Light-Induced Mechanistic Divergence in Gold(I) Catalysis: Revisiting the Reactivity of Diazonium Salts

Article abstract of DOI:10.1002/anie.201908268

In a systematic study of the Au-catalyzed reaction of o-alkynylphenols with aryldiazonium salts, we find that essentially the same reaction conditions lead to a change in mechanism when a light source is applied. If the reaction is carried out at room temperature using a Au^I catalyst, the diazonium salt undergoes electrophilic deauration of a vinyl Au^I intermediate and provides access to substituted azobenzofurans. If the reaction mixture is irradiated with blue LED light, C?C bond formation due to N₂-extrusion from the diazonium salt is realized selectively, using the same starting materials without the need for an additional photo(redox) catalyst under aerobic conditions. We report a series of experiments demonstrating that the same vinyl Au^I intermediate is capable of producing the observed products under photolytic and thermal conditions. The finding that a vinyl Au^I complex can directly, without the need for an additional photo(redox) catalyst, result in C?C bond formation under photolytic conditions is contrary to the proposed mechanistic pathways suggested in the literature till date and highlights that the role of oxidation state changes in photoredox catalysis involving Au is thus far only poorly understood and may hold surprises for the future. Computational results indicate that photochemical activation can occur directly from a donor–acceptor complex formed between the vinyl Au^I intermediate and the diazonium salt.

Full text of DOI:10.1002/anie.201908268

Angewandte
Research Articles
Chemie
International Edition: DOI: 10.1002/anie.201908268
German Edition: DOI: 10.1002/ange.201908268
Photoredox Catalysis
Light-Induced Mechanistic Divergence in Gold(I) Catalysis: Revisiting
the Reactivity of Diazonium Salts
Svenja Taschinski, Renꢀ Dçpp, Martin Ackermann, Frank Rominger, Folkert de Vries,
Maximilian F. S. J. Menger, Matthias Rudolph, A. Stephen K. Hashmi,* and
Johannes E. M. N. Klein*
Abstract: In a systematic study of the Au-catalyzed reaction of
o-alkynylphenols with aryldiazonium salts, we find that
essentially the same reaction conditions lead to a change in
mechanism when a light source is applied. If the reaction is
carried out at room temperature using a AuI catalyst, the
diazonium salt undergoes electrophilic deauration of a vinyl
AuI intermediate and provides access to substituted azobenzo-
furans. If the reaction mixture is irradiated with blue LED
2016 the group of Fensterbank reported the synthesis of
arylated benzofurans from o-alkynylphenols combining
a photo(redox) catalyst (Ru(bpy)3(PF6)2) and a Au catalyst.[3s]
À
light, C C bond formation due to N2-extrusion from the
diazonium salt is realized selectively, using the same starting
materials without the need for an additional photo(redox)
catalyst under aerobic conditions. We report a series of
experiments demonstrating that the same vinyl AuI intermedi-
ate is capable of producing the observed products under
photolytic and thermal conditions. The finding that a vinyl AuI
complex can directly, without the need for an additional
À
photo(redox) catalyst, result in C C bond formation under
photolytic conditions is contrary to the proposed mechanistic
pathways suggested in the literature till date and highlights that
the role of oxidation state changes in photoredox catalysis
involving Au is thus far only poorly understood and may hold
surprises for the future. Computational results indicate that
photochemical activation can occur directly from a donor–
acceptor complex formed between the vinyl AuI intermediate
and the diazonium salt.
P
hotoredox catalysis has emerged over the past years to
a highly competitive research area and many advances have
been made.[1] In particular, Au-catalyzed transformations[2]
that make use of light in combination with diazonium salts
have been identified.[3] In these transformations diazonium
salts commonly serve as aryl donors, leading to the extrusion
of N2 (for representative examples see Scheme 1A).[3k,v,w] In
Scheme 1. A) Selected examples for arylative Au photoredox cataly-
sis.[3s,v,w] B) Divergence in Au-catalyzed reactions leading to formation
of arylated benzofurans 7 (N2-extrusion) without additional photo-
(redox) catalyst and substituted azobenzofurans 8 (N2-retention).
[*] S. Taschinski, F. de Vries, Dr. J. E. M. N. Klein
Molecular Inorganic Chemistry, Stratingh Institute for Chemistry,
Faculty of Science and Engineering, University of Groningen
Nijenborgh 4, 9747 AG Groningen (The Netherlands)
E-mail: j.e.m.n.klein@rug.nl
Prof. Dr. A. S. K. Hashmi
Chemistry Department, Faculty of Science, King Abdulaziz University
Jeddah 21589 (Saudi Arabia)
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under https://doi.org/10.
1002/anie.201908268.
