Syntheses of Triangular Gold Complexes and Their Applications in Hydroamination Reaction

Article abstract of DOI:10.1002/ejic.202100572

Triangular all-metal complexes have aroused our research interest due to their unique structural and properties. Herein, through the facile reduction of μ³-oxo complex [μ₃-O(PPh₃Au)₃]⁺BF₄

Full text of DOI:10.1002/ejic.202100572

European Journal of Inorganic Chemistry
Accepted Article
Title: Syntheses of Triangular Gold Complexes and Their Applications
in Hydroamination Reaction
Authors: Jia Li, Xujun Li, Lei Sun, Xiaoshuang Wang, Lixia Yuan,
Lingang Wu, Xiang Liu, and Yanlan Wang
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202100572
Link to VoR: https://doi.org/10.1002/ejic.202100572
01/2020

10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
Syntheses of Triangular Gold Complexes and Their Applications
in Hydroamination Reaction
Jia Li,[a] Xujun Li,[a] Lei Sun,[a] Xiaoshuang Wang,[a] Lixia Yuan,[a] Lingang Wu,[a] Xiang Liu,[b] and Yanlan
Wang*[a]
Dedication ((optional))
[a]
[b]
J. Li, X. Li, L. Sun, X. Wang, L. Yuan, Dr. L. Wu, Prof. Y. Wang
Department of chemistry and chemical engineering
Liaocheng University, 252059, Liaocheng (China)
E-mail: wangyanlan@lcu.edu.cn
Dr. X. Liu
College of materials and chemical engineering, key laboratory of inorganic nonmetallic crystalline and energy conversion materials, material analysis and
testing center
China Three Gorges University, Yichang, Hubei 443002, China
Supporting information for this article is given via a link at the end of the document.((Please delete this text if not appropriate))
Abstract: Triangular all-metal complexes have aroused our research
interest due to their unique structural and properties. Herein, through
the facile reduction of μ3-oxo complex [μ3-O(PPh3Au)3]+BF4- (1), we
synthesized and isolated the triphenylphosphine stabilized triangular
Due to the characteristic gold-gold interactions (aurophilicity),[13]
simple mono or di-gold composed complexes have presented great
structural diversity, photoelectric properties and have been applied in
multiple catalysis,[14-18] biological imaging,[19-21] optoelectronics
sensors[22-29] and luminescent materials.[30-34] However, the
photochemical and electrochemical properties of triangular gold
complexes have not yet been explored.
-
tri-gold complex [(PPh3Au)3]+BF4 (2) for the first time (yield = 90%).
Both complexes showed interesting photochemical sensitivity to
temperatures and solvents. The cyclic voltammetry of these
complexes showed one single oxidation process in CH3CN. These tri-
gold complexes (2 mol % based on the complex itself) were further
applied in the catalytic hydroaminations for substituted
phenylacetylenes with anilines and gave the corresponding imine
products with great catalytic reactivity and regioselectivity without
aiding any promoters or additives. When the loading of the tri-gold
complexes was decreased to 1.0 mol%, 95% and 97% of conversions
were obtained using 1 and 2, respectively. When further decreased
the catalyst loading to 0.5 mol% in preparative scale, 83% and 80%
of isolated yields were achieved, respectively. This method presented
great significance for the syntheses of a series of imine-containing
pharmaceutical intermediates even in preparative scale. Moreover,
the investigations of catalytic mechanisms of this reaction indicated
that these tri-gold complexes played important roles as efficient pre-
catalysts in hydroaminations.
The reaction types that gold complexes could catalyze were
diversified like cyclization reactions,[35-37] hetero-/homogeneous cross-
coupling reactions[38-41] and so on. Among them, gold-catalyzed
hydroamination of alkynes was one of the most facile and effective
strategies to construct C-N bonds. In the past two decades, gold-
catalyzed hydroamination were mainly explored by mono- or di-gold
containing complexes with PPh3 or NHC as stabilizing ligands and
achieved remarkable advances.[42-44] But the utilization of trinuclear
gold catalyst were much less developed even they possessed
peculiar structures and properties.
In this work, in order to expand the scope of triangular all-metal
complexes and explore their unique properties, even further promote
their applications in catalysis, we synthesized the first
triphenylphosphine
stabilized
triangular
tri-gold
complex
-
[(PPh3Au)3]+BF4 (2) through simple reduction of its μ3-oxo precursor
[μ3-O(PPh3Au)3]+BF4 (1) and investigated their photochemical,
-
electrochemical properties and catalytic activities in the
hydroamination of substituted phenylacetylenes with anilines.
Generally, excellent catalytic reactivities and regioselectivities were
obtained.
Introduction
In recent years, the synthesis,[1-3] catalysis,[4-6] coordination
chemistry[7] and theoretical research[8-10] for triangular all-metal
aromatic complexes have aroused great interest in the metal-organic
field. Among the multiple diversity of transition metals involved in
triangular all-metal organometallics, tri-gold complexes hold great
potential applications for their unique structural and chemical
Results and Discussion
-
Synthesis and Characterization of [(PPh3Au)3]+ BF4 (2). The μ3-oxo
-
precursor [μ3-O(PPh3Au)3]+BF4 (1)[45,46] was prepared by treating
properties. For example, Sadighi reported the NHC stabilized
PPh3AuBF4 with NaBF4 in the presence of KOH with 81% yield.
