Oxidative Addition, Transmetalation, and Reductive Elimination at a 2,2′-Bipyridyl-Ligated Gold Center

Article abstract of DOI:10.1021/jacs.8b01411

Three-coordinate bipyridyl complexes of gold, [(κ²-bipy)Au(η²-C₂H₄)][NTf₂], are readily accessed by direct reaction of 2,2′-bipyridine (bipy), or its derivatives, with the homoleptic gold ethylene complex [Au(C₂H₄)₃][NTf₂]. The cheap and readily available bipyridyl ligands facilitate oxidative addition of aryl iodides to the Au(I) center to give [(κ²-bipy)Au(Ar)I][NTf₂], which undergo first aryl-zinc transmetalation and second C-C reductive elimination to produce biaryl products. The products of each distinct step have been characterized. Computational techniques are used to probe the mechanism of the oxidative addition step, offering insight into both the origin of the reversibility of this process and the observation that electron-rich aryl iodides add faster than electron-poor substrates. Thus, for the first time, all steps that are characteristic of a conventional intermolecular Pd(0)-catalyzed biaryl synthesis are demonstrated from a common monometallic Au complex and in the absence of directing groups.

Full text of DOI:10.1021/jacs.8b01411

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Cite This: J. Am. Chem. Soc. XXXX, XXX, XXX−XXX
Oxidative Addition, Transmetalation, and Reductive Elimination at a
2
,2′-Bipyridyl-Ligated Gold Center
† †
†
‡
†
,†
Matthew J. Harper, Christopher J. Arthur, John Crosby, Edward J. Emmett, Rosalyn L. Falconer,
Andrew J. Fensham-Smith, Paul J. Gates, Thomas Leman, John E. McGrady,* John F. Bower,*
and Christopher A. Russell*
†
†
†
,§
,†
†
School of Chemistry, University of Bristol, Bristol, BS8 1TS, United Kingdom
‡
Syngenta, Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY, United Kingdom
Department of Chemistry, University of Oxford, South Parks Road, Oxford, OX1 3QZ, United Kingdom
§
*
S Supporting Information
2
ABSTRACT: Three-coordinate bipyridyl complexes of gold, [(κ -bipy)Au-
2
(
(
[
η -C H )][NTf ], are readily accessed by direct reaction of 2,2′-bipyridine
2
4
2
bipy), or its derivatives, with the homoleptic gold ethylene complex
Au(C H ) ][NTf ]. The cheap and readily available bipyridyl ligands
facilitate oxidative addition of aryl iodides to the Au(I) center to give [(κ -
2
4 3
2
2
bipy)Au(Ar)I][NTf ], which undergo first aryl-zinc transmetalation and
2
second C−C reductive elimination to produce biaryl products. The products
of each distinct step have been characterized. Computational techniques are
used to probe the mechanism of the oxidative addition step, offering insight
into both the origin of the reversibility of this process and the observation
that electron-rich aryl iodides add faster than electron-poor substrates. Thus,
for the first time, all steps that are characteristic of a conventional
intermolecular Pd(0)-catalyzed biaryl synthesis are demonstrated from a
common monometallic Au complex and in the absence of directing groups.
INTRODUCTION
strong external oxidant limits the attractiveness of this strategy.
Accordingly, extensive efforts have been devoted to the
identification of oxidative addition processes that might allow
the routine exploitation of internal oxidants (e.g., aryl halides)
in Au catalysis. Three distinct strategies have emerged to
facilitate the oxidative addition step: (a) the use of directing
■
The development of the chemistry of gold has been one of the
most striking research themes of recent times. However, despite
the promise implied by the diagonal relationship between Au
and Pd, processes that imitate conventional Pd-catalyzed biaryl
formations (Negishi, Suzuki, etc.) are lacking. This is readily
explained by the “redox gold problem”, where the relative
1
7
,8
2
groups, (b) the use of highly electrophilic initiation motifs
4
,9−13
x/x+2
0
(e.g., allylic bromides, aryl diazoniums, CF −I),
and (c)
3
reluctance of gold to partake in M
redox processes (E :
= 1.41 V) renders oxidative addition
14
II/0
III/I
modification of the ancillary ligand on Au. The latter option is
most attractive, as it potentially offers the greatest substrate
scope; however, this avenue is also the least developed and
most challenging. Of specific relevance is the work of Amgoune,
Bourissou, and co-workers, who employed a bulky carboranyl
diphosphine ligand that subtends a bite angle of approximately
Pd = 0.92 V, Au
3
challenging. Notwithstanding this apparent obstacle, such
processes remain highly desirable, primarily because of the
biocompatibility of gold versus the toxicity of palladium.