S. Taschinski, Dr. R. Dçpp, Dr. M. Ackermann, Dr. F. Rominger,
Dr. M. Rudolph, Prof. Dr. A. S. K. Hashmi
Organisch-Chemisches Institut, Heidelberg University
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
E-mail: hashmi@hashmi.de
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co.
KGaA. This is an open access article under the terms of the Creative
Commons Attribution Non-Commercial License, which permits use,
distribution and reproduction in any medium, provided the original
work is properly cited, and is not used for commercial purposes.
Dr. M. F. S. J. Menger
Zernike Institute for Advanced Materials, Faculty of Science and
Engineering, University of Groningen
Nijenborgh 4, 9747 AG Groningen (The Netherlands)
&&&&
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
These are not the final page numbers!

Angewandte
Research Articles
Chemie
This reaction interested us in two ways: 1) Some of us recently
precautions to exclude moisture or oxygen before being
reported reactions involving diazonium salts that did not
require a photo(redox) catalyst[3h,v] and wondered if this
reaction could also be carried out in the absence of an
additional photo(redox) catalyst. 2) We were curious if there
was a way to probe the involvement of a vinyl Au interme-
diate.[2f,4,5]
Our investigation led us to find that under very similar
reaction conditions o-alkynylphenols 6 can be either con-
verted to arylated benzofurans 7 photolytically or in the
absence of a light source to the formation of azobenzofurans
8. With this observation we demonstrate the first application
of diazonium salts as electrophiles with vinyl AuI intermedi-
exposed to a light source.
Interestingly, we observed small amounts of the azoben-
zene product 8Me in the absence of light. Notably, the yield of
product 8Me increased when the less coordinating anion Tf2NÀ
was used. An attempt to use a more soluble base 2,6-di-tert-
butyl-pyridine (DTBP) had a detrimental effect on the
reaction under photolytic conditions and changed little with
regards to the formation of the azobenzene product 8Me
.
There are some conclusions that can be delineated from these
experiments. Under photolytic conditions the use of simple
Ph3PAuCl leads to arylated benzofuran 7Me, albeit in the
absence of a photo(redox)catalyst and under aerobic con-
ditions. The finding of azobenzofuran 8Me in the absence of
light gives a strong indication that the reaction proceeds via
a vinyl AuI intermediate and establishes, to the best of our
À
ates that do not lead to N2-extrusion and form a C N bond
(Scheme 1B).
We began our studies by first exploring the reactivity of o-
alkynylphenol 6Me towards diazonium salt 2H by simply
varying the base, the counter anion of the Au complex and
the solvent using blue LED light (Table 1). In these experi-
ments we omitted the previously used Ru(bpy)3(PF6)2 addi-
tive. We quickly realized that simple Ph3PAuCl in combina-
tion with NaHCO3 results in reasonable yields of the desired
product 7Me. Unlike reported before,[3s] changing from the
chloride anion to the weakly coordinating anion Tf2NÀ had
very little effect on the outcome of the reaction. We note that
these reactions are operationally extremely straightforward.
All reagents were simply combined in a vial without
knowledge, the first observation of a nitrogen-based electro-
I
À
phile in C N bond formation from a vinyl Au complex.
Control experiments confirm that the products 7Me and 8Me
are not formed in the absence of a Au catalyst and that 7Me is
not formed under the reaction conditions while irradiating 8Me
(for these and several additional control experiments, see the
Supporting Information (SI)).
The previously proposed mechanism by Fensterbank and
co-workers employing a photo(redox) catalyst[3s] proposes
a photochemical oxidative addition of the diazonium salt to
the AuI complex producing a highly Lewis acidic AuIII
intermediate, that provides an open coordination site able
to function as a p-acid. Here, as in many other studies,[2i,3e,k,ab]
a vinyl AuIII intermediate is proposed to then form upon
reaction with an o-alkynylphenol substrate and reductive
elimination results in the formation of the arylated benzofur-
an products. Stoichiometric experiments have indeed dem-
onstrated that the photochemical oxidative addition of
diazonium salts is feasible both in an inter- and intramolecular
fashion.[3v,6] In the present case, varying the conditions of the
reaction solely by irradiation with light yielded two different
products (Table 1, entry 2). We wanted to investigate where
this difference originates and if these two reactions have
a common intermediate. We probed if oxidative addition of
a diazonium salt to the (pre)catalyst is feasible by irradiating
solutions of Ph3PAuCl or Ph3PAuNTf2 in the presence of
a diazonium salt and base (NaHCO3). During a period of 2 h
we did not observe changes to the concentrations of the
diazonium salt or Au complexes (see SI). This result suggests
that oxidative addition is not feasible in the present case.
Together with the observation that azobenzofuran 8Me forms
we can speculate that a vinyl AuI complex can form under the
reaction conditions. We decided to prepare vinyl AuI complex
9 following a reported procedure[4c] and treated it with
diazonium salt 2H (Scheme 2).
