Synthesis, structure, and reactivity of ferrocenyl-NHC palladium complexes

Article abstract of DOI:10.1002/zaac.201300097

palladium complexes of ferrocenyl-functionalized N-heterocyclic carbenes with different substituents were synthesized. The molecular structures of selected complexes were determined by X-ray diffraction and show a pseudo-square-planar structure with a central palladium atom surrounded by carbene, pyridine, and two chloride ligands. The influence of the different substituents on the structure and reactivity of the complexes was studied. The catalytic properties of the complexes were investigated in the Larock indolization reactions of 2-bromoanilines with diphenylacetylene. Their performances slightly varied in this reaction, but the complex with mesityl substituent showed the best activity. Copyright

Full text of DOI:10.1002/zaac.201300097

ARTICLE
DOI: 10.1002/zaac.201300097
Synthesis, Structure, and Reactivity of Ferrocenyl-NHC Palladium
Complexes
Pan He,[a] Yufeng Du,[a] Shuzhan Wang,[a] Changsheng Cao,*[a] Xiaojun Wang,[a]
Guangsheng Pang,[b] and Yanhui Shi*[a,c]
Keywords: N-heterocyclic carbene; Palladium; Crystal Structure; Ferrocene; Indolization
Abstract. palladium complexes of ferrocenyl-functionalized N-hetero- reactivity of the complexes was studied. The catalytic properties of the
cyclic carbenes with different substituents were synthesized. The mo- complexes were investigated in the Larock indolization reactions of
lecular structures of selected complexes were determined by X-ray 2-bromoanilines with diphenylacetylene. Their performances slightly
diffraction and show a pseudo-square-planar structure with a central varied in this reaction, but the complex with mesityl substituent
palladium atom surrounded by carbene, pyridine, and two chloride li-
gands. The influence of the different substituents on the structure and
showed the best activity.
stitution on solid structure and on reactivity in the Larock
indolization reaction.
Introduction
Over the past few decades, N-heterocyclic carbenes (NHCs)
have attracted considerable attention and become an important
class of ligands, due to their successful application in organo-
metallic chemistry and homogeneous catalysis.[1,2] It was
known that the monodentate NHC with steric hindrance would
create more active catalysts for palladium-catalyzed cross-cou-
pling reactions.[3] We are interested in the steric influences ex-
hibited by ferrocenyl substituents, as the ferrocenyl moiety
represents a quite bulky group with unique spatial require-
ments due to its cylindrical shape. Various complexes of ferro-
cenyl-functionalized NHCs and their applications in catalysis
have been explored.[4] For over a century, the synthesis and
functionalization of indoles has been a major area of focus
for synthetic organic chemists, and numerous methods for the
preparation of indoles have been developed. In recent years,
the palladium-catalyzed indolization discovered by Larock has
emerged as a powerful tool to prepare indoles.[5]
Results and Discussion
Synthesis of the Imidazolium Chlorides 1
The ferrocenyl imidazolium chlorides 1 can be efficiency
synthesized starting from ferrocene according to the literature
method (Scheme 1).[4a,6] The reduction of acetylferrocene
prepared by Friedel-Crafts acylation reaction of ferrocene gave
1-ferrocenylethanol in excellent yield. Treatment of 1-ferro-
cenylethanol with 1-substituted imidazole (benzimidazole) in
Herein we present the synthesis and structural characteriza-
tion of several ferrocenyl functionalized NHC ligands with dif-
ferent N-substituents and we investigate the influence of sub-
* Prof. Dr. C. Cao
E-Mail: chshcao@jsnu.edu.cn
* Prof. Dr. Y. Shi
E-Mail: yhshi@jsnu.edu.cn
[a] School of Chemistry and Chemical Engineering and Jiangsu Key
Laboratory of Green Synthetic Chemistry for Functional Materials
Jiangsu Normal University
Xuzhou, Jiangsu 221116, P. R. China
[b] State Key Laboratory of Coordination Chemistry
Nanjing University
Nanjing, Jiangsu 210093, P. R. China
[c] State Key Laboratory of Inorganic Synthesis and Preparative
Chemistry
Jilin University
Changchun, Jilin 130012, P. R. China
Scheme 1. Synthesis of palladium(II) complexes 2a–2h.
