From cyclic (alkyl)(amino)carbene (CAAC) precursors to fluorinating reagents : experimental and theoretical study

Gruden, Evelin (author), Prinčič, Griša Grigorij (author), Hočevar, Jan (author), Iskra, Jernej (author), Kvíčala, Jaroslav (author), Tavčar, Gašper (author)

Addition of anhydrous HF to the hydrochloride [$^{Me}$CAACH][Cl(HCl)$_{0.5}$] resulted in the formation of salts with high HF content. By stepwise removal of HF in vacuo, we selectively prepared [$^{Me}$CAACH][F(HF)$_2$] (3) and [$^{Me}$CAACH][F(HF)$_3$] (4). We also characterised a salt with [F(HF)$_4$]$^−$ anions within the structure of [$^{Me}$CAACH][F(HF)$_{3.5}$] (5). Compounds with a lower content of HF were not accessible under vacuum conditions. $^{Me}$CAAC(H)F (1) was selectively prepared by abstraction of HF from 3 with CsF or KF, while [$^{Me}$CAACH][F(HF)] (2) was prepared by mixing 3 and 1 in a 1 : 1 ratio. Compound 2 proved to be quite unstable as it tends to disproportionate into 1 and 3. This observation triggered our computational study, in which the structural relationships between CAAC-based fluoropyrrolidines and dihydropyrrolium fluorides were investigated using different DFT methods. The study showed that the results were very sensitive to the computational method used. For a correct description, the quality of the triple-ζ basis set was crucial. Surprisingly, the isodesmic reaction of [$^{Me}$CAACH][F] + [$^{Me}$CAACH][F(HF)$_2$] → [$^{Me}$CAACH][F(HF)] + [$^{Me}$CAACH][F(HF)] did not confirm the low thermodynamic stability of 2. Furthermore, the use of 3 as a nucleophilic fluorinating reagent was tested on a range of organic substrates, as it is the most stable compound in this series. It was found to have the potential to fluorinate benzyl bromides, 1- and 2-alkyl bromides, silanes and sulfonyls with good to excellent yields of the target fluorides.

• Language: English
• Keywords: CAAC precursor, fluorinating reagent, polyhydrogen fluorides
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FKKT - Faculty of Chemistry and Chemical Technology
• Publication status: Published
• Publication version: Version of Record
• Year: 2023
• Number of pages: Str. 9562-9572
• Numbering: Vol. 52, iss. 28
• PID: 20.500.12556/RUL-152365
• UDC: 546
• ISSN on article: 1477-9234
• DOI: 10.1039/d3dt01476b
• COBISS.SI-ID: 160299011
• Publication date in RUL: 22.11.2023

Record is a part of a journal

• Title: Dalton transactions
• Shortened title: Dalton trans.
• Publisher: Royal Society of Chemistry
• ISSN: 1477-9234
• COBISS.SI-ID: 519833113

Licences

• License: CC BY 3.0, Creative Commons Attribution 3.0 Unported
• Link: https://creativecommons.org/licenses/by/3.0/deed.en
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Secondary language

• Language: Slovenian
• Keywords: CAAC prekurzor, fluorirni reagent, polivodikovi fluoridi