Well-defined dinuclear silver phosphine complexes based on nitrogen donor ligand and their high efficient catalysis for A3-coupling reaction

Article abstract of DOI:10.1016/j.ica.2017.05.018

Nitrogen donor ligands HL₁, HL₃, HL₄ and their silver complexes 1·OTf–4·OTf are prepared and fully characterized. Treatment of HL₁-HL₄ with AgOTf (OTf^??=?triflato) in presence of base Et

Full text of DOI:10.1016/j.ica.2017.05.018

Accepted Manuscript
Research paper
Well-defined dinuclear silver phosphine complexes based on nitrogen donor
ligand and their high efficient catalysis for A3-coupling reaction
Jing-Jing Chen, Zhi-Liang Gan, Qi Huang, Xiao-Yi Yi
PII:
S0020-1693(17)30349-3
http://dx.doi.org/10.1016/j.ica.2017.05.018
ICA 17587
DOI:
Reference:
Inorganica Chimica Acta
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6 May 2017
Please cite this article as: J-J. Chen, Z-L. Gan, Q. Huang, X-Y. Yi, Well-defined dinuclear silver phosphine
complexes based on nitrogen donor ligand and their high efficient catalysis for A3-coupling reaction, Inorganica
Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.05.018
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Well-defined dinuclear silver phosphine complexes based on
nitrogen donor ligand and their high efficient catalysis for
A3-coupling reaction
Jing-Jing Chen,1 Zhi-Liang Gan,1 Qi Huang,1 Xiao-Yi Yi *1,2
1. College of Chemistry and Chemical Engineering, Central South University,
Changsha, Hunan 410083, P. R. China
2. Hunan provincial Key Laboratory of Efficient and Clear Utilization of Manganese
Resources,Central South University, Changsha, Hunan 410083, P. R. China
Fax: 86 731 88879616; Tel: 86 731 88879616;
*To whom correspondence should be addressed.
Xiao-Yi Yi, E-mail: xyyi@csu.edu.cn

Abstract
Nitrogen donor ligands HL1, HL3, HL4 and their silver complexes 1·OTf - 4·OTf
are prepared and fully characterized. Treatment of HL1-HL4 with AgOTf (OTf- =
triflato) in presence of base Et3N and co-ligand PPh3 affords dinuclear Ag(I)
-
-
-
-
complexes [Ag2(L)(PPh3)2]·OTf (L=L1 , 1·OTf; L=L2 , 2·OTf; L=L3 , 3·OTf; L=L4 ,
4·OTf), respectively. The solid structure displays L acts as bis(bidentate) ligand,
bridging between two Ag(I) centres. The Ag···Ag interaction as well as other weak
interactions, such as Ag···Brintermolecular for 1+, Ag···Brintramolecular for 2+, Ag···S for 3+
are observed. These complexes are applied in the A3-coupling reaction of aldehydes,
alkynes and amines under mild conditions, and showed excellent catalytic efficiency
and recyclability. 1 mol% catalyst loading gives 99 % yield of propargylamines
o
product in 0.15 h at 35 C in open air atmosphere. 1·OTf can be recycled six times
without noticeable less of the catalyst activity.

Introduction
As one of the most important metal-catalysed reactions of alkynes, A3-coupling
of aldehydes, alkynes and amines, has been recognized as a worthwhile approach to
propargylamines, which supply molecular building blocks to assemble various
functional materials [1]. Transition-metal salts and complexes, such as Fe, Co, Ir, Ni,
Zn, Cd, Hg and coinage metals (Cu, Ag and Au) etc., have been developed as the
catalysts for this multicomponent reaction [1-5]. Among these complexes, silver
complexes have received special attention due to their alkynophilicity, referred to
favoring interactions with the carbon-carbon π-bond of alkyne [6]. In 2003, Li and
coworkers successfully developed the first silver-catalyzed A3-coupling reaction [7].
Following this pioneering work, simple silver salts (e.g., AgX, Ag2O etc) [8,9], silver
nanoparticles [10-14] and silver complexes [15-24] have been extensively studied in
improvements in terms of the substrate scope, reaction efficiency, and even catalyst
recycling. However, most of them still have to suffer from harsh catalytic conditions,
such as needing inert gas environment, relatively high catalyst loading, high reaction
temperature and/or long reaction time (up to 24 h). Silver-carbene complexes reported
by Navarro groups is an exception [23]. It gave 92 % GC yield of propargylamines at
o
25 C in 20 min with 1 mo% catalyst, while an atmosphere of nitrogen was still
required. Therefore, to seek more efficient silver complex for A3-coupling reaction
under mild conditions is though to be worth attempting.
Bispyridylpyrrole derivatives [25-29] featuring strong coordination ability,
varieties of coordination modes and easy modification are important ligands to
prepare metal catalysts with high performances. In this work, the syntheses and
characterizations of a series of dinuclear silver(I) phosphine complexes based on
bispyridylpyrrole nitrogen donor ligand will be reported. Their catalytic performances
for A3-coupling reaction will also be described.