Subsequently, carbon monoxide (30 psi) was employed as facile
reducing agent and the trinuclear gold complex 2 was obtained as a
brown solid with 90% of isolated yield (Scheme 1).
+
triangular
gold
cation
[LAu]3
(L
=
1,3-bis(2,6-
diisopropylphenyl)imidazol-2-ylidene) and confirmed that this type of
tri-gold complex possessed the similar σ-aromaticity to [H3]+ ion by
density functional theory (DFT).[11] The synthetic method of NHC
+
stabilized aromatic triangular gold complex [LAu]3 was further
updated by Bertrand’s group which also reported tentative application
of this complex in the carbonylation of amines and offered moderate
to good yields.[12]
1
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
max
PPh3
-
Au
PPh3
Au
-
green (λ =547 nm) emissions (Figure 2a). When the temperature
BF4
AgBF4
em
BF4
KOH, NaBF4
CO(30 psi)
THF
Cl
Ph3P
was diminished to 77 K, two emissions for complex 1 were shifted to
410 nm and 487 nm. The emission intensity was greatly increased
when the temperature decreased from 298 K to 77 K, meanwhile, the
main emission wavelength shifted from 547 to 487 nm (Figure 3).
Generally, the luminescence was assigned to the ligand-metal charge
transfer (LMCT).
O
Au
Au Au
H2O/MeOH
Au Au
Ph3P
PPh3
PPh3
Ph3P
[(PPh3Au)3]+BF4- (2)
[μ3-O(PPh3Au)3]+BF4- (1)
Scheme 1. Novel synthesis of triangular tri-gold complex 2 through the
reduction of complex 1 in the presence of CO.
Table 1. Luminescent spectral data (λmax) for triangular tri-gold complexes 1 and
2 at 298 K and 77 K.
The structure and composition of complex 2 was fully characterized
1
by 1H, 13C, 31P, 19F NMR, ESI-MS, UV-vis. and IR. The H and 13C
NMR presented the characteristic chemical shifts and integrations for
the triphenylphosphine moieties. The 31P NMR showed the only
chemical shift at 56.90 ppm which could be clearly differentiated with
its μ3-oxo precursor 1 at 23.91 ppm (Figure 1a). Even failed with
crystals, the high resolution of positive mode ESI-MS for cationic
complex 2 was found at 1377.1721 which was fully consistent with its
calculated values (Figure 1b).
λ [nm]
Tri-gold
Cation
298 K
77 K
Excitation
267
Emission
Excitation
267
Emission
407
547
410
487
1
2
410
550
413
549
263
263
Figure 2. The CIE coordinates diagram of tri-gold complexes 1 (a) and 2 (b) at
298 K and 77 K.
Figure 1. (a) Comparison of 31P NMR spectra for complexes 1 and 2. (b) The
ESI-MS for tri-gold complex 2.
Photoluminescent properties of triangular gold complexes. In an
effort to understand the luminescent properties of trinuclear gold
complexes 1 and 2, we firstly investigated their UV-vis. spectra and
these two complexes presented interesting absorptions like their
hexagold(I) analogues[47] (see SI Figure S7 and S14). Under UV-vis.,
complex 1 displayed one strong absorption at 245 nm in CH2Cl2, and
complex 2showedclear absorption at 230 nm which could be ascribed
to the intra-ligand π→π* transitions of phosphine ligand.[48]
Figure 3. Comparison of emissions of solid-state complex 1 with temperatures
Both solid-state tri-gold complexes
1
and
2
presented
gradually changing from 298 K to 77 K.
characteristic emissions and showed interesting photochemical
sensitivity to temperatures. When excitation at 267 nm, there were
two emissions at 407 and 547 nm for complex 1 at 298 K (Table 1).
According to the CIE coordinates, this μ3-oxo complex showed yellow-
However, when excited at 263 nm as shown in Table 1, complex 2
exhibited two apparent emissions at 410 nm and 550 nm at 298 K,
2
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
max
em
which showed yellow-green (λ =550 nm) emissions. At 77 K, the
positions of the two emissions of complex 2 were found at 413 and
549 nm, respectively. Which was not shifted significantly. According
to the CIE coordinates, they also mainly showed light yellow-green
max
em
(λ =549 nm) emission (Figure 2b). Contrary to complex 1, when the
temperature increased, the overall luminescence intensity tended to
increase for complex 2 (Figure 4). The clear luminescent differences
of these two complexes could be explained by that the reduced
complex was probably combined in the form of dimers and formed
bitetrahedral stereoscopic configuration at low temperature and they
were probably presented in a planar triangle at room temperature with
the luminescence intensity greatly enhanced.[49]
Figure 4. Comparison of emissions for solid-state 2with temperatures gradually
changing from 298 K to 77 K.
Figure 5. Comparison of emissions in different organic solvents for the tri-gold
complexes 1 (a) and 2 (b).
Interestingly, the luminescence intensity for complexes 1 and 2 in
solutions were found quite sensitive to organic solvents as well
(Figure 5). Complex 1 presented much enhanced emissions at 437
nm and 522 nm in methanol compared with data observed in other
organic solvents like dichloro-methane, acetonitrile, chloroform and
acetone. This clear difference was probably caused by the formation
of intermolecular hydrogen bond between the hydroxyl (-OH) in MeOH
and the oxygen in μ3-oxo complex 1 (Figure 5a).[50] In contrast with 1,
the weakest luminous intensity was observed in MeOH for the
reduced tri-gold complex 2 which showed the strongest emissions in
less polar CH2Cl2 with three obvious peaks at 410, 430 and 514 nm,
respectively (Figure 5b).
