Variations on the Theme of JohnPhos Gold(I) Catalysts: Arsine and Carbene Complexes with Similar Architectures

Article abstract of DOI:10.1021/acs.organomet.8b00276

Arsine and carbene gold(I) complexes with architectures closely related to those of 2-(di-tert-butylphosphino)biphenyl gold(I) complexes have been prepared and structurally characterized. As predicted, 2-(di-tert-butylarsine)biphenyl gold(I) complexes are more electrophilic catalysts in comparison to their phosphine analogues, whereas those based on 4-arylindazole behave similarly to NHC-gold(I) catalysts.

Full text of DOI:10.1021/acs.organomet.8b00276

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
Variations on the Theme of JohnPhos Gold(I) Catalysts: Arsine and
Carbene Complexes with Similar Architectures
†
†
†,‡
,†,‡
Javier Carreras, Ana Pereira, Margherita Zanini, and Antonio M. Echavarren*
†Institute of Chemical Research of Catalonia (ICIQ), Barcelona Institute of Science and Technology, Av. Països Catalans 16, 43007
Tarragona, Spain
‡
Departament de Química Analítica i Química Organica, Universitat Rovira i Virgili, C/Marcel·li Domingo s/n, 43007 Tarragona,
̀
Spain
*
S Supporting Information
ABSTRACT: Arsine and carbene gold(I) complexes with archi-
tectures closely related to those of 2-(di-tert-butylphosphino)-
biphenyl gold(I) complexes have been prepared and structurally
characterized. As predicted, 2-(di-tert-butylarsine)biphenyl gold(I)
complexes are more electrophilic catalysts in comparison to their
phosphine analogues, whereas those based on 4-arylindazole behave
similarly to NHC-gold(I) catalysts.
INTRODUCTION
■
The potential of gold(I) catalysts in the activation of multiple
bonds has been exploited to construct a wide range of complex
1
2
structures and natural products. The electrophilic activation
of alkynes is routinely carried out by using linear dicoordinated
chloride gold(I) complexes [LAuCl] (L = ligand) as
precatalysts, which are usually activated by chloride abstraction
using a silver salt, leading to cationic gold(I) species of the type
+
[
LAuL′] , where L′ is a weakly coordinating ligand, a solvent
3
molecule, or the reactive substrate. On the other hand,
reaction of complexes [LAuCl] with silver salts AgOTf and
AgNTf leads to neutral [LAuX] (X = OTf, NTf ) complexes.
Figure 1. Gold(I) complexes with dialkyl biphenyl phosphine (1−3),
phosphite (4), and N-heterocyclic carbene ligands (5).
2
2
The properties of gold(I) complexes can be tuned sterically
and electronically depending on the ligand, modulating their
reactivity in the activation of alkynes, alkenes, or allenes.
Complexes bearing bulky and strongly donating ligands are the
derivatives 1−3. The reason for the excellent performance of
these complexes in catalysis is not totally well understood.
Thus, the interaction between the metal center and the
1o,q,4
most used catalysts for the activation of enynes.
Among
6b
aromatic ring has been shown to be, at most, very weak.
these, commercially available complexes 1a−d with JohnPhos
However, this aromatic ring could still exert a certain degree of
stabilization of the carbocationic-like intermediates generated
in catalytic transformations of alkynes and other unsaturated
molecules.
and related ligands are among the most successful phosphine-
5
,6
gold(I) complexes.
Moreover, cationic complexes 2a−c
bearing a weakly coordinating ligand such as acetonitrile (or
benzonitrile) show analogous catalytic properties but are easier
to handle and do not require the use of any chloride
abstractor. The related neutral complexes 3a−c with a weakly
coordinating bis(trifluoromethanesulfonyl)amide ligand show
In contrast to that found in other transition-metal
complexes, the relation between the donor power of L ligands
7
+
and the electrophilicity of cationic [LAuL′] complexes is not
straightforward. This complex bonding phenomenon has been
8
similar reactivity (Figure 1). Complex 4 with a bulky
+
analyzed theoretically in detail in a series of [LAu(CO)]
phosphite as the ligand exhibits higher electrophilicity and
complexes with a variety of ligands, including phosphines and
9
therefore activates less reactive substrates. On the other side
11
NHC ligands. Interestingly, in these linear complexes, charge
of the spectrum of reactivity, complexes with electron-donating
N-heterocyclic carbene (NHC) ligands of general type 5 are
much less electrophilic, which makes these catalysts more
transfer (CT) is very significant for PPh (CT = 0.40 e) and
3
10
Special Issue: In Honor of the Career of Ernesto Carmona
Received: April 29, 2018
selective in many transformations.
Despite the wide variety of available gold(I) complexes, in
many cases the optimal catalysts are the biphenyl phosphine
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00276
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Organometallics
Article
JohnPhos (CT = 0.35 e) and low for NHC ligands such as IPr
The structures of new arsine gold(I) complexes 7−10 were
determined by X-ray diffraction (Figure 3). The As−Au bond
(
CT = 0.26 e). In general, back-donation from the L ligands is
I
+
very important in [LAu -S] (S = alkene, alkyne) complexes,
whereas the donation component is essentially constant even
for ligands with different charges (chloride vs phosphines and
NHC ligands).
There are only a few examples of gold(I) complexes or
other metals with an architecture similar to that of complexes
−3. With the aim of contributing to the understanding of the
1
2
13
1
4
1
ligand effects in gold(I) catalysis, we decided to explore other
related gold(I) complexes with steric environments closely
similar to that of JohnPhos but with very different electronic
properties. Thus, we prepared the first examples of 2-(di-tert-
butylarsine)biphenyl gold(I) complexes (Figure 2). Addition-
Figure 3. Structures of complexes 7 (a), 8 (b), 9 (c), and 10 (d) as
ORTEP plots (ellipsoids set at 50% probability). Hydrogen atoms,
solvate molecules, and anions are omitted for clarity.
Figure 2. New gold(I) complexes with 2-(di-tert-butylarsine)biphenyl
and 4-arylindazole ligand analogues of Johnphos Au(I) complex 1b.
ally, we also prepared in a simple manner a series of new 4-
arylindazole gold(I) complexes with highly donating ligands.
Here we describe the synthesis, structure, and reactivity of
both types of complexes in homogeneous gold(I) catalysis.
length in complex 7 is longer (2.352 Å) than the
corresponding P−Au bond in the analogous JohnPhos gold(I)
6
16
complexes 1b, 2b, and 3b (2.24−2.25 Å) (Table 1), in
Table 1. Selected Distances (Å) and Angles (deg) for 7−10
and 1b−3b
RESULTS AND DISCUSSION
Synthesis and Structure of Arsine Gold(I) Complexes.
We first synthesized the 2-(di-tert-butylarsine)biphenyl ligand
■
bond length
6
in two steps and overall 48% yield following a modified
bond angle
15
Au−X
X−Au−Cl,N
procedure for the synthesis of the analogous JohnPhos ligand
by reaction of the Grignard reagent of 2-bromobiphenyl with
tBu AsCl (Scheme 1). The structure of dialkylarylarsine 6 was
complex (X = P, As) Au−Cl,N
Au···Cipso
(X = P, As)
a
b
1
2
3
7
8
9
1
b
b
b
2.254(3)
2.2466(2)
2.2445(9)
2.3519(7)
2.332(5)
2.3400(5)
2.303(4)
2.0338(9)
2.113(3)
2.295(2)
2.103(3)
2.028(3)
2.045(2)
3.165
172.56(14)
174.43(3)
170.76(8)
175.29(5)
170.99(8)
174.81(9)
173.98(6)
2
a
c
3.024(1)
3.187(3)
3.247(7)
3.329(3)
3.154(3)
3.133(2)
Scheme 1. Synthesis of Biphenylarsine Gold(I) Complexes
7−10
0
2.3457(4)
a
b
Reference 15. The standard deviation of the calculated Au−C
ipso
distance could not be determined due to the applied constraints of the
coordinated atoms involved. Reference 13.
c
agreement with that previously reported for arsine gold
1
8−20
complexes.
