Catalytic Role of Nickel in the Decarbonylative Addition of Phthalimides to Alkynes

Density 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 steps

The driving force role of ruthenacyclobutanes

DFT calculations have been used to determine the thermodynamic and kinetic preference for ruthena-cyclobutanes resulting from the experimentally proposed interconversion pathways (olefin and alkylidene rotations) through the investigation of cross-metathesis reaction mechanism for neutral Grubbs catalyst, RuCl2 (=CHEt) NHC (A), with ethylene and 1-butene as the substrates. Our results show that although the proposed interconversions are feasible due to the predicted low energy barriers (2-6 kcal/mol), the formation of ruthenacyclobutane is kinetically favored over the competitive reactions involving alkylidene rotations. In comparison with catalyst A, the reaction energy profile for cationic Piers catalyst [RuCl2 (=CHPCy3)NHC+] (B) is more endothermic in nature with both ethylene and 1-butene substrates

The "innocent" role of Sc3+ on a non-heme Fe catalyst in an O-2 environment

Density functional theory calculations have been used to investigate the reaction mechanism proposed for the formation of an oxoiron(iv) complex [Fe-IV(TMC)0](2+) (P) (TIvIC = 1,4,8,11-tetramethylcyclam) starting from a non-heme reactant complex-EFell(TMC)1(2+) (R) and 02 in the presence of acid H+ and reductant BPV. 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 Sc3+ could trigger the 02 activation, mainly dictated by the availability of two electrons from BPV, by forming a thermodynamically stable Sc3+-peroxo-Fe3+ core that facilitates 0-0 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 02 activation at non-heme centers

Deconstructing Selectivity in the Gold-Promoted Cyclization of Alkynyl Benzothioamides to Six-Membered Mesoionic Carbene or Acyclic Carbene Complexes

We 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 Au-III complexes, is connected to a switch from thermodynamic to kinetic reaction control. The Au-III center pushes alkyne coordination toward a single Au-C(alkyne) (sigma-bond, conferring carbocationic character (and reactivity) to the distal alkyne C atom

Mechanistic Insights of a Selective C-H Alkylation of Alkenes by a Ru-based Catalyst and Alcohols

Density 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 energy

Comparing Ru and Fe-catalyzed olefin metathesis

Density functional theory calculations have been used to explore the potential of Fe-based complexes with an N-heterocyclic carbene ligand, as olefin metathesis catalysts. Apart from a less endothermic reaction energy profile, a small reduction in the predicted upper energy barriers (approximate to 2 kcal mol(-1)) is calculated in the Fe catalyzed profile with respect to the Ru catalysed profile. Overall, this study indicates that Febased catalysts have the potential to be very effective olefin metathesis catalysts

The activation mechanism of Fe-based olefin metathesis catalysts

Density functional theory calculations have been used to describe the first turnover for olefin metathesis reaction of a homogenous Fe-based catalyst bearing a N-heterocyclic carbene ligand with methoxyethene as a substrate. Equal to conventional Ru-based catalysts, the activation of its Fe congener occurs through a dissociative mechanism, however with a more exothermic reaction energy profile. Predicted upper energy barriers were calculated to be on average similar to 2 kcal/mol more beneficial for Fe catalyzed metathesis. Overall, this present computational study emphasises on advantages of Fe-based metathesis and gives a potential recipe for the design of an efficient Fe-based olefin metathesis catalysts. (C) 2014 Elsevier B.V. All rights reserved

The Right Computational Recipe for Olefin Metathesis with Ru-Based Catalysts: The Whole Mechanism of Ring-Closing Olefin Metathesis

The 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 presented; MO6/TZVP//BP86/SVP (PCM, P = 1354 atm)

Catalytic Role of Nickel in the Decarbonylative Addition of Phthalimides to Alkynes

Density 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 steps

Mechanism of CO2 Fixation by Ir-I-X Bonds (X = OH, OR, N, C)

Density functional theory calculations have been used to investigate the CO2 fixation mechanism proposed by Nolan et al. for the Ir-I 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 (R-1 = 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 bonds