CH3I Reaction Research Articles

Vibrational mode-specificity in the dynamics of the OH- + CH3I multi-channel reaction.

We report a comprehensive characterization of the vibrational mode-specific dynamics of the OH- + CH3I reaction. Quasi-classical trajectory simulations are performed at four different collision energies on our previously-developed full-dimensional high-level abinitio potential energy surface in order to examine the impact of four different normal-mode excitations in the reactants. Considering the 11 possible pathways of OH- + CH3I, pronounced mode-specificity is observed in reactivity: In general, the excitations of the OH- stretching and CH stretching exert the greatest influence on the channels. For the SN2 and proton-abstraction products, the reactant initial attack angle and the product scattering angle distributions do not show major mode-specific features, except for SN2 at higher collision energies, where forward scattering is promoted by the CI stretching and CH stretching excitations. The post-reaction energy flow is also examined for SN2 and proton abstraction, and it is unveiled that the excess vibrational excitation energies rather transfer into the product vibrational energy because the translational and rotational energy distributions of the products do not represent significant mode-specificity. Moreover, in the course of proton abstraction, the surplus vibrational energy in the OH- reactant mostly remains in the H2O product owing to the prevailing dominance of the direct stripping mechanism.

Dynamics of the Cl- + CH3I reaction on a high-level abinitio analytical potential energy surface.

We have developed a full-dimensional analytical abinitio potential energy surface (PES) for the Cl- + CH3I reaction using the Robosurfer program system. The energy points have been computed using a robust composite method defined as CCSD-F12b + BCCD(T) - BCCD with the aug-cc-pVTZ(-PP) basis set and have been fitted by the permutationally invariant polynomial approach. Quasi-classical trajectory simulations on the new PES reveal that two product channels are open in the collision energy (Ecoll) range of 1-80 kcal/mol, i.e., SN2 leading to I- + CH3Cl and iodine abstraction (above ∼45 kcal/mol) resulting in ICl- + CH3. Scattering angle, initial attack angle, product translational energy, and product internal energy distributions show that the SN2 reaction is indirect at low Ecoll and becomes direct-rebound-back-side (CH3-side) attack-type, as Ecoll increases. Iodine abstraction mainly proceeds with direct stripping mechanism with side-on/back-side attack preference. Comparison with crossed-beam experiments and previous direct dynamics simulations shows quantitative or qualitative agreement and also highlights possible theoretical and/or experimental issues motivating further research.

Dynamics of nucleophilic substitution on ambident nucleophiles CN- and iodomethane: insights into the competition mechanism with neutral isomeric products.

Bimolecular nucleophilic substitution (SN2) plays a vital role in organic synthesis. Compared with nucleophiles with one reactive center, ambident nucleophiles can form isomer products. Determining the isomer branching ratios through experiments is difficult, and research on related dynamics characteristics is limited. This study uses dynamics trajectory simulations to explore the dynamics characteristics of the SN2 reaction of ambident nucleophiles CN- and CH3I. The calculated rate constants reproduce the experimental results at room temperature. The dynamics simulations reveal the mechanism of the competition between isomer products CH3CN and CH3NC with a ratio of 0.93 : 0.07. This mechanism is attributed to the height of the central barrier, which strongly stabilizes the transition state of the CH3CN product channel of the formed C-C bond. The product internal energy partitionings and the velocity scattering angle distributions are calculated based on the trajectory simulations, and are in almost agreement with the experimental results obtained at a low collision energy. The dynamics of the title reaction with the ambident nucleophile CN- are also compared with the SN2 dynamics of one reactive center F- and the substrate CH3Y (Y = Cl, I) reactions. This intensive review shows the competition of isomer products for the SN2 reaction of the ambident nucleophile CN- in the current study. This work provides unique insights into reaction selectivity for organic synthesis.

Quasi-classical trajectory study of the OH- + CH3I reaction: theory meets experiment.