Furthermore, the idiosyncratic properties of gold, especially its
unique functional group tolerance and Lewis acidity, hold the
promise that known Pd-catalyzed processes will not simply be
replicated, but that milder transformations, offering broader
substrate scope and/or unusual selectivity, will be discovered.
The putative steps in a potential redox gold cycle are
analogous to those of Pd(0)-catalyzed cross-couplings,
consisting of oxidative addition, transmetalation, and reductive
1
4
9
0° at the Au center. This results in Au(I) complexes that
15
express enhanced π-back-donation and undergo facile non-
directed oxidative addition of both strained C−C bonds and
aryl iodides (Scheme 1B).
12b
14
Clearly, the evolution of redox gold catalysis will be
facilitated by gaining an in-depth understanding of fundamental
16
4
steps that might underpin a possible catalytic cycle. Although
the process in Scheme 1B is unique in its ability to promote
efficient nondirected oxidative addition of aryl iodides,
elimination (Scheme 1A). Of these, it is recognized that the
oxidative addition step is challenging, due to the “redox gold
problem” outlined above. Most commonly this is circumvented
by employing an external oxidant, which facilitates the Au(I) →
Au(III) transformation and allows the catalytic coupling of two
Received: February 5, 2018
5
,6
formally nucleophilic partners; however, the requirement of a
©
XXXX American Chemical Society
A
DOI: 10.1021/jacs.8b01411
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Journal of the American Chemical Society
Article
2
Scheme 1
Scheme 2. Synthesis of [(κ -5,5′-Difluoro-2,2′-
2
bipyridine)Au(η -C H )][NTf ], 2b
2
4
2
fragile, but reacts rapidly with bipy to yield [bipyAu(C H )]-
2
4
[
NTf ] (2a). This process occurs with similar efficacy for a
2
variety of substituted bipyridines; in particular, exposure of 1 to
,5′-difluoro-2,2′-bipyridine (F -bipy) generated [(F -bipy)Au-
5
2
2
(
C H )][NTf ] (2b), in which the fluorine substituents provide
2 4 2
19
a convenient F NMR spectroscopic handle for further studies.
The molecular structure of 2b was determined by single-crystal
X-ray diffraction (scXRD), which revealed a distorted trigonal
planar gold center with the F -bipy ligand adopting the
2
2
symmetric κ -mode. Most importantly, the Au−C distances are
contracted and the alkene CC bond is elongated significantly
2
+
in comparison to two-coordinate [LAu(η -alkene)] cations (L
20
=
PR , NHC) (see the SI). These observations are consistent
3
with enhanced π-back-donation enforced by the F -bipy ligand
2
system. Significantly, whereas 1 is exceptionally fragile,
complexes 2 show impressive stability, being handled readily
in air and tolerating nonanhydrous solvents in subsequent
reactions.
downstream cross-coupling steps (i.e., transmetalation and C−
With ample quantities of 2b in hand, investigations into its
behavior toward aryl-halide oxidative addition were undertaken.
When 2b was exposed to 4-fluoroiodobenzene (2 equiv) at 50
°C in CD Cl , the solution changed rapidly from colorless to
14
C reductive elimination) were not achieved. Indeed, while
several elementary organometallic processes have been
16
substantiated for gold only recently, there are no reports
where all steps of a possible intermolecular biaryl forming
cross-coupling cycle have been demonstrated from a common
monometallic Au complex. In this article, we show how
manipulation of the ligand environment at gold allows the
sequential observation of oxidative addition, transmetalation,
and reductive elimination from the same species (Scheme 1C).
Remarkably, this is all achieved using the commonplace 2,2′-
bipyridyl ligand (bipy) or its derivatives. Bipy has been
employed as an additive in several exciting reports on gold
2
2
1
9
pale yellow color (Scheme 3). Moreover, the F NMR
Scheme 3. Reaction of 2b with 4-Fluoroiodobenzene to Give
[
(F -bipy)Au(4−F-C H )I][NTf ], 3a
2
6
4
2
1
0c,e,f
catalysis,
although its precise function has not been
established; we suggest that this role might be revisited in
light of the results described herein.
