Computational Studies of Coinage Metal Anion M− + CH3X (X = F, Cl, Br, I) Reactions in Gas Phase

Abstract

We characterized the stationary points along the nucleophilic substitution (SN2), oxidative insertion (OI), halogen abstraction (XA), and proton transfer (PT) product channels of M− + CH3X (M = Cu, Ag, Au; X = F, Cl, Br, I) reactions using the CCSD(T)/aug-cc-pVTZ level of theory. In general, the reaction energies follow the order of PT > XA > SN2 > OI. The OI channel that results in oxidative insertion complex [CH3–M–X]− is most exothermic, and can be formed through a front-side attack of M on the C-X bond via a high transition state OxTS or through a SN2-mediated halogen rearrangement path via a much lower transition state invTS. The order of OxTS > invTS is inverted when changing M− to Pd, a d10 metal, because the symmetry of their HOMO orbital is different. The back-side attack SN2 pathway proceeds via typical Walden-inversion transition state that connects to pre- and post-reaction complexes. For X = Cl/Br/I, the invSN2-TS’s are, in general, submerged. The shape of this M− + CH3X SN2 PES is flatter as compared to that of a main-group base like F− + CH3X, whose PES has a double-well shape. When X = Br/I, a linear halogen-bonded complex [CH3−X∙··M]− can be formed as an intermediate upon the front-side attachment of M on the halogen atom X, and it either dissociates to CH3 + MX− through halogen abstraction or bends the C-X-M angle to continue the back-side SN2 path. Natural bond orbital analysis shows a polar covalent M−X bond is formed within oxidative insertion complex [CH3–M–X]−, whereas a noncovalent M–X halogen-bond interaction exists for the [CH3–X∙··M]− complex. This work explores competing channels of the M− + CH3X reaction in the gas phase and the potential energy surface is useful in understanding the dynamic behavior of the title and analogous reactions.

Mechanistic Insights into the Proton Transfer and Substitution Dynamics of N-Atom Center Reactions: A Study of CH3O– with NH2Cl

“…16−19 What is particularly exciting is that recent research on OH − + CH 3 F has revealed a novel oxide ion substitution pathway, resulting in products of HF + CH 3 O − . 20 And recent research has expanded to encompass a diverse range of nucleophiles, such as SH − , 21 PH 2 − , 21 CN − , 22,23 NH 2 − , 24 metal ion M − , 25 and HOO − with α-effect. 26 Research has also explored leaving groups 27−29 and solvent effects.…”

“…Since the discovery of the well-known Walden inversion mechanism, , more detailed mechanisms have been elucidated through both experiments and theoretical investigations, including the hydrogen-bonded complex − and the roundabout mechanism. − Moreover, composite mechanisms involving more than one transition state have been revealed, such as the two-transition-state mechanism and the double-inversion mechanism. − What is particularly exciting is that recent research on OH – + CH 3 F has revealed a novel oxide ion substitution pathway, resulting in products of HF + CH 3 O – . And recent research has expanded to encompass a diverse range of nucleophiles, such as SH – , PH 2 – , CN – , , NH 2 – , metal ion M – , and HOO – with α-effect . Research has also explored leaving groups − and solvent effects. − Together, these studies have contributed greatly to our understanding of the S N 2 reactions.…”

Computational Insights into SN2 and Proton Transfer Reactions of CH3O− with NH2Y and CH3Y

“…[2] The ion-molecular S N 2 model has been thoroughly investigated in theory and experiment, starting with the simple six-atom identity reaction (X À + CH 3 Y, X, Y = F, Cl, Br, I). [2a] There are many nucleophiles and leaving groups beyond the basic halogen ones, such as the normal nucleophiles and leaving groups (OH À , SH À , CN À , NH 2 À , PH 2 À , AsH 2 À , SeH À , etc [3] ), the α-nucleophiles [4] (HOO À , H 2 NO À , CH 3 OO À , CH 3 HNO À , HOHN À , etc) and metal anions as nucleophiles [5] M À + CH 3 X (M = Cu, Ag, Au, X = F, Cl, Br, I). S N 2 reactions of different central atoms have also been extensively studied, mainly focusing on second-period elements C, N, O and F, [6] third-period elements Si, [7] P, [8] S [9] and others.…”

“…The traditional conception of Walden inversion (inv‐S N 2) found in textbooks [2a] states that the inversion of the tetrahedron center occurs because the nucleophile attacks haloalkane on the back‐side of the central carbon and the leaving groups depart synchronously. With the gradual research of S N 2 reaction dynamics, more reaction mechanisms have been discovered, such as front‐side attack (ret‐S N 2), [12] roundabout, [12b,13] double inversion, [14] hydrogen‐bonded, [15] ion‐dipole [12b] and halogen‐bonded complexes, [5,15b] proton extraction [3f,14c,16] and oxide ion substitution [17] . Retention and inversion configurations of these mechanisms are distinguished, with retention configurations having only front‐side attack and double‐inversion at higher energy.…”