Experimental Section
General Considerations. 1H NMR and 31P NMR spectra were recorded on a
Bruker AVANCE spectrometer operating at 400 MHz (or 500 MHz), and 161 MHz
(or 202 MHz), and chemical shifts (δ, ppm) were reported with reference to SiMe4 and
H3PO4, respectively. Infrared spectra (KBr) were recorded on Nicolet 6700
spectrometer FT-IR spectrophotometer. Elemental analyses for C, H and N were
performed on a Perkin Elmer 240C elemental analyzer. UV-Vis absorption spectra
were recorded on LabTech, Inc. UV8100A machine. The starting
2,5-bis(6’-bromo-2’-pyridyl)pyrrole (HL2) were prepared according to literature
methods [30]. All of other chemicals were obtained from J&K Scientific.
Preparation of HL1. The method is similar with that of HL2.
1,4-Di(2-pyridyl)butan-1,4-dione. Sodium acetate (36.74 mg, 0.448 mmol) and
3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride(120.87 mg, 0.448
mmol) were added to degassed ethanol (10 mL). The mixture was heated under reflux
and the mixture of 5-bromo-2-pyridinecarboxaldehyde (500 mg, 2.688 mmol) and
divinyl sulfone (135 uL, 1.34 mmol) in ethanol (25 mL) was added dropwise over 30
min and then refluxed for further 12 h. The yellow precipitated product was separated
from the orange solution, washed with cold ethanol (30 mL) and diethyl ether (30
mL). 1,4-Di(2-pyridyl)butan-1,4-dione was obtained as a bright yellow precipitate.
Yield: 418.9 mg (78.3%). This compound was used without further purification.

2,5-bis(5’-bromo-2’-pyridyl)-pyrrolide (HL1).
The mixture of 1,4-Di(2-pyridyl)butan-1,4-dione (418.9 mg, 1.05 mmol) and an
o
excess of ammonium acetate (10 g, 129.7 mmol) was heated at 135 C for 16 h, and
then cooled to room temperature and poured into water (40 mL). The aqueous mixture
was extracted with dichloromethane (3 × 100 mL). The organic extracts were dried
with Na2SO4 and evaporated，which was purified by chromatography from silica gel
(CH2Cl2 : hexane, 1 : 4) to give HL1 with yield of 223.6 mg (56.2 %). The single
1
crystals were afforded by slow evaporation of a solution of HL1 in CH2Cl2/hexane. H
NMR (400 MHz, CDCl3): δ 10.55 (s, 1H), 8.57 (dd, J = 2.3, 0.8 Hz, 2H), 7.76 (dd, J =
8.5, 2.4 Hz, 2H), 7.47 (dd, J = 8.6, 0.9 Hz, 2H), 6.76 (d, J = 2.7 Hz, 2H). IR(KBr,
cm-1): 3431(s), 3097(w), 1574(s), 1449(s), 1277(s), 1243(m), 1121(m), 1087(m),
831(m), 786(s), 742(m), 626(m). Anal. Calc. for C14H9Br2N3: C, 44.36; H, 2.39; N,
11.09. Found: C, 45.27; H, 2.78; N, 10.78.
Preparation of HL3. The mixture of HL2 (379.1 mg, 1.0 mmol), 2-thiopheneboronic
acid (307 mg, 2.4 mmol), K2CO3 (1.38 g, 10 mmol) and Pd(PPh3)4 (115.5 mg, 0.1
mmol) in degassed solution of THF/H2O (40 mL/10mL) was refluxed overnight. The
mixture was cooled to room temperature, removed off THF solvent in vacuo, poured
into water (50 mL) and extracted with CH2Cl2 (4 × 50 mL). The extracts were dried
with anhydrous Na2SO4, and then concentrated, chromatographed on silica gel
(CH2Cl2 : hexane, 1 : 4). The pale yellow solid HL3 was obtained in a yield of 304 mg
(79 %). 1H NMR (400 MHz, CDCl3): δ 10.82(s, 1H), 7.68-7.64 (m, 4H), 7.47-7.43 (m,
6H), 7.16 (dd, J = 5.0, 3.6 Hz, 2H), 6.79 (d, J = 2.7Hz, 2H). IR(KBr, cm-1): 3426(s),
3097(w), 1587(s), 1560(m), 1452(s), 1424(m), 1266(m), 1220(w), 1157(m), 1077(m),
1049(m), 832(m), 762(s), 695(m), 656(m). Anal. Calc. for C22H15S2N3: C, 68.54; H,
3.92; N, 11.90. Found: C, 68.54; H, 4.07; N, 11.01.