Similar bond lengths were observed in
complexes 8−10 and JohnPhos gold(I) ligands (Table 1).
The Au−Cl or Au−N bond lengths in arsine complexes 7−10
are shorter than those in the JohnPhos complexes 1b−3b. The
As−Au−L angles for complexes 7−10 are in the 170−176°
range, similar to those observed in analogous phosphine
complexes 1b−3b (Table 1).
confirmed by X-ray diffraction. Gold chloride complex 7 was
Chloride-bridged dinuclear gold(I) complex 11 was
prepared in quantitative yield by mixing 7 with 0.5 equiv of
AgSbF in CH Cl as a noncoordinating solvent (Scheme 2),
prepared by reaction of 6 with [Au(SMe )Cl] in 86% yield.
2
Reaction of 7 with silver bis(trifluoromethanesulfonyl)amide
gave neutral gold complex 8, following the procedure described
6
2
2
in a manner similar to that observed before for the analogous
16
16
for the analogous JohnPhos complex. In addition, acetonitrile
and benzonitrile cationic complexes 9 and 10 were obtained in
quantitative yields from 7 using silver hexafluoroantimonate in
phosphine complexes. The Au−Au distance (3.44 Å) and
Au−Cl−Au angle (94.1°) for 11 are similar to those of the
analogous dinuclear gold(I) complex [(JohnPhosAu) Cl]-
2
17
16
the presence of an excess of the corresponding nitrile.
(SbF ) (Au−Au = 3.48 Å, Au−Cl−Au = 94.7°).
6
B
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Article
Scheme 2. Synthesis and Structure of Chloride-Bridged
Dinuclear Gold(I) Complex 11
phosphine complex has a higher Lewis acidity in comparison to
its arsine analogue.
a
In order to more clearly assess the differences between
arsine ligand 6 and JohnPhos, we decided to compare the
corresponding gold(I) π-alkene complexes. Complexes with
simple alkenes were synthesized by treating gold(I) complex 7
with 1.1 equiv of AgSbF in the presence of an excess of alkene
6
in dry CH Cl following the procedure reported by
2
2
2
3
Widenhoefer (Scheme 3). Interestingly, in the case of both
Scheme 3. Synthesis and Structure of Gold(I) π-Alkene
a
Complexes 12 and 13
a
An ORTEP plot (50% thermal ellipsoids) is given. Hydrogen atoms,
solvate molecules, and anions are omitted for clarity.
0
I
The substitution of PPh by AsPh in the case of Ni and Rh
3
3
carbonyl complexes has only minor effects on the ν
CO
0
−1
−1
frequency (Ni , 2069 cm for PPh3 vs 2068 cm for
I
−1
−1
21
AsPh ; Rh , 1979 cm for PPh vs 1975 cm for AsPh3).
3
3
However, the Rh−Cl bond distances in trans-[RhCl(CO)(L) ]
2
complexes are shorter for L = AsPh (2.354(2) Å) than for L =
3
a
An ORTEP plot (ellipsoids set at 50% probability) is given.
PPh (2.382(1) Å, which suggests a lower donor ability of the
3
Hydrogen atoms, solvate molecules, and anions are omitted for
clarity.
arsine ligand. As shown before, in our case, the Au−Cl and
Au−N bond lengths in arsine complexes 7−10 are in all cases
shorter than those of their phosphine analogues (Table 1),
which agrees with the lower donor capacity of the arsines.
11
However, as has been observed before, rationalizing ligand
effects in linear gold(I) is far from trivial. We decided to apply
the Gutmann−Beckett method to determine the relative Lewis
acidity of the gold(I) complexes by adding an excess of
phosphine oxides R PO to CH Cl solutions of gold(I)
methylencyclohexane and 2,3-dimethyl-2-butene, instead of
the direct formation of the π-complex with the double bond,
complexes 12 and 13 of the corresponding isomers arising
from a formal 1,3-hydrogen shift in the alkene were obtained as
the only products in quantitative yields. The structures of 12
and 13 were confirmed by X-ray diffraction.
We hypothesized that the double-bond isomerization takes
place outside the coordination sphere of the metal by a
Brønsted acid catalyzed pathway. In support of this
hypothesis, treatment of arsine complex 9 with an excess of
methylenecyclohexane in dry CH Cl under silver-free
conditions leads to the formation of complex 14 without
isomerization of the double bond, demonstrating that the silver
salt is fundamental for the in situ generation of the Brønsted
acid (Scheme 4). With 2,5-dimethylhexa-1,5-diene as the
starting material, the corresponding dicationic digold(I)
complex 15 was prepared. In the reaction of the same diene
3
2
2
complexes, measuring the chemical shift differences between
23
22
free and coordinated phosphite (Table 2). Surprisingly, no
significant differences were observed for the biphenylphos-
phine and arsine complexes (Table 2, entries 1−6), which
indicates that both types of complexes have similar Lewis
24
acidities. The comparison between [Au(PPh )Cl] and [Au-
3
2
2
(
AsPh )Cl] (Table 2, entries 7−10) actually suggests that the
3
Table 2. 31P Chemical Shift Differences upon Coordination
of Phosphine Oxides to Arsine and Phosphine Gold(I)
Complexes
with 7 and AgSbF , a mixture of oligomerization products was
6
entry
complex
T (°C)
R3PO
δ coord R PO
Δδ
obtained, supporting the hypothesis of the involvement of a
Brønsted acid in the reaction. However, under these reaction
conditions we never observed the formation of the non-
isomerized complex with 2,3-dimethyl-2-butene, probably due
3
a
1
2
3
4
5
6
7
8
9
1b
7
2b
9
3b
7
25
25
POPh Me
44.8
43.5
56.6
56.9
56.6
56.9
48.6
39.5
65.6
59.4
13.2
11.8
24.3
24.6
24.3
24.6
16.9
8.3
2
a
POPh Me
2
−50
−50
−50
−50
25
25
25
25
POPh Me
2
24
to steric reasons.
POPh Me
2
The Widenhoefer group reported that the reaction of
JohnPhos gold(I) complex 1b with excess alkenes in the
POPh Me
2
POPh Me
2
a
presence of AgSbF under anhydrous conditions leads to the π-
[Au(PPh )Cl]
POPh Me
6
3
2
a
alkene complexes without isomerization of the starting
[Au(AsPh )Cl]
POPh Me
3
2
23
a
alkenes. However, isomerization was observed when the
[Au(PPh )Cl]
POEt3
POEt3
11.3
5.1
3
a
1
0
[Au(AsPh )Cl]
reactions were performed with 1b and AgSbF in wet CH Cl
6
2
2
3
(
Scheme 5). The structures of the complexes 16a,b were
a
1
equiv of AgSbF6.
confirmed by X-ray diffraction.
C
DOI: 10.1021/acs.organomet.8b00276
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Article
Scheme 4. Synthesis and Structure of Gold(I) π-Alkene
Complexes 14 and 15
respectively. These structural data, as well as those found for
7−10 (Table 1), demonstrate the higher electrophilic
character of the arsine−gold frame in comparison to the
phosphine counterpart (Table 3).
Table 3. Selected X-ray Diffraction Distances (Å) for
Complexes 12, 13, and 16a,b
bond length
a
b
complex
Au−X (X = P, As)
Au−C1
Au−C2
1
1
1
1
2
3
6a
6b
2.375(2)
2.22(3)
2.32(3)
2.3844(3)
2.9414(18)
2.306(8)
2.197(4)
2.239(9)
2.24(5)
2.310(6)
2.351(11)
2.35(5)
a
2
b
2
Less substituted sp carbon. More substituted sp carbon.