Table 1: Comparison of reactions conditions for the mechanistic diver-
gence.
Entry
Catalyst
Base
Yield 7Me [%]
Irradiation with
blue-LED[a,c]
MeCN
Yield 8Me [%]
No irradiation[a,b]
CH2Cl2
MeCN
7
1
2
3
4
Ph3PAuCl
NaHCO3
46[d,e]
54[d,e]
4
5
Ph3PAuNTf2
NaHCO3
22[d]
11
Ph3PAuCl
DTBP
not observed not observed
Ph3PAuNTf2
DTBP
11
19
23
Without irradiation, azocompound 8Me was obtained in
46% yield after 24 h, as determined by H NMR spectrosco-
[a] Averages of duplicate runs are given. [b] General conditions: 6Me
(50 mmol), [Au] (5.00 mol%), 2H (100 mmol), base (100 mmol), solvent
(500 mL), r.t., 24 h, determined via 1H NMR spectroscopy using benzyl
acetate as internal standard. [c] General conditions: 6Me (100 mmol), [Au]
(5.00 mol%), 2H (200 mmol), base (200 mmol), solvent (1 mL), r.t., 2 h,
450 nm light source, determined via GC-MS using hexamethylbenzene
as internal standard. [d] Full conversion of starting material. [e] With Au
and a ruthenium photo(redox) catalyst present, similar yields were
obtained with related substrates, see Ref. [3s].
1
py. Both 9 and 8Me could be characterized by single-crystal X-
ray structure analysis (Figure 1).
When we carried this reaction out in the presence of
a light source, we observed arylated benzofuran 7Me after 2 h
in 65% yield (Scheme 2). We note that both reactions gave
full conversion. A by-product formed during both reactions is
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
&&&&
These are not the final page numbers!

Angewandte
Research Articles
Chemie
Scheme 2. Reactivity of the isolated vinyl AuI complex 9 towards
diazonium salt 2H with and without irradiation. Conditions: 60 mm,
1
1.10 equiv. reactant. [a] Determined by H NMR spectroscopy, using
benzyl acetate as internal standard. [b] Determined by GC-MS, using
hexamethylbenzene as internal standard.
Figure 1. Solid state X-ray structure of vinyl AuI complex 9 (left) and
azobenzofuran 8Me (right). Thermal ellipsoids are shown at 50%
probability, hydrogen atoms are omitted for clarity.
Scheme 3. Proposed mechanisms for the divergent Au catalysis.
2-(p-tolyl)benzofuran 10, which arises from protodeauration.
10 is also formed under catalytic conditions (see SI), where
a large excess of acidic 6Me is present, which we suspect to
serve as a proton donor. We confirmed this hypothesis by
treating 9 with 6Me and PhOH as proton sources which
proceeded slowly to 10 (see SI). As irradiation of Ph3PAuCl or
Ph3PAuNTf2 in the presence of a diazonium salt and base did
not show any reaction in the absence of substrate 6Me, we
might postulate that the formation of a vinyl AuI complex
precedes potential oxidative addition. The stoichiometric
reactions between 9 and diazonium salt 2H also demonstrate
the intrinsically nucleophilic nature of these complexes. These
experiments clearly demonstrate that vinyl AuI complexes
can form under the reaction conditions and may serve as
intermediates in these transformations, where they are of key
relevance to the photochemical activation required for N2-
extrusion. The mechanistic scenarios we propose are outlined
in Scheme 3.
a vinyl AuI intermediate is complete, the diazonium salt 2
reacts either as a N-electrophile to form the azobenzofuran
product 8 under N2-retention (Scheme 3, Path A) or as a C-
electrophile to give arylated benzofuran 7 with concomitant
N2-extrusion (Scheme 3, Path B). At this point we cannot
differentiate if the photochemical activation after formation
of the vinyl AuI intermediate 9a leads to oxidative addition or
À
results in direct C C bond formation from the vinyl Au
complex 9a due to loss of N2. Interestingly, a related
stoichiometric experiment between an isolated vinyl AuI
complex and a diazonium salt was reported by Shin and co-
workers.[3w] In this case, however, a catalytic amount of
Ru(bpy)3(PF6)2 was still required to achieve photochemical
À
C C bond formation, emphasizing the intrinsically different
reactivity observed here in the absence of such an additive.
