posted on 2022-08-03, 19:23authored byOriol Planas, Vytautas Peciukenas, Markus Leutzsch, Nils Nöthling, Dimitrios A. Pantazis, Josep Cornella
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.