Following the submission of this article, Amgoune,
Bourissou, and co-workers published a Au(I)/Au(III) catalytic
2
cycle involving a sequence of C−X oxidative addition, C(sp )−
spectrum showed three new multiplets in a 1:1:1 ratio,
H auration, and reductive elimination, by employing a P,N-
consistent with oxidative addition to give [(F -bipy)Au(4-F-
2
17
ligand (Me-Dalphos) on gold.
C H )I][NTf ] (3a). Further confirmation was obtained by
6
4
2
analysis of the reaction mixture using high-resolution electro-
spray ionization mass spectrometry (ESI-HRMS). An ion was
observed with m/z 610.9482, which is in agreement with the
RESULTS AND DISCUSSION
At the outset of our studies, we targeted higher (>2) coordinate
Au(I) complexes that might exhibit significant back-donation.
■
2
+
calculated m/z for the [(κ -F -bipy)Au(4-F-C H )I] ([3a −
2
6
4
+
Of particular interest was the chemistry of cationic [bipyAu-
NTf ] ) cation (610.9501). Subsequently, the molecular
2
+
(
alkene)] complexes bearing a variety of substituted 2,2′-
structure of 3a was confirmed unequivocally by scXRD, with
the Au(III) center adopting a slightly distorted square planar
geometry, as expected for a d8 metal (Figure 1). Given
subsequent observations (vide infra), it is important to note
that the C−I bond has clearly been broken in a formal oxidative
addition reaction.
The promise of our initial observation of oxidative addition
to afford 3a was tempered by the fact that the conversion was
only around 10%. By increasing the aryl iodide loading from 2
to 20 equiv an increased conversion of 35% was observed after
bipyridyl frameworks. Previous routes to such complexes are
18
prolonged and inefficient, and so we sought a more effective
entry, such that our investigations into downstream reactivity
might be facilitated. Ultimately, we found that the target
complexes can be accessed readily by addition of bipy or its
derivatives to homoleptic Au(I)-alkene complexes prepared in
situ. The gold alkene complex [Au(C H ) ][NTf ] (1) was
2
4 3
2
prepared in a manner analogous to that reported for
19
[
Au(C H ) ][SbF ] (Scheme 2). Complex 1 is extremely
2 4 3 6
B
DOI: 10.1021/jacs.8b01411
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Journal of the American Chemical Society
Article
Figure 1. Molecular structure of the cation of 3a. Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms and the NTf2
anion have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): Au−C 2.011(3), Au−I 2.5357(3), Au−N1 2.080(3),
Au−N2 2.130(3), N1−Au1−N2 78.92(12), N(2)−Au−I 99.37(8),
N(1)−Au−C 95.17(14), C−Au−I 86.54(11).
6
h at 50 °C. Raising the temperature to 80 °C increased the
consumption of 2b, but full conversion to 3a could still not be
achieved. 19F NMR spectroscopy revealed that conversion
reaches a plateau at 40−60 °C, whereas higher temperatures
(70 or 80 °C) lead to decomposition of 3a (see the SI). We
hypothesized that 3a may be in equilibrium with Au(I)-
ethylene complex 2b (i.e., that oxidative addition may be
reversible), and hence we devised experiments to explore this
most interesting proposition. We reasoned that if oxidative
addition to 2b is reversible, then removal of free ethylene from
the reaction mixture should drive the equilibrium to the right.
Thus, a solution of 2b and 4-fluoroiodobenzene (20 equiv) was
heated to 50 °C in a sealed tube under a static vacuum
−
2
(
approximately 10 mbar). Remarkably, using this simple
1
9
modification, full conversion to 3a was observed ( F NMR)
after 1 h. To confirm the reversibility of the oxidative addition
process, a solution of 3a was pressurized (1 bar) with ethylene,
and this resulted in >95% conversion to 2b after 1 h at 60 °C
(
Scheme 3). This latter result also provides unambiguous
Figure 2. Computed potential energy surface for the oxidative addition
reaction, starting from 2a. Calculations were performed using the
ωB97-XD functional, a def2-TZVP basis with associated 60-electron
pseudopotential on Au, def2-SVP with associated 28-electron
pseudopotential on I, def2-SVP on C/N, and def2-SV on H/O/F.
