Synthesis, Crystal Structures, and Catalytic Application of Two Triphenylphosphine-Cyclopalladated Ferrocenylpyrazine Complexes Containing Chlorine/Iodine Anion

Article abstract of DOI:10.1080/15533174.2014.989614

Two new triphenylphosphine-cyclopalladated ferrocenylpyrazine complexes containing chlorine/iodine anion 2-3 have been easily prepared from the bridge-splitting reaction of the palladacyclic dimer 1 and anion exchange reaction, respectively. They were characterized by elemental analysis, IR, and ¹H NMR. Additionally, the structures of these two complexes were determined by single-crystal X-ray analysis and C-H···N hydrogen bonds and π-π interactions were found in the their crystal structures. These complexes displayed good activity in the coupling of terminal alkynes with arylboronic acids under atmospheric conditions. This method provided the corresponding arylalkynes with good to excellent yields.

Full text of DOI:10.1080/15533174.2014.989614

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Synthesis, Crystal Structures, and Catalytic
Application of Two Triphenylphosphine-
Cyclopalladated Ferrocenylpyrazine Complexes
Containing Chlorine/Iodine Anion
Chen Xu, Hong-Mei Li, Zhi-Qiang Wang & Wei-Jun Fu
To cite this article: Chen Xu, Hong-Mei Li, Zhi-Qiang Wang & Wei-Jun Fu (2015): Synthesis,
Crystal Structures, and Catalytic Application of Two Triphenylphosphine-Cyclopalladated
Ferrocenylpyrazine Complexes Containing Chlorine/Iodine Anion, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2014.989614
To link to this article: http://dx.doi.org/10.1080/15533174.2014.989614
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Synthesis,
Crystal
Structures,
and
Catalytic
Application
Complexes
of
Two
Triphenylphosphine-Cyclopalladated
Chlorine/Iodine Anion
Ferrocenylpyrazine
Containing
Chen Xu1,*, Hong-Mei Li2, Zhi-Qiang Wang1, and Wei-Jun Fu1
1College of Chemistry and Chemical Engineering, Luoyang Normal University, Luoyang, P. R.
China
2Department of Life Science, Luoyang Normal University, Luoyang, P. R. China
*Address correspondence to Xu Chen, College of Chemistry and Chemical Engineering, Normal
University, Luoyang, Henan, 471022, P. R. China. E-mail: xubohan@163.com
Two new triphenylphosphine-cyclopalladated ferrocenylpyrazine complexes containing
chlorine/iodine anion 2–3 have been easily prepared from the bridge-splitting reaction of the
palladacyclic dimer 1 and anion exchange reaction, respectively. They were characterized by
1
elemental analysis, IR, H NMR. Additionally, the structures of these two complexes were
determined by single-crystal X-ray analysis and C–H···N hydrogen bonds and π–π interactions
were found in the their crystal structures. These complexes displayed good activity in the
coupling of terminal alkynes with arylboronic acids under atmospheric conditions. This method
provided the corresponding arylalkynes with good to excellent yields.
Keywords
Address correspondence to Xu Chen, College of Chemistry and Chemical Engineering, Normal University,
Luoyang, Henan, 471022, P. R. China. E-mail: xubohan@163.com
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cyclopalladated ferrocenylpyrazine complex, crystal structure, coupling reaction, alkyne,
arylboronic acid
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INTRODUCTION
Palladium-catalyzed coupling reactions such as Sonogashira reaction have become an
extremely powerful method in organic synthesis for the formation of carbon-carbon bonds. [1-2]
Among various Pd catalysts, palladacycles are one of the most developed and studied classes of
catalyst precursors because of their structural versatility and easy synthetic accessibility.[3]
Although great progress has been obtained for the coupling reactions, some drawbacks still
remained.[4] For example, the reaction generally does not work well for electron-deficient
alkynes. To overcome this limitation, palladium-catalyzed coupling of terminal alkynes with
arylboronic acids have been developed.[5–8] We have also reported N-heterocyclic carbene
adducts of cyclopalladated ferrocenylpyridine complexes catalyzed coupling of terminal alkynes
with arylboronic acids.[9] As a continuation of our interest in the synthesis and application of
cyclometalated complexes,[10–12] we prepared two new triphenylphosphine-cyclopalladated
ferrocenylpyrazine complexes containing chlorine/ iodine anion and examined their catalytic
activity in the coupling of terminal alkynes with arylboronic acids under atmospheric conditions.