Regarding OH- + CH3I, several studies have focused on the dynamics of the reaction. Here, high-level quasi-classical trajectory simulations are carried out at four different collision energies on our recently developed potential energy surface. In all, more than half a million trajectories are performed, and for the first time, the detailed quasi-classical trajectory results are compared with the reanalysed crossed-beam ion imaging experiments. Concerning the previously reported direct dynamics study of OH- + CH3I, a better agreement can be obtained between the revised experiment and our novel theoretical results. Furthermore, in the present work, the benchmark geometries, frequencies and relative energies of the stationary points are also determined for the OH- + CH3I proton-abstraction channel along with the earlier characterized SN2 channel.

Imaging the Atomistic Dynamics of Single Proton Transfer and Combined Hydrogen/Proton Transfer in the O- + CH3I Reaction.

We report on reactive scattering studies of the proton transfer and combined hydrogen/proton transfer in the O- + CH3I reaction. We combine state-of-the-art crossed-beam velocity map imaging and quantum chemistry calculations to understand the dynamics for the formations of the CH2I- + OH and CHI- + H2O products. The experimental velocity- and angle-differential cross section show for both products and at all collision energies (between 0.3 and 2.0 eV) that the product ions are predominantly forward scattered. For the CHI- + H2O channel, the data show lower product velocities, indicative of higher internal excitation, than in the case of single proton transfer. Furthermore, our results suggest that the combined hydrogen/proton transfer proceeds via a two-step process: In the first step, O- abstracts one H atom to form OH-, and then the transient OH- removes an additional proton from CH2I to form the energetically stable H2O coproduct.

Dynamical Effects of SN2 Reactivity Suppression by Microsolvation: Dynamics Simulations of the F-(H2O) + CH3I Reaction on a 21-Dimensional Potential Energy Surface.

A comparison of atomistic dynamics between microsolvated and unsolvated reactions can expose the precise role of solvent molecules and thus provide deep insight into how solvation influences chemical reactions. Here we developed the first full-dimensional analytical potential energy surface of the F-(H2O) + CH3I reaction, which facilitates the efficient dynamics simulations on a quantitatively accurate level. The computed SN2 reactivity suppression ratio of the monosolvated F-(H2O) + CH3I reaction relative to the unsolvated F- + CH3I reaction as a function of collision energy first increases and then decreases steadily, forming an inverted-V shape, due to the combined dynamical effects of interaction time, steric hindrance, and collision-induced dehydration. Moreover, further analysis reveals that the steric effect of the F-(H2O) + CH3I reaction resulting from the single water molecule is manifested mainly in dragging the F- anion away from the central C atom, rather than shielding F- from C. Our study shows there is great potential in rigorously studying the role of the solvent in more complicated reactions.

Kinetic Study of the Oxidative Addition Reaction between Methyl Iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] Complexes, Utilizing UV–Vis, IR Spectrophotometry, NMR Spectroscopy and DFT Calculations

The oxidative addition of methyl iodide to [Rh(β-diketonato)(CO)(PPh)3] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to [Rh(imino-β-diketonato)(CO)(PPh)3] complexes, as observed on UV–Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] and two isomers of [Rh(CH3COCHCNHCH3)(CO)(PPh3)] are observed—in agreement with density functional theory (DFT) calculations. Experimentally the [Rh(CH3COCHCNPhCH3)(CO)(PPh3)] + CH3I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the [Rh(CH3COCHCNHCH3)(CO)(PPh3)] + CH3I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH3I to the two [Rh(imino-β-diketonato)(CO)(PPh)3] complexes of this study was 7–11 times faster than the oxidative addition reaction rate of CH3I to [Rh(CH3COCHCOCH3)(CO)(PPh3)].

Quantum dynamics study of OH−+CH3I reaction: Reaction probability, integral cross section, and energy efficacy

We investigate the reaction probability, integral cross section, and energy efficiency of the OH−+CH3I reaction using the time-dependent quantum dynamics wave packet method. A four-degree-of-freedom dynamics model is developed for this study due to the synchronized SN2 bond-breaking and formation mechanism. We find that the reaction probability decreases as a function of the collision energy, which is a typical character of reactions with a negative energy barrier. The ground-state integral cross section calculated using this model is in excellent agreement with the quasi-classical trajectory results. The integral cross-section ratios of the vibrational excitations over the ground state, at the same equal amount of total energy, indicate that the vibrational motion of the CH3–I is more efficient in enhancing the reactivity than the translational motion, which, in turn, has a bigger contribution to the reactivity than the C–H3 vibrational motion. The energy efficacy order in the reactivity is confirmed by the sudden vector model prediction.

