Synthesis and structure of the bimetallic organoantimony catalyst and its application in diastereoselective direct Mannich reaction as facile separation catalytic system

Article abstract of DOI:10.1016/j.jorganchem.2021.121820

A bimetallic organoantimony catalyst with four Lewis/Br?nsted acidic/basic sites assembled orderly was successfully synthesized and showed high catalytic efficiency. It has been applied in diastereoselective direct Mannich reaction by adding 0.1 mol% catalyst. This reaction presented unexpected facile separation ability from homogenous solution to heterogeneous solution.

Full text of DOI:10.1016/j.jorganchem.2021.121820

Journal of Organometallic Chemistry 942 (2021) 121820
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Communication
Synthesis and structure of the bimetallic organoantimony catalyst and
its application in diastereoselective direct Mannich reaction as facile
separation catalytic system
Niu Tang a,1, Xingxing Songa,b,1, Tianbao Yang a, Renhua Qiua,∗, Shuang-Feng Yina,∗
a College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082, China
b Hefei Xinsheng Optoelectronics Technology Co., Ltd, Hefei, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A bimetallic organoantimony catalyst with four Lewis/Brønsted acidic/basic sites assembled orderly was
successfully synthesized and showed high catalytic efficiency. It has been applied in diastereoselective
direct Mannich reaction by adding 0.1 mol% catalyst. This reaction presented unexpected facile separation
ability from homogenous solution to heterogeneous solution.
Received 13 March 2021
Revised 3 April 2021
Accepted 7 April 2021
Available online 20 April 2021
© 2021 Elsevier B.V. All rights reserved.
Keywords:
Organoantimony
Lewis acid
Mannich rection
Diastereoselectivity
Bimetallic complex
Self-separation
1. Introduction
found a method to efficiently catalyse the direct diastereoselective
Mannich reaction and allylation of aldehydes using the organoan-
In recent years, the sustainable and economic chemical pro-
cesses have been always concerned, the chemists were dedicated
to develop the good reaction systems for molecular transforma-
tions by using abundant main-group elements [1–8]. As the fifth
main-group element, antimony has attracted considerable atten-
tion and been adopted in numerous chemical synthesis, pharma-
ceutical and materials [9–21]. Previous studies indicated that inor-
ganic antimony compounds are a kind of high activity Lewis acid in
a wide range of organic reactions [22–28]. At the same time, a va-
riety of organoantimony complexe also have been reported owning
to its unusual catalytic activity in organic synthesis [22–28]. In pre-
vious work, Nomura and coworkers developed a kind of antimony-
based organometallic complexes that could be selected as an effec-
tive catalyst for reactions such as chemical fixation of CO2 [29–31],
polymerization [32–34], esterification [35] and amidation [36,37].
Gabbaï et al. have designed a platform, a variety of inexpensive
antimony halides, to realize previously inaccessible reaction such
as activating the transition metals by direct interaction or anion
abstraction [38–42]. Lei [25] and Xia [27] et al. have separately
timoy complex (5% mol catalyst loading). Considering on reducing
the amount of catalyst and improving the efficiency of the catalyst,
herein, we have designed and characterized bimetallic organoanti-
mony catalysts, which displayed high catalytic efficiency in direct
diastereoselective Mannich reaction (0.1% mol catalyst loading).
2. Experiment
2.1. Materials and physical measurement
All chemicals were purchased from Sigma-Aldrich. Co. Ltd
unless otherwise indicated. The synthesis of Ph2SbCl [43] and
C8F17 SO3H [44] are according to the literature. The preparation of
catalyst was carried out under nitrogen atmosphere with freshly
distilled solvents unless otherwise noted. THF and hexane were
distilled from sodium/benzophenone system. Acetonitrile was dis-
tilled from CaH2 system. The NMR spectra were recorded at 25 °C
on INOVA-400 M (USA) (400 MHz to 1H NMR and 101 MHz to 13C
NMR) calibrated with tetramethyl silane (TMS) as an internal refer-
ence. The abbreviations are used to describe peal patterns: singlet
(s), doublet (d), triplet (t) and multiplet (m). TG-DSC analysis was
performed on a HCT-1 (HENVEN, Beijing, China) instrument. Thin-
layer chromatography (TLC) and column chromatography silica
gel (200–300) were purchased from Anhui Liangchen Co. Ltd. X-
∗
Corresponding authors.
E-mail addresses: renhuaqiu1@hnu.edu.cn (R. Qiu), sf_yin@hnu.edu.cn (S.-F. Yin).
1
N. Tang and X.X. Song contribute equally.
https://doi.org/10.1016/j.jorganchem.2021.121820
0022-328X/© 2021 Elsevier B.V. All rights reserved.

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
Scheme 1. Synthesis of ligand of C6H2(CH2NMe2)2Br2 (1).
ray single crystal diffraction analysis was performed over SMART-
APEX and RASA-7A by Shanghai Institute Organic Chemistry, China
Academy of Science. The acidity was measured by Hammett indi-
cator method as described previously [45]. Acid strength was ex-
pressed in terms of Hammett acidity function (Ho) as scaled by pKa
value of the indicators.