EXPERIMENTAL
Materials and General Methods
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Solvents were dried and freshly distilled prior to use. All other chemicals were commercially
available except for palladacyclic dimer 1 which was prepared according to the published
procedure.[12] Elemental analyses were determined with a Carlo Erba 1160 Elemental Analyzer.
1
IR spectra were collected on a Bruker VECTOR22 spectrophotometer in KBr pellets. H NMR
spectra were recorded on a Bruker DPX-400 spectrometer in CDCl3 with TMS as an internal
standard.
Synthesis of Complex 2
A solution of palladacyclic dimer 1 (0.1 mmol) and triphenylphosphine (0.21 mmol) in
CH2Cl2 (10 mL) was stirred at room temperature for 30 min. The product was separated by
passing through a short silica gel column with dichloromethane as eluent. The second band was
collected to afford complex 2 after the evaporation of the solvent. Red solid, yield: 92%. Anal.
Calcd. for C32H26ClFeN2PPd: C, 57.60; H, 3.93; N, 4.20; found: C, 57.89; H, 3.67; N, 4.34%. IR
(KBr, cm-1): 3079, 2968, 1610, 1528, 1502, 1434, 1327, 1302, 1250, 1163, 1142, 1096, 1026,
1
993, 823, 735, 695. H NMR (400 MHz, CDCl3):  9.24(s, 1H, Ar–H), 8.60(s, 1H, Ar–H), 8.39
(s, 1H, Ar–H), 7.78–7.82 (m, 6H, Ar–H), 7.36–7.46 (m, 9H, Ar–H), 4.71 (s, 1H, C5H3), 4.20 (s,
1H, C5H3), 3.71 (s, 5H, C5H5), 3.42 (s, 1H, C5H3).
Synthesis of Complex 3
A solution of complex 2 (0.1 mmol) and NaI (0.2 mmol) in acetone (10 mL) was stirred at
room temperature for 3 h. The product was separated by passing through a silica gel column with
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CH2Cl2 as eluent. The second band was collected to afford the corresponding complex 3 after
evaporation of the solvent. Red solid, yield: 98%. Anal. Calcd. for C32H26FeIN2PPd: C, 50.66; H,
3.45; N, 3.69; found: C, 50.93; H, 3.26; N, 3.87%. IR (KBr, cm-1): 3054, 2922, 1621, 1593, 1507,
1432, 1392, 1317, 1243, 1166, 1091, 1033, 998, 935, 835, 753, 689. 1H NMR (400 MHz, CDCl3):
 9.70 (s, 1H, Ar–H), 8.61 (s, 1H, Ar–H), 8.33 (s, 1H, Ar–H), 7.78–7.83 (m, 6H, Ar–H),
7.40–7.48(m, 9H, Ar–H), 4.70 (s, 1H, C5H3), 4.16 (s, 1H, C5H3), 3.67 (s, 5H, C5H5), 3.55 (s, 1H,
C5H3).
General Procedure for the Coupling of Terminal Alkynes with Arylboronic Acids
A mixture of arylboronic acids (0.5 mmol), alkynes (0.6 mmol), the prescribed amount of
catalysts, Ag2O (0.5 mmol) and KOAc (0.75 mmol) in 1,2-dichloroethane (DCE) (3 mL) under
o
air was stirred at 80 or 25 C for 24 h. After being cooled, the mixture was filtered. The solvent
was removed under reduced pressure. The resulting residue was purified by flash
chromatography on silica gel to afford the desired coupled products, which were characterized
by comparing their m.p. and 1H NMR spectra.