HL4 was synthesized by the similar method with that of HL3, only using
2-phenylboronic acid instead of 2-thiopheneboronic acid. The single crystals were
afforded by slow evaporation of a solution of HL4 in CH2Cl2/hexane. Yield of 306 mg
1
(82 %). H NMR (CDCl3, 500M): δ 10.956(s, 1H), 8.21-8.19 (m, 4H), 7.74 (t, J = 7.8
Hz, 2H), 7.58-7.53 (m, 8H), 7.49-7.46 (m, 2H), 6.83 (d, J = 2.7Hz, 2H). IR(KBr,
cm-1): 3432(s), 3038(w),1585(s), 1560(s), 1444(s), 1307(w), 1260(m), 1211(m),
1152(w), 1087(m), 805(m), 752(s), 688(m), 651(m). Anal. Calc. for C26H19N3: C,
83.62; H, 5.13; N, 11.25. Found: C, 83.06; H, 5.58; N, 10.91.
Preparation of complex 1·OTf. A mixture of HL1 (49.3 mg, 0.13 mmol) and AgOTf
(66.8 mg, 0.26mmol) in THF (5 mL) was added Et3N (26.3 mg, 0.26 mmol) to form a
yellow suspension solution. The PPh3 (68.2 mg, 0.26 mmol) in THF (5 mL) was
added, and the suspension solution immediately became clear. The resulting mixture
solution was stirred overnight, and then layered with CHCl3 and hexane to give
yellow crystals which were suitable for X-ray diffraction analysis. Yield: 120.4 mg
1
(66.8 %). H NMR (CDCl3, 400M)：δ 7.83-7.77 (m, 4H), 7.58 (d, J = 8.6 Hz,
2H),7.48-7.44 (m, 6H), 7.30 (td, J = 7.7, 1.6 Hz, 12H), 7.16 (dd, J = 12.1, 7.7 Hz,
12H), 6.94 (s, 2H). 31P NMR(CDCl3): δ15.17, 18.59 (s, PPh3). IR(KBr, cm-1):
3052(w), 1578(m), 1503(m), 1445(s), 1372(m), 1262(s), 1155(m), 1097(m),1028(s),
745(s), 693(s), 636(m), 521(m). Anal. Calc. for C51H38Ag2Br2F3N3O3P2S: C, 48.33; H,
3.02; N, 3.32. Found: C, 48.13; H, 3.20; N, 3.35.
Complexes 2·OTf - 4·OTf were synthesized by the similar method with that complex
1·OTf, only using HL2, HL3 and HL4 instead of HL1, respectively.