1004
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Z. Anorg. Allg. Chem. 2013, 639, (6), 1004–1010

Ferrocenyl-NHC Palladium Complexes
acetic acid at 60 °C for 6 h gave an imidazolium salt with the 176.28(3)° for 2a and 2b, and 170.45(8)° for 2f. The angle
hydroxide as a counter anion. Subsequently, addition of excess between the planes of imidazolylidene ring and pyridyl ring is
LiCl to the reaction mixture resulted in anion exchange to give different with different substitution on imidazole (46.40° for
ferrocenyl imidazolium chlorides 1. The imidazolium chlorides 2a, 37.09° for 2b and 53.93° for 2f). The ferrocenyl substituent
1a and 1f–1h have been reported previously,[4a,7] however, in these complexes is twisted with respect to the imidazol-2-
imidazolium chlorides 1b–1e are new compounds and were ylidene ligand, with angles ranging from 77.10° to 80.23°. The
characterized by their spectroscopic data and elemental analy- Pd–Ccarbene distance is 1.952(2) Å for 2a, 1.959(3) Å for 2b,
ses.
and 1.956(6) Å for 2f, similar to that shown by other palla-
dium-related species.[7] The Pd–Npyridine distance in complexes
Synthesis and Characterization of Ferrocenyl NHC-
Palladium Complexes 2
The synthesis of ferrocenyl NHC-palladium complexes 2 are
achieved by refluxing of the corresponding imidazolium salt
1a–1h, with palladium chloride (1.1 equiv.) in presence of
K2CO3 in pyridine in an argon atmosphere, as shown in
Scheme 1. All of these palladium complexes are air and moist-
ure stable and can be stored under air in solid state for more
than six months without any noticeable decomposition. These
complexes 2 were fully characterized by NMR spectroscopy
and gave satisfactory elemental analyses.
The proton signal of NCHN from the imidazolium chlordies
at ca. 10–12 ppm was absent in the 1H NMR of palladium
complexes, confirming carbene generation. In addition, the
formation of the metal complexes was evident from the dis-
tinctive Pd–Ccarbene peak ca.150–160 ppm, which significantly
shifted downfield relative to that of the imidazolinium NCHN
peak of the starting ligand precursor ca. 138 ppm. The molecu-
lar structures of 2a, 2b, and 2f were determined by X-ray dif-
fraction studies. The molecular diagrams of 2a, 2b, and 2f are
shown in Figure 1, Figure 2, and Figure 3, respectively, and
selected bond lengths and angles are given below the Figures.
All complexes show slightly distorted square-planar arrange-
ment around the central palladium atom, which is surrounded
by imidazolylidene, two chloride ligands in a trans configura-
tion, and one pyridine. The two chlorides in the complexes
are in a slightly bent arrangement, with Cl–Pd–Cl angles of
Figure 2. ORTEP structure of complex 2b with the probability ellip-
soids drawn at the 50% level. Hydrogen atoms and solvent are omitted
for clarity. Selected bond lengths /Å and angles /°: Pd1–C6 1.959(3),
Pd1–Cl1 2.3155(8), Pd1–Cl2 2.3005(9), Pd1–N1 2.109(3), C6–N2
1.344(4), C6–N3 1.353(4), C6–Pd1–Cl1 88.22(8), C6–Pd1–Cl2
88.14(8), Cl1–Pd1–N1 92.09(8), Cl2–Pd1–N1 91.61(8), N2–C6–N3
105.5(2).
Figure 1. ORTEP structure of complex 2a with the probability ellip-
soids drawn at the 50% level. Hydrogen atoms are omitted for clarity.
Selected bond lengths /Å and angles /°: Pd1–C6 1.952(2), Pd1–Cl1
Figure 3. ORTEP structure of complex 2f with the probability ellip-
soids drawn at the 50% level. Hydrogen atoms are omitted for clarity.
Selected bond lengths /Å and bond angles /°: Pd1–C6 1.956(6), Pd1–
2.2880(8), Pd1–Cl2 2.3009(8), Pd1–N1 2.096 (2), C6–N2 1.340(3), Cl1 2.3086(19), Pd1–Cl2 2.291(2), Pd1–N1 2.122(6), C6–N2 1.336(8),
C6–N3 1.343(3), C6–Pd1–Cl1 86.72(8), C6–Pd1–Cl2 89.71(8), Cl1–
Pd1–N1 91.13(7), Cl2–Pd1–N1 92.48(7), N2–C6–N3 105.8(2).
C6–N3 1.351(8), C6–Pd1–Cl1 88.51(19), C6–Pd1–Cl2 88.21(19),
Cl1–Pd1–N1 92.48(17), Cl2–Pd1–N1 91.41(17), N2–C6–N3 105.4(5).
Z. Anorg. Allg. Chem. 2013, 1004–1010
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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C. Cao, Y. Shi et al.