Crystallographic Data Collection and Structure Determination
Crystallographic data for compounds 2–3 were collected on a Bruker SMART APEX-II CCD
diffractometer equipped with a graphite monochromator at 296 K using Mo-Ka radiation (λ =
0.071073 Å). Structures were solved by direct methods and refined by full-matrix least-squares
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methods on F2 with the SHELX-97 program.[13] All non-hydrogen atoms were refined
anisotropically, while hydrogen atoms were placed in geometrically calculated positions. The
detailed crystallographic data and structure refinement parameters for 2–3 are summarized in
Table 1. CCDC reference numbers 969894 and 995704 for 2–3, respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre via www. ccdc. cam.
ac.uk/data_request/cif.
RESULTS AND DISCUSSION
Synthesis and Structures of Complexes 2–3
The synthesis route of complexes 2–3 is given in Scheme 1. Bridge-splitting reaction of
palladacyclic dimer 1 with triphenylphosphine in CH2Cl2 at room temperature readily afforded
the corresponding monomer 2 in good yield. The corresponding adduct containing iodine anion 3
has been readily prepared through anion exchange reaction of 2 with NaI in acetone. They are
air- and moisture-stable, both in the solid state and in solution. Complexes 2–3 were
1
characterized by elemental analysis, IR, and H NMR. Generally, the spectra of 3 was similar to
that of the corresponding 2, they exhibit similar peaks for the Cp ring, with a proton ratio of
1:1:1:5, clearly showing that they are both ortho-cyclopalladated complexes. In order to further
investigate the structures of these complexes, their crystal structures have been determined by
X-ray diffraction.
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The two crystals were obtained by recrystallization from CH2Cl2-petroleum ether solution at
room temperature. The single-crystal X-ray analysis indicates that the palladacycles 2-3 are trans
complexes in the solid state. The molecules are shown in Figs. 1 and 2. They crystallize in
triclinic P–1 space group with two mononuclear molecules in each asymmetric unit. The Pd atom
in each complex is in a slightly distorted square-planar environment bonded to the phosphorus
atom, the chlorine (iodine) atom, the nitrogen atom and the C atom of the ferrocenyl moiety. The
bicyclic system formed by the palladacycle and the C5H3 moiety is approximately coplanar
(dihedral angles of 3.2°(0.7°) and 4.9°(4.2°) for complexes 2 and 3). The Pd–N and Pd–P bond
lengths of 2 are similar to those of the corresponding 3, while Pd–Cl [2.3640(19)-2.3747(19) Å]
bond lengths of 2 are obviously shorter than Pd–I [2.6600(14)-2.6561(14) Å] bond lengths of 3.
Basically, the crystal structure of 3 is quite similar to that of 2. Fig.3 shows that 2 exists as a
dimer in the crystal due to intermolecular CH···N (H···N = 2.782 Å) hydrogen bonds[14] and π–π
stacking interactions involving the neighboring pyrazinyl and cyclopentadienyl rings (the
interplane distance is 3.727 Å).[15]
The Catalytic Coupling Reaction of Terminal Alkynes with Arylboronic Acids
Adducts of palladacycles have been successfully used in the coupling reactions.[3] Usually,
cyclopalladated ligands have little effect on the catalytic activity, however, the anionic ligand (Cl,
Br, I, etc.) is found to have some effect on the catalytic activity.[16-17] Here, we investigated the
coupling of terminal alkynes with arylboronic acids catalyzed by the palladacycle adducts 2–3
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since we are interested to see whether the effect of halogen anions (Cl and I) on the catalytic
activity. Based on our previous experiments,[9] the coupling of phenylacetylene with
phenylboronic acid using 1 equivalent of Ag2O as additive was performed under air in
o
1,2-dichloroethane (DCE) in the presence of KOAc as base at 80 C for 24 h (Table 2, entries
1-3). The dimer 1 generated the product in low yield (26%), while palladacycles precatalyst 2–3
led to good activity giving the coupled product in good yields (90-93%) and 3 showed slightly
more activity. The reactions were performed at room temperature and afforded product in
moderate yields (61-63%, entry entries 4-5). Increasing catalyst loading to 1 mol% resulted in
excellent yields (94-95%, entries 6-7). In addition, solvent CH2Cl2 also afforded excellent yields
(95-97%, entries 8-9).