Then the mixture was stirred at −60 °C for 1 hour and then the
reacting temperature was gradually increased to RT and stirred for
another 1 hour. The resulted mixture was setting in −80 °C bath
and was added with Ph2SbCl (3.787 mmol) in Et2O (8 mL) solu-
tion. After that, the mixture was stirred at −80 °C for 1 hour and
then the reacting temperature was gradually increased to RT and
stirred for another 1 hour. The final obtained mixture was evap-
orated and extracted with CH2Cl2 and evaporated again. The re-
sulted residue was subjected to column chromatograph on silica
gel (PE/EA = 20/1), and 111 mg white solid as pure product was
obtained (yield 9%). mp:224−227 °C; 1H NMR (CDCl3, 400 MHz,
TMS): δH (400 MHz; CDCl3; TMS) 7.43 (10H, t, J = 3.6 Hz, one Ph
of Ph2Sb), 7.26 (10H, t, J = 2.0 Hz, another Ph of Ph2Sb), 7.02 (2H, s,
ArH), 3.24(4H, s, 2CH2), 1.81(12H, s, 2NMe2); δC (100 MHz; CDCl3;
TMS) 143.6, 142.3, 140.7, 136.6, 136.1, 128.3, 127.6, 64.9, 43.7.
2.2. Synthesis and spectral data of precursor of 1 (Scheme 1)
2.2.1. Synthesis of p-C6H2(CH3)2Br2 (1b)
ao a 250 mL round flask was added 1,4-dimethylbenzene (1a)
(73.9 mL, 600 mmol), then the initiator of I2 was added and fol-
lowed with liquid bromine (66.0 mL,1280 mmol) by drop at 0 °C.
The resulting mixture was stirred in the absence of light for 8 h
at 0 °C to RT. After that, the mixture was washed with saturated
NaOH solution. Next, it was filtrated and the crude white solid
product was obtained. The pure white powder was obtained after
recrystallisation in anhydrous EtOH solution (yield 80%). mp:71−72
2−
(3)
2.3.2. Synthesis of [C6H2(CH2NHMe2SbPh2)2]2+[OSO2C8F17
]
To a 50 mL tube was added (0.2052 g, 0.276 mmol) and
C8F17 SO3H (0.2765 g, 0.552 mmol). After vacuum and refund-
ing nitrogen for 3 times, the mixture was added anhydrous THF
(5 mL) and anhydrous CH3CN (5 mL) and stirred at RT for 2 h.
The resulting mixture was evaporated and the white solid was
hence obtained (yield 95%). mp:150−151 °C; δH (400 MHz; CDCl3;
TMS) 9.451 (2H, s, ArH), 7.37−7.40 (20H, s, 2(Ph2Sb)), 4.20 (4H, d,
J = 3.6 Hz, 2CH2), 2.64 (12H, d, J = 4.8 Hz, 2NMe2); δC (100 MHz;
CDCl3; TMS) 145.3, 140.8, 136.3, 136.1, 130.9, 129.6, 129.6, 113.9,
110.9, 110.3, 108.2, 68.2, 62.9, 43.2, 30.4, 19.5, 14.1. Elemental Anal-
ysis calculation (%) for C52H40F34N2O6S2Sb2: C, 35.84; H, 2.31;
found: C, 35.91; H, 2.26.
°C; 1H NMR (CDCl3, 400 MHz, TMS): δ = 7.4 (2H, s), 2.3 (6H, s) ;13
NMR (CDCl3, 100 MHz, TMS); δ = 137.2, 135.9, 122.9, 23.1.
C
2.2.2. Synthesis of C6H2(CH2Br)2Br2 (1c)
To a two-necked round flask was added compound 1b (52.7 g,
ꢀ
200 mmol), NBS (71.2 g, 400 mmol), 1,1 - azobis (cyanocyclohex-
ane) (0.1 g). After vacuum and refunding nitrogen for three times,
the CCl4 (800 mL) was added. After the resulting mixture was
stirred at RT for 1 hour, it was elevated to refluxing until the
1b was consumed and monitored by TLC analysis. Then the re-
sulting mixture was filtrated at room temperature and washed
with CH2Cl2. The combined CH2Cl2 layer was washed with brine
for 3 times and filtrated, dried with anhydrous Na2SO4, evapo-
rated and recrystallized in anhydrous EtOH. The white needles
solid product was obtained (yield 43%). mp:156−158 °C; 1H NMR
(CDCl3, 400 MHz, TMS): δ = 7.7 (2H, s),4.5 (4H, s);13C NMR (CDCl3,
100 MHz, TMS): δ = 138.0, 134.3, 122.3, 30.5.
2−
2.3.3. Synthesis of [C6H2(CH2NHMe2SbPh2)2]2+[ClO4]
(4)
To a 50 mL tube was added complex 2 (0.2052 g, 0.276 mmol)
and HClO4 (0.055 g, 0.552 mmol). After three cycles of vacuum-
and-nitrogen purging, the mixture was added anhydrous THF
(5 mL) and anhydrous CH3CN (5 mL), and the resulted mixture was
stirred at RT for 2 h. The resulted mixture was subject to evapora-
tion to afford the formation of a white solid (yield 94%). mp > 300
°C; δH (400 MHz; acetone-d6; TMS) 7.67 (2H, s, ArH), 7.39−7.51
(20H, s, 2(Ph2Sb)), 4.71 (4H, s, 2CH2), 2.92 (12H, s, 2NMe2). Ele-
mental Analysis calculation (%) for C36H40Cl2N2O8Sb2: C, 45.85; H,
4.27; found: C, 45.89; H, 4.20.
