Fluorination of arylboronic esters enabled by bismuth redox catalysis

Article abstract of DOI:10.1126/science.aaz2258

Bismuth catalysis has traditionally relied on the Lewis acidic properties of the element in a fixed oxidation state. In this paper, we report a series of bismuth complexes that can undergo oxidative addition, reductive elimination, and transmetallation in a manner akin to transition metals. Rational ligand optimization featuring a sulfoximine moiety produced an active catalyst for the fluorination of aryl boronic esters through a bismuth (III)/bismuth (V) redox cycle. Crystallographic characterization of the different bismuth species involved, together with a mechanistic investigation of the carbonfluorine bond-forming event, identified the crucial features that were combined to implement the full catalytic cycle.

Full text of DOI:10.1126/science.aaz2258

RESEARCH
ronic acids, a transformation that is highly
coveted in the pharmaceutical and agrochem-
ical industries (27). This reaction is feasible
using stoichiometric transition metals, such
as Cu (28–30), Pd (31), and Ag (32), or hyper-
valent iodine compounds (33). The sole cat-
alytic variant makes use of trifluoroborate
aryl salts as substrates, which are converted
to aryl fluorides through single-electron trans-
fer processes catalyzed by Pd (34). On the basis
of the accessibility to Bi compounds in differ-
ent oxidation states (35), we report that the
rationally designed bismine complex (I) cat-
alyzes fluorination of aryl boronic esters through
a Bi(III)/Bi(V) redox cycle.
ORGANOMETALLICS
Fluorination of arylboronic esters enabled by bismuth
redox catalysis
Oriol Planas*, Feng Wang*, Markus Leutzsch, Josep Cornella†
Bismuth catalysis has traditionally relied on the Lewis acidic properties of the element in a fixed
oxidation state. In this paper, we report a series of bismuth complexes that can undergo oxidative
addition, reductive elimination, and transmetallation in a manner akin to transition metals. Rational
ligand optimization featuring a sulfoximine moiety produced an active catalyst for the fluorination
of aryl boronic esters through a bismuth (III)/bismuth (V) redox cycle. Crystallographic characterization
of the different bismuth species involved, together with a mechanistic investigation of the carbon-
fluorine bond-forming event, identified the crucial features that were combined to implement the full
catalytic cycle.
We hypothesized that a rationally designed
ligand would be crucial to exploit the Bi(III)/
Bi(V) redox couple. Building on precedents in
Bi coordination chemistry (36), we sought to
take advantage of Bi’s capacity for accommo-
dating additional neutral ligands in its coordi-
nation sphere, thereby affecting the geometry
and the electronics of the Bi center (37). Ac-
cordingly, we chose a tethered bis-anionic aryl
ligand, featuring a linking sulfonyl group in
the backbone (Fig. 2A). We predicted that the
use of a tether ligand would become important
for controlling the geometry in subsequent high-
valent intermediates in the catalytic cycle, as
Bi(V) compounds are known to undergo dy-
namic processes such as Berry pseudo-rotation
or turnstile rotation (38). On the basis of ligand
design approaches for high-valent transition
metals (39), we hypothesized that the lone pair
of the S-bound oxygen would become a weak
ligand for the Bi center, providing stabilization
of putative Bi(V) intermediates. The electron-
withdrawing nature of the sulfone group at
the ortho position is also expected to render
the Bi center more electrophilic, thereby prone
to transmetallation and reductive elimination.
Additionally, binding two of the three anionic
omogeneous transition-metal catalysis
has revolutionized organic synthesis, en-
abling fast and direct construction of
complex functionality. These reactions
rely, in large part, on the capacity of
(11), and group 13 to 17 elements are emerging
as acceptable alternatives in certain domains
of catalysis (12–16). These strategies represent
useful platforms for chemical synthesis. How-
ever, the exploitation of the redox properties
of main-group elements in catalysis to access
new modes of reactivity is still in its infancy
(17) and remains a major challenge in organo-
metallic and organic chemistry. We therefore
focused our attention on bismuth (Bi), an Earth-
abundant and inexpensive main-group element
(18) with under-explored redox properties (19).