In the following experiments, the coupling reactions between a variety of alkynes and
arylboronic acids were investigated by using 3 as catalyst under the reaction conditions (Ag2O,
o
KOAc, CH2Cl2, air, 25 C, 24 h) (Table 3). Similar to the results of phenylacetylene, excellent
yields were obtained in the cases of 4-methylphenylacetylene and arylboronic acids (94-97%,
entries 1–3). The hindered 2-methylphenylboronic acid also provided the product in a good yield
(88%, entry 4). For aliphatic alkynes oct-1-yne, they could provide the corresponding products in
good yields (80–89%, entries 5–8). A noticeable advantage of this reaction is that for
electron-deficient such as ethyl propiolate and 3-ethynylpyridine, they still gave the desired
product in good yields (81–86%, entries 9–12) since the traditional Sonogashira coupling
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procedure leads to low yields for electron-deficient alkynes.
CONCLUSION
Two new triphenylphosphine-cyclopalladated ferrocenylpyrazine complexes containing
chlorine/iodine anion 2–3 have been synthesized and characterized. Single-crystal X-ray analysis
confirms that there are C–H···N hydrogen bonds and π–π interactions in the their crystal
structures. These complexes are efficient catalysts for the coupling of terminal alkynes with
arylboronic acids at room temperature under atmospheric conditions.
FUNDING
This work was supported by the National Science Foundation of China (Nos. 21272110 and
U1204205), the Aid Project for the Leading Young Teachers in Henan Provincial Institutions of
Higher Education of China (2013GGJS–151), the tackle key problem of science and technology
Project of Henan Province (122102310452) and the Science Foundation of Henan Education
Department (14A150049).
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114, 1783–1826.
3. Dupont, J.; Pfeffer, M. Palladacycles: Synthesis, Characterization and Applications.
Wiley-VCH: Weinheim, 2008.
4. Chinchilla, R.; Nájera, C. Recent advances in Sonogashira reactions. Chem. Soc. Rev. 2011,
40, 5084–5121.
5. Zou, G.; Zhu, J. R.; Tang, J. Cross-coupling of arylboronic with terminal alkynes in air.
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Ferrocenylimine Catalyzed Cross-Coupling of Arylboronic Acids/Esters with Terminal
Alkynes. Eur. J. Org. Chem. 2007, 3476–3479.
7. Zhou, M. B.; Wei, W. T.; Xie, Y. X.; Lei, Y.; Li, J. H. Palladium-Catalyzed Cross-Coupling of
Electron-Poor Terminal Alkynes with Arylboronic Acids under Ligand-Free and Aerobic
Conditions. J. Org. Chem. 2010, 75, 5635–5642.
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8. Nie, X. P.; Liu, S. L.; Zong, Y.; Sun, P. P.; Bao, J. C. Facile synthesis of substituted alkynes
by nano-palladium catalyzed oxidative cross-coupling reaction of arylboronic acids with
terminal alkynes. J. Organomet. Chem. 2011, 696, 1570–1573.
9. Li, H. M.; Xu, C.; Duan, L. M.; Lou, X. H.; Wang, Z. Q.; Li, Z.; Fan, Y. T. N-heterocyclic
carbene adducts of cyclopalladated ferrocenylpyridine containing chlorine/iodine anion:
synthesis, crystal structures and application in the coupling of terminal alkynes with
arylboronic acids. Transition Met. Chem. 2013, 38, 313–318.