The synthesis of the two Ag(I) complexes 18 and 19 with
ligand 6 that are isoleptic with respect to 9 and 14 was also
performed by using essentially the same synthetic procedures
Scheme 5. Synthesis of Gold(I) π-Alkene Complexes 16a,b
(
Scheme 7).
Scheme 7. Synthesis of Bisphenylarsine Silver(I) Complexes
The structure of 18 was determined by X-ray diffraction
(
Figure 4). As already observed with analogous phosphine
6b
The 1,3-hydrogen migration can be induced on the
preformed complex with both JohnPhos and arsine ligands in
the presence of an exogenous Brønsted acid such as TfOH as
complexes, the As−Ag−N angle in 18 deviates more from
linearity than that in the gold(I) complex 9 (168.2° vs 174.8°).
2
5
25
the catalyst. Considering these and other related results, we
propose that, in the case of methylencyclohexane, the initial π-
complex 17 undergoes ligand exchange with triflate anion to
form neutral complex I (Scheme 6). The free alkene then
Scheme 6. Mechanism of the Formal 1,3-Hydrogen
Migration in the π-Complexes in the Presence of a Brønsted
Acid
Figure 4. Structure of complex 18 as an ORTEP plot (ellipsoids set at
5
=
1
0% probability). Selected bond lengths (Å) and angle (deg): Ag−As
2.444(4), Ag−N = 2.135(3), Ag−C = 3.222; As−Ag−N =
ipso
68.18(9).
undergoes a Brønsted acid catalyzed isomerization to form 1-
methyl-1-cycloxene, which reacts with I to form the
thermodynamically more stable complex 16a. In the case of
reaction with 2,3-dimethylbut-2-ene, the less hindered
complexes 13 and 16b are obtained, since in the initial
complexes two methyl groups point toward the phenyl ring of
the ligand, causing significant steric congestion.
Synthesis and Structure of Indazole Gold(I) Com-
plexes. We also decided to target 4-arylindazoles as
electronically modular ligands with a related JohnPhos
architecture. Only three examples of indazole gold(I)
26,27
complexes have been reported,
and their catalytic proper-
ties were only examined in one instance for the hydration of
2
6c
alkynes.
For the synthesis of these complexes, we
In all of the complexes with an isomerized double bond, the
alkene is bound asymmetrically to the metal center, with the
commenced with the Suzuki coupling of 4-bromo-1-methyl-
1H-indazole (20) to introduce aryl groups with different
28
less substituted carbon closer to gold. The C −gold(I)
electronic properties (Scheme 8). Nucleophilic aromatic
substitution was used to prepare the polyfluorinated tolyl
derivative 21e in good yield. Quaternization of the indazole
sp2
distances are shorter for arsine complexes 12 and 13 in
comparison to those found for phosphine complexes 16a,b,
D
DOI: 10.1021/acs.organomet.8b00276
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Organometallics
Article
Scheme 8. Preparation of 4-Arylindazole Gold(I)
Complexes 23a−e and 24b,c
proceeded in moderate to good yields using diethyl sulfate in
toluene at reflux, followed by treatment with an aqueous
NaBF solution (65−84%). The formation of salts 22·BF a−e
4
4
1
was confirmed by their H NMR spectra, which show the
characteristic downfield signal for the hydrogen at C-3. Anion
exchange by chloride gave salts 22·Cla−e in excellent yields by
−
29
treatment with Amberlyte 402 IRA Cl . The structures of
Figure 5. Structures of the complexes 23a (a), 23b (b), 23c (c), 23d
salts 22·BF b,c and 22·Clb were confirmed by X-ray
4
(
d), 23e (e) and 24b (f) as ORTEP plots (ellipsoids set at 50%
diffraction.
probability). Hydrogen atoms, solvate molecules, and anions are
omitted for clarity.
The synthesis of the gold(I) complexes was accomplished
30
using the silver−carbene transfer methodology. Indazolium
salts 22·Cla−e reacted with Ag O, and the resulting silver
2
complexes were directly transmetalated with [Au(SMe )Cl] to
Catalytic Studies. To determine the electrophilicity of the
new gold(I) complexes 7−9 and 23a−e, we investigated their
catalytic potential in the context of 1,6-enyne activation,
focusing initially on intramolecular transformations. First, we
examined the [4 + 2] cycloaddition reaction of phenyl-
2
give complexes 23a−e in excellent yields (81−94%) (Scheme
8
). Cationic gold(I) complexes 24b,c were synthesized using
AgSbF and benzonitrile as a weakly coordinating ligand.
6
Complexes 23a−e and 24b were characterized by X-ray
diffraction (Figure 5). The expected nearly linear arrangement
around gold was observed with C(3)−Au−Cl bond angles
from 173.4 to 178.4° (Table 4). The Au−Cl distances ranged
from 2.291 to 2.318 Å and those of Au−C(3) from 1.982 to
5
,33
substituted 1,6-enyne 27a to form tricyclic derivative 28
(Table 6). For this transformation, arsine complexes provide
excellent results, comparable to those reported with phosphine
33
ligands. Neutral complex 7, in combination with NaBArF,
gave tricyclic product 28 in excellent yield after 6 h (Table 6,
entry 1). Similar good results were obtained with neutral (8)
or cationic (9) complexes (Table 6, entries 2 and 3).
1
.990 Å, in agreement with those previously reported for
26
indazole gold complexes. Notably, complex 23e revealed
distance, which is
significant differences in the Au−C
ipso
approximately 0.2−0.3 Å shorter than those for the rest of the
For 4-arylindazole-gold(I) complexes, we observed a
significant difference between dimethoxyphenyl- and phenyl-
substituted complexes 23a,b, which gave product 28 in
moderate yields after relatively long reaction times (Table 6,
entries 4 and 5), and those substituted with electron-poor
aromatic rings, particularly the fluorinated complexes (Table 6,
entries 6−8), which gave results similar to those for
phosphines or arsine ligands regarding reaction times and
indazole complexes. The distance observed in 23e (3.245 Å) is
6
closer to the reported data for JohnPhosAuCl (3.165 Å). The
angle between the indazole and the aromatic ring is also very
different in this complex, with a value close to 90°, instead of
the 50−55° observed for the rest of the arylindazole gold(I)
complexes.
13C NMR spectroscopy has been used for the study of the
properties of N-heterocyclic carbenes and their corresponding
34
yield.
3
1
complexes, and a relation between the chemical shift of the
carbenic carbon and the acidity of the complex has been
We also tested the new catalysts in the intramolecular
cyclopropanation of dienyne 27b to afford tetracycle 29 or the
3
2
35
suggested (Table 5). In the case of our complexes, no
significant differences were observed in complexes 23a−e,
which display chemical shifts between 170.0 and 168.4 ppm,
slightly upfield with respect to the values reported for the
known complexes 25 and 26, in similar solvents (CD Cl vs
product of single-cleavage rearrangement (Table 7). Using
arsine-gold(I) complex 9 at −40 °C, 29 was obtained as the
main product together with triene 30 (Table 7, entry 1). When
the temperature was increased to 23 °C, the reaction was fast
and less selective, leading to a 57:43 mixture of 29 and 30
(Table 7, entry 2). The selective formation of tetracycle 29 was
2
2
26b,c
CDCl , entries 6 and 7, Table 5).