1
Yield of complex 2·OTf: 112.8 mg (68.5 %). H NMR (CDCl3, 400M): δ 7.73-7.66
(m, 4H), 7.45-7.41 (m, 6H), 7.27-7.16 (m, 26H), 7.01 (s, 2H); 31P NMR(CDCl3): δ
14.68, 18.96 (PPh3). IR(KBr, cm-1): 3052(w), 1620(w), 1578(m), 1503(m), 1438(s),
1372(m), 1263(s), 1156(m), 1097(m), 1029(s), 745(m), 693(s), 636(m), 521(m). Anal.
Calc. for C51H38Ag2Br2F3SO3N3P2: C, 48.33; H, 3.02; N, 3.32. Found: C, 47.68; H,
3.20; N, 3.30.
1
Yield of complex 3·OTf: 110.1 mg (66.5 %). H NMR (CDCl3, 500M): δ 7.88 (t, J =
7.8 Hz, 2H), 7.79 (d, J = 7.9Hz, 2H), 7.42-7.36 (m, 8H), 7.26-7.25 (d, J = 5Hz, 2H),
7.17 (dd, J = 15.9, 8.2 Hz, 14H), 6.95-6.91 (m, 12H), 6.75 (dd, J = 5.0, 3.6 Hz, 2H),
6.70 (dd, J = 5.0, 1.1 Hz ,2H). 31P NMR (CDCl3): δ 14.88, 18.79 (PPh3). IR(KBr,
cm-1): 3072(w), 1585(m), 1554(m), 1435(m), 1268(s), 1149(m), 1095(m), 1030(s),
745(m), 693(s), 636(m), 520(m). Anal. Calc. for C59H44Ag2F3N3O3P2S3: C, 55.63; H,
3.48; N, 3.30. Found: C, 55.51; H, 3.99; N, 3.31.
Yield of complex 4·OTf: 105.9 mg (64.6 %). 1H NMR (CDCl3, 500M): δ 7.97 (t, J =
7.7 Hz, 2H), 7.90 (dd, J = 8.0, 1.0 Hz, J = 7.5Hz,2H), 7.41 (td, J = 7.5, 1.4 Hz, 6H),
7.28 (ddd, J = 9.6, 7.7, 1.1 Hz, 6H), 7.19-7.16 (m, 14H), 7.134-7.103 (m, 2H), 6.77
(dt, J = 15.3, 8.2 Hz, 16H). 31P NMR (CDCl3): δ 13.69, 18.16 (PPh3). IR (KBr, cm-1):
3054(w), 1587(m), 1559(m), 1491(m), 1437(s), 1336(m), 1270(s), 1161(m), 1096(m),
1029(s), 749(m), 694(s), 637(m), 521(m). Anal. Calc. for C63H48Ag2F3N3O3P2S: C,
59.97; H, 3.83; N, 3.33. Found: C, 58.89; H, 4.10; N, 3.43.
General procedure for catalytic reaction In a typical experiment, the mixture of
disilver catalyst (1.0 mol%), phenylacetylene (1.0 mmol), aldehyde (1.3 mmol),
o
amine (1.3 mmol) in CH2Cl2 (0.5 mL) was stirred at 35 C in open air atmosphere.
The 1H NMR spectra was used to monitor the reaction. After reaction was proceeded
for a given time, the conversion of phenylacetylene and formation of the

1
propargylamine was calculated based on the H NMR of the reaction mixture. The
pure propargylamine product was isolated by column chromatography on silica using
ethyl acetate/hexane as the eluent.
X-ray crystallography Diffraction data of HL1, HL2, HL4 and metal complexes were
recorded on a Bruker CCD diffractometer with monochromatized Mo-Kα radiation
(λ = 0.71073 Å). The collected frames were processed with the software SAINT. The
absorption correction was treated with SADABS [31]. Structures were solved by
direct methods and refined by full-matrix least-squares on F2 using the SHELXTL
software package [32]. Atomic positions of non-hydrogen atoms were refined with
anisotropic parameters. All hydrogen atoms were introduced at their geometric
positions and refined as riding atoms. In complex 2·OTf, due to the serious disorder,
we employed PLATON/SQUEEZE to calculate the diffraction contribution of OTf-
anion.
Results and Discussion
Preparations and characterizations
meta-Br substituted bispyridylpyrrole ligand HL1 was synthesized in high yield
according
to
the
reported
method
[30].
Treatment
of
5-bromo-2-pyridinecarboxaldehyde and divinyl sulfone in presence of sodium acetate
and 3-benzyl-5-(2-hydroxyethyl)-4-methyl-1,3-thiazolium chloride in refluxing
ethanol gave 1,4-di(2-pyridyl)butan-1,4-dione, which was reacted with ammonium
acetate to afford HL1. Treatment of HL2 with 2-thiopheneboronic acid and
2-phenylboronic acid in presence of base K2CO3 and catalyst Pd(PPh3)4 in THF/H2O
mixture solution yielded HL3 and HL4 with yields of 79 % and 82 %, respectively.
1
The H NMR spectrum of these bispyridylpyrrole ligands shows a single peak at
10.5~10.9 ppm for imino N-H resonance, indicating of the formation of central