ARTICLE
Table 1. Larock indolization of 2-bromoaniline with 1,2-diphenylethyne by palladium complexes.
Entrya)
Catalyst (1 mol-%)
Additive
Solvent
Temp /°C
Time /h
Yieldb)
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2g
2h
2d
2d
2d
2d
2d
2d
2d
2d
2d
2c
2g
2h
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
TBAB
LiCl
DMF
DMF
DMF
DMF
DMF
DMF
DMF
DMF
140
140
140
140
140
140
140
140
140
140
140
120
100
140
140
140
140
140
140
140
24
24
24
24
24
24
24
24
24
24
24
24
24
12
24
24
24
24
24
24
45
49
50
60
53
54
56
58
0
70
78
0
0
51
0
9
DMSO
DMAC
10
11
12
13
14
15
16
17
18
19
20
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
none
0
(Bu4)NCl
TBAB
TBAB
TBAB
68
59
68
71
a) Reaction conditions: 2-bromoaniline (1 mmol), TBAB (1 mmol), diphenylacetylene (2 mmol) and K2CO3 (3 mmol) in solvent (2 mL).
b) Isolated yield with average of two runs.
2a [2.096(2) Å], 2b [2.109(3) Å] and 2f [2.122(6) Å] is com- when 1,4-dioxane was chosen as solvent instead of DMF, the
parable to that observed in other related palladium carbene an- other complexes showed better performances too, such as, the
alogues.[8] All other distances and angles lie in the expected yield with 2h increased from 58% to 71% (entry 8 versus
ranges.
entry 20). Form all the results showed herein, the palladium
complexes 2 with ferrocenyl-functionalized NHC were an ef-
fective indolization precatalyst, and 78% of yield achieved in
1 mol% palladium. The result is quite comparable to the re-
ported palladium catalytic system with phosphine ligand, in
which the 99% isolated yield was obtained with 5 mol% palla-
dium.[9]
Palladium Catalyzed Larock Indole Synthesis
To evaluate the catalytic activity of complexes 2a–2h in the
Larock indolization reaction, we performed the reaction of 2-
bromoaniline with 1,2-diphenylethyne in DMF in presence of
K2CO3 as base and TBAB as additive at 140 °C for 24 h,
using 1 mol% catalyst loading (Table 1). From the results, the
performances of these catalysts are only slightly different,
whereas complex 2d is of the best activity with 60% of yield
(entry 4).
Further experiments were performed to investigate the effect
of different solvents, additives, temperatures, reaction times
with catalyst 2d. The results show that the solvent has impor-
tant effect on the performance of the catalyst, and 1,4-dioxane
is the most suitable solvent among the solvents employed. The
relatively low yield of 70% was detected with DMAC (entry
10), however, DMSO is not effective at all (entry 9). The reac-
tion temperature and time have significant effect on the yield
as well. When the reaction temperature was lowered to 120 or
100 °C, no product was obtained at all (entries 11 and 12). The
yield was decreased with shorter reaction time and 51% of
yield was tested in 12 h (entry 14). TBAB is necessary to
achieve a good yield in the reactions. No product was observed
without any additive or with LiCl as additive, while 68% of
Conclusions
We synthesized and characterized a series of highly stable
palladium complexes with ferrocenyl-functionalized N-hetero-
cyclic carbenes. X-ray studies show that the different substitu-
ent on carbene affects the solid-state structure of these com-
plexes. The catalytic studies show that these complexes are
good catalyst for Larock indolization reaction and the substitu-
ent slightly affects the catalytic activity of these complexes.
The complex 2d with mesityl substituent appears good activity
in the indolization.
Experimental Section
Materials and General Procedures: Pyridine was distilled from cal-
cium hydride in an argon atmosphere. Potassium carbonate was ground
to a fine powder prior to use. All other reagents were commercially
available and were used without further purification. 1H and 13C NMR
yield was observed with (Bu4)NCl as additive. In addition, spectra were recorded with a Bruker DPX 400 MHz spectrometer at
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Ferrocenyl-NHC Palladium Complexes
1
room temperature and referenced to the residual signals of the solvent.
1g: Yield: 71% (0.37 g). H NMR (400 MHz, CDCl3): δ = 11.03 (s,
Elemental analyses were performed with a EuroVektor Euro EA-300 1 H, NCHN), 6.86 (s, 2 H, NCH), 5.82–5.86 (m, 2 H, CH), 4.32 (s, 4
elemental analyzer.
H, Fc–H), 4.20 (s, 14 H, Fc–H), 1.94 (d, J = 6.8 Hz, 6 H, CH3). 13C
NMR (CDCl3, 100 MHz): δ = 119.2, 85.4, 69.6, 69.5, 69.2, 68.8, 66.0,
65.8, 57.0, 21.9, 15.3 ppm.