Different interactions of gaseous CH3I with both Ag nanoparticles and Ag+ ions included in mercaptopropyl functionalized silica gels

Mercaptopropyl functionalized silica gels were prepared and interacted with Ag0 nanoparticles and Ag+ ions. After that, these gels were all exposed to gaseous CH3I. To investigate the silver oxidation states and interactions with the surrounding gels, peak shifts were observed using X-ray photoelectron spectroscopy. The cleavage of mercaptopropyl during the electron-beam irradiation applied for Ag0 nanoparticle production was also discussed. The produced Ag nanoparticles formed covalent bonds with the mercaptopropyls. However, in this study, decomposition of the gaseous CH3I was not observed, and the CH3I remained on the surfaces of the Ag nanoparticles. On the other hand, Ag+ ions formed ionic bonds with the mercaptopropyls, and the physisorption of gaseous CH3I on the Ag+ ions occurred. Thereafter, the gaseous CH3I was decomposed by UV light, and the Ag+ ions and iodide interacted to form AgI. Different reactions of gaseous CH3I were observed depending on the oxidation states of the silver.

Direct dynamics simulations on the atomic mechanisms of 4O+ + CH3I reaction

The reactions of oxygen radical cation O+ with haloalkanes are of importance in gas phase ion chemistry, but the studies on reactive patterns and dynamics are quite limited. In this work, the direct dynamics simulations have been carried out at the B3LYP/ECP/d level of theory for 4O+ + CH3I reaction at Ecoll = 4.5 eV, and the results are compared with the available experiments. The properties of stationary points on the potential energy surface for 4O+ + CH3I reaction have been characterized and supplemented in terms of our simulations. Variety of atomic reaction mechanisms are revealed and are found to be energetically accessible at high collision energy, including charge transfer, dissociative charge transfer, proton transfer, substitution, and complex rearrangement, which exclusively proceed by direct mechanism due to the high collision energy. Our work has confirmed the existence of the charge transfer product CH3I+, which is highly exothermic. The major product CH3+ can be produced in concert with IO molecule, besides the dissociative charge transfer process of CH3I+. Similarly, including the possible dissociation of CH3I+, product I+ can be formed by substitution reaction. Some trace products, i.e., CH2I+, H2CO+, and CH3O+, are also found in our simulations. This work is expected to enrich our understanding of the significant atmospheric concentrations of these methyl halides and their anthropogenic origins.

1,1′-2-Trisubstituted ferrocenyl dibismuthines containing N / O donor pendant arm

New unsymmetrical chiral 1,1′-2-ferrocenyl dibismuthines [(C5H4)(BiPh2)]Fe(2-{Me2NCH(R)}C5H3)(BiPh2) containing 2-[(Me2NCH(R)] where R = Me (1) or H (3) pendant arm on ferrocenyl ring were synthesized. An unsymmetrical 1,1′-ferrocenyl-bismuthine (5) in a low yield and 1,1′-2-ferrocenyl chlorodibismuthine (11) as an impurity were also isolated from the reaction mixture. Furthermore, Monoammonium salt [CpFe{2-(Me3N+CH2)C5H3}(BiPh2)2][I−] (6) and 1,1´,2-vinylferrocenyl dibismuthine derivative (7) were obtained by the reaction of CH3I with (3) and (1) respectively. The nucleophilic substitution reaction of (6) by o-hydroxyacetaphenone, salicylaldehyde, and N-methyl piperazine in acetonitrile gave the new functionalized 1,1′-2-substituted ferrocenyl dibismuthines [(C5H4)(BiPh2)]Fe[{2-(RCH2)C5H3}BiPh2] where R = OC6H4-2-C(O)Me (8), OC6H4-2-C(O)H (9) and N(CH2CH2)2NMe (10) respectively with different N or O containing pendant arm. 1,2-disubstituted ferrocenyl compounds presented in this work present planar chirality. These new compounds were characterized by IR, 1H-NMR, 13C-NMR spectroscopy, and High-Resolution Mass Spectrometry (HRMS). The X-ray structures of 1,1´,2-trisubstituted ferrocenyl dibismuthines (10) and (11) were determined. The molecular structure of (11) shows hypervalent Bi···N bonding in the solid-state. The compound (11) has planar chirality, central chirality, and Bi center-chirality with pseudo-trigonal bipyramidal geometry (see-saw structure) around the chiral Bi center while the other bismuth atom has distorted trigonal pyramidal geometry. The variable temperature 1H-NMR spectra of compound (3) in −40°C to 40°C range in CDCl3 indicates a lack of Bi···N coordination.

