Facile Preparation of Tetrabutylphosphonium Fluoride and Its HF Adducts. New Fluoride Anion Sources for Selective Nucleophilic Fluorination

Abstract

Anhydrous tetrabutylphosphonium hydrogen bifluoride (2), dihydrogen trifluoride prepared from aq. tetrabutylphosphonium hydroxide and aq. HF, and tetrabutylphosphonium fluoride prepared from 2 and BunLi were shown to be useful fluoride sources for selective nucleophilic fluorination of oxiranes, alkyl halides, alcohols and sulfonates of aliphatic and steroidal species.

Influence of Hydrogen Bonding in the Activation of Nucleophiles: PhSH−(Catalytic) KF in N-Methyl-2-pyrrolidone as an Efficient Protocol for Selective Cleavage of Alkyl/Aryl Esters and Aryl Alkyl Ethers under Nonhydrolytic and Neutral Conditions

“…The lesser catalytic effect of KHF 2 compared to that of KF is in conformity with the fact that the increase in the degree of protonation (e.g. F - , HF - , and H 2 F 3 - ) decreases the global reactivity whereas the ineffectiveness of NH 4 HF 2 may be the result of the increased degree of protonation in association with the “suicidal” hydrogen bonding of the fluoride anion with NH 4 + (resulting in catalyst poisoning). That the effective nucleophilic species is the thiolate anion is proved by the fact that no significant amount of ester cleavage takes place by the use of stoichiometric amount of KF, NaF, and KHF 2 in the absence of thiol (entries 8, 13, and 24, respectively, Table ).…”

Hexaalkylguanidinium and 2-(Dialkylamino)-1,3-dimethylimidazolinium Trimethyldifluorosiliconates and Perfluoroalkoxides. Accidental Isolation and Molecular Structure of [C(NMe2)3]+F-·6CH2Cl2

“…Among the most commonly used methods of introducing fluorine and fluorinated moieties into organic and inorganic molecules are nucleophilic displacement reactions requiring a respective reagent of reasonable high solubility in aprotic organic solvents, e.g. fluorides with lipophilic counterions Q + = Alk 4 N + , {[(Me 2 N) 3 P] 2 N} + , [S(NMe 2 ) 3 ] + (TAS + ), [C(NMe 2 ) 3 ] + (HMG + ), TDAE 2+ (TDAE = tetrakis(dimethylamino)ethylene), [P(NAlk 2 ) 4 ] + , and Bu 4 P + . − The onium fluorides with the best solubility in THF or monoglyme contain at least one phosphorus atom: {[(Me 2 N) 3 P] 2 N} + F - ; [P(NAlk 2 ) 4 ] + F - ; Bu 4 P + F - . An increasing countercation size also decreases the Q + F - lattice energy, favorable for the nucleophilic fluorination and perfluoroalkoxylation, too. , The advantages of Me 4 N + F - (TMAF) are the high thermal and chemical stability of the Me 4 N + cation and the high nucleophilicity of the very weak solvated fluoride ion. − A drawback of this salt is its low solubility in etheral solvents.…”

Computational and Experimental Studies of Regioselective SNAr Halide Exchange (Halex) Reactions of Pentachloropyridine

“…The subsequent reverse Halex reaction of 2,3,5,6-F 4 at the 2-position had a calculated Δ H ⧧ value of 33.0 kcal/mol and was not observed at this temperature. The resulting n -Bu 4 PF from this reverse Halex reaction would instead be expected to react with 2,3,5,6-F 4 at the 4-position (Δ H ⧧ = 12.7 kcal/mol) to regenerate F 5 much more quickly than it would react with 2,4,6-F 3 at the 3-position (Δ H ⧧ = 23.8 kcal/mol). Because of these relative differences in enthalpies of activation, this equilibrium lay toward the starting materials, F 5 and 2,4,6-F 3 .…”

“…Figure9. Comparison of the relative thermodynamic product distribution in the equilibration of F 5 and 2,4,6-F 3 for experimental (red)33 and computed (blue) data at 520 °C.…”