Cyclic Voltammetry. The redox properties of tri-gold complexes 1
and 2 under electrochemical conditions were investigated by cyclic
voltammetry in CH3CN with [n-Bu4N][PF6] (0.1 M) as electrolyte and
showed irreversible oxidative potentials at +1.88 V and +1.27 V,
respectively (see SI Figure S2). The oxidation potential of complex 1
may be attributable to the oxidation of AuI3 to AuII3 or AuIII3. Similarly,
the potential of the complex 2 was probably caused by the oxidation
of Au (1⁄ ) to more stable AuI3 or AuIII
3.
3
X-Ray Diffraction. Crystallization of complex 2 from a mixture of n-
hexane and CH2Cl2 at 0-8°C afforded brown needle-like crystals
suitable for X-ray diffraction. The single crystal structure of complex 2
-
crystallizes in the form of a dimer as [Au6(PPh)6]2+·[BF4]2 in the
monoclinic space group P21/c as shown in the ellipsoid diagram
(Figure 6). The six central gold atoms formed the edge-sharing
bitetrahedral geometry and triphenylphosphine ligands covered the
1
surface of gold core formed by six Au ( ⁄ ) atoms. The Au-Au
3
distances ranges from 2.6243(18) to 2.8316(17) and conform to the
bond lengths range of aurophilicity (2.75Å-3.25Å). The significant
contraction in the Au-Au bond lengths confirmed the Au-Au bonding
was significantly strong.
3
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
some of the most efficient gold monomers in the scope of
hydroamination for terminal alkynes.[56] In addition, 100% of
regioselectivity was obtained with the imine containing compounds as
the only product without formation of any C=C containing side
products.
Table 2. Triangular tri-gold catalyzed hydroamination of phenylacetylene with
mesitylamine[a]
.
NH2
[Au]
N
+
CH3CN
Entry
1
[Au]
1
T
atm.
N2
air
air
air
N2
air
air
air
air
air
air
air
air
t [h]
Conv.[b]
20
%
50°C
50°C
reflux
reflux
50°C
50°C
reflux
reflux
reflux
reflux
reflux
reflux
reflux
12
12
2
2
1
94
3
1
99
95[c]
28
Figure 6. X-ray diffraction structure for the dimer of complex 2 with 30%
probability ellipsoids. Hydrogen atoms have been omitted for the sake of clarity.
Selected bond lengths (Å) and angles (°) for 2: Au(1)-P(1), 2.287(10); Au(1)-
Au(2), 2.6243(18); Au(1)-Au(6), 2.7438(17); Au(1)-Au(3), 2.757(2); Au(1)-Au(4),
2.767(2); Au(1)-Au(5), 2.8316(17); Au(2)-P(2), 2.311(9); Au(2)-Au(5), 2.751(2);
Au(2)-Au(4), 2.7845(17); Au(2)-Au(6), 2.794(2); Au(2)-Au(3), 2.8046(18); Au(3)-
P(3), 2.234(9); Au(3)-Au(4), 2.6366(19); Au(4)-P(4), 2.270(9); Au(5)-P(5),
2.263(10); Au(5)-Au(6), 2.6300(19); Au(6)-P(6), 2.258(9).
4
1
2
5
2
12
12
6
6
2
91
7
2
99
8
2
6
97[c]
--
9
--
1
7
Catalytic Activity. Au(I/III)-catalyzed hydroamination of terminal
alkynes was one of the most facile and effective pathways to construct
C-N bond, because this reaction was 100% atom economy, no by-
product formation, environmentally friendly and in line with the
concept of green chemistry.[51-55] Thus triangular tri-gold complexes 1
10
11
12
13
2
83[d]
80[d]
--[e]
99[e]
2
6
PPh3AuCl
PPh3AuBF4
12
6
and
2 were preliminarily applied as catalysts in the model
hydroamination of phenylacetylene and mesitylamine (Table 2).
When 2 mol% of complex 1 was employed at 50°C in CH3CN, 20% of
conversion for phenylacetylene was obtained after stirring for 12 h
under N2 (Table 2, entry 1). Surprisingly, under identical conditions,
94% of conversion for phenylacetylene was realized when the
reaction was carried out in air (Table 2, entry 2). When stirring at
refluxing in CH3CN, quantitative conversion could be achieved within
much shorter time (Table 2, entry 3). When 1 mol% of complex 1 was
loaded, the conversion reached 95% in the same reaction time (Table
2, entry 4). Complex 2 was also employed under different gas
atmospheres and showed similar anaerobic effect (Table 2, entries 5,
6). 2 mol% of catalyst loading could offer up to 99% of conversion in
6 h (Table 2, entry 7). Similarly, when reducing the catalyst loading to
1 mol%, the conversion decreased to 97% under identical conditions
(Table 2, entry 8). As expected, it did not give any desired product in
the absence of any gold catalyst under standard conditions (Table 2,
entry 9).
