbonylative addition of phthalimides to alkynes. According to Kurahashi et al. the plausible reaction mechanism involves a nucleophilic attack of nickel at an imide group, giving a six-membered metallacycle, followed by a decarbonylation and insertion of an alkyne leading to a seven-membered metallacycle. Finally a reductive elimination process produces the desired product and regenerates the nickel(0) catalyst. In this paper, we present a full description of the complete reaction pathway along with possible alternative pathways, which are predicted to display higher upper barriers. Our computational results substantially confirm the proposed mechanism, offering a detailed geometrical and energetical understanding of all the elementary stepsA.P. and L.C. thank the HPC team of Enea for using the ENEA-GRID and the HPC facilities CRESCO in Portici (Italy) for access to remarkable computational resources. A.P. thanks the Spanish MICINN for a Ramon y Cajal contract (RYC-2009-05226), European Commission for a Career Integration Grant (CIG09-GA-2011-293900), and Generalitat de Catalunya (2012BE100824
Deconstructing selectivity in the gold-promoted cyclization of alkynyl benzothioamides to six-membered mesoionic carbene or acyclic carbene complexes
No full textWe demonstrate that the experimentally observed switch in selectivity from 5-exo-dig to 6-endo-dig cyclization of an alkynyl substrate, promoted by Au I and AuIII complexes, is connected to a switch from thermodynamic to kinetic reaction control. The AuIII center pushes alkyne coordination toward a single Au-C(alkyne) σ-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom. © 2014 American Chemical Society
The 'innocent' role of Sc3+ on a non-heme Fe catalyst in an O2 environment
No full textDensity functional theory calculations have been used to investigate the reaction mechanism proposed for the formation of an oxoiron(iv) complex [Fe IV(TMC)O]2+ (P) (TMC = 1,4,8,11-tetramethylcyclam) starting from a non-heme reactant complex [FeII(TMC)]2+ (R) and O2 in the presence of acid H+ and reductant BPh4 -. We also addressed the possible role of redox-inactive Sc3+ as a replacement for H+ acid in this reaction to trigger the formation of P. Our computational results substantially confirm the proposed mechanism and, more importantly, support that Sc 3+ could trigger the O2 activation, mainly dictated by the availability of two electrons from BPh4 -, by forming a thermodynamically stable Sc3+-peroxo-Fe3+ core that facilitates O-O bond cleavage to generate P by reducing the energy barrier. These insights may pave the way to improve the catalytic reactivity of metal-oxo complexes in O2 activation at non-heme center
In Silico Olefin Metathesis with Ru-Based Catalysts Containing N-Heterocyclic Carbenes Bearing C60 Fullerenes
No full textKGaA, Weinheim.Density functional theory calculations have been used to explore the potential of Ru-based complexes with 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene (SIMes) ligand backbone (A) being modified in silico by the insertion of a C60 molecule (B and C), as olefin metathesis catalysts. To this end, we investigated the olefin metathesis reaction catalyzed by complexes A, B, and C using ethylene as the substrate, focusing mainly on the thermodynamic stability of all possible reaction intermediates. Our results suggest that complex B bearing an electron-withdrawing N-heterocyclic carbene improves the performance of unannulated complex A. The efficiency of complex B is only surpassed by complex A when the backbone of the N-heterocyclic carbene of complex A is substituted by two amino groups. The particular performance of complexes B and C has to be attributed to electronic factors, that is, the electronic-donating capacity of modified SIMes ligand rather than steric effects, because the latter are predicted to be almost identical for complexes B and C when compared to those of A. Overall, this study indicates that such Ru-based complexes B and C might have the potential to be effective olefin metathesis catalystsA.P. thanks the Spanish MINECO for a project CTQ2014-59832-JIN, and the European Commission for a Career Integration Grant (CIG09-GA-2011-293900
The right computational recipe for olefin metathesis with ru-based catalysts: the whole mechanism of ring-closing olefin metathesis
No full textThe initiation mechanism of ruthenium methylidene complexes was studied detailing mechanistic insights of all involved reaction steps within a classical olefin metathesis pathway. Computational studies reached a good agreement with the rarely available experimental data and even enabled to complement them. As a result, a highly accurate computational and rather cheap recipe is presentedA.P. thanks the Spanish MINECO for a Ramon y Cajal contract (RYC-2009-05226) and European Commission for a Career Integration Grant (CIG09-GA-2011-293900). E.P. gratefully acknowledges the receipt of the "Chemical Monthly Fellowship" financed by Springer Verlag, the Austrian Academy of Sciences (OAW), and the Gesellschaft Osterreichischer Chemiker (GOCH
Synthesis of β-(Hetero)aryl Ketones via Ligand-Enabled Nondirected C–H Alkylation
No full text<p>This folder contains the DFT-optimized geometries (in .xyz format together with the gas-phase energy, E) accompanying the paper</p>
<p>"Synthesis of β-(Hetero)aryl Ketones via Ligand-Enabled Nondirected C–H Alkylation"</p>
Synthesis of β-(Hetero)aryl Ketones via Ligand-Enabled Nondirected C–H Alkylation
No full text<p>This folder contains the DFT-optimized geometries (in .xyz format together with the gas-phase energy, E) accompanying the paper</p>
<p>"Synthesis of β-(Hetero)aryl Ketones via Ligand-Enabled Nondirected C–H Alkylation"</p>
- …