Synthesis of Imidazolium Chlorides 1: 1-Ferrocenylethanol (0.23 g,
1.0 mmol) and 1-substituted imidazole (or benzimidazole) (1.1 mmol)
were dissolved in acetic acid (3 mL) and stirred at 60 °C for 7 h. After
removed most of acetic acid, a solution of LiCl (0.17 g, 4.0 mmol) in
EtOH (20 mL) was added, and stirred for 8 h at room temperature.
After removed the volatiles, filtered through Celite, and rinsed by
CH2Cl2, the crude was purified by flash column chromatography and
recrystallized from CH2Cl2/ether.
1
1h: Yield: 72% (0.42 g). H NMR (400 MHz, CDCl3): δ = 11.78 (s,
1 H, NCHN), 7.39–7.63 (m, 4 H, Ph–H), 6.11–6.19 (m, 2 H, CH),
4.35 (s, 4 H, Fc–H), 4.21 (s, 14 H, Fc–H), 2.34 (d, J = 6.8 Hz, 6 H,
CH3). 13C NMR (CDCl3, 100 MHz): δ = 130.4, 126.6, 115.0, 84.7,
69.9, 69.5, 69.1, 68.7, 68.3, 68.0, 67.6, 66.3, 66.1, 66.0, 65.5, 57.9,
14.9 ppm.
1
1a: Yield: 72% (0.24 g). H NMR (400 MHz, CDCl3): δ = 10.90 (s,
Synthesis of Palladium Complexes 2:
1 H, NCHN), 7.07 (s, 1 H, NCH), 6.97 (s, 1 H, NCH), 5.81–5.87 (m,
1 H, CH), 4.36 (s, 2 H, Fc–H), 4.28 (s, 1 H, Fc–H), 4.24 (s, 5 H, Fc–
H), 4.14 (s, 1 H, Fc–H), 4.08 (s, 3 H, CH3), 1.98 (s, 3 H, CH3). 13C
NMR (100 MHz, CDCl3): δ = 135.8, 123.4, 119.7, 85.4, 69.2, 69.0,
68.6, 68.3, 65.7, 56.2, 36.2, 21.0 ppm.
2a: To an oven-dried 50 mL of r.b.f. containing 1a (0.197 g,
0.6 mmol), PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol)
with a septum was injected into pyridine (15 mL) in an argon atmo-
sphere. The reaction mixture was stirred at 75 °C for 14 h. After cool-
ing to room temperature, the mixture was filtered through a plug of
Celite and washed by DCM. After the volatile was removed under
vacuum, the product was purified by flash column chromatography and
subsequent recrystallization from CH2Cl2/ether afforded the product as
1
1b: Yield: 76% (0.28 g). H NMR (400 MHz, CDCl3): δ = 10.83 (s,
1 H, NCHN), 7.30 (s, 1 H, NCH), 7.05 (s, 1 H, NCH), 6.05–6.15 (m,
1 H, CH), 4.40 (s, 1 H, Fc–H), 4.34(s, 1 H, Fc–H), 4.19 (s, 7 H, Fc–
H), 1.93 (d, J = 8.0 Hz, 3 H, CH3), 1.86 (s, 9 H, CH3). 13C NMR
(100 MHz, CDCl3): δ = 135.3, 119.2, 118.9, 85.6, 69.4, 69.3, 68.8,
68.6, 65.8, 60.2, 56.3, 30.1, 21.4. C19H25ClFeN2 (372.71 g·mol–1):
calcd. C 61.23; H 6.76; Cl 9.51; Fe, 14.98; N 7.52%; found: C 61.11;
H 6.67; N 7.64%.
1
yellow solid. Yield: 70% (0.23 g). H NMR (400 MHz, CDCl3): δ =
9.08 (d, J = 8.0 Hz, 2 H, Py–H), 7.80 (t, J = 8.0 Hz, 1 H, Py–H),7.40
(t, J = 8.0 Hz, 2 H, Py–H), 6.78 (d, J = 4.0 Hz, 1 H, NCH), 6.65–6.71
(m, 3 H, CH, NCH), 4.60 (d, J = 4.0 Hz, 1 H, Fc–H), 4.36 (s, 1 H,
Fc–H), 4.26 (s, 5 H, Fc–H), 4.18 (d, J = 12.0 Hz, 2 H, Fc–H), 4.12 (s,
3 H, CH3), 1.92 (d, J = 8.0 Hz, 3 H, CH3). 13C NMR (100 MHz,
CDCl3): δ = 151.3, 147.0, 138.1, 124.5, 123.1, 118.5, 87.2, 69.8, 69.3,
69.1, 67.8, 65.8, 56.4, 37.9, 21.0 ppm. C21H23Cl2FeN3Pd
(550.60 g·mol–1): calcd. C 45.81; H 4.21; N 7.63%; found: C 45.67;
H 4.14; N 7.75%.