[a] Reaction conditions: phenylacetylene (1.0 eq., 0.1 mmol), mesitylamine (3.0
eq., 0.3 mmol), 1 or 2 (2 mol%, 0.002 mmol) in CH3CN (0.2 mL). [b] Conversions
of phenylacetylene were determined by GC/GC-MS. [c] 1 mol% catalyst 1 or 2
were used. [d] Preparative scale yields. Conditions: phenylacetylene (1.0 eq.,
6.0 mmol), mesitylamine (3.0 eq., 18.0 mmol), 1 or 2 (0.5 mol%, 0.03 mmol) in
CH3CN (12 mL). [e] 6 mol% of mono-gold catalysts were used.
The substrate scope for the triangular tri-gold complexes 1and 2 (2
mol% based on the tri-gold cluster) catalyzed hydroaminations of
substituted phenylacetylenes and anilines was screened and the
corresponding imine products were obtained with excellent reactivity
and regioselectivity (Table 3). Through the investigations of electronic
and steric effects of substrates, we found that multiple substituents,
such as methyl, ethyl, methoxy, phenyl, fluoro, chloro, bromo and nitro
groups were well tolerated in the reaction. When tri-gold complex 1
was
employed,
4-ethylphenylacetylene
and
4-
methoxyphenylacetylene were consumed in 2 hours giving the
desired products in quantitative conversions and good isolated yields
(Table 3, entries 1 and 2). When halogens were brought into the
substituted phenylacetylenes on the para, meta or ortho positions, the
reactions were completed in 2-6 hours and moderate to high isolated
yields were obtained after the separation and purification procedures
(Table 3, entries 3-9). In the cases of 4-ethynylbiphenyl and 1,4-
diethynylbenzene, the corresponding imine products were obtained in
moderate isolated yield through purifications by silica column
chromatography (Table 3, entries 10-11). Methyl and methoxy
substituted anilines were reacted with phenylacetylene and gave
Moreover, we carried out the hydroamination of phenylacetylene
with mesitylamine in preparative scale when decreased the catalyst
loading to 0.5 mol% and gave the corresponding imine-containing
product with 83% and 80% of isolated yields for both catalysts (Table
2, entries 10, 11). Normally, the mono-gold complex PPh3AuCl could
not directly catalyze the hydroamination reaction[43] and our
experimental comparison have also confirmed its halogen inhibiting
effect (Table 2, entry 12). However, quantitative conversion could be
achieved when PPh3AuCl was mixed with halogen scavenger AgBF4
by ratio of 1:1 (Table 2, entry 13). These fantastic triangular tri-gold
complexes have accomplished comparative catalytic activities with
4
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
generally great conversions and single type product containing the
imine group (Table 3, entries 12, 13). When 4-bromoaniline was
reacted with phenylacetylene under optimized conditions, 99% of
conversions could be achieved in 7 hours and 85% of isolated yield
was obtained (Table 3, entries 14). When strong electron withdrawing
nitro group was brought in, as in the case of reactions between 4-
nitroaniline and phenylacetylene, 99% of conversion in 6 hours and
91% of isolated yield were achieved (Table 3, entry 15).
Meanwhile, the reduced triangular tri-gold complex 2 was also
applied in hydroamination with the same substituted substrates and
generally gave comparative catalytic efficiencies with its μ3-O
precursor. Multiple types of substituted groups in phenylacetylenes
and anilines were proved to be tolerable for this catalyst and gave the
desired imine products in great conversions and isolated yields (Table
3). When the sterically demanding mesitylamine was employed in the
presence of catalyst 2 under optimised conditions, substituted
phenylacetylenes with electron-donating ethyl or methoxy groups
were fluently conversed to imines under optimised reaction condition
(Table 3, entries 1-2). When the fluoro, chloro, bromo groups were
brought in the para, meta or ortho positions of phenylacetylene, good
reactivities were generally achieved through overcoming the
electronic and steric effects and gave 82-96% of isolated yields (Table
3, entries 3-9). In the case of 4-ethynylbiphenyl and 1,4-
diethynylbenzene, the isolated yields were obtained in 79% and 77%,
respectively (Table 3, entries 10, 11).
In addition, when
phenylacetylene was reacted with substituted anilines separately like
4-methylaniline, 4-methoxyaniline, 4-bromoaniline and 4-nitroaniline,
afforded good isolated yields and excellent regioselectivity under
optimised conditions (Table 3, entries 12-15).
5
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
FULL PAPER
Table 3. Hydroamination of substituted phenylacetylenes and anilines catalyzed by tri-gold complexes 1 or 2 [a]
R2
N
[Au] (2 mol%)
+
H2N
R1
R1
CH3CN, reflux
air
R2
-
[(PPh3Au)3]+BF4
-
[μ3-O(PPh3Au)3]+BF4
Alkyne
Product
Entry
1
Amine
NH2
Conv.[b]/Yield[c]
Conv.[b]/Yield[c]
t [h]
t [h]
2
99/85
2
99/82
N
N
NH2
NH2
NH2
2
4
99/92
99/93
2
6
99/90
99/91
2
OMe
MeO
3
4
N
F
F
F
N
2
6
99/95
98/83
6
6
96/92
99/82
F
F
NH2
NH2
NH2
5
6
7
N
F
N
2
2
99/92
99/94
7
7
99/89
99/94
Cl
Cl
N
N
Cl
Cl
Cl
NH2
NH2
8
9
2
2
5
9
99/96
99/94
99/96
99/87
Cl
N
Br
Br
NH2
NH2
N
10
11
-/79
-/77
2
4
-/78
-/78
2
4
N
N
12
13
H2N
H2N
N
4
10
7
96/87
99/90
99/85
99/91
6
5
95/83
83/78
98/79
99/89
O
O
N
Br
12
12
14
15
H2N
Br
N
NO2
6
H2N
NO2
N
[a] Reaction condition: substituted phenylacetylenes (0.1 mmol, 1 eq.), substituted anilines (0.3 mmol, 3 eq.), [Au] (0.002 mol, 2 mol%) in CH3CN (0.2 mL) at reflux
in air. [b] Conversions of substituted phenylacetylenes determined by GC/GC-MS. [c] Isolated yields obtained by silica column chromatography.