10. Xu, C.; Zhang, Y. P.; Wang, Z. Q.; Fu, W. J.; Hao, X. Q.; Xu, Y.; Ji, B. M. Design and
synthesis of tetranuclear cluster monophosphine-cyclopalladated ferrocenylpyrimi- dinone
complexes from the palladium-catalyzed hydroxylation of chloropyrimidine. Chem. Commun.
2010, 6852–6854.
11. Xu, C.; Hao, X. Q.; Xiao, Z. Q.; Wang, Z. Q.; Yuan, X. E.; Fu, W. J.; Ji, B. M.; Song, M. P.
One-Pot Synthesis of Ferrocenyl Ketones Containing Biaryls and 6-Aryl-2-ferrocenyl-
quinolines via Ir/Pd-Cocatalyzed α-Alkylation/Suzuki Reaction. J. Org. Chem. 2013, 78,
8730–8738.
12. Xu, C.; Li, H. M.; Yuan, X. E.; Xiao, Z. Q.; Wang, Z. Q.; Fu, W. J.; Ji, B. M.; Hao, X. Q.;
Song, M. P. N-Heterocyclic carbene (NHC)-modulated Pd/Cu cocatalyzed three- component
synthesis of 2,6-diarylquinolines. Org. Biomol. Chem. 2014, 12, 3114–3122.
13. Sheldrick, G. M. SHELXS-97, Program for Solution of Crystal Structures; University of
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Göttingen, Germany, 1997.
14. Berg, Jan-Albert.; Seddon, K. R. Critical Evaluation of C–H···X Hydrogen Bonding in the
Crystalline State. Cryst. Growth. Des. 2003, 3, 643–661.
15. Janiak, C. A critical account on π–π stacking in metal complexes with aromatic
nitrogen-containing ligands. J. Chem. Soc., Dalton Trans. 2000, 3885–3896.
16. Bedford, R. B.; Cazin, C. S. J. High-Activity Catalysts for Suzuki Coupling and Amination
Reaction with Deactivated Aryl Chloride Substrates: Importance of the Palladium Source.
Organometallics 2003, 22, 987–999.
17. Bedford, R. B.; Cazin, C. S. J.; Holder, D. The development of palladium catalysts for C-C
and C-heteroatom bond forming reactions of aryl chloride substrates. Coord. Chem. Rev.
2004, 248, 2283–2321.
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TABLE 1 Crystallographic data for complexes 2 and 3
Empirical formula
Fw
C64H52Cl2Fe2N4P2Pd2 2
1334.44
C64H52I2Fe2N4P2Pd2 3
1517.34
Crystal system
Space group
a (Å)
Triclinic
Triclinic
P-1
P-1
11.252(3)
14.495(3)
18.089(4)
104.236(3)
99.780(3)
103.529(3)
2698.2(11)
2
11.611(6)
14.524(7)
17.666(9)
101.892(6)
97.748(6)
103.944(6)
2775(2)
b (Å)
c (Å)
α (o)
β (o)
γ (o)
Volume (Å3)
Z
2
Dc (g/cm3)
GOF
1.643
1.028
1.816
1.011
Data / restraints /
parameters
Final R indices
[I>2sigma(I)]
R indices (all data)
9972 / 0 / 685
10258 / 0 / 685
R1 = 0.0557, wR2 = 0.1066 R1 = 0.0612, wR2 = 0.1003
R1 = 0.1149, wR2 = 0.1265 R1 = 0.1455, wR2 = 0.1287
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TABLE 2 The coupling of phenylacetylene with phenyl boronic acid catalysed by palladacycles
1–3a
Cat, Ag2O
(HO)2B
KOAc, Solvent
Entry
Solvent
DCE
Temperature Catalyst (mol%)
Yieldb (%)
80 oC
80 oC
80 oC
25 oC
25 oC
25 oC
25 oC
25 oC
25 oC
1(0.5)
2(0.5)
3(0.5)
2(0.5)
3(0.5)
2(1)
1
2
3
4
5
6
7
8
9
26
90
93
61
63
94
95
95
97
DCE
DCE
DCE
DCE
DCE
DCE
3(1)
CH2Cl2
CH2Cl2
2(1)
3(1)
a
Reaction conditions: phenylacetylene (0.6 mmol), PhB(OH)2 (0.5 mmol), Ag2O (0.5 mmol),
KOAc (0.75 mmol), solvent (3 mL), 24 h.
b Isolated yields.