The effects of solvent were incorporated using the SMD solvation
2
confirmation of the feasibility of C(sp )−I reductive
21
elimination from complex 3a. That 2b and 3a lie in a finely
balanced equilibrium contrasts sharply with both the oxidative
addition behavior of Pd(0) complexes toward aryl iodides and
14
the work of Amgoune and Bourissou (Scheme 1B).
model (CH Cl2 solvent). Energies shown include zero-point
corrections. The inset compares the transition structure for the
The apparent differences in reactivity between 2a/b and
Amgoune and Bourissou’s carboranyl diphosphine system
2
reaction with 4-OMe-iodobenzene (L) and 4-CF -iodobenzene (R).
3
(Scheme 1B) prompted us to explore the potential energy
surface for the oxidative addition step using density functional
theory (Figure 2, black pathway). Starting from the ethylene
complex, 2a, initial substitution of C H by a representative
1
4
dicarbaclosododecarborane-ligated system, the most conspic-
uous difference appears to be the relative stability of 2a/b
compared to LAu-NTf2.
2
4
electron-deficient aryl iodide, 4-CF -iodobenzene, to form an
3
2
η -arene complex is moderately endothermic (ΔE = +17.6
kcal/mol). In comparison, Joost et al. computed a value of +3
kcal/mol for the corresponding initiation step in Scheme 1B,
With conditions in hand for the efficient oxidative addition of
4-fluoroiodobenzene to 2b, we explored the scope of the
reaction with respect to the aryl iodide component (Table 1).
Within 1−6 h at 50 °C, full conversion to the corresponding
Au(III) complex was observed with a range of aryl iodides, as
2
2
−
14
where anionic [NTf ] is displaced by 4-fluoroiodobenzene:
2
the neutral ethylene ligand present in 2a/b clearly stabilizes the
−
2
19
Au(I) precursor more effectively than [NTf ] . From the η -
determined by F NMR spectroscopy. Both electron-rich (3f/
2
arene intermediate, the oxidative addition step is moderately
exothermic (ΔE = −13.2 kcal/mol), with a barrier of only 10.1
kcal/mol for the forward reaction and 23.3 kcal/mol for the
microscopic reverse (C−I reductive elimination). The combi-
nation of an endothermic ligand displacement step and a
moderately exothermic oxidative addition makes the overall
reaction very marginally endothermic (+4.4 kcal/mol). This
observation, alongside the surmountable barrier for the reverse
step, is consistent with the experimental evidence for an
equilibrium. Comparing again to the computed surface for
Amgoune and Bourissou’s 1,2-bis(diphenylphosphino)-1,2-
g) and electron-poor (3d) aryl iodides are tolerated, as well as
substrates with bulky groups adjacent to iodine (3f/g/h).
Furthermore, heteroaromatic (3j) and halide-containing
substrates (3b/c/e) are also compatible. For 3b and 3e, the
high selectivity of 2b toward the C−I bond is significant; no
competing C−Cl/Br oxidative addition was observed. Oxida-
tive addition products 3a−j were isolated in good to excellent
1
13
yields and were characterized by ESI-MS, H NMR, and
C
NMR spectroscopies. The molecular structures of complexes
3b/c/f/h/j were also confirmed by scXRD. These complexes
are air stable for days at room temperature and stable for
C
DOI: 10.1021/jacs.8b01411
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Journal of the American Chemical Society
Article
a
Table 1. Scope of Aryl Iodide Oxidative Addition to 2b
contrasts to the reactivity of Pd(0) toward aryl iodides, where
23
electron-poor substrates have been shown to react faster. In
Figure 2 we also show the computed potential energy surface
for the reaction with 4-OMe-iodobenzene (Figure 2, red
pathway) for comparison. While the energetic differences for
the two aryl iodides (R = CF vs OMe) are undeniably small,
3
the trend is consistent with the measured rates, inasmuch as the
barrier for the forward reaction is lower for 4-OMe-
iodobenzene than for 4-CF -iodobenzene (+9.4 vs +12.1
3
kcal/mol). In the two transition structures shown in the inset
at the top of Figure 2, the coordination at Au is approximately
linear (Cipso−Au−N = 169°), with short bonds to the ipso
carbon and one of the two bipy nitrogen atoms. The second
Au−N bond, in contrast, is much longer (∼2.4 Å), as is the
Au−I distance (∼2.75 Å), while the C−I bond is only
marginally elongated compared to 4-CF -iodobenzene (2.11
3
Å). These structural features are collectively characteristic of an
early transition state with Au(I) character, where the dominant
interaction between the arene and the [(bipy)Au] fragment
a
+
Isolated yields are quoted.