2.2.3. Synthesis of C6H2(CH2NMe2)2Br2 (1)
To a 250 mL two-necked round flask was added compound 1c
(8.435 g, 20.0 mmol). After vacuum and refunding nitrogen for 3
times, then the Me2NH in ether solution (100 mL, 320 mmol) was
added and stirred for 4 h at RT. Then washed with water and dried
with Na2SO4, filtrated and evaporated. The resulted residue was re-
crystallized in petroleum ether and the white solid was hence ob-
tained (yield 81%). mp:74−75 °C; 1H NMR (CDCl3, 400 MHz, TMS):
δ = 7.6 (2H, s), 3.5 (4H, s), 2.3 (12H, s), 13C NMR (CDCl3, 100 MHz,
TMS): δ = 138.5, 134.4, 134.1, 123.3, 62.5, 45.5, 45.4.
3. Results and discussion
3.1. Physicochemical properties
The complexes 2 − 4 remain intact in the open air for a test
period of one year. The Lewis acidity of complexes 2 − 4 as esti-
mated by the Hammett indicator method are 6.8 < Ho < 7.2, 4.8 <
Ho < 6.8 and 4.8 < Ho <6.8 (Ho is Hammett acidity function), re-
spectively (detail procedure see SI), indicating that there is increase
of Lewis acidity with the incorporation of HX. According to the
colour change of indicators, complex 3 is in fact higher than com-
2.3. Synthesis and spectral data of precursor of 2–4 (Scheme 2)
2.3.1. Synthesis of catalyst C6H2(CH2NMe2SbPh2)2 (2)
To a 50 mL tube was added compound 1 (0.631 g, 1.803 mmol),
after vacuum and refunding nitrogen for 3 times, 10 mL anhydrous
Et2O was added, until the compound 1 was completely dissolved
in Et2O. The solution was setting in −60 °C and the 2.4 M n-BuLi
(1.58 mL, 3.787 mmol) in hexane was dropping added with syringe.
−
plex 4 in Lewis acidity, in agreement with the fact that C8F17 SO3
−
is higher than ClO4 in electron-withdrawing ability. The TG-DSC
result shows that complex 3 is thermal stable up to 150 °C (Fig. 1).
2

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
Scheme 2. Synthesis of organoantimony complexes 2–4.
Table 1
Crystallographic data of complex 2 and 4.
Complex
2
4
Formula
C36 H38 N2 Sb2
C36 H40 Cl2 N2 O8 Sb2
CCDC No.
951,219
951,218
Formula weight
Crystal system, space group
742.18
943.13
Monoclinic, P2(1)/n
Monoclinic, P2(1)/n
˚
a A
15.5729(11)
13.3543(8)
˚
b A
6.3228(5)
12.4528(7)
˚
c A
17.5148(13)
11.8911(7)
α, deg
β, deg
90
90
108.005(2)
105.6520(10)
γ , deg
90
90
3
˚
V, A
1640.1(2)
1904.14
Z, Dx, Mg cm−3
2, 1.503
4, 1.503
μ, mm–1
1. 673
1. 611
F(000)
740
940
Crystal size, mm
0.257 × 0.136 × 0.127
1.53~26.00
0.30 × 0.20 × 0.15
2.28~30.53
θ range for data collection, deg
Limiting indices
−18≤h ≤ 19, -7 ≤ k ≤ 7, −18≤l ≤ 21
9415 / 3222, Rint = 0.0273
1.052
−19≤h ≤ 19, -9 ≤ k ≤ 17, −16≤l ≤ 16
5813 / 5276, Rint = 0.0178
0.994
Reflections collected/unique
Goodness of fit on F2
Final R indices [I>2σ(I)]
R indices (all data)
Largest diff peak and hole
R1 = 0.0280, wR2 = 0.0660
R1 = 0.0343, wR2 = 0.0693
0.439 and −0.317
R1 = 0.00176, wR2 = 0.0441
R1 = 0.00210, wR2 = 0.00463
0.485 and −0.555
2
Note: w (for 2) = 1/[σ2(Fo2) + (0.090P)2], where P = (Fo + 2Fc2)/3; w (for 4) = 1/[σ2(Fo2) + (0.0218 P)2 + 1.1062P] where
2
P = (Fo + 2Fc2)/3.
crystal owing to the long flexible chain of C8F17 group. Complex
2 and 4 were crystallized in monoclinic space group P21/n. One
can see that the complex 2 rotates around the symmetric axis of
˚
Sb(1)-Sb(1A). The N(1)-Sb(1) distance is 2.942(3) A, as shown in
the X-ray structure (Fig 2, left), which is slightly longer than the
˚
sum of the covalent radii (2.11 A) [46], shorter than the sum of the
˚
van der Waals radii of nitrogen and antimony atoms (3.74 A) [47],
illustrating that coordinated bond exists between the nitrogen and
antimony atoms. Upon reaction of complex 2 with HClO4, there
˚
˚
is elongation of N(1)-Sb(1) distance from 2.942(3) A to 3.685(1) A
(Fig 2, right) resulting from the protonation of N(1), closing to the
˚
boundary of VDW radii (3.74 A). This inferred that the coordination
exists between two atoms is small, even can be neglected.