The use of Bi in catalysis has relied largely on
its Lewis acidic properties (20), where recent
interest has revitalized its use in fields such as
C–H activation (21), carbonylation (22), trans-
fer hydrogenation (23), and as the initiator in
radical processes (24–26). We sought to pre-
pare a Bi complex capable of mimicking the
canonical, fundamental steps in a transition-
metal catalytic cycle: transmetallation (TM),
oxidative addition (OA), and reductive elim-
ination (RE) (Fig. 1B). To this end, we focused
on the oxidative fluorination of aromatic bo-
H
noble metals to cycle easily between different
oxidation states (Fig. 1A) (1). With the goal of
providing more sustainable strategies in cat-
alysis, efforts have shifted to unveil the reactivity
of more Earth-abundant, first-row transition
metals (Fe, Ni, Co, Cu, Mn, and Cr) (2–4). Chem-
ists have also sought to discover and exploit
transition-metal–like reactivity among elements
beyond the d-block (5–7). The concept of the
frustrated Lewis pair (FLP) can be applied to
boron and phosphorus cooperatively to pro-
mote transformations traditionally restricted
to transition metals (8). Furthermore, meth-
odologies based on alkali (9, 10), alkaline earth
Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-
Platz 1, 45470, Mülheim an der Ruhr, Germany.
*These authors contributed equally to this work.
†Corresponding author. Email: cornella@kofo.mpg.de
Fig. 1. Can Bi mimic
transition-metal behavior
in electrophilic fluorina-
tion? (A) General catalytic
two-electron redox cycle of a
transition metal. (B) Devel-
opment of an electrophilic
fluorination of boronic acid
derivatives through a
catalytic Bi redox process.
L, ligand; M, metal;
n, oxidation number;
R, organic residue;
X, halogen atom (A) or
non-anionic ligand (B);
Y, anionic ligand.
Planas et al., Science 367, 313–317 (2020)
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RESEARCH
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ligands in a cyclic framework would favor
selective reactivity of the unrestrained phenyl
group.
place of one of the O atoms in the sulfone
group (4), a notable reduction in yield was
observed (3, 28%, Fig. 2B). However, when
the methyl group in 4 was replaced with CF3
(5), a 94% yield of fluorobenzene (3) was ob-
tained after thermal decomposition of the cor-
responding Bi(V) intermediate. Both 4 and
5 were characterized by x-ray crystallography
(Fig. 2B). Despite their comparable Bi–N dis-
tances [3.055(2) Å in 4 and 3.038(3) Å in 5],
the electronic nature of the CF3 group clearly
has a notable promotional effect on the re-
ductive elimination process. The elimination
of fluorobenzene (3) was accompanied by the
smooth formation of the corresponding fluo-
robismine (6), which was confirmed by x-ray
crystallography. At this point, we presumed
that the productive elimination of fluoroben-
zene from 5 could be ascribed to the low pro-
pensity of the NCF3 group to coordinate to Bi
after oxidation, which results in a monomeric
Bi(V) difluoride complex. Although attempts
to crystallize Bi(V) difluoride compounds de-
rived from 4 and 5 were unsuccessful, the
installation of a methyl residue at the ortho po-
sition, with respect to the Bi center (7), permitted
the crystallization of difluorobismine (8) (Fig.
2C). X-ray analysis of 8 revealed a monomeric
pentavalent complex with trigonal bipyramid
geometry (TBP), in which both F atoms occupy
apical positions. This geometry is in agree-
ment with the polarity rule for TBP complexes,
which predicts that the most electronegative
and least sterically demanding substituents
are always placed in apical positions—in this
case, the fluorides (42). As anticipated, coordi-
nation of the pending group in 8 is weaker
[Bi–N 3.566(4) Å] than in the dimeric sulfone
counterpart 2 [Bi–O 3.430(6) Å].