pyrrole ring. In HL3 and HL4, the additional peaks at 7.67~7.43 ppm and 8.20~7.56
ppm are attributed to the hydrogen of o-thienyl and benzyl rings, respectively.
To the mixture of HL1-HL4 and silver salt, such as AgNO3, AgOTf, with
ligand/metal salt raito from 1: 2 to 2:1 in presence of Et3N afforded yellow suspension
solution immediately. Much efforts were made on characterization of the yellow solid,
while it failed. Black solid always appeared after placing its solution of CH2Cl2
overnight even in the dark. When PPh3 was added, the yellow suspension solution
became clear immediately. Yellow dinuclear complexes 1·OTf - 4·OTf were
generated in high yield (Scheme 1). There complexes are air stable, and readily
soluble in organic solvent, such as CH2Cl2, THF and CH3CN.
These complexes were characterized by IR, 1H NMR, 31P NMR and single-crystal
X-ray diffraction analysis. The IR spectra of these complexes clearly reveals the
formation of N(pyrrole)-Ag bond, which is indicated by the absence of the imino N–H
resonance at 3430 cm-1 of free bispyridylpyrrole ligand. The bispyridylpyrrole ligand
in metal complex has a distinctive signals, including the weak aromatic C–H
stretching at 3052-3072 cm−1 and a region from 1435 to 1587 cm−1 corresponding to
the in-plane vibrations of the C=C and C=N bonds. In addition, these complexes show
a strong stretching band at 1262–1270 cm−1 due to S=O stretching frequencies of the
1
coordinated triflato group. Compared with the H NMR of free ligand, disappearance
of imino hydrogen signal in 1·OTf - 4·OTf also indicates of coordination of
N(pyrrole)-Ag. The 31P NMR displays peaks of these metal complexes at around 15
ppm and 19 ppm due to the coordinated PPh3 ligand. The absorption spectra of
ligands and metal complexes are shown in Fig. S3. The organic ligands have intense
absorption bands of 355-380 nm, mainly due to the π-π* transition of aromatic
bispyridylpyrrole. For the corresponding silver complexes, besides of absorption
bands of bispyridylpyrrole ligands, more intense π-π* transitions in 200-280 nm
region is attributed to additional PPh3 ligand. New intense absorption band centered at
ca. 420 nm could be assigned to metal-to-ligand charge transfer transitions.

Structures description
Ligands HL1, HL2, HL4 and metal complexes 1·OTf - 3·OTf are characterized by
the X-ray diffraction analysis. Slow evaporation of HL1, HL2, HL4 solution in
CH2Cl2-hexane gave yellow crystals. HL3 was also obtained as yellow crystals by the
evaporation method, while it failed to collect the X-ray diffraction data due to such
thin layered crystals. The solution of metal complexes 1·OTf - 4·OTf in CHCl3 and/or
CH2Cl2 was layered by hexane to give yellow block single crystals. The
crystallographic data and experimental details for ligands HL1, HL2, HL4 and metal
complexes 1·OTf - 3·OTf are shown in Table 1. Their Selected bond distances and
bond angles are listed in Table 2. Their ORTEP diagrams are displayed in Figure 1, 2,
respectively. 4·OTf has poor crystal quality, of which crystallographic data is listed in
S5.
As shown in Fig. 1, HL1, HL2, HL4 display almost planar structure, indicating
that free ligand has aromatic properties. Two side pyridyl ring have only slightly
o
o
twisted to form interplanar angles with central pyrrole ring (9.3 and 9.0 for HL1;
8.5 o and -6.0 o for HL2; 0.9 o and 3.0 o for HL3). Their packing mode is very different.
In the case of HL1, molecules adopt a stacking mode of H-type aggregation, while
J-type aggregation occurs in HL2 along the b axis (S4). Face-to-face π-π
intermolecular interactions are extensively observed in these ligands.
Modifying ligand anticipates to construct novel structures, while complexes
1·OTf - 4·OTf show the same core structure (Fig. 2, S6). Each cation of metal
complex contains two Ag atoms, one substituted bispyridylpyrrole ligand L and two
PPh3 co-ligands. Bis-bidentated L ligand bridges two silver atoms via N atom of
central pyrrole group. Its side pyridyl rings and central pyrrole ring are twisted with
o
dihedral angles of 9.1 - 27.8 . Each Ag atom is three-fold coordinated by two N
atoms from bispyridylpyrrole and one P atom from PPh3. The bond distances of
Ag-Npyridine and Ag-Npyrrole are in the range of 2.212(4)-2.393(2) Å and