involves donation of electron density from the arene via the ipso
carbon. The electron-donating methoxy group in the 4-position
enhances the negative charge at the ipso carbon, and the result
is a slightly shorter and stronger Au−C bond in the transition
months at −20 °C. So far, attempts to extend the oxidative
addition behavior beyond aryl iodides have not been successful;
studies on this aspect are ongoing. We have also confirmed that
the oxidative addition behavior is not specific to F -bipy
2
structure for 4-OMe-iodobenzene (2.16 Å vs 2.23 Å in 4-CF -
3
complex 2b. Indeed, 2a reacts with 4-fluoroiodobenzene
iodobenzene).
2
(
[
CH Cl , 3 h, 50 °C), giving [(κ -2,2′-bipy)Au(4-F-C H )I]-
2
2
6
4
Having established that oxidative addition is facile, we
undertook investigations into subsequent cross-coupling steps.
Accordingly, we exposed CH Cl solutions of complex 3a to a
NTf ] (3k) in 72% isolated yield; the structure of 3k was
2
confirmed by scXRD (see the SI). Accordingly, oxidative
addition to Au(I) can be realized using cheap (approximately
2
2
variety of 4-tolyl-bearing organometallic reagents and raised the
reaction temperature until reactivity was observed (Table 2).
$
2/g) and readily available bipy.
Analysis of the relative reaction rates of oxidative addition to
b showed that electron-rich aryl iodides react significantly
a
2
Table 2. Reaction of 3a with Organometallic Nucleophiles
faster than electron-poor systems (initial rate order for 4-R-
C H I: R = OMe > H > CF ; Scheme 4). This order of
6
4
3
reactivity is in agreement with the trend reported by Amgoune,
14
Bourissou, et al. for the process outlined in Scheme 1B and
Scheme 4. Reaction Profiles for Oxidative Addition of 4-
,
a b
Substituted Aryl Iodides to 2b
entry
[M]
B(OH)2
T/°C
60
3a/% 4/% 5/% ArI/%
1
2
3
4
5
6
7
8
9
53
55
58
0
0
0
0
0
26
39
30
4
Bpin
50
SiMe3
rt
0
0
[B(pin)(t-Bu)]Li
MgBr
−78 to rt
−78 to rt
−78 to rt
−78 to rt
−78 to rt
−78 to rt
3
36
21
0
0
24
0
0
Li
0
35
11
7
Sn(n-Bu)3
SnMe3
ZnCl
0
51
61
72
9
0
0
0
5
18
a
Yields were determined by 19F NMR spectroscopy.
Boronic acid, boronic acid pinacol ester, and trimethylsilane-
based nucleophiles showed very little reactivity (entries 1−3),
and only reductive elimination to release 4-fluoroiodobenzene
was observed (25−40% yield). Li[4-tolylB(pin)(t-Bu)] resulted
in complete and rapid consumption of 3a, and, promisingly, 3%
of the desired cross-coupled product 4 was formed (entry 4). In
this case, homocoupling predominated to generate 4,4′-
difluorobiphenyl 5 in 36% yield. Nevertheless, this result
suggested that other classes of organometallic reagent may
favor heterocoupling to a greater extent. 4-Tolyllithium did not
give any of the desired product, but by switching to 4-
a
Reaction progress monitored by 19F NMR spectroscopy. Reaction
conditions: 2.87 μmol of 2b, 28.7 μmol of aryl iodide, 0.0041 M with
respect to 2b in CH Cl under N .
b
2
2
2
D
DOI: 10.1021/jacs.8b01411
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Journal of the American Chemical Society
Article
tolylMgBr we were able to form 4 in 24% yield (entries 5, 6). 4-
TolylSnBu and 4-tolylSnMe offered further benefits, generat-
ing 4 in 51% and 61% yield, respectively (entries 7, 8); in the
Despite observing the formation of 7, we have so far been
unable to render the overall three-step process catalytic. We
speculate that the relative conditions required for the oxidative
addition (greater than 50 °C) versus the transmetalation/
reductive elimination steps (operating below −30 °C),
combined with the fragility of 7 under the reaction conditions,
mean that decomposition occurs before subsequent reoxida-
tion.