1
1c: Yield: 67% (0.28 g). H NMR (400 MHz, CDCl3): δ = 10.58 (s,
1 H, NCHN), 7.63 (s, 1 H, NCH), 7.31 (s, 1 H, NCH), 7.16(s, 3 H,
Ph–H), 6.25–6.75 (m, 1 H, CH), 4.44 (s, 2 H, Fc–H), 4.28 (s, 6 H,
Fc–H), 4.11 (s, 1 H, Fc–H), 2.09–2.15 (m, 9 H, CH3). 13C NMR
(100 MHz, CDCl3): δ = 137.7, 134.7, 134.5, 133.3, 130.9, 129.2,
122.4, 119.9, 85.3, 69.8, 69.5, 69.1, 68.7, 56.8, 21,2. 20.9, 17.6 ppm.
C23H25ClFeN2 (420.76 g·mol–1): calcd. C 65.65; H 5.99; N 6.66%;
found: C 65.46; H 5.88; N 6.74%.
2b: To an oven-dried 50 mL of r.b.f. containing 1b (0.223 g,
0.6 mmol), PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol)
with a septum was injected into pyridine (15 mL) in an argon atmo-
sphere. The reaction mixture was stirred at 75 °C for 14 h. After cool-
ing to room temperature, the mixture was filtered through a plug of
Celite and washed by DCM. After the volatile was removed under
vacuum, the product was purified by flash column chromatography and
subsequent recrystallization from CH2Cl2/ether afforded the product as
1
1d: Yield: 73% (0.32 g). H NMR (400 MHz, CDCl3): δ = 10.71 (s,
1 H, NCHN), 7.42 (s, 1 H, NCH), 7.02 (s, 1 H, NCH), 6.96(s, 2 H,
Ph–H), 6.45–6.71 (m, 1 H, CH), 4.56 (s, 1 H, Fc–H), 4.38 (s, 1 H,
Fc–H), 4.28 (s, 7 H, Fc–H), 2.31 (s, 3 H, CH3), 2.04 (s, 9 H, CH3).
13C NMR (100 MHz, CDCl3): δ = 140.9, 139.7, 134.2, 131.0, 130.0,
124.9, 122.6, 85.6, 70.2, 70.0, 69.1, 68.7, 66.9, 57.7, 22.9, 21.4, 19.3,
18.9 ppm. C24H27ClFeN2 (434.78 g·mol–1): calcd. C 66.30; H 6.26; N
6.44%; found: C 66.17; H 6.18; N 6.55%.
1
yellow solid. Yield: 81% (0.29 g). H NMR (400 MHz, CDCl3): δ =
9.08 (d, J = 8.0 Hz, 2 H, Py–H), 7.80 (t, J = 8.0 Hz, 1 H, Py–H), 7.39
(t, J = 8.0 Hz, 2 H, Py–H), 7.29–7.31 (m, 1 H, CH), 6.97 (d, J =
8.0 Hz, 1 H, NCH), 6.72 (d, J = 4.0 Hz, 1 H, NCH), 4.75 (s, 1 H, Fc–
H), 4.39 (s, 1 H, Fc–H), 4.26 (s, 5 H, Fc–H), 4.19 (d, J = 8.0 Hz, 2
H, Fc–H), 2.08 (s, 9 H, CH3), 1.97 (d, J = 4.0 Hz, 3 H, CH3). 13C
NMR (100 MHz, CDCl3): δ = 151.5, 137.9, 124.6, 120.4, 117.8, 113.2,
87.5, 70.3, 69.3, 69.1, 67.6, 65.9, 58.8, 58.0, 32.1, 20.6 ppm.
C24H29Cl2FeN3Pd (592.68 g·mol–1): calcd. C 48.64; H 4.93; N 7.09%;
found: C 48.53; H 4.84; N 7.19%.
