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. 2022 Aug 17;144(32):14489-14504.
doi: 10.1021/jacs.2c01072. Epub 2022 Aug 3.

Mechanism of the Aryl-F Bond-Forming Step from Bi(V) Fluorides

Oriol Planas  1 , Vytautas Peciukenas  1 , Markus Leutzsch  1 , Nils Nöthling  1 , Dimitrios A Pantazis  1 , Josep Cornella  1
Affiliations

Mechanism of the Aryl-F Bond-Forming Step from Bi(V) Fluorides

Oriol Planas et al. J Am Chem Soc. .

Abstract

In this article, we describe a combined experimental and theoretical mechanistic investigation of the C(sp2)-F bond formation from neutral and cationic high-valent organobismuth(V) fluorides, featuring a dianionic bis-aryl sulfoximine ligand. An exhaustive assessment of the substitution pattern in the ligand, the sulfoximine, and the reactive aryl on neutral triarylbismuth(V) difluorides revealed that formation of dimeric structures in solution promotes facile Ar-F bond formation. Noteworthy, theoretical modeling of reductive elimination from neutral bismuth(V) difluorides agrees with the experimentally determined kinetic and thermodynamic parameters. Moreover, the addition of external fluoride sources leads to inactive octahedral anionic Bi(V) trifluoride salts, which decelerate reductive elimination. On the other hand, a parallel analysis for cationic bismuthonium fluorides revealed the crucial role of tetrafluoroborate anion as fluoride source. Both experimental and theoretical analyses conclude that C-F bond formation occurs through a low-energy five-membered transition-state pathway, where the F anion is delivered to a C(sp2) center, from a BF4 anion, reminiscent of the Balz-Schiemann reaction. The knowledge gathered throughout the investigation permitted a rational assessment of the key parameters of several ligands, identifying the simple sulfone-based ligand family as an improved system for the stoichiometric and catalytic fluorination of arylboronic acid derivatives.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Fluorination protocol from 1 via an oxidation/C(sp2)–F bond formation sequence.
Figure 2
Figure 2
Synthesis of pentavalent complex 4 and XRD structure analysis. Hydrogen atoms, disordered parts, and solvent molecules omitted for clarity.
Figure 3
Figure 3
(A) VT 19F NMR measurements of 4 in CD2Cl2. (B) 19F–19F EXSY NMR spectrum at 183 K in CD2Cl2 showing chemical exchange. (C) 1H–19F HOESY cross peaks of 4 in CD2Cl2 at 298 K.
Figure 4
Figure 4
(A) Left, reaction profile of reductive elimination from 4 over a range of concentrations. Right, plot of kobs vs [4]0. (B) 19F NMR reaction monitoring of reductive elimination from 4 (red) with 1-fluoro-4-nitrobenzene (purple) as internal standard, showing formation of fluorobenzene (3, green) and 6 (blue). t = time. (C) Putative mixed-valent Bi(V)–Bi(III) species after C–F formation from 4.
Figure 5
Figure 5
Electronic analysis of reductive elimination from 4–13. (A) Hammett plot vs σp.values. (B) Hammett plot vs σp+ values.
Figure 6
Figure 6
(A) Synthesis of monomeric pentavalent bismine fluoride complex 25 and 26 and XRD structure analysis. Hydrogen atoms and solvent molecules omitted for clarity. (B) VT 19F NMR measurements of 26 in CD2Cl2. (C) 19F–19F and 13C–19F J-coupling constants of 26 in CD2Cl2 and CDCl3 respectively, together with JFF constants at different temperatures. (D) 1H–19F HOESY measurements of 26 in CD2Cl2. For simplicity, orange and blue arrows are not used to show all C–F and H–F interactions, but only to represent the distinct ones.
Figure 7
Figure 7
Reaction profile of reductive elimination from 25 (red) and 26 (purple) measured by 19F NMR with 1-fluoro-4-nitrobenzene as internal standard.
Figure 8
Figure 8
Electronic and thermodynamic analysis of reductive elimination from 25 and 29–31. (A) Hammett plot for the reductive elimination of para-substituted σ-aryl-Bi(V) difluorides 25 and 29–31. (B) Eyring analysis for 25.
Figure 9
Figure 9
Electronic analysis of reductive elimination from 4, 5, and 32–34. (A) Hammett plot vs σm values. (B) Hammett plot vs σS–L values.
Figure 10
Figure 10
(A) Synthesis of anionic species 35 from 4 in the presence of several fluoride sources. (B) Left, reductive elimination of fluorobenzene from 4 in the presence of different amounts of TBAT. Right, decay of 4 dependence on TBAT concentration.
Figure 11
Figure 11
(A) Gibbs energy profile of the reductive elimination of fluorobenzene from species 4 at 363 K. (B) Selected structural and electronic parameters for TSF3. Relative Gibbs energy values are given in kcal·mol–1.
Figure 12
Figure 12
Gibbs energy profile of the reductive elimination of fluorobenzene from sterically congested monomeric species 26 at 363 K. Relative Gibbs energy values are given in kcal·mol–1.
Figure 13
Figure 13
(A) Synthesis of fluorobismuthonium species 37 and (B) ORTEP representation of XRD structure of 37. Hydrogen atoms and solvent molecules omitted for clarity.
Figure 14
Figure 14
Electronic analysis of reductive elimination from 4, 5, and 32–34 in the presence of 1.0 equiv of BF3·OEt2. (A) Hammett plot vs σm values. (B) Hammett plot vs σS–L values.
Figure 15
Figure 15
Electronic analysis of reductive elimination from 4 and 8–12 in the presence of 1.0 equiv of BF3·OEt2. (A) Hammett plot vs σp. (B) Hammett plot vs σp+ taking into account resonance contributions.
Figure 16
Figure 16
(A) Gibbs energy profile of the reductive elimination of fluorobenzene from fluorobismuthonium species 36 at 298 K. (B) Selected structural and electronic parameters for TSF′′. Relative Gibbs energy values are given in kcal·mol–1.
Figure 17
Figure 17
Reactivity of 1 with 1-fluoro-2,6-dichloropyridinium tetrafluoroborate 2 in MeCN-d3 (reaction 1) and 4 with BF3·OEt2 complex in the presence of 2,6-dichloropyridine in MeCN-d3 (reaction 2).
Figure 18
Figure 18
Overview of the C(sp2)–F reductive elimination from Bi(V).
See this image and copyright information in PMC

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