2.266(4)-2.551(4) Å, respectively. The Ag-P bond distance of 2.341(13)-2.372(6) Å in
this work is normal, which is consistent with that of the early reported [29,33]. Beside
of the strong coordination, weak interactions between silver atom and its neighboring
atoms or groups are observed. The separation of two silver atoms (2.975 - 3.067 Å in
1+ - 3+) is shorter than the van der waal radius, indicating there is a strong Ag···Ag
interaction compared to other multinuclear silver complexes [29,34]. Other weak
interactions, such as Ag1···Br2intermolecular (3.378 Å) for 1+, Ag···Brintramolecular (3.513,
3.607 Å) for 2+, Ag···S (3.144, 3.257 Å) for 3+ are also observed (Table 2).
Catalytic application for A3-coupling reaction 1·OTf - 4·OTf were investigated as
catalysts for A3-coupling reaction between aldehydes, alkynes and amines. The
optimization of reaction conditions is summaried in Table 3. Solvent and coupling
partners are obtained without any purification. The reaction is proceeded well in the
o
presence of 1 mol % of disilver complex 1·OTf - 4·OTf in open air at 35 C. The
expected propargylamine is generated with nearly quantitative yield. All complexes
1·OTf - 4·OTf have similar catalytic activity. 1·OTf is chose as a model compound
for catalytic reaction. Solvent effects are apparent. Solvent CH2Cl2 is optimum.
Following the optimization protocol, phenylacetylene was used as a model
substrate and various aldehydes and amines were explored. The results are outlined in
Table 4. It indicates 1·OTf is highly active for A3-coupling reaction. All the reactions
proceeded smoothly to generated the desired products in high yields. For example,
just in 15 min reaction time, pyrrolidine combined with aliphatic aldehydes gave >
97 % yields of corresponding products. Further studies revealed that even a catalyst
loading as low as 0.2 mol%, the reaction still proceeded well with 93 % yield (Table 3,
entry 1). Notably, in the case of benzaldehyde or N,N-dibenzylamine involved, a
relatively long reaction time is required, possibly due to the steric effect of the rigid
aromatic group of aldehyde and/or amine.
The recyclability of catalyst was also studied. After carrying out the reaction, the

catalyst 1·OTf was separated by precipitation by adding hexane, washed with diethyl
ether, and reused directly without further purification. After six catalytic cycles,
1·OTf still had good catalytic performance (Table 5). Comparison of catalytic activity
of other metal catalysts for A3-coupling reaction which mentioned in the introduction
section [23] the behavior of complex 1·OTf is very promising. (1.0 mol% loading, 15
o
min reaction time, yield up to 99%, in air, 35 C). To our knowledge, complex 1·OTf
is one of the most efficient catalysts reported for A3-coupling reaction. Furthermore, it
could carry out the reaction in open air and be recyclable.
According to the above information, we believe the structural stability and
coordinative accessibility of silver in 1·OTf may play a key role in the catalytic cycle.
The strong coordination originated from bis-bidentated bispyridylpyrrole ligand may
make disilver complexes have high structural stability. Release of the intermolecular
weak interaction of Ag···Br in solution may allow the substrates to access the silver
centers easily. Thus, a tentative mechanism is proposed in Scheme 2. This involves
the formation of silver acetylide, as proposed in earlier reports [15-24]. In the
presence of 1·OTf, silver-acetylide complex A would be generated via activation of
the C-H bond of phenylacetylene, and compound B would be yielded from
condensation reaction of aldehyde and amine. Subsequently, silver-propargylamine
intermediate would be formed by the reaction between A and B, followed by the
release of propargylamine from silver center by replacement with free amine.
Conclusions
Nitrogen donor bispyridylpyrrole HL1, HL3, HL4 and their silver complexes
1·OTf - 4·OTf were prepared and fully characterized. Free ligands has almost planar
geometry. Complexes 1·OTf - 4·OTf are easy to prepare and have a stable dinuclear
structure. The bispyridylpyrrole ligands act as bridging linker to chelate two silver

