Computational Investigations on Base-Catalyzed Diaryl Ether Formation

Abstract

We report investigations with the dispersion-corrected B3LYP density functional method on mechanisms and energetics for reactions of group I metal phenoxides with halobenzenes as models for polyether formation. Calculated barriers for ether formation from para-substituted fluorobenzenes are well correlated with the electron-donating or -withdrawing properties of the substituent at the para position. These trends have also been explained with the distortion/interaction energy theory model which show that the major component of the activation energy is the energy required to distort the arylfluoride reactant into the geometry that it adopts at the transition state. Resonance-stabilized aryl anion intermediates (Meisenheimer complexes) are predicted to be energetically disfavored in reactions involving fluorobenzenes with a single electron-withdrawing group at the para position of the arene, but are formed when the fluorobenzenes are very electron-deficient, or when chelating substituents at the ortho position of the aryl ring are capable of binding with the metal cation, or both. Our results suggest that the presence of the metal cation does not increase the rate of reaction, but plays an important role in these reactions by binding the fluoride or nitrite leaving group and facilitating displacement. We have found that the barrier to reaction decreases as the size of the metal cation increases among a series of group I metal phenoxides due to the fact that the phenoxide becomes less distorted in the transition state as the size of the metal increases.

Alkali‐Metal Ion Catalysis and Inhibition in SNAr Displacement: Relative Stabilization of Ground State and Transition State Determines Catalysis and Inhibition in SNAr Reactivity

“…[20] However, their calculations revealed that presence of M + ions increases the barrier height due to formation of stable reactant complexes upon interaction with the fluorobenzenes. [20] Our experimental results, shown in Table 1, appear to be consistent with the computational results reported by Jones et al, since M + ions (except 18C6-crowned K + ion) inhibit the reaction of 7 a and the inhibitory effect increases as the size of www.chemeurj.org M + ions decreases. [20] Our experimental results, shown in Table 1, appear to be consistent with the computational results reported by Jones et al, since M + ions (except 18C6-crowned K + ion) inhibit the reaction of 7 a and the inhibitory effect increases as the size of www.chemeurj.org M + ions decreases.…”

“…[20] Their calculations using DFT methods have shown that M + ions (M + = Li + , Na + , and K + ) complex the fluoride leaving group and facilitate expulsion of the leaving group as modeled by TS III in Scheme 4. [20] Their calculations using DFT methods have shown that M + ions (M + = Li + , Na + , and K + ) complex the fluoride leaving group and facilitate expulsion of the leaving group as modeled by TS III in Scheme 4.…”

“…[20] Their calculations using DFT methods have shown that M + ions (M + = Li + , Na + , and K + ) complex the fluoride leaving group and facilitate expulsion of the leaving group as modeled by TS III in Scheme 4. [20] They also found that the activation energy decreases as the size of M + ions increases, due to the fact that phenoxide becomes less distorted in the TS as the size of M + ions increases. [20] They also found that the activation energy decreases as the size of M + ions increases, due to the fact that phenoxide becomes less distorted in the TS as the size of M + ions increases.…”

The α-Effect in SNAr Reaction of 1-Fluoro-2,4-dinitrobenzene with Hydrazine: Ground-State Destabilization versus Transition-State Stabilization

“…19 Thus, one might suggest that the current reaction would proceed also through a cyclic intermediate as modeled by IV. It is apparent that expulsion of the leaving group from IV could be facilitated through the H-bonding interaction.…”

Alkali-Metal Ion Catalysis and Inhibition in SNAr Reaction of 1-Halo-2,4-dinitrobenzenes with Alkali-Metal Ethoxides in Anhydrous Ethanol

“…Recently, Jones et al have carried out computational investigations on the S N Ar reaction of activated fluorobenzenes with alkali-metal phenoxides. 12 The results their DFT calculations have shown that the presence of alkali-metal ion does not increase the rate of reaction but plays an important role through TS IV , in which M + ion facilitates expulsion of the leaving group.…”