3.3. Catalytic activities of complexes 2 to 4 in the Mannich reaction
The Mannich reaction is one of the most useful approaches to
synthesize nitrogen-containing compounds, as well as an effective
method for the construction of C − C bond [25,48–50]. In our pre-
vious works, our group have developed several efficient catalysts
for such reactions, but the catalyst loading is still as high as 5
mol% [25,51–53]. Now, the complex 3 was used to catalyse the
three-component (aldehyde, amine and ketone) direct diastereos-
elective Mannich reaction in assessing the catalytic activity. Noting
that, the catalyst loading could be reduced to 0.1 mol% (shown as
Table 4).
Fig. 1. TG-DSC curve of complex 3 in nitrogen flow (5 °C/min);
Left: (TG/%), Right: (DSC, mg/mW).
3.2. X-ray structure of complexes (2 and 4)
The ORTEP views of complex 2 and 4 are shown in Fig 2. The
complexes of 2 and 4 were crystallized by CH2Cl2 and confirmed
by a single-crystal X-ray diffraction. The essential bond parameters
were given in Table 1-3. The complex 3 failed to obtain a single-
3

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
Fig. 2. The ORTEP views of complex 2 (left) and 4 (right).
Table 2
˚
Selected bond lengths (A) and angles (°) of complex 2.
˚
˚
Selected bond lengths and angles
(A) or (°)
Selected bond lengths and angles
(A) or (°)
Sb(1)-C(7)
2.142(3)
2.161(3)
2.168(3)
2.942(5)
1.499(7)
1.388(6)
98.40(10)
93.57(11)
95.36(11)
115.2(5)
112.0(5)
108.2(5)
C(1)-C(2)
1.380(5)
1.383(5)
1.351(5)
1.382(7)
1.385(7)
1.365(9)
117.4(3)
124.9(2)
117.6(3)
118.6(6)
119.1(6)
122.2(5)
Sb(1)-C(13)
C(2)-C(3)
Sb(1)-C(1)
C(3)-C(4)
Sb(1)-N(1)
C(13)-C(14)
N(1)-C(17)
C(13)-C(15A)
C(14)-C(15)
N(1)-C(16)
C(7)-Sb(1)-C(13)
C(7)-Sb(1)-C(1)
C(13)-Sb(1)-C(1)
C(16)-N(1)-C(18)
C(16)-N(1)-C(17)
C(18)-N(1)-C(17)
C(2)-C(1)-C(6)
C(2)-C(1)-Sb(1)
C(6)-C(1)-Sb(1)
C(14)-C(15)-C(13A)
C(14)-C(15)-C(16)
C(13A)-C(15)-C(16)
Table 3
˚
Selected bond length (A) and angles (°) of complex 4.
˚
˚
Selected bond lengths and angles
(A) or (°)
Selected bond lengths and angles
(A) or (°)
Sb(1)-C(7)
2.149(1)
2.154(1)
2.193(1)
3.685(5)
1.509(2)
1.493(2)
97.65(5)
94.26(5)
95.12(5)
115.2(5)
112.7(1)
110.9(1)
C(1)-C(2)
1.401(2)
1.407(1)
1.399(2)
1.992(2)
1.392(2)
1.395(2)
117.6(1)
121.03(2)
121.22(9)
120.2(1)
118.3(1)
121.5(1)
Sb(1)-C(13)
C(2)-C(3)
Sb(1)-C(3)
C(3)-C(1)
Sb(1)-N(1)
C(13)-C(14)
C(13)-C(18)
C(14)-C(15)
C(1)-C(3)-C(2)
C(1)-C(3)-Sb(1)
C(2)-C(3)-Sb(1)
C(1)-C(2)-C(3)
C(1)-C(2)-C(4)
C(3)-C(2)-C(4)
N(1)-C(4)
N(1)-C(5)
C(3)-Sb(1)-C(7)
C(3)-Sb(1)-C(13)
C(13)-Sb(1)-C(7)
C(4)-N(1)-C(5)
C(4)-N(1)-C(6)
C(5)-N(1)-C(6)
As shown in Table 4, the poor yield and diastereoselectivity
were observed when the reaction was carried out in polar sol-
vents (entries 1 − 4, 6). When the n-Hexane (Table 4, entry
5) as solvent, the yield and diastereoselectivity increased up to
88% and anti/syn = 88/12. In short, this reaction took place in
the non-polar organic solvent resulting the best yield (yield 88%,
anti/syn = 88/12), which showed a different result comparing with
previous work [25,27]. Upon investigation of the typical procedure
for solubility measurement of catalyst 3, we found that the solu-
bility of 3 is 0.15 g/L in hexane at 20 °C (detail data see ESI). Cat-
alyst 3 has best catalytic effect in Mannich reaction using hexane
as solvent. Perhaps the catalyst 3 and raw materials have stronger
polarity than hexane, which could result in stronger interaction
between the catalyst and substrates and more effective precipi-
tation of products (Fig 3, entry 5). The catalyst loadings, reaction
temperature and substrate ratio were also screened as shown in
Table 5–7, respectively. As shown in Table 8, complex 3 is supe-
rior to complex 4, precursor 2 and HOSO2C8F17 as well as superior
to our previous reported complex C6H11 N(C6H4CH2)2SbOSO2C8F17
[27] in terms of catalytic efficiency and diastereoselectivity. There-
fore, the optimized reaction condition was shown as the follow-
ing:1.0 equivalent of 5a,1.2 equivalent of 6a and 3.0 equivalent of
7 in the presence of 0.1 mol% of complex 3 at 20 °C in n-hexane
solution for 6–24 hrs.