1
1e: Yield: 71% (0.32 g). H NMR (400 MHz, CDCl3): δ = 10.34 (s,
1 H, NCHN), 7.63 (s, 1 H, NCH), 7.39 (s, 1 H, NCH), 7.18 (s, 2 H,
Ph–H), 7.10 (s, 1 H, Ph–H) 6.52–6.57 (m, 1 H, CH), 4.50 (s, 1 H, Fc–
H), 4.40 (s, 1 H, Fc–H), 4.24 (s, 6 H, Fc–H), 4,10 (s, 1 H, Fc–H), 2.24
(s, 4 H, CH2), 2.04 (s, 3 H, CH3), 1.07 (s, 6 H, CH3). 13C NMR
(100 MHz, CDCl3): δ = 140.4, 138.8, 132.1, 131.4, 127.3, 125.0,
122.3, 85.5, 70.0, 69.8, 69.1, 68.7, 68.3, 66.6, 57.5, 24.9, 24.7, 22.3,
2c: To an oven-dried 50 mL of r.b.f. containing 1c (0.285 g, 0.6 mmol),
15.4 ppm. C25H29ClFeN2 (448.81 g·mol–1): calcd. C 66.90; H 6.51; N PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol) with a septum
6.24%; found: C 66.79; H 6.40; N 6.35%.
was injected into pyridine (15 mL) in an argon atmosphere. The reac-
tion mixture was stirred at 75 °C for 12 h. After cooling to room tem-
perature, the mixture was filtered through a plug of Celite and washed
1
1f: Yield: 69% (0.33 g). H NMR (400 MHz, CDCl3): δ = 10.38 (s,
1 H, NCHN), 7.61 (d, J = 4.0 Hz, 1 H, NCH), 7.52 (d, J = 4.0 Hz, 1 by DCM. After the volatile was removed under vacuum, the product
H, NCH), 7.29 (s, 2 H, Ph–H), 7.05 (s, 1 H, Ph–H), 4.63 (s, 1 H, Fc– was purified by flash column chromatography and subsequent
H), 4.39 (s, 2 H, Fc–H), 4.37 (s, 5 H, Fc–H), 4.10–4.29 (m, 1 H, Fc–
H), 3.49 (s, 3 H, CH3), 2.21–2.08 (m, 5 H, CH, CH3), 1.13–1.19 (m,
9 H, CH3) ppm.
recrystallization from CH2Cl2/ether afforded product as yellow solid.
Yield: 68% (0.26 g). 1H NMR (400 MHz, CDCl3): δ = 8.86 (d, J =
4.0 Hz, 2 H, Py–H), 7.72 (t, J = 4.0 Hz, 1 H, Py–H), 7.23–7.35 (m, 5
Z. Anorg. Allg. Chem. 2013, 1004–1010
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1007

C. Cao, Y. Shi et al.
ARTICLE
H, Py–H, Ph–H), 7.03–7.09(m, 1 H, CH), 6.91 (s, 1 H, NCH), 6.80 (s,
8.0 Hz, 3 H, CH3), 1.41 (t, J = 4.0 Hz, 6 H, CH3), 1.03 (d, J = 8.0 Hz,
1 H, NCH), 4.76 (s, 1 H, Fc–H), 4.45 (s, 1 H, Fc–H), 4.31 (s, 5 H, 3 H, CH3), 0.96 (d, J = 8.0 Hz, 3 H, CH3). 13C NMR (100 MHz,
Fc–H), 4.26 (s, 2 H, Fc–H), 2.32 (s, 3 H, CH3), 2.27 (s, 3 H, CH3),
2.05 (t, J = 8.0 Hz, 3 H, CH3). 13C NMR (100 MHz, CDCl3): δ =
151.4, 137.7, 137.3, 136.9, 136.8, 129.3, 128.4, 124.3, 123.9, 118.7,
CDCl3): δ = 151.3, 147.1, 137.7, 130.1, 125.7, 124.3, 123.9, 117.9,
87.6, 70.1, 69.3, 69.2, 67.7, 66.0, 57.0, 28.4, 28.3, 26.5, 23.2, 21.0
ppm. C32H37Cl2FeN3Pd (696.83 g·mol–1): calcd. C 55.16; H 5.35; N
87.4, 70.0, 69.4, 69.2, 67.7, 65.9, 56.9, 20.8, 19.1,19.0 ppm. 6.03%; found: C 55.07; H 5.28; N 6.12%.
C28H29Cl2FeN3Pd (640.72 g·mol–1): calcd. C 52.49; H 4.56; N 6.56%;
found: C 52.34; H 4.44; N 6.65%.