3
3
case of 4-tolylSnBu , homocoupling product 5 was also
3
observed. Ultimately, we found that 4-tolylZnCl offered the
best reactivity, providing 4 in 72% yield and with high
selectivity over 5 (entry 9). This result demonstrates the
feasibility of efficient fragment coupling and C−C bond
formation, while also providing the first example of a Negishi
cross-coupling at gold, albeit under stoichiometric conditions.
The most probable pathway for the Au-mediated Negishi
CONCLUSION
In summary, we show that the Au(I) complex [(F -bipy)Au-
■
(
2
16,24
coupling involves transmetalation
of the arylzinc reagent
C H )][NTf ] undergoes sequential aryl-iodide oxidative
2
4
2
with 3a to give intermediate 6, which undergoes reductive
elimination to release 4 and generate complex 7 (Scheme 5A).
addition, aryl-zinc transmetalation, and C−C reductive
elimination to provide the first example of a Au-mediated
Negishi cross-coupling. Accordingly, elementary steps that are
typical of Pd-catalyzed biaryl formations have now been
demonstrated from a simple monometallic Au center in the
absence of directing groups. The chemistry is switched on by
the simple bipyridyl ligand framework, which enhances back-
donation from Au to facilitate the key Ar−I oxidative addition
step. The studies described here underpin our ongoing efforts
to devise oxidant-free Au-catalyzed biaryl formations using
readily available aryl halides as the electrophilic partner.
Scheme 5. Transmetalation and Reductive Elimination from
3
a
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/jacs.8b01411.
■
*
S
Experimental details and characterization data (PDF)
Crystallographic data (CIF)
(CIF)
(CIF)
(CIF)
(CIF)
(CIF)
(CIF)
AUTHOR INFORMATION
Corresponding Authors
john.mcgrady@chem.ox.ac.uk
john.bower@bris.ac.uk
chris.russell@bris.ac.uk
■
*
*
*
ORCID
Paul J. Gates: 0000-0001-8619-7745
John F. Bower: 0000-0002-7551-8221
Christopher A. Russell: 0000-0003-2921-5278
Notes
The authors declare no competing financial interest.
To gain further evidence for these steps, we monitored the
reaction of 3a with 4-tolylZnCl by variable-temperature 19
NMR spectroscopy (Scheme 5B). This showed complete
consumption of 3a at −78 °C to give an intermediate
consistent with 6. This species was stable up to approximately
F
ACKNOWLEDGMENTS
■
M.J.H., A.J.F.-S., and R.L.F. thank the Bristol Chemical
Synthesis Centre for Doctoral Training, funded by the
EPSRC (EP/G036764/1), for funding. M.J.H. thanks Syngenta
for funding. We thank the Royal Society for a University
Research Fellowship (to J.F.B). We thank Dr. Natalie Pridmore
and Dr. Hazel Sparkes (Bristol) for assistance with X-ray
crystallography.
−40 °C, at which point it decomposed rapidly to form 4 and a
small amount of 5. Aliquots of the reaction mixture were
analyzed by ESI mass spectrometry (Scheme 5A), and an ion
was observed with m/z 575.0997, which agrees with the
calculated m/z for the cation of 6 (575.1004). Tandem mass
spectrometry showed that this ion fragments to a new ion with
m/z 389.0140, which corresponds to the calculated m/z for the
cation of 7 (m/z 389.0159). These data amount to the direct
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■
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25
observation of reductive elimination from 6 to give 4 and 7.
E
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(
3) Bratsch, S. G. J. Phys. Chem. Ref. Data 1989, 18, 1.