With the best condition in hand, we explored the scope of
substrates in this catalytic system over bimetallic organoantimony
catalyst 3 (Table 9). It is noted that aromatic amines with the
weak electron-withdrawing inductive effect groups (p-Cl, p-Me, en-
4

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
Table 4
Direct Mannich reaction of benzaldehyde, aniline and cyclohexanone in various solvents.
Entry
Solvent
Time (h)
anti/synb
Yield (%)c
1
2
3
4
5
6
CHCl3
12
12
12
12
12
12
81/19
82/18
79/21
76/24
88/12
69/31
79
78
74
84
88
84
CH2Cl2
THF
H2O
Hexane
[bmim]BF4
a
PhNH2 (1.5 mmol), PhCHO (1.5 mmol), Cyclohexanone (4.5 mmol), Solvent (4 mL), Catalyst 3
b
(0.0015 mmol, 0.1 mol% based on PhNH2), stirring at 20 °C for 12−18 hrs. Determined by 1H
NMR. cGC Yield.
Table 5
Effect of catalyst 3 loading on product yielda.
Entry
mol%
Yield (%)b
1
2
3
4
5
0
14
63
83
88
89
0.01
0.05
0.1
1
a
PhNH2 (1.5 mmol), PhCHO (1.5 mmol), Cyclohexanone (4.5 mmol), n-hexane (4 mL), stirring
for 12 h at RT.
b
GC yield.
Table 7
Effect of substrate ratio on yielda.
Entry
Ratio of PhNH2: PhCHO: Cyclohexanone
Yield (%)b
1
2
3
4
5
1:1:3
87
88
94
96
85
1:1.05:3
1:1.1:3
1:1.2:3
1:1.5:3
aPhNH2 (1.5 mmol), PhCHO (x mmol), Cyclohexanone (4.5 mmol),
n-hexane (4 mL), Catalyst 3 (0.1 mol%), stirring for 12 h at 20 °C.
b
GC yield.
Fig. 3. Reaction-induced self-separation Mannich reaction catalysed by complex 3
in solvents corresponding to those of Table 4: Upper (beginning), lower (ending).
implying that the formation of the (E)-N-benzylideneaniline inter-
mediate played a great role on diastereoselectivity. Compared to
the para-ones (entries 2, 4, 6, 7, 9), the ortho- substituted aro-
matic amines have a negative impact on catalytic efficiency (en-
tries 3, 5, 8) due to steric influence. In addition, more aromatic
aldehydes were explored and afforded moderate to excellent yields
and diastereoselectivity (entries 10–15). It was found that the aro-
matic aldehydes with different functional groups exhibited distinct
reactivity. An electron-withdrawing group is beneficial for prod-
uct yield and diastereoselectivity (entries 10–13) due to the en-
hancement electrophilicity of aldehyde in favour of the formation
of imine (The details of mechanism can be found in the SI). In
this case, the reactivity ortho-CF3-aldehydeis poor (entry 14) due to
steric hindrance. 2-furylaldehyde with heterocycle provided mod-
erate yield and diastereoselectivity (yield 79%, anti/syn=65/35). A
series of aromatic amines (5a-5d, 5f-5i) and aromatic aldehydes
(6a-6 g) could get the desired products and reaction-induced self-
Table 6
Effect of reaction temperature on yielda.
Entry
Temperature ( °C)
Yield (%)b
1
2
3
4
0
62
88
44
10
20
40
80
aPhNH2 (1.5 mmol), PhCHO (1.5 mmol), Cy-
clohexanone (4.5 mmol), n-hexane (4 mL),
Catalyst 3 (0.1 mol%), stirring for 12 h. bGC
yield.
tries 2 and 9) showed higher reactivity compared to those with
strong ones (p-NO2, entry 4; p-MeO, p-EtO, entries 6–7). And the
substrate with strong electron-donating para-substituent generated
high diastereoselectivity with anti/syn ratio up to 90/10 (entry 6),
5

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
Table 8
The Mannich reaction catalysed by various catalystsa.
Entry
Catalyst (0.1 mol%)
Yield (%)c
anti/synb
2−
1
2
3
4
5
[C6H2(CH2NHMe2SbPh2)2]2+[OSO2C8F17
]
(3)
96
79
16
70
66
88/12
87/13
–
2−
[C6H2(CH2NHMe2SbPh2)2]2+[ClO4]
(4)
C6H2(CH2NMe2SbPh2)2 (2)
d
HOSO2C8F17
61/39
85/15
d
C6H11N(C6H4CH2)2SbOSO2C8F17
a
PhNH2 (1.5 mmol), PhCHO (1.8 mmol), Cyclohexanone (4.5 mmol), n-hexane (4.0
b
c
mL), Catalyst (0.1 mol%), stirring for 12 h at 20 °C. Determined by 1H NMR. Isolated
d
yield. 0.2 mol%.
Table 9
The Mannich reaction with various amines catalysed by 3a.