With these considerations in mind, we syn-
thesized bismine (1) and attempted its oxida-
tion to Bi(V) from the 6s2 orbital, through
reaction with XeF2. A smooth conversion to
high-valent Bi(V) species was achieved (>95%
yield), and x-ray crystallographic analysis re-
vealed a symmetric Bi(V) dimeric structure (2)
(Fig. 2A). Each Bi atom in 2 adopts a distorted
octahedral geometry, with two fluorine atoms
positioned trans to each other [F1–Bi1–F2 and
F3–Bi2–F4, 164.2(2)°], one of them bridging to
the other metal center. The bridging Bi–F bonds
are 0.47 Å longer than the terminal bonds.
Moreover, the O atoms of the sulfone moiety
interact with the Bi centers [Bi1–O1 and Bi2–
O2, 3.430(6) Å], thereby forcing the F atom
away from linearity and engaging in binding
with another Bi, forming a dimer in the solid
state. When 2 was heated to 110°C in CDCl3,
an unexpected 45% yield of fluorobenzene (3)
was obtained. This reductive elimination of
C–F bond stands in stark contrast to previous
reports, in which attempts to thermally in-
duce C–F bond formation from Bi(V) fluoride
compounds resulted in decomposition or traces
of fluorinated arenes (40, 41). On the basis of
the crystallographic information, we antici-
pated that tuning the electronic properties of
the sulfone could influence the Bi(V) center,
thus affecting the C–F bond-formation step.
Indeed, with a NMe (Me, methyl) group in
We then turned our attention to the mech-
anism of this unusual C–F bond reductive
elimination. Several para-substituted aryl-
bismine complexes were synthesized (5 and 9
to 13, Fig. 3A) and oxidized with XeF2 to the
corresponding pentavalent bismine species
(14 to 19, Fig. 3A). Thermal decomposition
of 14 at 90°C exhibited a first-order kinetic
profile (kobs = 1.3 × 10−4 s−1, where kobs is the
apparent reaction rate constant), in which
fluorobenzene (3) was produced at the same
rate as fluorobismine (6) (kobs = 1.0 × 10−4 s−1
and kobs = 1.1 × 10−4 s−1, respectively), reach-
ing 94% yield after 7 hours (Fig. 3A1). An
Eyring analysis over a 25°C range revealed a
small enthalpy barrier (DH‡ = 15.5 0.7 kcal
mol−1, where DH‡ is the change in enthalpy
between reactants and transition state) but a
surprisingly high entropic contribution [DS‡ =
–34.7 1.9 entropy unit (1 e.u. = 1 cal K−1 mol−1),
where DS‡ is the change in entropy between
reactants and transition state]. A large and
negative value of the entropy parameter is
consistent with an associative process in the
transition state, although cationic pathways
with high degrees of solvent reorganization
have also been postulated (43, 44). Hammett
kinetic analysis of the thermal decomposition
of 14 to 19 to aryl fluorides (3 and 20 to 24)
Fig. 2. Design principle and proof of concept. (A) Design of the bismine complexes to enable C–F reductive elimination. (B) Oxidative addition and reductive
elimination sequence to forge C–F bonds. (C) Trigonal bipyramidal monomeric Bi(V) difluoride bearing NCF3. Unless specified, yields were calculated by 19F NMR.
Planas et al., Science 367, 313–317 (2020)
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and 6, revealed a moderately positive slope (r =
ductive elimination when electron-withdrawing
groups are present in the aryl ring (39, 45).