2g: To an oven-dried 50 mL of r.b.f. containing 1g (0.316 g,
0.6 mmol), PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol)
with a septum was injected into pyridine (15 mL) in an argon atmo-
sphere. The reaction mixture was stirred at 75 °C for 13 h. After cool-
ing to room temperature, the mixture was filtered through a plug of
Celite and washed by DCM. After the volatile was removed under
vacuum, the product was purified by flash column chromatography
and subsequent recrystallization from CH2Cl2/ether afforded product
as yellow solid. Yield: 80% (0.36 g). 1H NMR (400 MHz, CDCl3):
δ = 9.17 (d, J = 4.0 Hz, 2 H, Py–H), 7.82 (t, J = 8.0 Hz, 1 H, Py–H),
7.43 (t, J = 8.0 Hz, 2 H, Py–H), 6.67–6.72 (m, 2 H, CH), 6.58 (s, 2
H, NCH), 4.59 (s, 2 H, Fc–H), 4.32 (s, 2 H, Fc–H), 4.25 (s, 1 H, Fc–
H), 4.24 (s, 9 H, Fc–H), 4.15 (d, J = 8.0 Hz, 4 H, Fc–H), 1.91 (d, J =
8.0 Hz, 6 H, CH3). 13C NMR (100 MHz, CDCl3): δ = 151.4, 145.2,
138.1, 124.6, 118.6, 113.2, 87.5, 69.9, 69.1, 67.6, 65.8, 56.4, 20.9 ppm.
C32H33Cl2Fe2N3Pd (748.64 g·mol–1): calcd. C 51.34; H 4.44; N
5.61%; found: C 51.21; H 4.35; N 5.70%.
2d: To an oven-dried 50 mL of r.b.f. containing 1d (0.260g, 0.6 mmol),
PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol) with a septum
was injected into pyridine (15 mL) in an argon atmosphere. The reac-
tion mixture was stirred at 75 °C for 12 h. After cooling to room tem-
perature, the mixture was filtered through a plug of Celite and washed
by DCM. After the volatile was removed under vacuum, the product
was purified by flash column chromatography and subsequent
recrystallization from CH2Cl2/ether afforded product as yellow solid.
Yield: 77% (0.30 g). 1H NMR (400 MHz, CDCl3): δ = 8.86 (d, J =
4.0 Hz, 2 H, Py–H), 7.69 (t, J = 8.0 Hz, 1 H, Py–H), 7.25–7.29 (m, 2
H, Py–H), 7.00–7.06 (m, 3 H, Ph–H, CH), 6.87 (d, J = 2.0 Hz, 1 H,
NCH), 6.75 (d, J = 2.0 Hz, 1 H, NCH), 4.73 (s, 1 H, Fc–H), 4.42 (s,
1 H, Fc–H), 4.29 (s, 5 H, Fc–H), 4.21–4.23 (m, 2 H, Fc–H), 2.35 (s,
3 H, CH3), 2.25 (s, 3 H, CH3), 2.20 (s, 3H CH3), 2.02 (d, J = 4.0 Hz,
3 H, CH3). 13C NMR (100 MHz, CDCl3): δ = 151.4, 148.7, 139.0,
137.8, 136.5, 136.4, 134.9, 129.2, 124.3, 118.6, 87.5, 70.0, 69.4, 69.2,
67.7, 65.9, 56.9, 21.2, 20.8, 19.0,15.3 ppm. C29H31Cl2FeN3Pd
(654.75 g·mol–1): calcd. C 53.20; H, 4.77; N, 6.42%; found: C 53.09;
H, 4.66; N, 6.51%.
2h: To an oven-dried 50 mL of r.b.f. containing 1h (0.346 g,
0.6 mmol), PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol)
with a septum was injected into pyridine (15 mL) in an argon atmo-
sphere. The reaction mixture was stirred at 75 °C for 13 h. After cool-
ing to room temperature, the mixture was filtered through a plug of
Celite and washed by DCM. After the volatile was removed under
vacuum, the product was purified by flash column chromatography
and subsequent recrystallization from CH2Cl2/ether afforded product
as yellow solid. Yield: 75% (0.36 g). 1H NMR (400 MHz, CDCl3):
δ = 9.18 (d, J = 8.0 Hz, 2 H, Py–H), 7.84 (t, J = 8.0 Hz, 1 H, Py–H),
7.51–7.59 (m, 2 H, Py–H), 7.45 (t, J = 8.0 Hz, 2 H, Ph–H), 7.07–7.10
(m, 2 H, Ph–H), 6.85–6.89 (m, 2 H, CH), 4.79 (s, 1 H, Fc–H), 4.74
(s, 1 H, Fc–H), 4.56 (s, 2 H, Fc–H), 4.32 (d, J = 4.0 Hz, 10 H, Fc–H),
4.19 (d, J = 8.0 Hz, 2 H, Fc–H), 4.14 (d, J = 8.0 Hz, 2 H, Fc–H),
2.03–2.07 (m, 6 H, CH3). 13C NMR (100 MHz, CDCl3): δ = 160.6,
151.2, 138.3, 132.8, 124.8, 122.1, 112.5, 86.1, 70.9, 69.6, 69.4, 67.3,
66.7, 57.6, 17.8 ppm. C36H35Cl2Fe2N3Pd (798.69 g·mol–1): calcd. C
54.14; H 4.42; N 5.26%; found: C 54.02; H 4.33; N 5.37%.