Very recently Fensterbank and co-workers also described the
reaction between an isolated vinyl AuI intermediate, essen-
tially the same as the one reported here just differing by the
phosphine ligand used, and an iodoalkyne which resulted in
We propose, that both reaction pathways proceed through
p-coordination of the catalyst A. The subsequent activation of
the triple bond leads to intramolecular nucleophilic attack of
the oxygen atom and forms intermediate B via a 5-endo-dig
cyclization (Scheme 3). Deprotonation of intermediate B by
base provides vinyl AuI complex 9a. Once the formation of
C C bond formation under photolytic conditions.[7] However,
À
this reaction also benefitted largely from the presence of an Ir
photosensitizer, which the authors attributed to energy
&&&&
www.angewandte.org
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
These are not the final page numbers!

Angewandte
Research Articles
Chemie
transfer from an excited triplet state of the Ir complex to the
middle). This is also very well reflected in the natural
transition orbitals which are shown in the SI. Vertical
vinyl AuI intermediate, where the subsequent C C bond
À
forming reaction takes place on the triplet surface. The
excitation to the computed S1 state lies 45.8 kcalmolÀ1 above
the S0 ground state (Figure 2, bottom left). Notably, we found
that the triplet state (T1) within this geometry is energetically
lower lying (29.7 kcalmolÀ1). Optimization of this triplet state
II further lowers the energy to 13.2 kcalmolÀ1 and more
reaction we report here does not make use of such an additive
À
and yet efficiently results in C C bond formation. We may
therefore ask how photochemical activation promotes this
reaction, especially as both reaction partners are essentially
colorless (see Figure 2, top right). A possible scenario is the
formation of a donor–acceptor complex between the vinyl
AuI complex and the diazonium salt, which we explored
computationally (for technical details and a more detailed
description see SI). We first fully optimized the geometry of
the non-covalently bound complex I between the Au complex
9 and PhN2+ (see Figure 2, top left) at the TPSS-D3(BJ)/def2-
SVP/PCM(MeCN) level of theory and then explored excited
states through TD-DFT calculations (CAM-B3LYP-D3(BJ)/
def2-SVPD/PCM(MeCN)).[8] We found a low-lying S1 excited
state that corresponds to charge transfer from the HOMO,
which is located at the electron rich vinyl AuI portion, to the
À
interestingly results in elongation of the C N bond distance in
+
the PhN2 unit from 1.362 to 1.449 ꢀ with the spin density
+
being distributed over both the vinyl Au and the PhN2
À
fragments (Figure 2, bottom right), indicating C N bond
activation. These results show that photochemical activation
from donor–acceptor complex I is possible and point us in the
direction that subsequent steps may take place on the triplet
surface, similar to the proposed pathway by Fensterbank and
co-workers.[7] The exact pathway of internal conversion,
intersystem crossing and especially the contribution from
the heavy element Au remain to be elucidated and should
give further insight on how Au-catalyzed transformations can
benefit from photochemical activation. We shall note here,
+
LUMO, which is located on the PhN2 unit (see Figure 2,
À
that the non-covalently bound complex I is also primed for C
N bond formation, the reaction we observe in the absence of
a light source. Thus, complex I lies at the heart of the
mechanistic divergence between the two pathways described
in this paper.
In both reaction paths shown in Scheme 3 the Au center
has to be readily available to act as a p-acid, a pathway that is
favored when using a weakly coordinating anion, such as
Tf2NÀ The photoreaction using Ph3PAuCl might therefore
require the replacement of the counter anion (chloride)
leading to a cationic species. As Table 1 entry 1 demonstrates
that Ph3PAuCl even leads to small amounts of product 8Me
,
which we judge to fully rely on the p-acidic nature of AuI, we
believe that the generation of a cationic AuI intermediate is
possible under the reaction conditions. Our study therefore
demonstrates that the presence or absence of light can
completely change the outcome of Au-catalyzed reactions at
the stage of a common vinyl AuI intermediate 9a and that no
additional photo(redox) catalyst is required.
With this mechanistic scenario in mind, we briefly probed
the reaction conditions for a small set of substrates. We first
continued our efforts to optimize the formation of azocom-
pounds and replaced Ph3PAuNTf2 with the NHC-Au complex
IMesAuNTf2, which has also been shown previously to lead to
stable vinyl AuI complexes,[4c,9] an intermediate that is key to
this reaction. Following a brief screening we identified that
the more soluble base DTBP in combination with IMe-
sAuNTf2 resulted in improved yields (for screening, see SI).
We then briefly investigated the scope of the reaction towards
electron donating and electron withdrawing groups at the
para-position of the diazonium salt and the alkyne, respec-
tively (Table 2).