Imaging Reaction Dynamics of F-(H2O) and Cl-(H2O) with CH3I.

The dynamics of microhydrated nucleophilic substitution reactions have been studied using crossed beam velocity map imaging experiments and quasiclassical trajectory simulations at different collision energies between 0.3 and 2.6 eV. For F–(H2O) reacting with CH3I, a small fraction of hydrated product ions I–(H2O) is observed at low collision energies. This product, as well as the dominant I–, is formed predominantly through indirect reaction mechanisms. In contrast, a much smaller indirect fraction is determined for the unsolvated reaction. At the largest studied collision energies, the solvated reaction is found to also occur via a direct rebound mechanism. The measured product angular distributions exhibit an overall good agreement with the simulated angular distributions. Besides nucleophilic substitution, also ligand exchange reactions forming F–(CH3I) and, at high collision energies, proton transfer reactions are detected. The differential scattering images reveal that the Cl–(H2O) + CH3I reaction also proceeds predominantly via indirect reaction mechanisms.

Uncovering the role of the stationary points in the dynamics of the F- + CH3I reaction.

We describe an analysis method which assigns geometries to stationary points along (quasi)classical trajectories. The method is applied to the F- + CH3I reaction, thereby uncovering the role of the minima and transition states in the dynamics of the SN2 inversion, SN2 retention via front-side attack and double inversion, induced inversion, and proton-transfer channels. Stationary-point probability distributions, stationary-point-specific trajectory orthogonal projections, root-mean-square distance distributions, transition probability matrices, and time evolutions of the stationary points reveal long-lived front-side (F-ICH3) and hydrogen-bonded (F-HCH2I) complexes in the entrance channel and significant post-reaction ion-dipole complex (FCH3I-) formation in the SN2 exit channel. Most of the proton-transfer stationary points (FHCH2I-) participate in all the reaction channels with larger distance deviations than the double-inversion transition state. Significant forward-backward transitions are observed between the minima and transition states indicating complex, indirect dynamics. The utility of distance and energy constraints is also investigated, thereby restricting the assignment into uniform configuration or energy ranges around the stationary points.

High-Level-Optimized Stationary Points for the F-(H2O) + CH3I System: Proposing a New Water-Induced Double-Inversion Pathway.

We report 29 stationary points for the F-(H2O) + CH3I reaction obtained by using the high-level explicitly correlated CCSD(T)-F12b method with the aug-cc-pVDZ basis set for the determination of the benchmark structures and frequencies and the aug-cc-pVQZ basis for energy computations. The stationary points characterize the monohydrated F-- and OH--induced Walden-inversion pathways and, for the first time, the front-side attack and F--induced double-inversion mechanisms leading to CH3F with retention as well as the novel H2O-induced double-inversion retention pathway producing CH3OH. Hydration effectively increases the relative energies of the stationary points, but the monohydrated inversion pathways are still barrierless, whereas the front-side attack and double-inversion barrier heights are around 30 and 20 kcal/mol, respectively.

Theoretical Study of the Reactions of H Atoms with CH3I and CH2I2.