Entry
R1
R2
Product (8)
Yield (%)c
anti/synb
1
Ph (5a)
Ph (6a)
8a
8b
8c
8d
8e
8f
96
95
64
31
NRe
55
79
62
94
92
95
85
79
67
79
88/12
70/30
79/21
50/50
–
2
p-ClC6H4 (5b)
o-ClC6H4 (5c)
p-NO2C6H4 (5d)
o-NO2C6H4 (5e)
p-EtOC6H4 (5f)
p-MeOC6H4 (5 g)
o-MeOC6H4 (5 h)
p-MeC6H4 (5i)
Ph (5a)
Ph (6a)
3
Ph (6a)
4d
5d
6
Ph (6a)
Ph (6a)
Ph (6a)
90/10
85/15
51/49
83/17
69/31
82/18
68/32
69/31
77/23
65/35
7
Ph (6a)
8g
8h
8i
8
Ph (6a)
9
Ph (6a)
10f
11f
12f
13
14
15
p-ClC6H4 (6b)
p-CF3C6H4 (6c)
p-MeC6H4 (6d)
p-MeOC6H4 (6e)
o- CF3C6H4 (6f)
2- Furyl (6 g)
8j
Ph (5a)
8k
8l
Ph (5a)
Ph (5a)
8m
8n
8o
Ph (5a)
Ph (5a)
a
Reaction conditions: 5, 1.5 mmol; 6, 1.8 mmol; 7, 4.5 mmol; n-Hexane, 4 mL; catalyst 3, 0.1 mol%;
b
c
d
e
20 °C; 6–24 h. Determined by 1H NMR. Isolated yield. Reaction temperature, 50 °C. No reaction.
f
Reaction temperature, −20 °C.
precipitation of products and catalyst 3 were observed in this re-
action.
Notes
The authors declare no competing financial interest.
In conclusion, we successfully synthesized and characterized
an air-stable bimetallic organoantimony catalyst 2–4. Upon a se-
ries of research, the catalyst 3 has been applied in catalysing the
three-component direct Mannich reaction with high catalytic ef-
ficiency (0.1 mol% catalyst loading) and diastereoselectivity(yield
96%, anti/syn=88/12) when n-hexane as solvent. Reaction-induced
precipitation of products and catalyst were easy to be isolate at the
end of the reaction. We expect with continuous effort more effi-
cient and greener methods for exploiting more powerful organoan-
timony catalyst for organic synthesis.
Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgments
The authors thank the Natural Science Foundation of China
(Nos. 21073040, 21373003, 21676076), Natural Science Foundation
of Changsha (kq2004008), Hu-Xiang High Talent of Hunan Province
(2018RS3042), and Recruitment Program for Foreign Experts of
China (WQ20164300353) for financial support.
Associated content
Detailed experimental procedures, characterization data, copies
of the 1H, 13C NMR spectra.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.jorganchem.2021.
121820.
Accession codes
CCDC 951,218 and 951,219 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free
of charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK.
References
[1] C. Weetman, S. Inoue, The Road Travelled: after Main-Group Elements as Tran-
sition Metals, ChemCatChem 10 (2018) 4213.
[2] T. Chu, G.I. Nikonov, Oxidative Addition and Reductive Elimination at Main–
Group Element Centers, Chem. Rev. 118 (2018) 3608.
6

N. Tang, X. Song, T. Yang et al.
Journal of Organometallic Chemistry 942 (2021) 121820
[3] R.C. Fischer, P.P. Power, π-Bonding and the Lone Pair Effect in Multiple Bonds
Involving Heavier Main Group Elements: developments in the New Millen-
nium, Chem. Rev. 110 (2010) 3877.
[28] F. Liu, A.s. Martin-Mingot, M.-.P. Jouannetaud, F. Zunino, S.b. Thibaudeau, Su-
perelectrophilic Activation in Superacid HF/SbF5 and Synthesis of Benzofused
Sultams, Org. Lett. 12 (2010) 868.
[4] L.C. Wilkins, R.L. Melen, Enantioselective Main Group Catalysis: modern Cata-
lysts for Organic Transformations, Coord. Chem. Rev. 324 (2016) 123.
[5] K. Revunova, G.I. Nikonov, Main Group Catalysed Reduction of Unsaturated
Bonds, Dalton Tran. 44 (2015) 840.
[6] M.M. Hansmann, G. Bertrand, Transition-metal-like Behavior of Main Group
Elements: ligand Exchange at a Phosphinidene, J. Am. Chem. Soc. 138 (2016)
15885.
[7] P.P. Power, Main-Group Elements as Transition Metals, Nature 463 (2010) 171.
[8] R.J. Less, R.L. Melen, D.S. Wright, Catalytic Versus Stoichiometric Dehydrocou-
pling Using Main Group Metals, RSC Adv 2 (2012) 2191.
[29] H. Matsuda, A. Ninagawa, R. Nomura, Reaction of Carbon Dioxide with Epox-
ides in The Presence of Pentavalent Organoantimony Compounds, Chem. Lett.
8 (1979) 1261.
[30] R. Nomura, A. Ninagawa, H. Matsuda, Synthesis of Cyclic Carbonates from Car-
bon Dioxide and Epoxides in The Presence of Organoantimony Compounds as
Novel Catalysts, J. Org. Chem. 45 (1980) 3735.