chemical shift was found at 45.33 ppm, which was ascribed to the
Mechanistic Studies: The mechanisms of these triangular tri-gold
catalysts participated hydroaminations of terminal alkynes were
further investigated using phenylacetylene and mesitylamine as
model substrates. We firstly tracked the reaction process by 31P NMR.
The chemical shift of complex 1 was found at 23.91 ppm, after
phenylacetylene was added and stirred at refluxing for 1h, the only
reactive intermediate, the alkyne coordinated gold (I) complex A.[57,58]
Similarly, the chemical shift of phosphine in complex 2 at 56.90 ppm
was disappeared with the adding of phenylacetylene and heating,
identical intermediate was found at 45.33 ppm (see SI Figure S3).
Therefore, it was speculated that tri-gold complexes 1 and 2 played
the roles as efficient pre-catalysts in this hydroamination process.
6
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10.1002/ejic.202100572
European Journal of Inorganic Chemistry
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In conclusion, we synthesized and characterized the first
triphenylphosphine stabilized triangular tri-gold complex 2 through the
facile reduction of its μ3-oxo precursor 1. The electrochemical and
photochemical properties for these tri-gold complexes were
investigated, both showed irreversible redox potentials and strong
fluorescence sensitivities to temperatures and solvents. Both tri-gold
complexes showed one single oxidation process in cyclic voltammetry
which was consistent with their catalytic behaviors. The μ3-oxo
complex 1 could form intermolecular hydrogen bonds with alcohol
solvents to enhance the luminescence, while the reduced complex 2
presented stronger luminescence in less polar solvents.
Finally, these triangular tri-gold clusters were successfully
applied in the hydroamination of substituted phenylacetylenes and
anilines. Excellent catalytic reactivities, regioselectivities and isolated
yields (77%-96%) were achieved for a range of electron-withdrawing
and electron-donating groups decorated substrates. Experimental
data indeed showed high catalytic activities at lower catalyst loading
for both catalysts. Excellent conversions and isolated yields were
obtained when the catalyst loading was decreased to 1.0 mol% and
further lower 0.5 mol%, respectively. The preparative scale
hydroamination with 0.5 mol% of catalysts loading gave good isolated
yields for both tri-gold complexes. These tri-gold catalysts and their
catalytic pathways hold great significance to the syntheses of a series
of imine containing medicines and natural anti-cancer materials. The
mechanism of tri-gold complex 1 or 2 catalyzed hydroamination for
mesitylenes and phenylacetylenes was investigated by monitoring the
31P NMR shifts and found that both triangular complexes transformed
to active gold(I) intermediates during the reaction and played as
efficient pre-catalysts in the catalytic hydroamination process.
Figure 7. Proposed catalytic cycle for the hydroamination of phenylacetylene
with mesitylamine catalyzed by tri-gold complexes 1 or 2.
DFT studies vigorously promoted the investigations of
mechanism for Au(I)-catalyzed hydroamination[59-62] and gave the
general information of intermediate bonding, N-nucleophile types in
the dehydrogenation step and the energetics of the whole catalytic
cycle. Based on the mechanism of gold(I) catalyzed
hydroamination,[63-66] the triangular tri-gold species were proposed to
firstly interact with an terminal alkyne and form a catalytically active
cationic Au(I)-alkyne complex in situ. For gold catalyzed
functionalization of terminal alkynes like hydroamination or
hydrophenoxylation, di-gold σ, π-acetylide complexes are more and
more considered as the activated intermediates due to their easy
access and properties.[67-77] Then the proposed catalytic cycle for the
hydroamination of phenylacetylene with mesitylamine was probably
carried out as following (Figure 7). The Au(I)-π complex A was
activated by coordination of phenylacetylene to the gold(I) center,
then mesitylamine was incorporated smoothly through a nucleophilic
attack and gave the trans-alkenyl intermediates B. Different with using
ammonia or hydrazine as nucleophiles, the formation of σ, π -
binuclear gold alkynyl intermediate C was favorable when considering
the hydroamination of phenylacetylene with aniline. The first H+
transfer and elimination of one gold complex assisted the
transformation to D. Then two subsequent tautomerizations were
demanded to complete the catalytic circle. The first tautomerization
was mediated by the gold-center: the gold-moiety migrated from the
carbon to the nitrogen atom leading to the enamine-tautomer E. Then
proton migration from the nitrogen to the carbon atom lead to the
formation of intermediate F. The desired imine-containing structure
and the gold catalyst was released in the presence of another
molecular of phenylacetylene and started a new circle. Dual-Gold
intermediate and the nucleophilic mesitylamine facilitated H+ transfer
and tautomerizations were plausible in the hydroamination.