3
E
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Table 4. Selected X-ray Diffraction Distances (Å) and Angles (deg) for 23a−e
bond length
angle
complex
Au−Cl
Au−C(3)
Au···Cipso
C(3)−Au−Cl
C−C−C−C
2
2
2
2
2
3a
3b
3c
3d
3e
2.293(2)
1.982(7)
1.988(8)
1.988(2)
1.983(5)
1.990(2)
3.586(7)
3.463(9)
3.539(2)
3.458(6)
3.245(2)
176.5(2)
178.4(2)
178.41(7)
175.79(16)
173.42(7)
52.3(9)
55.8(9)
50.4(3)
51.1(8)
84.0(3)
2.3184(17)
2.2905(6)
2.2934(14)
2.2986(7)
Table 5. Chemical Shift of Carbene Carbon for Indazole
Gold(I) Complexes
Table 7. Gold(I)-Catalyzed Cyclization of Dienyne 27b
a
b
entry
catalyst
T (°C)
time (h)
yield (%)
entry
complex
Ar
δc(Au−C)
solvent
1
2
3
4
5
6
7
9
9
−40
23
24
0.5
1
1
1
84 (88:12)
92 (57:43)
70 (100:0)
92 (100:0)
89 (100:0)
55 (100:0)
52 (100:0)
1
2
3
4
5
6
7
23a
23b
23c
23d
23e
3,5-MeOC H
170.0
170.0
169.3
169.1
168.4
172.6
173.7
CD Cl2
6
3
2
C H
6
CD Cl2
23a/AgSbF
23b/AgSbF
23c/AgSbF
23d/AgSbF
6
−40
−40
−40
−40
−40
5
2
3,5-CF C H
CD Cl2
6
3
6
3
2
2-NO C H
CD Cl2
6
2
6
4
2
3-CF C F
CD Cl2
6
1
1
3
6
4
2
a
25
CDCl3
CDCl3
23e/AgSbF
6
b
a
26
See the Supporting Information for detailed reaction conditions.
Yields determined by H NMR using diphenylmethane as internal
standard for entries 1 and 2; isolated yields for entries 3−7. Product
ratios are given in parentheses.
b
1
a
b
Reference 26c. Reference 26b.
Table 6. [4 + 2] Cycloaddition of 27a To Form 28 with
Different Gold(I) Complexes
Table 8. Gold(I)-Catalyzed Cyclization of 1,6-Enyne 27c
a
b
entry
catalyst
time (h)
yield (%)
a
b
7/NaBArF
entry
catalyst
time (h)
yield (%)
1
2
3
4
5
6
7
8
6
1
1
7
95
86
93
55
60
89
73
87
c
7/NaBArF
8
9
1
2
3
0.25
1
1
0.5
0.25
0.5
92 (92:7:1)
73 (97:0:3)
70 (97:0:3)
87 (39:58:3)
96 (97:0:3)
24 (42:51:7)
d
7/NaBArF
e
7/NaBArF
23a/AgSbF6
23b/AgSbF6
23c/AgSbF6
23d/AgSbF6
23e/AgSbF6
7
4
5
6
8
9
24b
1.5
1.25
1
a
See the Supporting Information for detailed reaction conditions.
Yields determined by H NMR spectroscopy using diphenylmethane
as internal standard. Product ratios are given in parentheses.
Conditions A: see text. Conditions B: see text. Conditions C:
b
1
a
See the Supporting Information for detailed reaction conditions.
b
1
Yields determined by H NMR using diphenylmethane as internal
c
d
e
standard for entries 1−4; isolated yields for entries 5−9.
see text.
achieved in high yields when the reaction was performed at
−
40 °C with the less electrophilic indazole-gold complexes
diene 31 were achieved under conditions A, in line with what
we have observed before for phosphine gold(I) complexes.
16
2
3a−c (Table 7, entries 3−5). In the case of the more
electrophilic catalysts 23d,e, 29 was again selectively formed,
although the yields were lower (Table 7, entries 6 and 7).
To further delineate the reactivity of our new gold(I)
Presumably, when precatalyst 7 is activated in situ in the
presence of the substrate (conditions A), formation of the less
reactive chloride-bridged dinuclear complex 11 is minimized. A
similar result was obtained using cationic complex 9, which
does not require activation by a silver salt (Table 8, entry 5).
Using neutral bistriflimide complex 8, a significant amount of
the product of double-bond isomerization, 32, was obtained
(Table 8, entry 4). Indazole gold complex 24b led to poor
results in terms of both reactivity and selectivity (Table 8,
entry 6).
3
5−37
complexes, the cycloisomerization of 1,6-enyne 27c
was
examined (Table 8). First, we examined the reaction with
neutral arsine complex 7 under three different conditions: (A)
in situ generation of the catalyst from 7 in the presence of the
substrate (Table 8, entry 1), (B) in situ generation of the
catalyst followed by the addition of the substrate (Table 8,
entry 2), and (C) filtration of the catalyst through Celite after
its generation in situ followed by the addition of the substrate
Our study was extended to intermolecular reactions between
3
8
(Table 8, entry 3). The fastest reaction and highest yield of
different nucleophiles and 1,6-enynes or alkynes. We
F
DOI: 10.1021/acs.organomet.8b00276
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
explored first the reaction of 1,6-enyne 27d with indole (Table
40
for 16 h in aqueous methanol using just 1 mol % of catalyst
(Table 10, entries 1 and 2). Two unsymmetrical alkynes could
be efficiently converted to the corresponding mixture of
ketones (Table 10, entries 3 and 4). Under these reaction
conditions, indazole-gold(I) complexes suffered decomposi-
tion.
39
9
). This reaction has been studied by our group and others
Table 9. Gold(I)-Catalyzed Addition of Indole to 1,6-Enyne
2
7d
CONCLUSIONS
■
We have reported the synthesis and characterization of a series
of arsine and carbene gold(I) complexes structurally related to
a 2-(di-tert-butylphosphino)biphenyl gold(I) complex. In
comparison to the biphenylphosphine complexes, the arsine
analogues are more electrophilic but have similar Lewis acidity.
We additionally synthesized a series of arsine gold(I) π-alkene
complexes. Under conditions in which Brønsted acids are
generated in situ, the initial alkenes undergo isomerization by
formal 1,3-H shifts to finally form gold(I) complexes with the
most stable alkene isomers. In the 4-arylindazole series, the
new complexes show structural features in line with previously
reported indazole-containing complexes, although complex
23e revealed significant differences, having an architecture
closer to JohnPhosAuCl in comparison to the rest of the series.
Additionally, we performed several catalytic studies with the
two new families of complexes. As expected from structural
studies, the arsine series are more electrophilic, whereas the 4-
arylindazole family shows a behavior similar to that of NHC-
gold(I) complexes.
a
b
entry
catalyst
yield (%)
1
2
3
4
5
6
9
95 (69:31)
21 (20:80)
42 (25:75)
73 (40:60)
41 (33:67)
61 (75:25)
23a/AgSbF6
23b/AgSbF6
23c/AgSbF6
23d/AgSbF6
23e/AgSbF6
a
See the Supporting Information for detailed reaction conditions.
Yields determined by H NMR using 1,3,5-trimethoxybenzene as
internal standard for entry 1; isolated yields for entries 2−6. Product
b
1
ratios are given in parentheses.
as a test of the electrophilicity of gold(I) catalysts. Two
different adducts can be obtained in this reaction: product 34
from attack of indole at the cyclopropane of the key reaction
intermediate, which is favored by the more electrophilic
catalysts, or 35 from attack at the gold(I) carbene carbon,
39
ASSOCIATED CONTENT
Supporting Information
favored by the less electrophilic catalysts. As expected, an
electrophilic complex such as cationic arsine-gold(I) 9 favors
formation of 34 (Table 9, entry 1), whereas indazole gold(I)
complexes 23a−d led preferentially to 35 (Table 9, entries 2−
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00276.
5
). Interestingly, complex 23e essentially gives the same result
(
2
Table 9, entry 6) previously obtained with JohnPhos complex
All procedures and characterization data for new
compounds (PDF)
39a
b (74% yield, 80:20).
Finally, we focused on the hydration of alkynes, one of the
41
most studied reactions in gold catalysis. Among the many
experimental procedures, the general procedure reported by
Nolan using low catalyst loadings of a [(NHC)Au(I)]-based
complex stands out because no acidic promoters are
required. With this in mind, we decided to study the
catalytic activity of our newly prepared complexes in the
hydration of different alkynes under Brønsted acid free
conditions (Table 10). Hence, cationic arsine complex 9
provided excellent results in the hydration of 1-octyne and
diphenylacetylene when the reaction was carried out at 70 °C
Accession Codes
CCDC 1839790−1839811 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
4
2
AUTHOR INFORMATION
Corresponding Author
E-mail for A.M.E.: aechavarren@iciq.es.