[31] R. Nomura, M. Yamamoto, H. Matsuda, Preparation of Cyclic Ureas from Carbon
Dioxide and Diamines Catalyzed by Triphenylstibine Oxide, Ind. Eng. Chem.
Res. 26 (1987) 1056.
[32] R. Nomura, H. Hisada, A. Ninagawa, H. Matsuda, Die Makromolekulare Chemie,
Rapid Communications 1 (1980) 135.
[9] P. Sharma, D. Castillo, N. Rosas, A. Cabrera, E. Gomez, A. Toscano, F. Lara,
S Hernández, G. Espinosa, Synthesis and Structures of Organoantimony Com-
pounds Containing Intramolecular Sb–N interactions, J. Organomet. Chem. 689
(2004) 2593.
[10] F. Frézard, R. Monte-Neto, P.G. Reis, Antimony Transport Mechanisms in Resis-
tant Leishmania Parasites, Biophys. Rev. 6 (2014) 119.
[33] R. Nomura, H. Hisada, A. Ninagawa, H. Matsuda, Die Makromolekulare Chemie
183 (1982) 1073.
[34] R. Nomura, Y. Shiomura, A. Ninagawa, H. Matsuda, Die Makromolekulare
Chemie 184 (1983) 1163.
[35] R.c. Nomura, S.-.I. Miyazaki, T. Nakano, H. Matsuda, Facile Esterification Pro-
moted by The Triphenylstibine Oxide-Phosphorus Sulfide (Ph3SbO/P4S10 ) Sys-
tem, Appl. Organomet. Chem. 5 (1991) 513.
[11] M. Shekarchi, F.K. Behbahani, Antimony(V) Chloride, SbCl5 as a Labile Reagent
in Organic Transformations, Catal. Lett. 147 (2017) 2950.
[12] R.S.P. Turbervill, J.M. Goicoechea, From Clusters to Unorthodox Pnictogen
Sources: solution-Phase Reactivity of [E7]3–(E = P–Sb), Anions. Chem. Rev. 114
(2014) 10807.
[13] X. Li, J. Ni, S.V. Savilov, L. Li, Materials Based on Antimony and Bismuth for
Sodium Storage, Chem. Eur. J. 24 (2018) 13719.
[36] R. Nomura, H. Hisada, A. Ninagawa, H. Matsuda, Die Makromolekulare Chemie,
Rapid Communications 1 (1980) 705.
[37] R. Nomura, Y. Hasegawa, M. Ishimoto, T. Toyosaki, H. Matsuda, Carbonylation
of Amines by Carbon Dioxide in The Presence of An Organoantimony Catalyst,
J. Org. Chem. 57 (1992) 7339.
[14] J. Mishra, A. Saxena, S. Singh, Chemotherapy of Leishmaniasis: past, Present
and Future, Curr. Med. Chem. 14 (2007) 1153.
[38] J. James, W. Casey, F.P. Gabbaï, Redox and Anion Exchange Chemistry of a Stib-
ine–Nickel Complex: writing the L, X, Z Ligand Alphabet with a Single Element,
Angew. Chem. Int. Ed. 53 (2014) 8876.
[15] N. Kakusawa, Y. Tobiyasu, S. Yasuike, K. Yamaguchi,
rita, Hypervalent Organoantimony Compounds 12-ethynyl-tetrahy-
H Seki, J. Ku-
[39] M. Yang, D. Tofan, C.H. Chen, K.M. Jack, F.P. Gabbaï, Digging the Sigma-Hole
of Organoantimony Lewis Acids by Oxidation, Angew. Chem. Int. Ed. 57 (2018)
13868.
drodibenz[c,f][1,5]azastibocines: highly Efficient New Transmetallating Agent
for Organic Halides, J. Organomet. Chem. 691 (2006) 2953.
[16] H. Breunig, T. Koehne, O. Moldovan, A. Preda, A. Silvestru, C. Silvestru, R. Varga,
[40] D. Tofan, F.P. Gabbaï, Fluorinated Antimony(V) Derivatives: strong Lewis Acidic
Properties and Application to The Complexation of Formaldehyde in Aqueous
Solutions, Chem. Sci. 7 (2016) 6768.
[41] H. Yang, F.P. Gabbaı¨, Activation of a Hydroamination Gold Catalyst by Oxi-
dation of a Redox-Noninnocent Chlorostibine Z-Ligand, J. Am. Chem. Soc. 137
(2015) 13425.
L
Piedra-Garza, U. Kortz, Syntheses, Structures and Intermolecular Interac-
tions of Tetraorganoammonium, -phosphonium and -stibonium dimethyl- and
Diphenyltetrahaloantimonates, J. Organomet. Chem. 695 (2010) 1307.
[17] L.D. Freedman, G.O. Doak, Antimony Annual Review Covering The Year 1991, J.
Organomet. Chem. 486 (1995) 1.
[18] P. Sharma, A. Cabrera, N.K. Jha, N. Rosas, R. Le Lagadec, M. Sharma, J.L. Arias,
Novel Organoantimony Compounds Containing Sb-Sb Bonds: a Review, Main
Group Met. Chem. (1997) 20.
[42] A.M. Christianson, F.P. Gabbaï, A Lewis Acidic, π-Conjugated Stibaindole with
a Colorimetric Response to Anion Binding at Sb(III), Organometallics 36 (2017)
3013.