Experimental Section
-
Synthesis of [(PPh3Au)3]+BF4 (2). A THF solution (3 mL) of complex 1
(148 mg, 0.1 mmol) was stirred under CO (30 psi) for 12 h. The solvent
was removed under vacuum and the obtained solid was washed with ether
and benzene sequentially, then filtered. The filtrate was dried in vacuo,
gave the complex 2 as a brown solid (132 mg, yield: 90%). CCDC:
2099219 (for 2). 1H NMR (500 MHz, Chloroform-d, 25°C ): δppm 7.34 – 7.30
(m, 9H, Ar-H), 7.25 – 7.15 (m, 18H, Ar-H), 7.05 – 6.87 (m, 18H, Ar-H). 13
C
NMR (125 MHz, Chloroform-d, 25°C): δppm 134.13, 133.77, 132.00, 129.42.
31P NMR (202 MHz, Chloroform-d, 25°C): δppm 56.90. 19F NMR (471 MHz,
Chloroform-d, 25°C): δppm -154.36. IR (cm-1): 1633.48, 1479.85, 1435.56,
1098.47, 1055.32, 748.46, 692.30, 524.56, 503.85, 435.37. UV-Vis.: λmax
230 nm. HRMS(ESI): m/z calcd for C54H45P3Au3 1377.1725, found
=
+
1377.1721.
General procedure for the catalytic hydroamination of substituted
phenylacetylenes with anilines. In a typical run, a mixture of substituted
phenylacetylene (1.0 eq., 0.1 mmol), substituted aniline (3.0 eq., 0.3 mmol)
and catalyst 1 or 2 (2 mol%, 0.002 mmol) was refluxed in CH3CN (0.2 mL)
under air. The conversions of phenylacetylenes to imine products were
determined by GC/GC-MS. The isolated yields were obtained by column
chromatography using a mixture of petroleum ether and ethyl acetate as
the eluent.
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (Grant No. 21901097).
Conclusion
7
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[34] S. N. Islam, A. Sil, S. K. Patra, Dalton Trans. 2017, 46, 5918-5929.
[35] V. Pirovano, E. Arpini, M. D. Acqua, R. Vicente, G. Abbiati, E. Rossi, Adv.
Synth. Catal. 2016, 358, 403-409.
Keywords: Gold catalysis
• Hydroamination • Imines •
Photochemical properties • Triangular gold complex
[36] M. Nanko, S. Shibuya, Y. Inaba, S. Ono, S. Ito, K. Mikami, Org. Lett.
2018, 20, 7353-7357.
[1]
[2]
[3]
[4]
[5]
[6]
[7]
X. W. Li, W. T. Pennington, G. H. Robinson, J. Am. Chem. Soc. 1995,
117, 7578-7579.
[37] F. Xie, B. Zhang, Y. Chen, H. Jia, L. Sun, K. Zhuang, L. Yin, M. Cheng,
B. Lin, Y. Liu, Adv. Synth. Catal. 2020, 362, 3886-3897.
[38] A. Nijamudheen, D. Ayan, Chem. Eur. J. 2020, 26, 1442-1487.
[39] M. D. Patil, B. S. Kale, R.-S. Liu, Adv. Synth. Catal. 2020, 362, 5658-
5668.
R. J. Wright, M. Brynda, P. P. Power, Angew. Chem., Int. Ed. 2006, 45,
5953-5956.
S. Blanchard, L. Fensterbank, G. Gontard, E. Lacôte, G. Maestri, M.
Malacria, Angew. Chem. Int. Ed. 2014, 53, 1987-1991.
P. A. Deyris, T. CaÇeque, Y. Wang, P. Retailleau, F. Bigi, R. Maggi, G.
Maestri, M. Malacria, ChemCatChem. 2015, 7, 3266-3269.
A. Monfredini, V. Santacroce, L. Marchiꢀ, R. Maggi, F. Bigi, G. Maestri,
M. Malacria, ACS Sustainable Chem. Eng. 2017, 5, 8205-8212.
M. Lanzi, T. Caꢁeque, L. Marchiꢀ, R. Maggi, F. Bigi, M. Malacria, G.
Maestri, ACS Catal. 2018, 8, 144-147.
[40] H. Zhu, Y. Shen, Q. Deng, J. Chen, T. Tu, ACS Catal. 2017, 7, 4655-
4659.
[41] H. Zhu, Y. Shen, D. Wen, Z. G. Le, T. Tu, Org. Lett. 2019, 21, 974-979.
[42] E. Mizushima, T. Hayashi, M. Tanaka, Org. Lett. 2003, 5, 3349-3352.
[43] K. Anuj, S. Chandan, T. Hendrik, V. H. Han, Organometallics. 2020, 39,
172-181.
Y. Wang, A. Monfredini, P. A. Deyris, F. Blanchard, E. Derat, G. Maestri,
M. Malacria, Chem. Sci. 2017, 8, 7394-7402.
[44] B. Marco, B. Edoardo, T. Cristina, B. Andrea, A. Lidia, R. Marzio, G.
Claudia, Organometallics. 2018, 37, 4213-4223.