The formation of the azocompound is favored if the aryl
group on the alkyne contains an electron donating substitu-
ent, resulting in yields up to 88% (Table 2, entry 1). The
reaction time increases significantly and yields decrease as the
substituent does not contain an electron donating group
(entries 3–4). The substitution pattern of the diazonium salt
also influences the reactivity. 2-(p-Tolylethynyl)phenol 6Me
Figure 2. Top: Proposed donor–acceptor complex I relevant for photo-
chemical activation and photos of 9 and PhN2BF4; Middle: depictions
of the HOMO and LUMO of the donor–acceptor complex I; Bottom:
Energy profile of the excited states for I and II and spin density plot for
II. All data shown was obtained at the CAM-B3LYP-D3(BJ)/def2-SVPD/
PCM(MeCN)//TPSS-D3(BJ)/def2-SVP/PCM(MeCN) level of theory.
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
&&&&
These are not the final page numbers!

Angewandte
Research Articles
Chemie
Table 2: Substrate scope for the formation of substituted azobenzofur-
ans and arylated benzofurans.
are formed in moderate to high yields. Stoichiometric experi-
ments demonstrate that these products are accessible from
the same vinyl AuI intermediate and lead us to propose that
the often suggested photochemical oxidative addit-
ion[3a–c,d–l,o–x,y–ae] either occurs after the formation of a vinyl
AuI species or may even not involve oxidation state changes.
We expect our findings to further fuel the research area of
Au-catalyzed photoredox catalysis and inspire new strategies
for transformations using light in combination with Au
catalysts.
Acknowledgements
Entry
R1
R2
Time [h]
Isolated yield [%]
No irradiation
We thank Prof. Dr. A. J. Minnaard (University of Groningen)
for providing access to a photoreactor. S.T. is grateful for
a Ph.D. scholarship from the German Academic Exchange
Service (DAAD). J.E.M.N.K. acknowledges access to com-
putational facilities at the Peregrine high-performance com-
puting cluster (University of Groningen) and access to the
national computing facilities provided by the Netherlands
Organisation for Scientific Research (NWO project number
17664). J.E.M.N.K. acknowledges funding from the Nether-
lands Organisation for Scientific Research (NWO START-
UP grant). A.S.K.H. is grateful for support by the Deutsche
Forschungsgemeinschaft (DFG, German Research Founda-
tion) under Germanyꢁs Excellence Strategy (2082/1–
390761711).
1
2
3
4
5
6
7
8OMe
8Me
8H
OMe
Me
H
H
H
H
H
OMe
Me
F
16
27
168
21 d
48
88
78
22
33
39
69
59
8F
F
8Me,OMe
8Me,Me
8Me,F
Me
Me
Me
27
48
Entry
R1
R2
Time [h]
Isolated yield [%]
Irradiation
8
9
10
11
7Me
7Me,Me
7Me,F
Me
Me
Me
Me
H
Me
F
2
4
2
2
51 (64[a])
46
53
7Me,NO2
NO2
32 (34[b])
[a] 10 mol% [Au]. [b] Reaction time: 30 minutes.
reacts in moderate yields with electron donating and with-
drawing groups at the diazonium salt (entries 5–7). For the
Conflict of interest
À
photochemical gold-catalyzed C C bond formation we pro-
The authors declare no conflict of interest.
bed reactivity using a set of diazonium salts with varying
electronic properties and obtained the desired products in
moderate yields (entries 8–11). In particular, we find that the
yield for the diazonium salt with the most electron with-
drawing group gave a surprisingly low yield, which is in
contrast to the previous finding reported by Fensterbank and
co-workers which found this to be particularly high-yield-
ing.[3s] Upon closer inspection we noticed that the product was
in fact partially consumed by the excess of diazonium salt
used under photolytic conditions (see SI). A reduction of the
reaction time to 30 min unfortunately did not increase the
yield of product 7Me,NO2, yet resulted in full conversion of the
starting material. One possible scenario for this more rapid
reaction could be a more efficient photochemical activation
from the proposed donor–acceptor complex I (see above). In
addition, we found that for the more electron rich diazonium
salt 2Me product formation was retarded (entry 9).
In summary, we have demonstrated that the mechanistic
pathway of Au-catalyzed reactions using diazonium salts can
be altered through the application of a light source. If the
reaction is carried out under blue-LED irradiation, arylated
benzofurans are obtained with N2-extrusion from the diazo-
nium salt under aerobic conditions without the need for an
additional photo(redox) catalyst in moderate yields. If the
reaction is carried out in the absence of a light source, the N2-
unit from the diazonium salt is retained and azobenzofurans
Keywords: diazo compound · homogeneous gold catalysis ·
mechanistic divergence · photochemistry ·
vinyl gold intermediate
[1] For selected reviews on photoredox catalysis, see: a) R. C.
McAtee, E. J. McClain, C. R. J. Stephenson, Trends Chem. 2019,
1, 111 – 125; b) L. Marzo, S. K. Pagire, O. Reiser, B. Kçnig,
Angew. Chem. Int. Ed. 2018, 57, 10034 – 10072; Angew. Chem.
