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 (S_N2), 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 > S_N2 > 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 S_N2-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 S_N2 pathway proceeds via typical Walden-inversion transition state that connects to pre- and post-reaction complexes. For X = Cl/Br/I, the invS_N2-TS's are, in general, submerged. The shape of this M^- + CH₃X S_N2 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 S_N2 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.

SUBMITTER: Wang F 

PROVIDER: S-EPMC8746851 | biostudies-literature |

REPOSITORIES: biostudies-literature