[8]
[9]
A. C. Tsipis, C. A. Tsipis, J. Am. Chem. Soc. 2005, 127, 10623-10638.
S. Pan, R. Saha, S. Mandal, P. K. Chattaraj, Phys. Chem. Chem. Phys.
2016, 18, 11661-11676.
[45] A. N. Nesmeyanov, E. G. Perevalova, Y. T. Struchkov, M. Yu. Antipin,
K. I. Grandberg, V. P. Dyadchenko, J. Organomet. Chem. 1980, 201,
343-349.
[10] I. A. Popov, A. A. Starikova, D. V. Steglenko, A. I. Boldyrev, Chem. Eur.
J. 2018, 24, 292-305.
[46] Y. Yang, R. Visalakshi, R. S. Paul, Inorg. Chem. 1993, 32, 1946-1950.
[47] Z. Lei, K. Nagata, H. Ube, M. Shionoya, J. Organomet. Chem. 2020, 917,
121271.
[11] T. J. Robilotto, J. Bacsa, T. G. Gray, J. P. Sadighi, Angew. Chem. Int. Ed.
2012, 51, 12077-12080.
[48] J. R. Shakirova, E. V. Grachova, V. V. Gurzhiy, I. O. Koshevoy, A. S.
Melnikov, O. V. Sizova, S. P. Tunik, A. Laguna, Dalton Trans. 2012, 41,
2941-2949.
[12] L. Jin, D. S. Weinberger, M. Melaimi, C. E. Moore, A. L. Rheingold, G.
Bertrand, Angew. Chem. Int. Ed. 2014, 53, 9059-9063.
[13] N. Mirzadeh, S. H. Privér, A. J. Blake, H. Schmidbaur, S. K. Bhargava,
Chem. Rev. 2020, 120, 7551-7591.
[49] E. M. Gussenhoven, J. C. Fettinger, D. M. Pham, M. M. Malwitz, A. L.
Balch, J. Am. Chem. Soc. 2005, 127, 10838-10839.
[50] G. J. Zhao, B. H. Northrop, K. L.Han, P. J. Stang, J. Phys. Chem. A. 2010,
114, 9007-9013.
[14] A. Corma, A. L. Pérez, M. J. Sabater, Chem. Rev. 2011, 111, 1657-1712.
[15] K. Yamamoto, E. López, P. Barrio, J. Borge, L. A. López, Chem. Eur. J.
2020, 26, 6999-7003.
[51] C. Dash, M. M. Shaikh, R. J. Butcher, P. Ghosh, Inorg. Chem. 2010, 49,
4972-4983.
[16] M. M. Luna, O. N. Faza, C. S. López, Front. Chem. 2019, 7, 296.
[17] E. S. Smirnova, A. M. Echavarren, Angew. Chem. Int. Ed. 2013, 52,
9023-9026.
[52] M. Katari, M. N. Rao, G. Rajaraman, P. Ghosh, Inorg. Chem. 2012, 51,
5593-5604.
[18] D. Weber, M. R. Gagné, Topics in Current Chemistry, Vol. 357 (Eds.: L.
M. Slaughter), Springer International Publishing Switzerland, Springer,
Cham, 2015, pp. 167-212.))
[53] A. G. Nair, R. T. McBurney, M. R. D. Gatus, S. C. Binding, B. A. Messerle,
Inorg. Chem. 2017, 56, 12067-12075.
[54] A. S. K. Hashmi, Chem. Rev. 2007, 107, 3180-3211.
[55] D. Liu, Q. Nie, R. Zhang, M. Cai, Adv. Synth. Catal. 2018, 360, 3940-
3948.
[19] J. Zhang, H. Zou, J. Lei, B. He, X. He, H. H. Y. Sung, R. T. K. Kwok, J.
W. Y. Lam, L. Zheng, B. Z. Tang, Angew. Chem. Int. Ed. 2020, 59, 7097-
7105.
[56] M. Veguillas, G. M. Rosair, M. W. P. Bebbington, A. L. Lee, ACS
Catal. 2019, 9, 2552-2557.
[20] Z. Lei, J. Y. Zhang, Z. J. Guan, Q. M. Wang, Chem. Commun. 2017, 53,
10902-10905.
[57] J. C. Wang, Acta Cryst. 1996, C52, 611-613.
[58] R. E. M. Brooner, T. J. Brown, R. A. Widenhoefer, Chem. Eur. J. 2013,
19, 8276-8284.
[21] E. E. Langdon-Jones, S. J. A. Pope, Chem. Commun. 2014, 50, 10343-
10354.
[22] R. Malmberg, T. Arx, M. Hasan, O. Blacque, A. Shukla, S. K. M.
McGregor, S. C. Lo, E. B. Namdas, K. Venkatesan, Chem. Eur. J. 2021,
27, 1-11.
[59] X. Giner, C. Nꢂjera, G. Kovꢂcs, A. LLedꢃs, G. Ujaque, Adv. Synth. Catal.
2011, 353, 3451−3466.
[60] J. H. Kim, S.-W. Park, S. R. Park, S. Lee, E. Kang, J. Chem. Asian J.
2011, 6, 1982−1986.
[23] W. B. Li, W. J. Luo, K. X. Li, W. Z. Yuan, Y. M. Zhang, Chinese. Chem.
Lett. 2017, 28, 1300-1305.
[61]
K. Kovꢂcs, G. Ujaque, A. Lledꢃs, J. Am. Chem. Soc. 2008, 130,
853−864.