■
*
Table 10. Gold(I)-Catalyzed Hydration of Alkynes with
Complex 9
ORCID
Antonio M. Echavarren: 0000-0001-6808-3007
Notes
The authors declare no competing financial interest.
entry
alkyne
1-octyne
diphenylacetylene
2-hexyne
yield (%)
a
1
2
3
4
99
99
ACKNOWLEDGMENTS
This article is dedicated to Professor Ernesto Carmona on the
occasion of his 70th birthday. We thank Agencia Estatal de
■
a
b
,
c
96 (45:55)
99 (43:57)
b
,
d
1-phenyl-1-butyne
Investigacion (AEI)/FEDER, UE (CTQ2016-75960-P), Sev-
́
a
ero Ochoa Excellence Acreditation 2014-2018 (SEV-2013-
0319 and La Caixa-Severo Ochoa predoctoral fellowship to
M.Z.), the European Research Council (Advanced Grant No.
321066), the AGAUR (2017 SGR 1257 and Beatriu de Pinos
́
Postdoctoral Fellowship to J.C.), and CERCA Program/
Yields were determined by GC-FID using a single-point calibration
b
method and diphenylmethane as internal standard. Yields were
1
determined by H NMR using diphenylmethane as internal standard.
c
d
Ratio 2-hexanone:3-hexanone. Ratio 1-phenyl-2-butanone:butyro-
phenone.
G
DOI: 10.1021/acs.organomet.8b00276
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Generalitat de Catalunya for financial support. We also thank
the ICIQ X-ray Diffraction unit.
Reactions of Enynes. Angew. Chem., Int. Ed. 2006, 45, 5452−5455.
(
b) Rao, W.; Susanti, D.; Ayers, B. J.; Chan, P. W. H. Ligand-
Controlled Product Selectivity in Gold-Catalyzed Double Cyclo-
isomerization of 1,11-Dien-3,9-Diyne Benzoates. J. Am. Chem. Soc.
REFERENCES
■
2015, 137, 6350−6355. (c) Yang, J.-M.; Tang, X.-Y.; Shi, M. Gold(I)-
(
1) (a) Zhang, L.; Sun, J.; Kozmin, S. A. Gold and Platinum
Catalysis of Enyne Cycloisomerization. Adv. Synth. Catal. 2006, 348,
̈
271−2296. (b) Furstner, A.; Davies, P. W. Catalytic Carbophilic
Activation: Catalysis by Platinum and Gold π Acids. Angew. Chem.,
Int. Ed. 2007, 46, 3410−3449. (c) Hashmi, A. S. K. Gold-Catalyzed
Organic Reactions. Chem. Rev. 2007, 107, 3180−3211. (d) Li, Z.;
Brouwer, C.; He, C. Gold-Catalyzed Organic Transformations. Chem.
Rev. 2008, 108, 3239−3265. (e) Arcadi, A. Alternative Synthetic
Methods through New Developments in Catalysis by Gold. Chem.
Catalyzed Intramolecular Cycloisomerization of Propargylic Esters
with Furan Rings. Chem. - Eur. J. 2015, 21, 4534−4540. (d) Gimeno,
A.; Rodriguez-Gimeno, A.; Cuenca, A. B.; Ramirez de Arellano, C.;
Medio-Simon, M.; Asensio, G. Gold(I)-Catalysed Cascade Reactions
in the Synthesis of 2,3-Fused Indole Derivatives. Chem. Commun.
2
2
(
015, 51, 12384−12387.
8) (a) Buzas, A. K.; Istrate, F. M.; Gagosz, F. Gold(I)-Catalyzed 5-
Endo Hydroxy-and Alkoxycyclization of 1,5-Enynes: Efficient Access
to Functionalized Cyclopentenes. Angew. Chem., Int. Ed. 2007, 46,
Rev. 2008, 108, 3266−3325. (f) Jimenez-Nunez, E.; Echavarren, A. M.
́
́
̃
1
141−1144. (b) Bohringer, S.; Gagosz, F. Gold(I)-Catalyzed [4 + 2]
̈
Gold-Catalyzed Cycloisomerizations of Enynes: A Mechanistic
Perspective. Chem. Rev. 2008, 108, 3326−3350. (g) Gorin, D. J.;
Sherry, B. D.; Toste, F. D. Ligand Effects in Homogeneous Au
Catalysis. Chem. Rev. 2008, 108, 3351−3378. (h) Michelet, V.;
Annelation/Nucleophilic Addition Sequence: Stereoselective Syn-
thesis of Functionalized Bicyclo[4.3.0]nonenes. Adv. Synth. Catal.
2
008, 350, 2617−2630. (c) Hashmi, A. S. K.; Loos, A.; Littmann, A.;
Braun, I.; Knight, J.; Doherty, S.; Rominger, F. Gold(I) Complexes of
KITPHOS Monophosphines: Efficient Cycloisomerisation Catalysts.
Adv. Synth. Catal. 2009, 351, 576−582. (d) Preindl, J.; Jouvin, K.;
Toullec, P. Y.; Genet, J.-P. Cycloisomerization of 1,n-Enynes:
̂
Challenging Metal-Catalyzed Rearrangements and Mechanistic In-
sights. Angew. Chem., Int. Ed. 2008, 47, 4268−4315. (i) Abu Sohel, S.
M.; Liu, R.-S. Carbocyclisation of Alkynes with External Nucleophiles
Catalysed by Gold, Platinum and other Electrophilic Metals. Chem.
Soc. Rev. 2009, 38, 2269−2281. (j) Belmont, P.; Parker, E. Silver and
Gold Catalysis for Cycloisomerization Reactions. Eur. J. Org. Chem.
Laurich, D.; Seidel, G.; Furstner, A. Gold- or Silver-Catalyzed
̈
Syntheses of Pyrones and Pyridine Derivatives: Mechanistic and
Synthetic Aspects. Chem. - Eur. J. 2016, 22, 237−247.
(9) See for example: (a) Gorin, D. J.; Watson, I. D. G.; Toste, F. D.
Fluorenes and Styrenes by Au(I)-Catalyzed Annulation of Enynes and
Alkynes. J. Am. Chem. Soc. 2008, 130, 3736−3737. (b) Kazem
Shiroodi, R.; Soltani, M.; Gevorgyan, V. Gold-Catalyzed 1,3-
Transposition of Ynones. J. Am. Chem. Soc. 2014, 136, 9882−9885.
2
009, 2009, 6075−6089. (k) Furstner, A. Gold and Platinum
̈
Catalysisa Convenient Tool for Generating Molecular Complexity.
Chem. Soc. Rev. 2009, 38, 3208−3221. (l) Shapiro, N. D.; Toste, F. D.
A Reactivity-Driven Approach to the Discovery and Development of
Gold-Catalyzed Organic Reactions. Synlett 2010, 2010, 675−691.
(c) Yu, Z.; Ma, B.; Chen, M.; Wu, H.-H.; Liu, L.; Zhang, J. Highly
Site-Selective Direct C−H Bond Functionalization of Phenols with α-
Aryl-α-diazoacetates and Diazooxindoles via Gold Catalysis. J. Am.
Chem. Soc. 2014, 136, 6904−6907.
(
m) Aubert, C.; Fensterbank, L.; Garcia, P.; Malacria, M.; Simonneau,
A. Transition Metal Catalyzed Cycloisomerizations of 1,n-Allenynes
and -Allenenes. Chem. Rev. 2011, 111, 1954−1993. (n) Krause, N.;
Winter, C. Gold-Catalyzed Nucleophilic Cyclization of Functionalized
Allenes: A Powerful Access to Carbo- and Heterocycles. Chem. Rev.