Furthermore, a slower reaction rate for the
thermal decay of 14 at 90°C in CDCl3 was ob-
tained in the presence of 1.0 equivalent (equiv.)
of Bu4NF (Bu, butyl group) (kobs ≈ 3.5 × 10−5 s−1,
partial decomposition observed). Thus, the highly
negative entropic value, the excellent linearity
obtained when resonance effects are considered,
and the slower rate in the presence of fluoride
anions suggest a cationic intermediate 14-cation
(Fig. 3B) in equilibrium with 14 (39, 43, 45). From
0.43) when relative constants were plotted ver-
+
sus sp (substituent constant), showing good
linearity (R2 = 0.9735, where R2 is the coef-
ficient of determination and R is the coefficient
of correlation). This indicates a slightly faster re-
Fig. 3. Mechanistic studies of the reductive elimination. (A) Kinetic
profile of the reductive elimination from 14, Eyring analysis, and
Hammett studies. (B) Experimental evaluation of the reductive
elimination step. a, apical position; e, equatorial position. (C) Use of
fluoropyridinium salts as fluorinating agents. h, hours; k, reaction
rate constant; kB, Boltzmann constant; T, temperature; kX, reaction
rate constant with para-substituent X; kH, reaction rate constant
with para-substituent H; eu, entropy unit.
Planas et al., Science 367, 313–317 (2020)
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Fig. 4. Bi-mediated fluorination of organoboron compounds. (A) Trans-
metallation of boronic acid derivatives to a Bi(III) complex. Standard conditions:
bismine (1.0 equiv.), arylboronic acid derivative (2.0 equiv.), KF (3.0 equiv.),
CH3CN, 90°C, 16 hours. (B) Two-step method for the fluorination of boronic
acids. Yields are given for step 1 (isolated) and step 2 (determined by
19F NMR), respectively. Step 1: chlorobismine 29 (1.0 equiv.), arylboronic
acid (2.0 equiv.), KF (3.0 equiv.), CH3CN, 90°C, 16 hours. Step 2: arylbismine
(1.0 equiv.), 27 (1.1 equiv.), CHCl3, 60°C, 6 hours. (C) Catalytic fluorination of aryl
boronic esters. Standard conditions: 26 (10 mol%), 27 (1.0 equiv.), arylboronic
pinacol ester (3.0 equiv.), NaF (5.0 equiv.), CDCl3, 90°C, 16 hours. Yields determined
by 19F NMR. * denotes use of CHCl3 as solvent. † denotes use of 0.66 equiv. of 33.
‡ denotes use of K2CO3 as base. § denotes reaction performed at 110°C. ¶ denotes
yield of isolated material after column chromatography. # denotes isolated product
contains ~5% of proto-deborylated arene. tBu, tert-butyl; TMS, trimethylsilyl.
this, elimination of fluorobenzene (3) is pro-
posed, with concomitant formation of fluoro-
bismine (6). In 14-cation, coordination of the
NCF3 group to the Bi is expected, providing
these Bi intermediates with the adequate
balance between stabilization and electronic
perturbation to enable C–F bond formation.
Reductive elimination from pentavalent com-
plexes with TBP geometry is usually governed
by orbital symmetry rules; the Woodward-
Hoffmann model (46–48) predicts that the
coupling of equatorial-equatorial and apical-
apical ligands should be much more favorable
than the equatorial-apical coupling apparently
observed in PhF (Ph, phenyl group) elimina-
tion from 14. Recently, Paton and McNally
have reported the possibility of bypassing these
rules in pentavalent TBP P-based compounds
via alternative mechanisms (49). Therefore, the
formation of a cationic Bi intermediate repre-
sents another example which circumvents this
constraint (50).
To assess the formation of cation inter-
mediates experimentally, we speculated that
a Lewis acid could coordinate the apical flu-
orine syn to the NCF3 group in 14 and thereby
notably elongate the Bi–F bond (51), leading to
a compound that is geometrically similar to
14-cation. When 14 was mixed with 1.0 equiv.
of BF3·OEt2 (Et, ethyl group) at –45°C (Fig.