atoms. Each silver atom is not only strongly coordinated with two N atoms from
bispyridylpyrrole and one P atom from PPh3, but also weakly interacted with
neighboring Ag atom and substituted bromide or thienyl group. Complex 1·OTf
shows excellent catalytic efficiency and recyclability for A3-coupling reaction under
mild conditions with only low loading, short reaction time and in open air atmosphere.
High stability of the dinuclear structure and ready formation of coordinative
unsaturated cationic species in solution may result in its high catalytic activity.
Studies on expanding the scope of catalytic reactions, such as activation of carbon
dioxide, and the development of an enantioselective protocol is ongoing.
Acknowledgements
This work was supported by the National Natural Science Foundation of China
(project 21571190), Hunan Provincial Science and Technology Plan Project, China
(No. 2016TP1007), and Grants from the Project of Innovation-driven Plan in Central
South University (2015CXS004).
Notes and references
† Electronic Supplementary Information (ESI) available. CCDC reference numbers
1533516, 1533518-1533522 for HL1, HL2, HL4 and 1·OTf - 3·OTf, respectively. see
DOI: 10.1039/b000000x/.
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Scheme 1 syntheses of 1·OTf - 4·OTf
OTf
N
Et3N in thf
N
N
+ 2 AgOTf + 2 PPh3
H
N
N
N
R
R
Ag Ag
R
R
Ph3P
PPh3
R = m-Br, 1·OTf
o-Br, 2·OTf
o-2-thienyl, 3·OTf
o-benzyl, 4·OTf

Scheme 2 Proposed mechanism for A3-coupling reaction by 1·OTf
Ph
R1
[Ag2]+
Ph
H
N
R2
R3
R1
OH
N
Ph
Ag2
R2
R3
A
B
R1
R3
O
H
N
OH
N
R1
R2
R2
R3
B

Table 1 X-ray Crystallographic Data of HL1, HL2, HL4 and their disilver complexes 1·OTf - 3·OTf.

2+
HL1
HL2
HL4
1·OTf·CHCl3
3·OTf
C52H39Ag2Br2Cl3F3N3
O3 P2S
C50H38Ag2Br2N3P2 C59H44Ag2F3N3O3P2S3
formula
C14H9Br2N3
C14H9Br2N3
C26H19N3
1386.77
Monoclinic
P21/c
1118.32
Triclinic
1273.83
Triclinic
fw
crystal system
space group
a, Å
379.06
Monoclinic
C2/c
379.06
Orthorhombic
Pna21
373.10
Monoclinic
C2/c
P-1
P-1
20.3456(15)
16.0513(13)
18.4188(16)
90
12.4261(3)
15.2070(4)
15.9534(4)
63.0890(10)
80.909(2)
78.942(2)
12.0499(6)
15.3128(8)
16.6363(8)
81.8760(10)
75.5220(10)
88.9040(10)
30.5658(13)
6.1351(3)
8.314(5)
13.457(8)
12.294(8)
90
42.0728(4)
5.0303(2)
18.6760(7)
90
b, Å
c, Å
17.3692(7)
90
α, deg
116.379(5)
90
β, deg
124.545(2)
90
90
101.542(3)
90
γ, deg
90

V, Å3
Z
2682.8(2)
8
1375.5(15)
4
3872.60(3)
8
5388.8(8)
4
2629.51(12)
2
2942.0(3)
2
ρcalc, g cm-3
T, K
1.877
293(2)
6.031
10542
1.830
293(2)
5.882
4535
1.281
296(2)
0.076
12207
1.709
293(2)
2.512
45537
1.413
1.438
293(2)
0.881
13292
296(2)
2.358
µ, mm-1
no. of refln.
44774
no. of indep.
refln.
12435
12035
13292
3137
2770
4320
0.0698
1.005
0.0465
1.017
0.0156
1.047
Rint
0.0224
1.026
0.0661
0.990
0.0315
0.996
GoF a
R1, b wR2 c [I >
2σ(I)]
0.0478, 0.0938
0.1305, 0.1225
0.0473, 0.0978
0.1046, 0.1061
0.0336, 0.0820
0.0475, 0.0877
0.0370, 0.0839
0.0702, 0.0952
0.0419, 0.0696
0.1288, 0.0791
0.0498, 0.1199
0.1157, 0.1574
R1, wR2 (all data)

½
a GoF = [Σw(|Fo| − |Fc|)2/(Nobs − Nparam)] . b R1 = Σ||Fo| − |Fc||/Σ|Fo|. c wR2 [(Σw|Fo| − |Fc|)2/Σw2|Fo|2]½.