011, 111, 1994−2009. (o) Obradors, C.; Echavarren, A. M. Gold-
Catalyzed Rearrangements and Beyond. Acc. Chem. Res. 2014, 47,
02−912. (p) Fensterbank, L.; Malacria, M. Molecular Complexity
(
10) See, for example: (a) Lop
́
́
ez, S.; Herrero-Gom
, P.; Nieto-Oberhuber, C.; Echavarren, A. M. Gold(I)-Catalyzed
ez, E.; Perez-
́ ́
Galan
Intermolecular Cyclopropanation of Enynes with Alkenes: Trapping
2
of two Different Gold Carbenes. Angew. Chem., Int. Ed. 2006, 45,
6029−6032. (b) Kim, S. M.; Park, J. H.; Kang, Y. K.; Chung, Y. K. N-
9
Heterocyclic Carbene Gold(I) Catalyzed Transformation of N-
Tethered 1,5-Bisallenes to 6,7-Dimethylene-3-Azabicyclo[3.1.1]-
heptane. Angew. Chem., Int. Ed. 2009, 48, 4532−4535. (c) Zhu, S.;
Guo, Z.; Huang, Z.; Jiang, H. Bioinspired Intramolecular Diels-Alder
Reaction: a Rapid Access to the Highly-Strained Cyclopropane-Fused
Polycyclic Skeleton. Chem. - Eur. J. 2014, 20, 2425−2430. (d) Blanco
from Polyunsaturated Substrates: The Gold Catalysis Approach. Acc.
Chem. Res. 2014, 47, 953−965. (q) Dorel, R.; Echavarren, A. M.
Gold(I)-Catalyzed Activation of Alkynes for the Construction of
Molecular Complexity. Chem. Rev. 2015, 115, 9028−9072.
(
2) (a) Hashmi, A. S. K.; Rudolph, M. Gold Catalysis in Total
Synthesis. Chem. Soc. Rev. 2008, 37, 1766−1775. (b) Rudolph, M.;
Jaimes, M. C.; Ahrens, A.; Pflasterer, D.; Rudolph, M.; Hashmi, A. S.
̈
K. Synthesis of Highly Substituted γ-Butyrolactones by a Gold-
Catalyzed Cascade Reaction of Benzyl Esters. Chem. - Eur. J. 2015, 21,
Hashmi, A. S. K. Gold Catalysis in Total Synthesisan Update.
Chem. Soc. Rev. 2012, 41, 2448−2462. (c) Furstner, A. From
̈
Understanding to Prediction: Gold- and Platinum-Based π-Acid
Catalysis for Target Oriented Synthesis. Acc. Chem. Res. 2014, 47,
4
(
27−433.
11) Ciancaleoni, G.; Scafuri, N.; Bistoni, G.; Macchioni, A.;
9
25−938. (d) Zhang, Y.; Luo, T.; Yang, Z. Strategic Innovation in the
Total Synthesis of Complex Natural Products Using Gold Catalysis.
Nat. Prod. Rep. 2014, 31, 489−503.
3) Ranieri, B.; Escofet, I.; Echavarren, A. M. Anatomy of Gold
Catalysts: Facts and Myths. Org. Biomol. Chem. 2015, 13, 7103−7118.
4) Dorel, R.; Echavarren, A. M. Gold-Catalyzed Reactions via
Cyclopropyl Gold Carbene-like Intermediates. J. Org. Chem. 2015, 80,
321−7332.
5) Nieto-Oberhuber, C.; Lop
Tarantelli, F.; Zuccaccia, D.; Belpassi, L. When the Tolman Electronic
Parameter Fails: A Comparative DFT and Charge Displacement
0
/−
0/+
(
Study of [(L)Ni(CO)
]
3
and [(L)Au(CO)] . Inorg. Chem. 2014,
53, 9907−9916.
(
(12) Zuccaccia, D.; Belpassi, L.; Macchioni, A.; Tarantelli, F. Ligand
Effects on Bonding and Ion Pairing in Cationic Gold(I) Catalysts
Bearing Unsaturated Hydrocarbons. Eur. J. Inorg. Chem. 2013, 2013,
4121−4135.
7
(
́
ez, S.; Echavarren, A. M. Intra-
molecular [4 + 2] Cycloadditions of 1,3-Enynes or Arylalkynes with
Alkenes with Highly Reactive Cationic Phosphine Au(I) Complexes.
J. Am. Chem. Soc. 2005, 127, 6178−6179.
(13) (a) Francos, J.; Grande-Carmona, F.; Faustino, H.; Iglesias-
Sigu
̈
enza, J.; Díez, E.; Alonso, I.; Fernan
as, J. L. Axially Chiral Triazoloisoquinolin-3-
́
dez, R.; Lassaletta, J. M.;
́
Lopez, F.; Mascaren
̃
(
6) (a) Herrero-Gom
́
ez, E.; Nieto-Oberhuber, C.; Lop
́
ez, S.; Benet-
ylidene Ligands in Gold(I)-Catalyzed Asymmetric Intermolecular (4
+ 2) Cycloadditions of Allenamides and Dienes. J. Am. Chem. Soc.
2012, 134, 14322−14325. (b) Maeta, N.; Yamamoto, J.; Fuku-en, S.-
I.; Shang, R.; Yamamoto, Y. Z. Synthesis of New Dipyrido-Annulated
N-Heterocyclic Carbenes with Aryl Substituents. Z. Anorg. Allg. Chem.
2015, 641, 2199−2203. (c) Espina, M.; Rivilla, I.; Conde, A.; Díaz-
1
2
Buchholz, J.; Echavarren, A. M. Cationic η /η -Gold(I) Complexes of
Simple Arenes. Angew. Chem., Int. Ed. 2006, 45, 5455−5459.
(
b) Perez-Galan, P.; Delpont, N.; Herrero-Gomez, E.; Maseras, F.;
́ ́ ́
Echavarren, A. M. Metal-Arene Interactions in Dialkylbiarylphos-
phane Complexes of Copper, Silver, and Gold. Chem. - Eur. J. 2010,
́
Requejo, M. M.; Perez, P. J.; Alvarez, E.; Fernandez, R.; Lassaletta, J.
́ ́
1
(
6, 5324−5332.
7) See for example: (a) Jimen
Oberhuber, C.; Echavarren, A. M. Prins Cyclizations in Au-Catalyzed
́
ez-Nun
́
̃
ez, E.; Claverie, C. K.; Nieto-
M. Chiral, Sterically Demanding N-Heterocyclic Carbenes Fused into
a Heterobiaryl Skeleton: Design, Synthesis, and Structural Analysis.
H
DOI: 10.1021/acs.organomet.8b00276
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Organometallics 2015, 34, 1328−1338. (d) Grande-Carmona, F.;
Triflates. J. Org. Chem. 2011, 76, 9353−9361. (c) Brown, T. J.;
Widenhoefer, R. A. Cationic Gold(I) π-Complexes of Terminal
Alkynes and Their Conversion to Dinuclear σ,π-Acetylide Complexes.
Organometallics 2011, 30, 6003−6009. (d) Kanno, O.; Kuriyama, W.;
Wang, Z. J.; Toste, F. D. Regio- and Enantioselective Hydroamination
of Dienes by Gold(I)/Menthol Cooperative Catalysis. Angew. Chem.,
Int. Ed. 2011, 50, 9919−9922. (e) Brooner, R. E. M.; Robertson, B.
D.; Widenhoefer, R. A. Mechanism of 1,3-Hydrogen Migration in a
Gold Bicyclo[3.2.0]heptene Complex: The Role of Brønsted Acid in
the Gold-Catalyzed Cycloisomerization of 7-Aryl-1,6-Enynes. Organo-
metallics 2014, 33, 6466−6473. (f) Kim, N.; Brooner, R. E. M.;
Widenhoefer, R. A. Unexpected Skeletal Rearrangement in the
Gold(I)/Silver(I)-Catalyzed Conversion of 7-Aryl-1,6-enynes to
Bicyclo[3.2.0]hept-6-enes via Hidden Brønsted Acid Catalysis.