3B), exclusive formation of 25 was confirmed
in solution by 1H, 11B, 19F, and 13C nuclear mag-
netic resonance (NMR) and high-resolution
mass spectrometry (HRMS). When this com-
plex was heated to 60°C, fluorobenzene (3)
was formed in just 5 min, with concomitant
formation of tetrafluoroborate bismine (26).
To further confirm the nature of 26, 1.0 equiv.
eliminate fluorobenzene (3) and form the cor-
responding bismine (26).
of BF3·OEt2 was added to 6, and immediate
conversion to 26 (whose structure was con-
firmed by x-ray crystallography) was observed.
In this case, because of the weakly coordi-
nating nature of the tetrafluoroborate ligand,
formation of 3 and 26 occurs readily from the
cationic species 25-cation. An Eyring analy-
sis of the reductive elimination from in situ
generated 25 (fig. S11) revealed a high enthalpic
contribution to forge 3 and 26 (DH‡ = 24.3
1.6 kcal mol−1). In contrast to complex 14, the
reductive elimination from this cationic inter-
mediate showed a minimal entropic contri-
bution (DS‡ = 6.48 5.3 e.u.) (39). Taken
together, these results provide additional
evidence for the intermediacy of a cationic
species in the reductive elimination from the
pentavalent difluorobismine 14. With this
mechanistic information in hand, we hy-
pothesized that a milder and more syntheti-
cally useful fluorinating oxidant could afford
similar intermediates. Oxidation of Bi(III) com-
pounds to high-valent Bi(V) fluorides has been
limited to strong fluorinating agents, such as
XeF2 or F2 (40, 41). However, when complex 5
was mixed with 1.2 equiv. of 1-fluoro-2,6-
dichloropyridinium 27 in CHCl3 (52), smooth
C–F bond formation occurred at 60°C (Fig.
3C). The high conversion was ascribed to the
high lability of the neutral and sterically en-
cumbered 2,6-dichloropyridine ligand after
oxidation (28), thus enabling coordination
of the lone pair from the NCF3 handle. The
resulting intermediate (25-cation) can then
With the goal of turning over the catalytic
cycle, we then focused our attention on the
transmetallation process between organoboron
compounds and chlorobismine (29) (Fig. 4A).
Whitmire reported the possibility of trans-
metallating highly nucleophilic tetrarylbo-
rates with Bi salicylate salts (53). However,
transmetallation of less-nucleophilic orga-
noboron compounds to (pseudo)halobismines
remains a challenge. Capitalizing on the use of
KF as activator, when boronic acid (30) was
mixed with 29, smooth transmetallation took
place (93% yield). When tetrafluoroborate
bismine (26) was subjected to transmetal-
lation, a 95% yield of 5 was obtained. Under
the same conditions, other organoboron com-
pounds such as PhBpin (pin, pinacol group)
(31, 67%), PhB(neop) (neop, neopentyl glyco-
lato group) (32, 72%), and (PhBO)3 (33, 80%)
were converted in good yields to phenylbismine
(5), demonstrating versatility. With the aim
of exploring the scope of a two-step method
for fluorination, transmetallation of various
phenylboronic acids was surveyed. High yields
of arylation were obtained (67 to 90%), inde-
pendently of the functional group in the aryl
ring. The resulting arylbismines were then
oxidized with 27 and reacted, as above, to
release the corresponding arylfluorides (Fig.
4B). The protocol proved general with a va-
riety of para-substituted arylfluorides includ-
ing tert-butyl (20, 85%), trifluoromethyl (21,
35%), cyano (22, 71%), chloride (23, 57%),
methoxy (24, 21%), fluoride (34, 50%), ester
Planas et al., Science 367, 313–317 (2020)
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RESEARCH
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(35, 96%), and trimethylsilyl (36, 77%) sub-
stituents. Furthermore, ortho-bromide (37,
74%), naphthalene (38, 75%), vinyl (39, 49%),
and meta-methoxy (40, 93%) groups could
also be accommodated.
