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Origin of Salt Effects in SN2 Fluorination Using KF Promoted by Ionic Liquids: Quantum Chemical Analysis.

ABSTRACT: Quantum chemical analysis is presented, motivated by Grée and co-workers' observation of salt effects [Adv. Synth. Catal. 2006, 348, 1149-1153] for SN2 fluorination of KF in ionic liquids (ILs). We examine the relative promoting capacity of KF in [bmim]PF6 vs. [bmim]Cl by comparing the activation barriers of the reaction in the two ILs. We also elucidate the origin of the experimentally observed additional rate acceleration in IL [bmim]PF6 achieved by adding KPF6. We find that the anion PF6- in the added salt acts as an extra Lewis base binding to the counter-cation K+ to alleviate the strong Coulomb attractive force on the nucleophile F-, decreasing the Gibbs free energy of activation as compared with that in its absence, which is in good agreement with experimental observations of rate enhancement. We also predict that using 2 eq. KF together with an eq. KPF6 would further activate SN2 fluorination.

SUBMITTER: Oh YH

PROVIDER: S-EPMC8510065 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Origin of Salt Effects in SN2 Fluorination Using KF Promoted by Ionic Liquids: Quantum Chemical Analysis.

Oh Young-Ho YH Lee Sungyul S

Molecules (Basel, Switzerland) 20210922 19

Quantum chemical analysis is presented, motivated by Grée and co-workers' observation of salt effects [Adv. Synth. Catal. 2006, 348, 1149-1153] for SN2 fluorination of KF in ionic liquids (ILs). We examine the relative promoting capacity of KF in [bmim]PF6 vs. [bmim]Cl by comparing the activation barriers of the reaction in the two ILs. We also elucidate the origin of the experimentally observed additional rate acceleration in IL [bmim]PF6 achieved by adding KPF< ...[more]

PMID: 34641282

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