Organometallics 2017, 36, 673−678.
́
Iglesias-Siguenza, J.; Alvarez, E.; Díez, E.; Fernandez, R.; Lassaletta, J.
̈
́
M. Synthesis and Characterization of Axially Chiral Imidazoisoqui-
nolin-2-ylidene Silver and Gold Complexes. Organometallics 2015, 34,
5
(
073−5080.
14) (a) Alcarazo, M.; Roseblade, S. J.; Cowley, A. R.; Fernandez, R.;
́
Brown, J. M.; Lassaletta, J. M. Imidazo[1,5-a]pyridine: A Versatile
Architecture for Stable N-Heterocyclic Carbenes. J. Am. Chem. Soc.
2005, 127, 3290−3291. (b) Burstein, C.; Lehmann, C. W.; Glorius, F.
Imidazo[1,5-a]pyridine-3-ylidenespyridine Derived N-Heterocyclic
Carbene Ligands. Tetrahedron 2005, 61, 6207−6217. (c) Quinteros,
G. J.; Uberman, P. M.; Martín, S. E. Bulky Monodentate
Biphenylarsine Ligands: Synthesis and Evaluation of Their Structure
Effects in the Palladium-Catalyzed Heck Reaction. Eur. J. Org. Chem.
2
(
015, 2015, 2698−2705.
15) (a) Aranyos, A.; Old, D. W.; Kiyomori, A.; Wolfe, J. P.; Sadighi,
(25) See the Supporting Information for the monitoring of the
1
J. P.; Buchwald, S. L. Novel Electron-Rich Bulky Phosphine Ligands
Facilitate the Palladium-Catalyzed Preparation of Diaryl Ethers. J. Am.
Chem. Soc. 1999, 121, 4369−4378. (b) Meiners, J.; Friedrich, A.;
Herdtweck, E.; Schneider, S. Facile Double C−H Activation of
Tetrahydrofuran by an Iridium PNP Pincer Complex. Organometallics
progress of the reaction by H NMR.
(26) (a) Jothibasu, R.; Huynh, H. V. Versatile Coordination
Chemistry of Indazole-Derived Carbenes. Chem. Commun. 2010, 46,
2986−2988. (b) Sivaram, H.; Jothibasu, R.; Huynh, H. V. Gold
Complexes of an Alicyclic Indazole-Derived N-Heterocyclic Carbene:
Syntheses, Characterizations, and Ligand Disproportionation. Organo-
metallics 2012, 31, 1195−1203. (c) Zhou, Y.; Liu, Q.; Lv, W.; Pang,
Q.; Ben, R.; Qian, Y.; Zhao, J. Indazolin-s-ylidene−N-Heterocyclic
Carbene Complexes of Rhodium, Palladium, and Gold: Synthesis,
Characterization, and Catalytic Hydration of Alkynes. Organometallics
2013, 32, 3753−3759.
(27) (a) For related pyrazole complexes, see: Wright, R.; Young, P.
C.; Lucas, N. T.; Lee, A.-L.; Crowley, J. D. Gold(I) and Palladium(II)
Complexes of 1,3,4-Trisubstituted 1,2,3-Triazol-5-ylidene “Click”
Carbenes: Systematic Study of the Electronic and Steric Influence
on Catalytic Activity. Organometallics 2013, 32, 7065−7076. (b) See
reference 13 for triazole or imidazole complexes..
2
(
009, 28, 6331−6338.
16) Homs, A.; Escofet, I.; Echavarren, A. M. On the Silver Effect
and the Formation of Chloride-Bridged Digold Complexes. Org. Lett.
013, 15, 5782−5785.
17) (a) Nieto-Oberhuber, C.; Mun
Nunez, E.; Nevado, C.; Herrero-Gomez, E.; Raducan, M.; Echavarren,
2
(
̃
oz, M. P.; Lopez, S.; Jimenez-
́ ́
́
̃
́
A. M. Gold(I)-Catalyzed Cyclizations of 1,6-Enynes: Alkoxycycliza-
tions and Exo/Endo Skeletal Rearrangements. Chem. - Eur. J. 2006,
1
2, 1677−1693. (b) Zhdanko, A.; Strobele, M.; Maier, M. E.
̈
Coordination Chemistry of Gold Catalysts in Solution: a Detailed
NMR Study. Chem. - Eur. J. 2012, 18, 14732−14744.
(
18) See, for example: (a) Shawkataly, O. B.; Tariq, A.; Khan, I. A.;
Yeap, C. S.; Fun, H.-K. [μ-1,6-Bis(diphenylarsanyl)hexane]bis-
chloridogold(I)]. Acta Crystallogr., Sect. E: Struct. Rep. Online 2011,
7, m427−m428. (b) Shawkataly, O. B.; Goh, C.-P.; Tariq, A.; Khan,
(28) The use of CyJohnPhos was necessary in the case of electron-
poor boronic acids (products 21c,d). See the Supporting Information
for more details.
[
6
I. A.; Fun, H.-K.; Rosli, M. M. Synthesis, Spectral Characterization
and Crystals Structure of some Arsane Derivatives of Gold (I)
Complexes: A Comparative Density Functional Theory Study. PLoS
One 2015, 10, e0119620. (c) Barnes, N. A.; Flower, K. R.; Godfrey, S.
M.; Hurst, P. A.; Khan, R. Z.; Pritchard, R. G. Structural relationships
between o-, m- and p-tolyl substituted R EI (E = As, P) and
(29) See for example: Bidal, Y. D.; Lesieur, M.; Melaimi, M.; Cordes,
D. B.; Slawin, A. M. Z; Bertrand, G.; Cazin, C. S. J. A Ssimple Access
to Transition Metal Cyclopropenylidene Complexes. Chem. Commun.
2015, 51, 4778−4781.
(30) Wang, H. M. J.; Lin, I. J. B. Facile Synthesis of Silver(I)−
Carbene Complexes. Useful Carbene Transfer Agents. Organometallics
1998, 17, 972−975.
3
2
[
(R E)AuX] (E = As, P; X = Cl, Br, I). CrystEngComm 2010, 12,
3
(31) (a) Tapu, D.; Dixon, D. A.; Roe, C. 13C NMR Spectroscopy of
“Arduengo-type” Carbenes and Their Derivatives. Chem. Rev. 2009,
109, 3385−3407. (b) Huynh, H. V.; Han, Y.; Jothibasu, R.; Yang, J. A.
4
(
240−4251.
19) Dube, J. W.; Zheng, Y.; Thiel, W.; Alcarazo, M. α-Cationic
Arsines: Synthesis, Structure, Reactivity, and Applications. J. Am.
1
3
Chem. Soc. 2016, 138, 6869−6877.
C NMR Spectroscopic Determination of Ligand Donor Strengths
(
20) For gold(I)-stibine complexes, see: Bojan, V. R.; Fernan
́
dez, E.
Using N-Heterocyclic Carbene Complexes of Palladium(II). Organo-
metallics 2009, 28, 5395−5404. Examples of gold complexes: (c) de
́
Fremont, P.; Scott, N. M.; Stevens, E. D.; Nolan, S. P. Synthesis and
Structural Characterization of N-Heterocyclic Carbene Gold(I)
Complexes. Organometallics 2005, 24, 2411−2418. (d) Gaillard, S.;
Slawin, A. M. Z.; Bonura, A. T.; Stevens, E. D.; Nolan, S. P. Synthetic
J.; Laguna, A.; Lopez-de-Luzuriaga, J. M.; Monge, M.; Olmos, M. E.;
́
Puelles, R. C.; Silvestru, C. Study of the Coordination Abilities of
Stibine Ligands to Gold(I). Inorg. Chem. 2010, 49, 5530−5541.