High level ab initio methods have been used to provide reliable kinetic data for the H + CH3I and H + CH2I2 gas-phase reactions. The (H, I)-abstraction and I-substitution reaction pathways were identified. The structures were determined on the potential energy surface at the MP2/aug-cc-pVTZ level of theory. The energetics was then refined using the coupled cluster theory. For the iodinated species, the spin-orbit coupling was calculated using the MRCI approach. The core valence and the scalar relativistic corrections were considered. Thermal rate constants were reported using the canonical transition-state theory (TST) and compared to computed values with the canonical variational transition-state theory (CVT) using the zero curvature tunneling (ZCT) and the small curvature tunneling (SCT) corrections over a wide temperature range (250-2500 K) to show the importance of quantum tunneling effects at low temperatures. They are given by the following expressions for the overall reactions using the CVT/SCT method: kH+CH3I( T) = 1.07 × 10-17 × T2.13 exp(2.68 (kJ mol-1)/ RT) and kH+CH2I2( T) = 5.73 × 10-21 × T2.97 exp(3.15 (kJ mol-1)/ RT). The I-abstraction is predicted to be the major pathway for both H + CH3I and H + CH2I2 reactions. The obtained kinetic parameters for the H + CH3I reaction are in excellent agreement with their experimental counterparts over the temperature range 300-750 K. On the basis of our calculated reaction enthalpies, a new evaluation of the standard enthalpy of formation at 298 K of CH2I and CHI2 has been provided. Obtained values are Δf H°298K (CH2I) = 219.5 kJ mol-1 and Δf H°298K(CHI2) = 296.3 kJ mol-1.

Effects of the Level of Electronic Structure Theory on the Dynamics of the F- + CH3I Reaction.

Accuracy of the different levels of electronic structure theory is frequently studied for stationary-point properties; however, little is known about the effects of the electronic structure methods and basis sets on the dynamics of chemical reactions. Here we report such an investigation for the F- + CH3I SN2 and proton-transfer reactions by developing 20 different analytical potential energy surfaces (PESs) obtained at the HF/DZ, HF/TZ, HF-D3(BJ)/DZ, HF-D3(BJ)/TZ, MP2/DZ, MP2/TZ, MP2-F12/DZ, MP2-F12/TZ, CCSD/DZ, CCSD-F12b/DZ, CCSD(T)/DZ, CCSD(T)-F12b/DZ, OQVCCD(T)/DZ, B97-1/TZ, PBE0/TZ, PBE0-D3(BJ)/TZ, M06-2X/TZ, M06-2X-D3(0)/TZ, B2PLYP/TZ, and B2PLYP-D3(BJ)/TZ levels of theory, where DZ and TZ denote the aug-cc-pVDZ and aug-cc-pVTZ basis sets with a relativistic effective core potential and the corresponding bases for iodine. Millions of quasiclassical trajectories on these PESs reveal that (a) in the case of standard methods, increasing the basis from DZ to TZ decreases the SN2 cross sections by 20-30%; (b) the explicitly correlated F12 reactivity is converged with a DZ basis;

Kinetic Studies of Oxidative Addition Reaction of Arylplatinum(II) Complex Containing 4,4′‐Bipyridine and Calculation of Activation Parameters

ABSTRACTNew complexes of arylplatinum(II) and arylplatinum(IV) containing a bridging ligand, 4,4′‐bipyridine, were synthesized by the reaction of starting material of platinum(II) including para‐tolyl groups,[(p‐MeC6H4)2Pt(SMe2)2], with the 4,4′‐bipyridine ligand in 1:1 molar stoichiometry. In the synthesized complexes, the ligand was bonded to the platinum center through the nitrogen donor atoms. To investigate the kinetic reaction of the platinum(II) complex with iodomethane (CH3‐I) as a reagent, the oxidative addition reaction of this reagent with Pt(II) was performed in dichloromethane and a Pt(IV) complex with the octahedral geometry was formed. The synthesized complexes have been characterized by different spectroscopic methods such as FT‐IR, 1H NMR, UV–vis, and elemental analysis. Moreover, the conductivity measurements showed nonelectrolyte characteristics for these complexes. The obtained data showed that the complexes have 1:1 metal‐to‐ligand molar ratio. Also, the oxidative addition reaction of CH3I with the arylplatinum(II) complex at different temperatures was used for obtaining kinetic parameters such as rate constants, activation energy, entropy, and enthalpy of activation using the Microsoft Excel solver. From the acquired data, an SN2 mechanism was suggested for the oxidative addition reaction.