Bi complexes by careful tuning of the ligand
properties could potentially be expanded to
other similar scenarios, in which a catalyst
maneuvers between different oxidation states—
a property traditionally associated with tran-
sition metals.
35. J.-P. Finet, Ed., Ligand Coupling Reactions with Heteroatomic
Compounds (Elsevier, 1998).
36. G. G. Briand, N. Burford, Adv. Inorg. Chem. 50, 285–357 (2000).
37. K. Ohkata, S. Takemoto, M. Ohnishi, K.-Y. Akiba, Tetrahedron
Lett. 30, 4841–4844 (1989).
38. I. Ugi, D. Marquarding, H. Klusacek, P. Gillespie, F. Ramirez,
Acc. Chem. Res. 4, 288–296 (1971).
39. T. Furuya et al., J. Am. Chem. Soc. 132, 3793–3807
(2010).
40. T. Ooi, R. Goto, K. Maruoka, J. Am. Chem. Soc. 125,
10494–10495 (2003).
41. S. A. Lermontov, I. M. Rakov, N. S. Zefirov, P. J. Stang,
Tetrahedron Lett. 37, 4051–4054 (1996).
42. E. L. Muetterties, W. Mahler, R. Schmutzler, Inorg. Chem. 2,
613–618 (1963).
43. N. P. Mankad, F. D. Toste, Chem. Sci. 3, 72–76 (2012).
44. A. J. Canty, H. Jin, B. W. Skelton, A. H. White, Inorg. Chem. 37,
3975–3981 (1998).
45. J. M. Racowski, A. R. Dick, M. S. Sanford, J. Am. Chem. Soc.
131, 10974–10983 (2009).
46. R. Hoffmann, J. M. Howell, E. L. Muetterties, J. Am. Chem. Soc.
94, 3047–3058 (1972).
47. R. B. Woodward, R. Hoffmann, Angew. Chem. Int. Ed. 8,
781–853 (1969).
48. K.-Y. Akiba, Ed., Organo Main Group Chemistry (Wiley, 2011).
49. M. C. Hilton et al., Science 362, 799–804 (2018).
50. J. Moc, K. Morokuma, J. Am. Chem. Soc. 117, 11790–11797
(1995).
51. Y. Matano, S. A. Begum, T. Miyamatsu, H. Suzuki,
Organometallics 17, 4332–4334 (1998).
52. G. S. Lal, G. P. Pez, R. G. Syvret, Chem. Rev. 96, 1737–1756
(1996).
53. V. Stavila, J. H. Thurston, D. Prieto-Centurión, K. H. Whitmire,
Organometallics 26, 6864–6866 (2007).
We then turned our attention to merging all
these steps into a catalytic cycle. On the basis
of our initial hypothesis (Fig. 1B), transmetal-
lation of an arylboronic acid derivative to an
electrophilic Bi(III) center (I) would deliver
the aryl bismine (II). Subsequently, II could
be oxidized by the electrophilic fluorine source
27 to furnish a high-valent Bi(V) compound
containing both fluoride and tetrafluorobo-
rate ligands (III). Rapid decomposition of
this intermediate would forge a C–F bond
and I, thereby restoring the catalyst. Indeed,
using tetrafluoroborate bismine (26), a cata-
lytic protocol based on Bi for the oxidative
fluorination of arylboronic esters was success-
fully implemented. After a short optimization
of the fluoride source, required to activate
the boronic ester, a variety of ArBpin were
smoothly converted to the corresponding aryl
fluorides (Fig. 4C). Using 10 mole % of bismine
(26), phenylboronic acid pinacol ester (31) af-
forded a 90% yield of fluorobenzene (3). Sub-
stitution in para-position was also tolerated,
as exemplified by the presence of trimethyl-
silyl (36, 90%), phenyl (41, 71%), methyl (42,
77%), alkynyl (43, 67%), and bromo (46, 84%)
groups. Substitution of the aryl group at the
meta-position presented more difficulties, af-
fording moderate yields of aryl fluoride: me-
thoxy (40, 55%), cyano (44, 28%), and chloride
(45, 36%). p-Extended aromatics (38, 49%) and
sterically hindered substitution, such as a Me
group at the ortho position (47, 45%), were also
amenable for fluorination. The Bi catalyst was
essential for the reaction to proceed.