2018, 130, 10188 – 10228; c) L. Revathi, L. Ravindar, W. Y. Fang,
K. P. Rakesh, H. L. Qin, Adv. Synth. Catal. 2018, 360, 4652 – 4698;
d) J. Twilton, C. Le, P. Zhang, M. H. Shaw, R. W. Evans, D. W. C.
MacMillan, Nat. Rev. Chem. 2017, 1, 0052; e) D. Menigaux, P.
Belmont, E. Brachet, Eur. J. Org. Chem. 2017, 2008 – 2055;
f) C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev.
2013, 113, 5322 – 5363; g) D. P. Hari, B. Kçnig, Angew. Chem. Int.
Ed. 2013, 52, 4734 – 4743; Angew. Chem. 2013, 125, 4832 – 4842.
[2] For selected reviews on Au catalysis, see: a) D. Pflꢂsterer, A. S. K.
Hashmi, Chem. Soc. Rev. 2016, 45, 1331 – 1367; b) R. Dorel, A. M.
Echavarren, Chem. Rev. 2015, 115, 9028 – 9072; c) L. Zhang, Acc.
Chem. Res. 2014, 47, 877 – 888; d) H. Ohno, Isr. J. Chem. 2013, 53,
869 – 882; e) I. Braun, A. M. Asiri, A. S. K. Hashmi, ACS Catal.
2013, 3, 1902 – 1907; f) L.-P. Liu, G. B. Hammond, Chem. Soc. Rev.
2012, 41, 3129 – 3139; For recent reviews on Au catalysis involving
photochemical activation, see: g) M. Zidan, S. Rohe, T. McCal-
&&&&
www.angewandte.org
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
These are not the final page numbers!

Angewandte
Research Articles
Chemie
lum, L. Barriault, Catal. Sci. Technol. 2018, 8, 6019 – 6028; h) T.
5697 – 5705; b) A. S. K. Hashmi, Angew. Chem. Int. Ed. 2010, 49,
McCallum, S. Rohe, L. Barriault, Synlett 2017, 28, 289 – 305; i) M.
Zhang, C. Zhu, L.-W. Ye, Synthesis 2017, 49, 1150 – 1157; j) M. D.
Levin, S. Kim, F. D. Toste, ACS Cent. Sci. 2016, 2, 293 – 301;
k) M. N. Hopkinson, A. Tlahuext-Aca, F. Glorius, Acc. Chem.
Res. 2016, 49, 2261 – 2272.
5232 – 5241; Angew. Chem. 2010, 122, 5360 – 5369; c) A. S. K.
Hashmi, T. D. Ramamurthi, F. Rominger, Adv. Synth. Catal. 2010,
352, 971 – 975; d) A. S. K. Hashmi, T. Dondeti Ramamurthi, F.
Rominger, J. Organomet. Chem. 2009, 694, 592 – 597; e) A. S. K.
Hashmi, A. M. Schuster, F. Rominger, Angew. Chem. Int. Ed.
2009, 48, 8247 – 8249; Angew. Chem. 2009, 121, 8396 – 8398;
f) L. P. Liu, G. B. Hammond, Chem. Asian J. 2009, 4, 1230 – 1236;
g) L.-P. Liu, B. Xu, M. S. Mashuta, G. B. Hammond, J. Am. Chem.
Soc. 2008, 130, 17642 – 17643; h) J. A. Akana, K. X. Bhattachar-
yya, P. Mꢅller, J. P. Sadighi, J. Am. Chem. Soc. 2007, 129, 7736 –
7737; i) A. S. K. Hashmi, G. J. Hutchings, Angew. Chem. Int. Ed.
2006, 45, 7896 – 7936; Angew. Chem. 2006, 118, 8064 – 8105.
[5] For selected examples of reactions involving vinyl AuI complexes,
see: a) A. Zhdanko, M. E. Maier, ACS Catal. 2015, 5, 5994 – 6004;
b) A. Zhdanko, M. E. Maier, Chem. Eur. J. 2014, 20, 1918 – 1930;
c) A. S. K. Hashmi, T. D. Ramamurthi, M. H. Todd, A. S.-K.
Tsang, K. Graf, Aust. J. Chem. 2010, 63, 1619 – 1626; d) J. P.
Weyrauch, A. S. K. Hashmi, A. Schuster, T. Hengst, S. Schetter,
A. Littmann, M. Rudolph, M. Hamzic, J. Visus, F. Rominger, W.
Frey, J. W. Bats, Chem. Eur. J. 2010, 16, 956 – 963; e) D. Weber,
M. A. Tarselli, M. R. Gagnꢆ, Angew. Chem. Int. Ed. 2009, 48,
5733 – 5736; Angew. Chem. 2009, 121, 5843 – 5846; f) H. A.