Table 2 Selected bond distances (Å) and bond angles (o) of 1·OTf - 3·OTf.
Selectred bond distances (Å)
Complex
Ag-Npyr
2.266(4)
Ag-Npy
Ag-P
Ag···Ag
3.067
Ag···Br/S
3.378
2.212(4)
2.3586(12)
1·OTf
2.551(4)
2.304(4)
2.3414(13)
2.369(3)
2.257(3)
2.393(2)
2.391(2)
3.153
3.607
3.144
3.257
2.279(3)
2.450(3)
2.3661(11)
2.3549(12)
2.975
3.001
2·OTf
3·OTf
2.2455(19)
2.2954(18)
2.3567(6)
2.3720(6)
Selected bond angles (o)
Npyr-Ag-Npy
Npy-Ag-P
Npyr-Ag-P
72.63(14)
119.18(9)
144.76(11)
168.02(12)
1·OTf
75.39(14)
137.95(10)
72.44(12)
2·OTf
123.45(8)
145.53(9)
135.62(9)
145.66(9)
137.56(5)
72.65(12)
72.64(7)
3·OTf
137.57(5)
148.95(5)
74.25(7)
143.85(5)

Table 3 Catalytic reaction optimizationa
O
H
H
N
[cat.] (x mol%), t
solvent, 35 oC
+
+
NH
Entry
1
Catalyst
1·OTf
1·OTf
1·OTf
2·OTf
3·OTf
4·OTf
1·OTf
1·OTf
1·OTf
1·OTf
1·OTf
1·OTf
1·OTf
1·OTf
1·OTf
Catalyst (mol %)
0.2 %
solvent
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
Dioxane
DMF
t (h)
3.8
Yield (%)
93
2
0.5 %
2.0
93
3
1.0 %
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
0.25
99
4
1.0 %
99
5
1.0 %
99
6
1.0 %
99
7
1.0 %
95
8
1.0 %
81
9
1.0 %
toulene
CH3CN
CH3OH
CHCl3
THF
41
10
11
12
13
14
15
1.0 %
97
1.0 %
97
1.0 %
85
1.0 %
93
1.0 %
EA
79
1.0 %
H2O
86
a
reaction condition: phenylacetylene (1.0 mmol), cyclohexanecarboxaldehyde (1.3 mmol),
pyrrolidine (1.3 mmol), solvent (0.5 mL) in open air atmosphere, at 35 oC, yields determined by
1H NMR, average of 2 runs.

Table 4 A3-coupling reaction catalyzed by 1·OTf.a
NR2R3
Ph
1·OTf, 1.0 mol%
R1CHO + NHR2R3 +
R1
CH2Cl2, 35 oC
Ph
N
N
N
N
Ph
0.70 h, 98%
Ph
Ph
Ph
0.50 h, 97%
0.25 h, 97%
0.25 h, 99%
Ph
Ph
Ph
Ph
N
N
N
Ph
Ph
Ph
2.0 h, 95%
1.5 h, 90%
1.50 h, 91%
a
reaction condition: 1·OTf (1.0 mol%), phenylacetylene (1.0 mmol),
aldehyde (1.3 mmol), amine (1.3 mmol), CH2Cl2 (0.5 mL), in open air
atmosphere, at 35 oC, yields determined by 1H NMR, average of 2 runs.

Table 5 Catalytic recyclability of 1·OTf for A3-coupling reactiona
O
H
N
1·OTf, 1.0 mol%
CH2Cl2, 35 o
H
+
+
NH
C
cycle
Yield (%)
1
2
3
4
5
99
98
97
97
96
a
reaction condition: phenylacetylene (1.0 mmol), cyclohexanecarboxaldehyde (1.3 mmol),
pyrrolidine (1.3 mmol), CH2Cl2 (0.5 mL), reaction time 15 min for each cycle, in open air
o
1
atmosphere, at 35 C, yields determined by H NMR, average of 2 runs. After one cycle, the
catalyst 1·OTf was separated by precipitation by adding hexane, washed with diethyl ether, and
reused directly without further purification for the next cycle.

Fig. 1 ORTEP diagrams of ligands HL1 (a), HL2 (b) and HL4 (c).
(a)

(b)

(c)