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TABLE 3 The coupling of alkynes with arylboronic acids catalysed by 3a
3, Ag2O
Ar
R
Ar B(OH)2
R
KOAc, CH2Cl2
Entry
R
Ar
Yieldb (%)
1
2
p-MeC6H4
p-MeC6H4
Ph
94
95
p-MeC6H4
3
p-MeC6H4
p-MeC6H4
Me(CH2)5
Me(CH2)5
Me(CH2)5
Me(CH2)5
COOEt
p-MeOCC6H4
o-MeC6H4
Ph
97
88
89
85
87
80
81
83
85
86
4
5
6
p-MeC6H4
p-MeOC6H4
p-EtOOCC6H4
Ph
7
8
9
10
11
12
COOEt
p-MeC6H4
Ph
Pyridin-3-yl
Pyridin-3-yl
p-MeC6H4
a
Reaction conditions: catalyst 3 (1 mol%), alkyne (0.6 mmol), arylboronic acid (0.5 mmol),
KOAc (0.75 mmol), Ag2O (0.5 mmol), CH2Cl2 (3 mL), 25 oC, 24 h.
b Isolated yields.
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N
N
N
N
N
N
PPh3
Fe
NaI
Pd
Cl
Fe
Fe
Pd
Cl
Pd
PPh3
I
acetone
2
PPh3
1
2
3
SCH. 1. Synthesis route of cyclopalladated ferrocenylpyrazine complexes 2–3.
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FIG. 1. ORTEP drawing of 2 at the 30% probability level for thermal displacement ellipsoids,
with hydrogen atoms being omitted for clarity (representation of one of the two independent
molecules). Selected bond lengths (Å) and angles (°) are as follows (corresponding values for the
unshown second structure are given in brackets): Pd(1)–C(10) 1.987(6) [1.990(6)], Pd(1)–N(1)
2.134(5) [2.146(5)], Pd(1)–P(1) 2.2488(18) [2.2486(18)], Pd(1)–Cl(1) 2.3640(19) [2.3747(19)]
and C(10)–Pd(1)–N(1) 81.2(2) [80.8(2)], C(10)–Pd(1)– P(1) 93.10(19) [93.6(2)],
P(1)–Pd(1)–Cl(1) 95.27(7) [95.69(7)], N(1)–Pd(1)–Cl(1) 90.50(15) [90.12(16)].
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FIG. 2. ORTEP drawing of 3 at the 30% probability level for thermal displacement ellipsoids,
with hydrogen atoms being omitted for clarity (representation of one of the two independent
molecules). Selected bond lengths (Å) and angles (°) are as follows (corresponding values for the
unshown second structure are given in brackets): Pd(1)–C(2) 1.988(9) [2.028(10)], Pd(1)–N(1)
2.155(8) [2.160(5)], Pd(1)–P(1) 2.256(3) [2.258(3)], Pd(1)–I(1) 2.6600(14) [2.6561(14)] and
C(2)–Pd(1)–N(1) 79.8(3) [81.0(4)], C(2)–Pd(1)–P(1) 93.1(3) [92.2(3)], P(1)–Pd(1)–I(1) 96.03(7)
[95.19(8)], N(1)–Pd(1)–I(1) 91.3(2) [91.7(2)].
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FIG. 3. The dimeric structure of complex 2 showing C–H···N hydrogen bonds and π–π
interactions. Non-hydrogen bonding H atoms are omitted for clarity.
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