[24] A. Morag, N. Froumin, D. Mogiliansky, V. Ezersky, E. Beilis, S. Richter,
R. Jelinek, Adv. Funct. Mater. 2013, 23, 5663-5668.
[62]
Z. J. Wang, D. Benitez, E. Tkatchouk, W. A. Goddard III, F. D. Toste, J.
Am. Chem. Soc. 2010, 132, 13064−13071.
[25] C. W. Hsu, C. C. Lin, M. W. Chung, Y. Chi, G. H. Lee, P. T. Chou, C. H.
Chang, P. Y. Chen, J. Am. Chem. Soc. 2011, 133, 12085-12099.
[26] X. He, V. W. W. C. Yam, Coordin. Chem. Rev. 2011, 255, 2111-2123.
[27] V. K. M. Au, K. M. C. Wong, D. P. K. Tsang, M. Y. Chan, N. Zhu, V. W.
W. Yam, J. Am. Chem. Soc. 2010, 132, 14273-14278.
[28] R. Czerwieniec, T. Hofbeck, O. Crespo, A. Laguna, M. C. Gimeno, H.
Yersin, Inorg. Chem. 2010, 49, 3764-3767.
[63] A. Leyva, A. Corma, Adv. Synth. Catal. 2009, 351, 2876-2886.
[64] A. Zhdanko, M. E. Maier, Angew. Chem. Int. Ed. 2014, 53, 7760-7764.
[65] C. H. Leung, M. Baron, A. Biffis, Catalysts. 2020, 10, 1210.
[66] A. Couce-Rios, G. Kovꢂcs, G. Ujaque, A. Lledꢃs, ACS Catal. 2015, 5,
815-829.
[67] I. Abdellah, A. Poater, J. F. Lohier, A. C. Gaumont, Catal. Sci. Technol.
2018, 8, 6486-6492.
[29] M. A. Rawashdeh-Omary, M. A. Omary, J. P. Fackler, R. Galassi, B. R.
Pietroni, A. Burini, J. Am. Chem. Soc. 2001, 123, 9689-9691.
[30] R. Visbal, M. C. Gimeno, Chem. Soc. Rev. 2014, 43, 3551-3574.
[31] M. M. Zhang, K. Li, S. Q. Zang, Adv. Opt. Mater. 2020, 8, 1902152.
[32] J. Yang, K. Li, J. Wang, S. Sun, W. Chi, C. Wang, X. Chang, C. Zou, W.
P. To, M. D. Li, X. Liu, W. Lu, H. X. Zhang, C. M. Che, Angew. Chem. Int.
Ed. 2020, 59, 6915-6922.
[68] C. Michon, J. Gilbert, X. Trivelli, F. Nahra, C. S. J. Cazin, F. Agbossou-
Niedercorn, S. P. Nolan, Org. Biomol. Chem. 2019, 17, 3805-3811.
[69] O. F. González-Belman, A. Brotons-Rufes, M. Tomasini, L. Falivene, L.
Caporaso, J. O. C. Jiménez-Halla, A. Poater, Catalysts 2021, 11, 704.
[70] M. Anania, L. Jaꢄíkovꢂ, J. Zelenka, E. Shcherbachenko, J. Jaꢄĺk, J.
Roithová, Chem. Sci. 2020, 11, 980-988.
[33] S. Bose, A. Chatterjee, S. K. Jenifer, B. Mondal, P. Srikrishnarka, D.
Ghosh, A. R. Chowdhuri, M. P. Kannan, S. V. Elchuri, T. Pradeep, ACS
Sustainable Chem. Eng. 2021, 9, 4554-4563.
[71] O. F. González-Belman, J. O. C. Jiménez-Halla, F. Nahra, C. S. J. Cazin,
A. Poater, Catal. Sci. Technol. 2018, 8, 3638-3648.
8
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FULL PAPER
[72] A. Gómez-Suárez, Y. Oonishi, A. R. Martin, S. V. C. Vummaleti, D. J.
Nelson, D. B. Cordes, A. M. Z. Slawin, L. Cavallo, S. P. Nolan, A. Poater,
Chem. Eur. J. 2016, 22, 1125-1132.
[73] M. Larsen, K. N. Houk, A. S. K. Hashmi, J. Am. Chem. Soc. 2015, 137,
10668-10676.
[74] J. Roithovꢂ, Š. Jankovꢂ, L. Jaꢄíkovꢂ, J. Vꢂňa, S. Hybelbauerovꢂ, Angew.
Chem. Int. Ed. 2012, 51, 8378-8382.
[75] A. Cavarzan, A. Scarso, P. Sgarbossa, G. Strukul, J. N. H. Reek, J. Am.
Chem. Soc. 2011, 133, 2848-2851.
[76] A. C. H. Jans, A. Gómez-Suárez, S. P. Nolan, J. N. H. Reek, Chem. Eur.
J. 2016, 22, 14836-14839.
[77] L. Jaꢄíkovꢂ, M. Anania, S. Hybelbauerovꢂ, J. Roithova, J. Am. Chem.
Soc. 2015, 137, 13647-13657.
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An all-metal triangular gold complex was synthesized through facile one-step reduction for the first time. This complex demonstrated
exciting photoelectric properties and excellent catalytic reactivities and regioselectivities in the hydroamination reactions of aromatic
terminal alkynes.
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