REFERENCES AND NOTES
1. A. de Meijere, F. Diederich, Eds., Metal-Catalyzed Cross-
Coupling Reactions (Wiley, 2004).
2. J. E. Zweig, D. E. Kim, T. R. Newhouse, Chem. Rev. 117,
11680–11752 (2017).
3. B. Su, Z.-C. Cao, Z.-J. Shi, Acc. Chem. Res. 48, 886–896
(2015).
4. R. J. M. Klein Gebbink, M. Moret, Eds., Non-Noble Metal
Catalysis: Molecular Approaches and Reactions (Wiley, 2019).
5. R. L. Melen, Science 363, 479–484 (2019).
6. P. P. Power, Nature 463, 171–177 (2010).
7. C. Weetman, S. Inoue, ChemCatChem 10, 4213–4228
(2018).
8. G. C. Welch, R. R. San Juan, J. D. Masuda, D. W. Stephan,
Science 314, 1124–1126 (2006).
9. L. Wu et al., Nat. Commun. 10, 2786 (2019).
10. A. A. Toutov et al., Nature 518, 80–84 (2015).
11. H. Bauer et al., Nat. Catal. 1, 40–47 (2018).
12. M.-A. Légaré, M.-A. Courtemanche, É. Rochette, F.-G. Fontaine,
Science 349, 513–516 (2015).
13. I. G. Molnár, R. Gilmour, J. Am. Chem. Soc. 138, 5004–5007
(2016).
14. N. L. Dunn, M. Ha, A. T. Radosevich, J. Am. Chem. Soc. 134,
11330–11333 (2012).
15. J. C. Sarie, J. Neufeld, C. G. Daniliuc, R. Gilmour, ACS Catal. 9,
7232–7237 (2019).
16. S. M. Banik, J. W. Medley, E. N. Jacobsen, J. Am. Chem. Soc.
138, 5000–5003 (2016).
17. T. V. Nykaza et al., J. Am. Chem. Soc. 140, 15200–15205
(2018).
18. R. Mohan, Nat. Chem. 2, 336 (2010).
19. M. B. Kindervater, K. M. Marczenko, U. Werner-Zwanziger,
S. S. Chitnis, Angew. Chem. Int. Ed. 58, 7850–7855 (2019).
20. T. Ollevier, Ed., Bismuth-Mediated Organic Reactions
(Springer, 2012).
21. B. Ritschel, J. Poater, H. Dengel, F. M. Bickelhaupt,
C. Lichtenberg, Angew. Chem. Int. Ed. 57, 3825–3829
(2018).
22. J. Ramler et al., Chem. Sci. 10, 4169–4176 (2019).
23. F. Wang, O. Planas, J. Cornella, J. Am. Chem. Soc. 141,
4235–4240 (2019).
24. J. Ramler, I. Krummenacher, C. Lichtenberg, Angew. Chem.
Int. Ed. 58, 12924–12929 (2019).
25. R. J. Schwamm, M. Lein, M. P. Coles, C. M. Fitchett,
Chem. Commun. 54, 916–919 (2018).
26. S. Yamago et al., Angew. Chem. Int. Ed. 46, 1304–1306
(2007).
27. G. Pattison, Org. Biomol. Chem. 17, 5651–5660 (2019).
28. P. S. Fier, J. Luo, J. F. Hartwig, J. Am. Chem. Soc. 135,
2552–2559 (2013).