Wegner, S. Ahles, M. Neuburger, Chem. Eur. J. 2008, 14,
11310 – 11313; g) A. Kar, N. Mangu, H. M. Kaiser, M. Beller,
M. K. Tse, Chem. Commun. 2008, 386 – 388; h) M. Yu, G. Zhang,
L. Zhang, Org. Lett. 2007, 9, 2147 – 2150; i) S. A. Worlikar, T.
Kesharwani, T. Yao, R. C. Larock, J. Org. Chem. 2007, 72, 1347 –
1353; j) I. Nakamura, U. Yamagishi, D. Song, S. Konta, Y.
Yamamoto, Angew. Chem. Int. Ed. 2007, 46, 2284 – 2287; Angew.
Chem. 2007, 119, 2334 – 2337; k) I. Nakamura, T. Sato, M. Terada,
Y. Yamamoto, Org. Lett. 2007, 9, 4081 – 4083; l) S. F. Kirsch, J. T.
Binder, B. Crone, A. Duschek, T. T. Haug, C. Liꢆbert, H. Menz,
Angew. Chem. Int. Ed. 2007, 46, 2310 – 2313; Angew. Chem. 2007,
119, 2360 – 2363; m) B. Crone, S. F. Kirsch, J. Org. Chem. 2007, 72,
5435 – 5438; n) A. S. K. Hashmi, M. Rudolph, S. Schymura, J.
Visus, W. Frey, Eur. J. Org. Chem. 2006, 4905 – 4909.
[6] a) S. Kim, F. D. Toste, J. Am. Chem. Soc. 2019, 141, 4308 – 4315;
b) L. Huang, F. Rominger, M. Rudolph, A. S. K. Hashmi, Chem.
Commun. 2016, 52, 6435 – 6438; c) A. Tlahuext-Aca, M. N.
Hopkinson, C. G. Daniliuc, F. Glorius, Chem. Eur. J. 2016, 22,
11587 – 11592; d) E. O. Asomoza-Solꢇs, J. Rojas-Ocampo, R. A.
Toscano, S. Porcel, Chem. Commun. 2016, 52, 7295 – 7298.
[7] Z. Xia, V. Corcꢆ, F. Zhao, C. Przybylski, A. Espagne, L. Jullien, T.
Le Saux, Y. Gimbert, H. Dossmann, V. Mouriꢄs-Mansuy, C.
Ollivier, L. Fensterbank, Nat. Chem. 2019, 11, 797 – 805.
[8] For a complete list of references regarding the computational
methods chosen see the Supporting Information.
[9] a) R. Dçpp, C. Lothschꢅtz, T. Wurm, M. Pernpointner, S. Keller,
F. Rominger, A. S. K. Hashmi, Organometallics 2011, 30, 5894 –
5903; b) K. E. Roth, S. A. Blum, Organometallics 2010, 29, 1712 –
1716.
[3] For selected examples on photoredox Au catalysis involving
diazonium salts, see: a) M. O. Akram, S. Banerjee, S. S. Saswade,
V. Bedi, N. T. Patil, Chem. Commun. 2018, 54, 11069 – 11083; b) S.
Witzel, K. Sekine, M. Rudolph, A. S. K. Hashmi, Chem. Com-
mun. 2018, 54, 13802 – 13804; c) J. Xie, K. Sekine, S. Witzel, P.
Krꢂmer, M. Rudolph, F. Rominger, A. S. K. Hashmi, Angew.
Chem. Int. Ed. 2018, 57, 16648 – 16653; Angew. Chem. 2018, 130,
16890 – 16895; d) A. Tabey, M. Berlande, P. Hermange, E.
Fouquet, Chem. Commun. 2018, 54, 12867 – 12870; e) I. Chakra-
barty, M. O. Akram, S. Biswas, N. T. Patil, Chem. Commun. 2018,
54, 7223 – 7226; f) B. Dong, H. Peng, S. E. Motika, X. Shi, Chem.
Eur. J. 2017, 23, 11093 – 11099; g) A. H. Bansode, S. R. Shaikh,
R. G. Gonnade, N. T. Patil, Chem. Commun. 2017, 53, 9081 –
9084; h) S. Witzel, J. Xie, M. Rudolph, A. S. K. Hashmi, Adv.
Synth. Catal. 2017, 359, 1522 – 1528; i) C. Sauer, Y. Liu, A.
De Nisi, S. Protti, M. Fagnoni, M. Bandini, ChemCatChem 2017,
9, 4456 – 4459; j) J.-R. Deng, W.-C. Chan, N. Chun-Him Lai, B.
Yang, C.-S. Tsang, B. Chi-Bun Ko, S. Lai-Fung Chan, M.-K.