[19] P. Sharma, A. Cabrera, S. Singh, N.K. Jha, Schiff Base Complexes of Antimony: a
Review, Main Group Met. Chem. 20 (8) (1997).
[43] G. Becker, O. Mundt, M. Sachs, H.J. Breunig, E. Lork, J. Probst, A. Silvestru,
Untersuchungen am Chlordiphenyl- und Tribenzylstiban sowie am Triben-
zyldibromstiboran – Molekülstrukturen und Isotypie, Z. Anorg. Allg. Chem. 627
(2001) 699.
[44] R. Qiu, X. Xu, L. Peng, Y. Zhao, N. Li, S. Yin, Strong Lewis Acids of Air-Stable
Metallocene Bis(perfluorooctanesulfonate)s as High-Efficiency Catalysts for
Carbonyl-Group Transformation Reactions, Chem. Eur. J. 18 (2012) 6172.
[45] H.A. Benesi, Acidity of Catalyst Surfaces. II. Amine Titration Using Hammett
Indicators, J. Phys. Chem. 61 (1957) 970.
[20] J. He, Y. Wei, T. Zhai, H. Li, Antimony-Based Materials as Promising Anodes
for Rechargeable Lithium-Ion and Sodium-Ion Batteries, Mater. Chem. Front. 2
(2018) 437.
[21] J. Wang, Q. Qi, Z. Feng, X. Zhang, B. Huang, A. Chen, L. Prestegarden, X. Li,
J. Wang, Berberine Induces Autophagy in Glioblastoma by Targeting The
AMPK/Mtor/ULK1-Pathway, Oncotarget 7 (2016) 66944.
[22] N. Li, Y. Wang, F. Liu, X. Zhao, X. Xu, Q. An, K. Yun, Air-Stable Zirconium
(IV)-Salophen Perfluorooctanesulfonate as A Highly Efficient and Reusable Cat-
alyst for The Synthesis of 3,4-Dihydropyrimidin-2-(1H)-Ones/Thiones Under
Solvent-Free Conditions, Appl. Organomet. Chem. 34 (2020) e5454.
[23] H.R. Darabi, K. Aghapoor, F. Mohsenzadeh, F. Taala, N. Asadollahnejad,
A. Badiei, Silica-Supported Antimony(III) Chloride as Highly Effective and
Reusable Heterogeneous Catalyst for the Synthesis of Quinoxalines, Catal. Lett.
133 (2009) 84.
[46] P. Pyykkö, M. Atsumi, Molecular Single-Bond Covalent Radii for Elements
1–118, Chem. Eur. J. 15 (2009) 186.
[47] S.S. Batsanov, Van der Waals Radii of Elements, Inorg. Mater. 37 (2001) 871.
[48] A. Córdova, The Direct Catalytic Asymmetric Mannich Reaction, Acc. Chem. Res.
37 (2004) 102.
[49] T. Kano, Y. Yamaguchi, K. Maruoka, A Designer Axially Chiral Amino Sulfon-
amide as an Efficient Organocatalyst for Direct Asymmetric Mannich Reactions
of N-Boc-Protected Imines, Angew. Chem. Int. Ed. 48 (2009) 1838.
[50] S. Mukherjee, J.W. Yang, S. Hoffmann, B. List, Asymmetric Enamine Catalysis,
Chem. Rev. 107 (2007) 5471.
[24] M. Paraja, A. Gini, N. Sakai, S. Matile, Pnictogen-Bonding Catalysis: an Inter-
active Tool to Uncover Unorthodox Mechanisms in Polyether Cascade Cycliza-
tions, Chem. Eur. J. 26 (2020) 15471.
[25] J. Lei, L. Peng, R. Qiu, Y. Liu, Y. Chen, C.-.T. Au, S.-.F. Yin, Establishing The Corre-
lation Between Catalytic Performance and N→Sb Donor–Acceptor Interaction:
systematic Assessment of Azastibocine Halide Derivatives as Water Tolerant
Lewis Acids, Dalton Trans 48 (2019) 8478.
[51] Tuberculous Meat Bacillus, Bmj-Brit Med. J. 1 (1889) 1492.
[52] R. Qiu, X. Xu, L. Peng, Y. Zhao, N. Li, S. Yin, Strong Lewis Acids of Air-Stable
Metallocene Bis(perfluorooctanesulfonate)s as High-Efficiency Catalysts for
Carbonyl-Group Transformation Reactions, Chem. Eur. J. 18 (2012) 6172.
[53] M. Stanbury, Jeremy N.In Green, in: Encyclopedia of Global Archaeology,
Springer International Publishing, 2020, pp. 4759–4761.
[26] A. Saito, J. Kasai, Y. Odaira, H. Fukaya, Y. Hanzawa, Synthesis of 2,3-Dihy-
droquinolin-4(1H)-ones through Catalytic Metathesis of o-Alkynylanilines and
Aldehydes, J. Org. Chem. 74 (2009) 5644.
[27] J. Xia, R. Qiu, S. Yin, X. Zhang, S. Luo, C.-.T. Au, K. Xia, W.-.Y. Wong, Synthesis
and Structure of An Air-Stable Organoantimony Complex and Its Use as A Cat-
alyst for Direct Diastereoselective Mannich Reactions in Water, J. Organomet.
Chem. 695 (2010) 1487.
7