(
21) Otto, S.; Roodt, A. Quantifying the Electronic Cis Effect of
Phosphine, Arsine and Stibine Ligands by Use of Rhodium(I) Vaska-
Type Complexes. Inorg. Chim. Acta 2004, 357, 1−10.
and Structural Studies of [AuCl (NHC)] Complexes. Organometallics
3
(
22) (a) Yang, H.; Gabbaï, F. P. Activation of a Hydroamination
2010, 29, 394−402.
Gold Catalyst by Oxidation of a Redox-Noninnocent Chlorostibine Z-
Ligand. J. Am. Chem. Soc. 2015, 137, 13425−13432. (b) Reiner, B. R.;
Bezpalko, M. W.; Foxman, B. M.; Wade, C. R. Lewis Acid Catalysis
with Cationic Dinuclear Gold(II,II) and Gold(III,III) Phosphorus
Ylide Complexes. Organometallics 2016, 35, 2830−2835.
(32) Herrmann, W. A.; Runte, O.; Artus, G. J. Synthesis and
Structure of an Ionic Beryllium-“Carbene” Complex. J. Organomet.
Chem. 1995, 501, C1−C4.
(33) Nieto-Oberhuber, C.; Per
Lauterbach, T.; Rodríguez, C.; Lop
Cardenas, D. J.; Echavarren, A. M. Gold(I)-Catalyzed Intramolecular
́
ez-Galan
́
, P.; Herrero-Gom
́
ez, E.;
́
ez, S.; Bour, C.; Rosellon
́
, A.;
(
23) Brown, T. J.; Dickens, M. G.; Widenhoefer, R. A. Syntheses and
́
X-Ray Crystal Structures of Cationic, Two-Coordinate Gold(I) Π-
Alkene Complexes that Contain a Sterically Hindered O-Biphenyl-
phosphine Ligand. Chem. Commun. 2009, 42, 6451−6453.
[4 + 2] Cycloadditions of Arylalkynes or 1,3-Enynes with Alkenes:
Scope and Mechanism. J. Am. Chem. Soc. 2008, 130, 269−279.
(34) The different behavior of the indazole-gold complexes in this
reaction was followed by GC-MS. See the Supporting Information for
more details.
(
24) (a) Taylor, J. G.; Adrio, L. A.; Hii, K. K. Hydroamination
Reactions by Metal Triflates: Brønsted Acid vs. Metal Catalysis?
Dalton Trans 2010, 39, 1171−1175. (b) Dang, T. T.; Boeck, F.;
Hintermann, L. Hidden Brønsted Acid Catalysis: Pathways of
Accidental or Deliberate Generation of Triflic Acid from Metal
(35) (a) Nieto-Oberhuber, C.; Mun
C.; Cardenas, D. J.; Echavarren, A. M. Cationic Gold(I) Complexes:
oz, M. P.; Bunuel, E.; Nevado,
̃ ̃
́
Highly Alkynophilic Catalysts for the Exo- and Endo-Cyclization of
I
DOI: 10.1021/acs.organomet.8b00276
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Enynes. Angew. Chem., Int. Ed. 2004, 43, 2402−2406. (b) Nieto-
Oberhuber, C.; Lop
E.; Car
molecular Cyclopropanation of Dienynes. Chem. - Eur. J. 2006, 12,
694−1702.
36) Ferrer, C.; Raducan, M.; Nevado, C.; Claverie, C. K.;
ez, S.; Munoz, M. P.; Jimenez-Nunez, E.; Bunuel,
̃ ̃ ̃
́ ́
́
denas, D. J.; Echavarren, A. M. Gold(I)-Catalyzed Intra-
́
1
(
Echavarren, A. M. Missing Cyclization Pathways and new Rearrange-
ments Unveiled in the Gold(I) and Platinum(II)-Catalyzed
Cyclization of 1,6-Enynes. Tetrahedron 2007, 63, 6306−6316.
(
37) Schro
̈
der, F.; Tugny, C.; Salanouve, E.; Clavier, H.; Giordano,
-Mansuy, V.; Goddard, J.-P.;
L.; Moraleda, D.; Gimbert, Y.; Mouries
̀
Fensterbank, L. Secondary Phosphine Oxide−Gold(I) Complexes
and Their First Application in Catalysis. Organometallics 2014, 33,
4
(
051−4056.
38) See the Supporting Information for additional examples.
(
39) (a) Amijs, C. H. M.; Ferrer, C.; Echavarren, A. M. Gold(I)-
Catalysed Arylation of 1,6-Enynes: Different Site Reactivity of
Cyclopropyl Gold Carbenes. Chem. Commun. 2007, 698−700.
(
b) Amijs, C. H. M.; Lopez-Carrillo, V.; Raducan, M.; Perez-Galan,
́ ́ ́
P.; Ferrer, C.; Echavarren, A. M. Echavarren. Gold(I)-Catalyzed
Intermolecular Addition of Carbon Nucleophiles to 1,5- and 1,6-
Enynes. J. Org. Chem. 2008, 73, 7721−7730. (c) Smirnova, E. S.;
Echavarren, A. M. A Hexanuclear Gold Cluster Supported by Three-
Center−Two-Electron Bonds and Aurophilic Interactions. Angew.
Chem., Int. Ed. 2013, 52, 9023−9026.
(
40) (a) Seo, H.; Roberts, B. P.; Abboud, K. A.; Mez, K. M.; Hong,
S. Novel Acyclic Diaminocarbene Ligands with Increased Steric
Demand and Their Application in Gold Catalysis. Org. Lett. 2010, 12,
4
860−4863. (b) de Fremont, P.; Clavier, H.; Rosa, V.; Aviles, T.;
Braunstein, P. Synthesis, Characterization, and Reactivity of Cationic
Gold(I) α-Diimine Complexes. Organometallics 2011, 30, 2241−
2
251. (c) Arumugam, K.; Varghese, B.; Brantley, J. N.; Konda, S. S.;
Lynch, V. M.; Bielawski, C. W. 1,6-Enyne Cyclizations Catalyzed by
N-Heterocyclic Carbene Supported Gold Complexes: Deconvoluting
Sterics and Electronics. Eur. J. Org. Chem. 2014, 2014, 493−497.
(
41) (a) Mizushima, E.; Sato, K.; Hayashi, T.; Tanaka, M. Highly
Efficient Au(I)-Catalyzed Hydration of Alkynes. Angew. Chem., Int.
Ed. 2002, 41, 4563−4565. (b) Casado, R.; Contel, M.; Laguna, M.;
Romero, P.; Sanz, S. Organometallic Gold(III) Compounds as
Catalysts for the Addition of Water and Methanol to Terminal
Alkynes. J. Am. Chem. Soc. 2003, 125, 11925−11935. (c) Roembke,
P.; Schmidbaur, H.; Cronje, S.; Raubenheimer, H. Application of
(
Phosphine)Gold(I) Carboxylates, Sulfonates and Related Com-
pounds as Highly Efficient Catalysts for the Hydration of Alkynes. J.
Mol. Catal. A: Chem. 2004, 212, 35−42. (d) Ebule, R. E.; Malhotra,
D.; Hammond, G. B.; Xu, B. Ligand Effects in the Gold Catalyzed
Hydration of Alkynes. Adv. Synth. Catal. 2016, 358, 1478−1481.
(
e) Gatto, M.; Baratta, W.; Belanzoni, P.; Belpassi, L.; Del Zotto, A.;
Tarantelli, F.; Zuccaccia, D. Hydration and Alkoxylation of Alkynes
Catalyzed by NHC−Au−OTf. Green Chem. 2018, 20, 2125−2134.
I
(
42) Marion, N.; Ramon
́
, R. S.; Nolan, S. P. [(NHC)Au ]-Catalyzed
Acid-Free Alkyne Hydration at Part-per-Million Catalyst Loadings. J.
Am. Chem. Soc. 2009, 131, 448−449.
J
DOI: 10.1021/acs.organomet.8b00276
Organometallics XXXX, XXX, XXX−XXX