Benchmark ab Initio Characterization of the Complex Potential Energy Surface of the Cl- + CH3I Reaction.

Benchmark stationary-point structures, vibrational frequencies, and classical/adiabatic relative energies (kcal/mol) are reported for the Cl- + CH3I reaction along the back-side attack (ΔETS = -5.48/-5.54) inversion, front-side attack (ΔETS = 36.73/35.89) and double-inversion (ΔETS = 46.97/42.55) retention SN2 pathways, the proton-transfer channel, and the hydride-substitution reaction path. The structures and frequencies are obtained by the frozen-core CCSD(T), CCSD(T)-F12a, and CCSD(T)-F12b methods with the aug-cc-pVnZ [n = D, T, and Q for structures and n = D and T for frequencies] basis sets and all-electron CCSD(T) with aug-cc-pwCVnZ [n = D and T for structures and n = D for frequencies]. The benchmark relative energies are determined using the focal-point analysis approach based on electron correlation methods up to CCSDT(Q), extrapolations to the complete basis set limits using aug-cc-pVnZ [n = 2(D), 3(T), 4(Q), and 5] bases, core correlation contributions obtained at CCSD(T)/aug-cc-pwCVQZ, and, for the adiabatic energies, zero-point energy corrections at the CCSD(T)-F12b/aug-cc-pVTZ level of theory. We usually find significant method and modest basis dependence for the energies. The post-CCSD(T) and core correlation effects are often about 0.4 kcal/mol, but almost cancel each other. The explicitly correlated CCSD(T)-F12 methods are recommended for geometry and frequency computations as well as for energy computations if the basis set dependence is significant.

Deciphering Front-Side Complex Formation in SN2 Reactions via Dynamics Mapping.

Due to their importance in organic chemistry, the atomistic understanding of bimolecular nucleophilic substitution (SN2) reactions shows exponentially growing interest. In this publication, the effect of front-side complex (FSC) formation is uncovered via quasi-classical trajectory computations combined with a novel analysis method called trajectory orthogonal projection (TOP). For both F- + CH3Y [Y = Cl,I] reactions, the lifetime distributions of the F-···YCH3 front-side complex revealed weakly trapped nucleophiles (F-). However, only the F- + CH3I reaction features strongly trapped nucleophiles in the front-side region of the prereaction well. Interestingly, both back-side and front-side attack show propensity to long-lived FSC formation. Spatial distributions of the nucleophile demonstrate more prominent FSC formation in case of the F- + CH3I reaction compared to F- + CH3Cl. The presence of front-side intermediates and the broad spatial distribution in the back-side region may explain the indirect nature of the F- + CH3I reaction.

Temperature and Pressure Dependences of the Reactions of Fe+ with Methyl Halides CH3X (X = Cl, Br, I): Experiments and Kinetic Modeling Results.

The pressure and temperature dependences of the reactions of Fe+ with methyl halides CH3X (X = Cl, Br, I) in He were measured in a selected ion flow tube over the ranges 0.4 to 1.2 Torr and 300-600 K. FeX+ was observed for all three halides and FeCH3+ was observed for the CH3I reaction. FeCH3X+ adducts (for all X) were detected in all reactions. The results were interpreted assuming two-state reactivity with spin-inversions between sextet and quartet potentials. Kinetic modeling allowed for a quantitative representation of the experiments and for extrapolation to conditions outside the experimentally accessible range. The modeling required quantum-chemical calculations of molecular parameters and detailed accounting of angular momentum effects. The results show that the FeX+ products come via an insertion mechanism, while the FeCH3+ can be produced from either insertion or SN2 mechanisms, but the latter we conclude is unlikely at thermal energies. A statistical modeling cannot reproduce the competition between the bimolecular pathways in the CH3I reaction, indicating that some more direct process must be important.