29. M. Tredwell et al., Angew. Chem. Int. Ed. 53, 7751–7755
(2014).
ACKNOWLEDGMENTS
We thank A. Fürstner and T. Ritter for insightful discussions
and generous support and B. Morandi and C. Obradors for
insightful suggestions and for proofreading the manuscript.
N. Noethling and R. Goddard are acknowledged for crystallographic
data analysis. We also thank the analytical department at the
MPI-Kohlenforschung for support in the characterization of
compounds. Funding: Financial support for this work was provided
by Max-Planck-Gesellschaft, Max-Planck-Institut für
Kohlenforschung, Fonds der Chemischen Industrie (FCI-VCI),
Alexander von Humboldt Foundation (to O.P.), and the European
Commission (Marie Skłodowska Curie Fellowship, grant no.
833361, to O.P.). Author contributions: J.C. and O.P. conceived
the idea. All experiments were conducted by O.P. and F.W. NMR
experiments and analysis were conducted by O.P. and M.L. The
manuscript was written by O.P. and J.C. The project was directed
by J.C. Competing interests: The authors declare no competing
interests. Data and materials availability: Crystallographic
data for structures 2, 4, 5, 6, 7, 8, 26, and 29 are available
free of charge from the Cambridge Crystallographic Data
Center under reference numbers 1949430, 1949432, 1949433,
1949435, 1949434, 1949431, 1956313, and 1949436,
respectively.
The design presented here enables a Bi
complex to undergo transmetallation, oxi-
dative addition with a mild fluorinating agent,
and C–F reductive elimination to deliver aryl
fluoride compounds. A detailed study of each
step paved the way to the development of a
catalytic cycle based on the Bi(III)/Bi(V) redox
couple, a feat that remained elusive for Bi until
now. This mode of reactivity for Bi represents
a step forward in mimicking transition-metal–
like behavior by an element outside the d-block.
Although still limited to considerably oxidizing
electrophiles and narrow substrate scope, the
possibility of performing redox processes with
SUPPLEMENTARY MATERIALS
30. Y. Ye, M. S. Sanford, J. Am. Chem. Soc. 135, 4648–4651
(2013).
31. T. Furuya, H. M. Kaiser, T. Ritter, Angew. Chem. Int. Ed. 47,
5993–5996 (2008).
32. T. Furuya, T. Ritter, Org. Lett. 11, 2860–2863 (2009).
33. B. H. Rotstein, N. A. Stephenson, N. Vasdev, S. H. Liang,
Nat. Commun. 5, 4365 (2014).
34. A. R. Mazzotti, M. G. Campbell, P. Tang, J. M. Murphy, T. Ritter,
J. Am. Chem. Soc. 135, 14012–14015 (2013).
science.sciencemag.org/content/367/6475/313/suppl/DC1
Materials and Methods
Figs. S1 to S26
Tables S1 to S22
Spectral Data
References (54–69)
26 August 2019; accepted 17 December 2019
10.1126/science.aaz2258
Planas et al., Science 367, 313–317 (2020)
17 January 2020
5 of 5

Fluorination of arylboronic esters enabled by bismuth redox catalysis
Oriol Planas, Feng Wang, Markus Leutzsch and Josep Cornella
Science 367 (6475), 313-317.
DOI: 10.1126/science.aaz2258
Teaching bismuth to make and break bonds
One major reason why transition metals are good catalysts is that they can shuttle between oxidation states. This
flexibility lets them slide in and out of chemical bonds; so, for instance, they can snip a bond between carbon and boron
and then stitch a carbonfluorine bond in its place. Planas et al. now report that bismuth can also orchestrate such
bond-swapping events. They implement a fully catalytic cycle for fluorination of aryl boronates, in which bismuth hops
between its +3 and +5 oxidation states.
Science, this issue p. 313
ARTICLE TOOLS
http://science.sciencemag.org/content/367/6475/313
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MATERIALS
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REFERENCES
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