(
4) Bimetallic Au-catalyzed cross-couplings of aryl boronic acids with
allylic bromides via a transmetalation, oxidative addition, reductive
elimination sequence: Levin, M. D.; Toste, F. D. Angew. Chem., Int. Ed.
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ez, L.; Mallet-Ladeira, S.; Miqueu, K.; Amgoune,
2
014, 53, 6211. Intramolecular stoichiometric studies using a
mononuclear Au complex support each key step.
5) For recent reviews, see: (a) Hopkinson, M. N.; Gee, A. D.;
́
(
A.; Bourissou, D. Angew. Chem., Int. Ed. 2014, 53, 14512.
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́
ez, L.; Mallet-Ladeira, S.; Miqueu, K.;
(
(
Au-catalyzed C−C bond formations that use Selectfluor as the oxidant,
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2
Chem. Soc. 2010, 132, 1474. (h) Melhado, A. D.; Brenzovich, W. E., Jr.;
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4
2
(
009, 48, 3112. (g) Zhang, G.; Cui, L.; Wang, Y.; Zhang, L. J. Am.
(
Chem. Soc. 2009, 131, 6350. (b) Hooper, T. N.; Green, M.; McGrady,
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(
21) C−I reductive elimination from Au(III) has been reported
previously (see ref 8).
22) Examples of structurally characterized Au(I) η -arene
Shunatona, H. P.; Tkatchouk, E.; Goddard, W. A., III; Toste, F. D.
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2
(
complexes: (a) Li, Q.-S.; Wan, C.-Q.; Zou, R.-Y.; Xu, F.-B.; Song,
H.-B.; Wan, X.-J.; Zhang, Z.-Z. Inorg. Chem. 2006, 45, 1888.
2
011, 133, 14293.
6) One or both R−M coupling partners can be replaced by R−H.
(
b) Herrero-Gom
Buchholz, J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2006, 45, 5455.
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́ ́
ez, E.; Nieto-Oberhuber, C.; Lopez, S.; Benet-
(
Examples of oxidative Au-catalyzed biaryl formation: (a) Ball, L. T.;
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T.; Lloyd-Jones, G. C.; Russell, C. A. J. Am. Chem. Soc. 2014, 136, 254.
(
́
́
́
(
1
c) Cambeiro, X. C.; Ahlsten, N.; Larrosa, I. J. Am. Chem. Soc. 2015,
37, 15636 and references cited therein..
7) Examples of directing group controlled oxidative addition to
(
̈
(
1
(
Au(I): (a) Guenther, J.; Mallet-Ladeira, S.; Estevez, L.; Miqueu, K.;
Amgoune, A.; Bourissou, D. J. Am. Chem. Soc. 2014, 136, 1778.
(
(
b) Tlahuext-Aca, A.; Hopkinson, M. N.; Daniliuc, C. G.; Glorius, F.
Chem. Sci. 2015, 6, 288. (b) Kumar, R.; Linden, A.; Nevado, C. J. Am.
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Chem. Sci. 2017, 8, 946.
(25) Analogous results were obtained using another arylZnCl reagent
(
8) Examples of Au-catalyzed processes enabled by directing group
(
see the SI).
controlled oxidative addition: Serra, J.; Whiteoak, C. J.; Acuna-Pares,
F.; Font, M.; Luis, J. M.; Lloret-Fillol, J.; Ribas, X. J. Am. Chem. Soc.
2
(
015, 137, 13389 See also ref 7c..
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Porcel, S. Chem. Commun. 2016, 52, 7295.
10) Au-catalyzed bond formations using aryl diazonium salts (often
5
(
under photochemical conditions): (a) Shu, X.-z.; Zhang, M.; He, Y.;
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Shi, X. Angew. Chem., Int. Ed. 2015, 54, 8772. (d) Tlahuext-Aca, A.;
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(
e) Peng, H.; Cai, R.; Xu, C.; Chen, H.; Shi, X. Chem. Sci. 2016, 7,
6
2
190. (f) Cornilleau, T.; Hermange, P.; Fouquet, E. Chem. Commun.
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(
(
i) Gauchot, V.; Lee, A.-L. Chem. Commun. 2016, 52, 10163.
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885. (k) Witzel, S.; Xie, J.; Rudolph, M.; Hashmi, A. S. K. Adv. Synth.
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F
DOI: 10.1021/jacs.8b01411
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX