Yong-Cheng Wang

A DFT study on the mechanism of gold(III)-catalyzed synthesis of highly substituted furans via [3,3]-sigmatropic rearrangements and/or [1,2]-acyloxy migration based on propargyl ketones

The mechanisms of gold(III)-catalyzed synthesis of highly substituted furans via [3,3]-sigmatropic rearrangements and/or [1,2]-acyloxy migration based on propargyl ketones have been investigated using density functional theory calculations at BHandHLYP/6-31G(d,p) (SDD for Au) level of theory. Solvent effects on these reactions were explored using calculations that included a polarizable continuum model (PCM) for the solvent (toluene). Two plausible pathways that lead to the formation of Au(III) vinyl carbenoid and an allenyl structure through [3,3]-sigmatropic rearrangements, [1,2]-acyloxy migration via oxirenium and dioxolenylium were performed. Our calculated results suggested: (1) the major pathway of the cycle causes an initial Rautenstrauch-type [1,2]-migration via oxirenium to form an Au(III) vinyl carbenoid. Subsequent cycloisomerization of this intermediate then provides the corresponding furan whether for the methyl-substituted propargylic acetates or the phenyl-substituted propargylic acetates; (2) for the methyl-substituted propargylic acetates, the formation of Au(III) vinyl carbenoid structures was the rate-determining step. However, intramolecular nucleophilic attack and subsequent cycloisomerization to give the final product was rate-determining for the phenyl-substituted propargylic acetates. The computational results are consistent with the experimental observations of Gevorgyan, et al. for gold(III)-catalyzed synthesis of highly substituted furans based on propargyl ketones.

CH4 activation by W atom in the gas phase: a case of two-state reactivity process.

Gas-phase methane activation by tungsten (W) atoms was studied at the density functional level of theory using the hybrid exchange correlation functional B3LYP. Four reaction profiles corresponding to the septet, quintet, triplet, and singlet multiplicities were investigated in order to ascertain the presence of some spin inversion during the methane activation. Methane activation mediated by W atoms was found to be a spin-forbidden process resulting from the crossing among the multistate energetic profiles. On the basis of the Hammond postulate, this is a typical two-state reactivity (TSR) reaction. The minimum energy crossing points lead to decrease in the barrier heights of TS01, TS12, TS23, and TS24 that correspond to the first, second, and third hydrogen transfer and the reductive elimination step of H(2), respectively. The spin-orbit coupling is calculated between electronic states of different multiplicities at the crossing points (MECPs) to estimate the intersystem crossing probabilities, and the probability of hopping from one surface to the other in the vicinity of the crossing region is calculated by the Landau-Zener type model.

Methane activation by MH+ (M = Os, Ir, and Pt) and comparisons to the congeners of MH+ (M = Fe, Co, Ni and Ru, Rh, Pd).

The mechanism of ligated-transition-metal- [MH(+) (M = Os, Ir, and Pt)] catalyzed methane activation has been computed at the B3LYP level of density functional theory. The B3LYP energies of important species on the potential energy surfaces were compared to CCSD(T) single-point energy calculations. Newer kinetic and dispersion-corrected methods such as M05-2X provide significantly better descriptions of the bonding interactions. The reactions take place more easily along the low-spin potential energy surface. The minimum-energy pathway proceeds as MH(+) + CH(4) → M(H)(2)(CH(3))(+) → TS → MH(CH(2))(H(2))(+) → MH(CH(2))(+) + H(2). The ground states are (5)Π, (4)Σ(-), and (1)Σ(+) for OsH(+), IrH(+), and PtH(+), respectively. The energy level differences of the reactants between the high- and low-spin states gradually become smaller from OsH(+) to PtH(+), being 30.66, 9.17, and 0.09 kcal/mol, respectively. The C-H bond can be readily activated by MH(+) (M = Os, Ir, and Pt) with a negligible barrier in the low-spin state; thus, OsH(+), IrH(+), and PtH(+) are likely to be excellent mediators for the activition of the C-H bond of methane. H(2) elimination is quite facile without barriers in the presence of excess reactants. The products of the reactions of MH(+) (M = Os, Ir, and Pt) + methane are all carbene complexes MH(CH(2))(+). The exothermicities of the reactions are 3.99, 15.66, and 12.14 kcal/mol, respectively. The results for MH(+) (M = Os, Ir, and Pt) are compared with those for the first- and second-row congeners, and the differences in behavior and mechanism are discussed.

Density functional study of SN2 substitution reactions for CH3Cl + CX1X2•− (X1X2 = HH, HF, HCl, HBr, HI, FF, ClCl, BrBr, and II)†

A systematic investigation on the SN2 displacement reactions of nine carbene radical anions toward the substrate CH3Cl has been theoretically carried out using the popular density functional theory functional BHandHLYP level with different basis sets 6‐31+G (d, p)/relativistic effective core potential (RECP), 6‐311++G (d, p)/RECP, and aug‐cc‐pVTZ/RECP. The studied models are CX1X2•− + CH3Cl → X2X1CH3C• + Cl−, with CX1X2•− = CH2•−, CHF•−, CHCl•−, CHBr•−, CHI•−, CF2•−, CCl2•−, CBr2•−, and CI2•−. The main results are proposed as follows: (a) Based on natural bond orbital (NBO), proton affinity (PA), and ionization energy (IE) analysis, reactant CH2•− should be a strongest base among the anion‐containing species (CX1X2•−) and so more favorable nucleophile. (b) Regardless of frontside attacking pathway or backside one, the SN2 reaction starts at an identical precomplex whose formation with no barrier. (c) The back‐SN2 pathway is much more preferred than the front‐SN2 one in terms of the energy gaps [ΔE  cent≠ (front)−ΔE  cent≠ (back)], steric demand, NBO population analysis. Thus, the back‐SN2 reaction was discussed in detail. On the one hand, based on the energy barriers (ΔE  cent≠ and ΔE  ovr≠ ) analysis, we have strongly affirmed that the stabilization of back attacking transition states (b‐TSs) presents increase in the order: b‐TS‐CI2 < b‐TS‐CBr2 < b‐TS‐CCl2 < b‐TS‐CHI < b‐TS‐CHBr < b‐TS‐CHCl < b‐TS‐CF2 < b‐TS‐CHF < b‐TS‐CH2. On the other hand, depended on discussions of the correlations of ΔE  ovr≠ with influence factors (PA, IE, bond order, and ΔE  def≠ ), we have explored how and to what extent they affect the reactions. Moreover, we have predicted that the less size of substitution (α‐atom) required for the gas‐phase reaction with α‐nucleophile is related to the α‐effect and estimated that the reaction with the stronger PA nucleophile, holding the lighter substituted atom, corresponds to the greater exothermicity given out from reactants to products.

Theoretical investigation for the cycle reaction of N2O (x1∑+) with CO (1∑+) catalyzed by IrO(n)+ (n = 1, 2) and utilizing the energy span model to study its kinetic information.

The mechanisms of the reactions between N(2)O and CO catalyzed by IrO(n)(+) (n = 1, 2) have been investigated using B3LYP and CCSD(T) levels of theory. Spin inversion among three reaction profiles corresponding to the quintet, triplet, and singlet multiplicities was discussed by using spin-orbit coupling (SOC) calculations. The probability of electron hopping in the vicinity of the (MECP) has been calculated by the Landau-Zener-type model. The single P(1)(ISC) and double P(2)(ISC) passes estimated at MECP1(#) (SOC = 198.61 cm(-1)) are approximately 0.11 and 0.20, respectively. Important analysis and explanations were done using molecular orbital theory and natural bonding orbital (NBO). The energetic span (δE) model coined by Kozuch was applied in this cycle. The turnover frequency (TOF)-determining transition state (TDTS) and TDI (TOF-determining intermediate) were confirmed. Finally, TOF(IrO(+))/TOF(IrO(2)(+)) = 0.38 at 298 K.

Density Functional Theory Studies of Thermal Activation of Methane by MH+ (M = Ru, Rh, and Pd)

The dehydrogenation reaction mechanisms of methane catalyzed by a ligated transition metal MH(+) (M = Ru, Rh, and Pd) have been investigated theoretically. Activation of methane by MH(+) complexes is proposed to proceed in a one-step manner via one transition state: MH(+) + CH(4) --> MH(+)CH(4) --> [TS] --> (MCH(3)(+))H(2) -->MCH(3)(+) + H(2). Both high-spin and low-spin potential energy surfaces are characterized in detail. Our calculations indicate that the ground-states species have low electron spin and a dominant 4d(n) configuration for RuH(+), RhH(+), and PdH(+), and the whole reaction proceeds on the ground-states potential energy surfaces with a spin-allowed manner. The MH(+) (M = Ru, Rh, and Pd) complexes are expected from the general energy profiles of the reaction pathways to efficiently convert methane to metal methyl, thus RuH(+), RhH(+), and PdH(+) are likely to be excellent mediators for the activity of methane. In the reactions of MH(+) with methane, the H(2) elimination from the dihydrogen complex is quite facile without barriers. The exothermicities of the reactions are close for Ru, Rh, and Pd: 11.1, 1.2, and 5.2 kcal/mol, respectively.

Theoretical Study on the Reaction Mechanism of Ti with CH3CN in the Gas Phase

To gain a deeper understanding of the reaction mechanisms of Ti with acetonitrile molecules, the triplet and singlet spin-state potential energy surfaces (PESs) has been investigated at B3LYP level of density functional theory (DFT). Crossing points between the different PESs and possible spin inversion processes are discussed by spin-orbit coupling (SOC) calculation. In addition, the bonding properties of the species along the reaction were analyzed by electron localization function (ELF), atoms in molecules (AIM) and natural bond orbital (NBO). The results showed that acetonitrile activation by Ti is a typical spin-forbidden process; larger SOC (by 220.12 cm(-1)) and the possibility of crossing between triplet and singlet imply that intersystem crossing (ISC) would occur near the minimum energy crossing point (MECP) during the transfer of the hydrogen atom.

Theoretical study of Ni+ assisted CC and CH bond activations of propionaldehyde in the gas phase

Graphical abstract

Theoretical study of spin-orbit coupling and intersystem crossing in the two-state reaction between Nb(NH2)3 and N2O

The two-state mechanism of the reaction of Nb(NH2)3 with N2O on the singlet and triplet potential energy surfaces has been investigated at the B3LYP level. Crossing points between the potential energy surfaces have been located using different methods. Analysis of the strain model shows that the singlet state of the four-coordinate (N2O)Nb(NH2)3 complex with N2O bonded via terminal N atom coordination (12) is more stable in the initial stage of reaction, since the bending of the N2O fragment [Edef(N2O) = 86.1 kcal mol−1] results in an energy splitting of the doubly degenerate LUMO; the low-energy LUMO can now strongly couple with the occupied Nb-localized d orbitals, forming a back-bond and transferring charge (q = 0.82 e) from Nb(NH2)3 to the N2O ligand. Going from 32 to 12, the reacting system changes spin multiplicity near the MECP (minimal energy crossing point) region, which takes place with a spin crossing barrier of 9.6–10.0 kcal mol−1. Analysis of spin-orbit coupling (SOC) indicates that MECP will produce a significant SOC matrix element. The value of SOC is 111.52 cm−1, due to the electron shift between two perpendicular ϕ orbitals with the same rotation direction, and the magnitude of the spin-multi-plicity mixing increases in the small energy gap between high- and low-spin states, greatly enhancing the probability of intersystem crossing. The probabilities of single (P1ISC) and double (P2ISC) passes estimated at MECP (SOC = 111.52 cm−1) are approximately 1.17×10−2 and 2.32×10−2, respectively.

Reaction mechanism and chemoselectivity of gold(I)-catalyzed cycloaddition of 1-(1-alkynyl) cyclopropyl ketones with nucleophiles to yield substituted furans

The mechanisms of gold(I)-catalyzed cycloaddition of 1-(1-alkynyl) cyclopropyl ketones with nucleophiles have been investigated using density functional theory calculations at the B3LYP/6-31G (d, p) level of theory. A polarizable continuum model (PCM) has been established in order to evaluate the effects of solvents on the reactions. The results of the calculations indicate that the first step of the catalytic cycle is the cyclization of the carbonyl oxygen onto the triple bond which forms a new and stable resonance structure of an oxonium ion and a carbocation intermediate. The subsequent ring expansion step results in the formation of the final product and regeneration of the catalyst. Furthermore, the regioselectivity and effect of substituents has been discussed, including an analysis of energy, bond length, and natural bond orbital (NBO) charge distributions in the rate-determining step. Our computational results are consistent with earlier experimental observations.