Wong, Chem. Sci. 2017, 8, 7537 – 7544; k) B. Alcaide, P. Almen-
dros, E. Busto, F. Herrera, C. Lꢃzaro-Milla, A. Luna, Adv. Synth.
Catal. 2017, 359, 2640 – 2652; l) B. Alcaide, P. Almendros, B.
Aparicio, C. Lꢃzaro-Milla, A. Luna, O. N. Faza, Adv. Synth. Catal.
2017, 359, 2789 – 2800; m) V. Gauchot, D. R. Sutherland, A. L.
Lee, Chem. Sci. 2017, 8, 2885 – 2889; n) A. Tlahuext-Aca, M. N.
Hopkinson, R. A. Garza-Sanchez, F. Glorius, Chem. Eur. J. 2016,
22, 5909 – 5913; o) T. Cornilleau, P. Hermange, E. Fouquet, Chem.
Commun. 2016, 52, 10040 – 10043; p) A. Tlahuext-Aca, M. N.
Hopkinson, B. Sahoo, F. Glorius, Chem. Sci. 2016, 7, 89 – 93; q) V.
Gauchot, A.-L. Lee, Chem. Commun. 2016, 52, 10163; r) S. Kim,
J. Rojas-Martin, F. D. Toste, Chem. Sci. 2016, 7, 85 – 88; s) Z. Xia,
O. Khaled, V. Mouriꢄs-Mansuy, C. Ollivier, L. Fensterbank, J.
Org. Chem. 2016, 81, 7182 – 7190; t) J. Um, H. Yun, S. Shin, Org.
Lett. 2016, 18, 484 – 487; u) B. Alcaide, P. Almendros, E. Busto, A.
Luna, Adv. Synth. Catal. 2016, 358, 1526 – 1533; v) L. Huang, M.
Rudolph, F. Rominger, A. S. K. Hashmi, Angew. Chem. Int. Ed.
2016, 55, 4808 – 4813; Angew. Chem. 2016, 128, 4888 – 4893;
w) D. V. Patil, H. Yun, S. Shin, Adv. Synth. Catal. 2015, 357, 2622 –
2628; x) R. Cai, M. Lu, E. Y. Aguilera, Y. Xi, N. G. Akhmedov,
J. L. Petersen, H. Chen, X. Shi, Angew. Chem. Int. Ed. 2015, 54,
8772 – 8776; Angew. Chem. 2015, 127, 8896 – 8900; y) Y. He, H.
Wu, F. D. Toste, Chem. Sci. 2015, 6, 1194 – 1198; z) M. N.
Hopkinson, B. Sahoo, F. Glorius, Adv. Synth. Catal. 2014, 356,
2794 – 2800; aa) X.-z. Shu, M. Zhang, Y. He, H. Frei, F. D. Toste, J.
Am. Chem. Soc. 2014, 136, 5844 – 5847; ab) B. Sahoo, M. N.
Hopkinson, F. Glorius, J. Am. Chem. Soc. 2013, 135, 5505 – 5508;
For related computational studies, see: ac) R. Bhattacharjee, A.
Datta, Chem. Eur. J. 2018, 24, 13636 – 13646; ad) Y. Liu, Y. Yang,
R. Zhu, C. Liu, D. Zhang, Chem. Eur. J. 2018, 24, 14119 – 14126;
ae) Q. Zhang, Z.-Q. Zhang, Y. Fu, H.-Z. Yu, ACS Catal. 2016, 6,
798 – 808.
Manuscript received: July 12, 2019
Revised manuscript received: September 2, 2019
[4] For selected examples of isolated vinyl AuI complexes, see: a) W.
Wang, G. B. Hammond, B. Xu, J. Am. Chem. Soc. 2012, 134,
Version of record online: && &&
,
&&&&
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
&&&&
These are not the final page numbers!

Angewandte
Research Articles
Chemie
Research Articles
Photoredox Catalysis
S. Taschinski, R. Dçpp, M. Ackermann,
F. Rominger, F. de Vries,
M. F. S. J. Menger, M. Rudolph,
A. S. K. Hashmi,*
The Au-catalyzed reaction of o-alkynyl-
phenols with aryldiazonium salts under-
goes a change in mechanism when a light
source is applied. If the reaction is carried
out at room temperature using a AuI
catalyst, the diazonium salt undergoes
electrophilic deauration of a vinyl AuI
intermediate generating substituted azo-
benzofurans. If the reaction mixture is
J. E. M. N. Klein*
&&&& — &&&&
À
Light-Induced Mechanistic Divergence in
Gold(I) Catalysis: Revisiting the
Reactivity of Diazonium Salts
irradiated with blue LED light, C C bond
formation due to N2-extrusion from the
diazonium salt is observed.
&&&&
www.angewandte.org
ꢀ 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2019, 58, 2 – 8
These are not the final page numbers!