2e: To an oven-dried 50 mL of r.b.f. containing 1e (0.269 g, 0.6 mmol),
PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol) with a septum
was injected into pyridine (15 mL) in an argon atmosphere. The reac-
tion mixture was stirred at 75 °C for 13 h. After cooling to room tem-
perature, the mixture was filtered through a plug of Celite and washed
by DCM. After the volatile was removed under vacuum, the product
was purified by flash column chromatography and subsequent
recrystallization from CH2Cl2/ether afforded product as yellow solid.
1
Yield: 85% (0.34 g). H NMR (400 MHz, CDCl3) : δ = 8.80 (d, J =
8.0 Hz, 2 H, Py–H), 7.67 (t, J = 8.0 Hz, 1 H, Py–H), 7.43 (t, J =
8.0 Hz, 1 H, Py–H), 7.24–7.28 (m, 4 H, Py–H, Ph–H), 7.00–7.05 (m,
1 H, CH), 6.87 (d, J = 2.0 Hz, 1 H, NCH), 6.81 (d, J = 4.0 Hz, 1 H,
NCH), 4.74 (s, 1 H, Fc–H), 4.43 (s, 1 H, Fc–H), 4.29 (s, 5 H, Fc–H),
4.24 (s, 2 H, Fc–H), 2.72–2.83 (m, 2 H, CH2), 2.31–2.46 (m, 2 H,
CH2), 2.03 (d, J = 8.0 Hz, 3 H, CH3), 1.15 (t, J = 8.0 Hz, 3 H, CH3),
1.10 (t, J = 8.0 Hz, 3 H, CH3). 13C NMR (100 MHz, CDCl3): δ =
151.4, 149.3, 142.4, 142.3, 137.7, 135.9, 129.7, 126.2, 124.7, 124.3,
118.3, 87.4, 70.1, 69.4, 69.2, 67.7, 65.9, 56.9, 24.7, 20.9, 14.9 ppm.
C30H33Cl2FeN3Pd (668.77 g·mol–1): calcd. C 53.88; H 4.97; N 6.28%;
found: C 53.75; H 4.88; N 6.34%.
Procedure for the Pd-catalyzed Indolization: 2-Bromoaniline
(1 mmol), alkyne (2 mmol), palladium catalyst (1 mol%), TBAB
(1 mmol), and K2CO3 (3 mmol) were dissolved in dioxane (2 mL) in
a 5 mL vial in air and heated at 140 °C for 24 h. After the reaction
was complete (monitored by GC-MS or TLC), the mixture was diluted
with ethyl acetate (10 mL), filtered through a pad of Celite, and the
Celite pad was washed multiple times with ethyl acetate. The com-
bined organic layer was dried with anhydrous Na2SO4, filtered, and
evaporated under reduced pressure and the residue was purified by
flash chromatography on silica gel to afford the pure product.
2f: To an oven-dried 50 mL of r.b.f. containing 1f (0.285 g, 0.6 mmol),
PdCl2 (0.117 g, 0.66 mmol), K2CO3 (0.829 g, 6 mmol) with a septum
was injected into pyridine (15 mL) in an argon atmosphere. The reac-
tion mixture was stirred at 75 °C for 12 h. After cooling to room tem-
perature, the mixture was filtered through a plug of Celite and washed
by DCM. After the volatile was removed under vacuum, the product
X-ray Crystallography: Intensity data were collected with a Rigaku
was purified by flash column chromatography and subsequent Mercury CCD area detector in ω scan mode by using Mo-Kα radiation
recrystallization from CH2Cl2/ether afforded product as yellow solid. (λ = 0.71073 Å). The diffracted intensities were corrected for Lorentz
1
Yield: 68% (0.28 g). H NMR (400 MHz, CDCl3,): δ = 8.85 (d, J = polarization effects and empirical absorption corrections. Details of the
4.0 Hz, 2 H, Py–H), 7.68 (t, J = 8.0 Hz, 1 H, Py–H), 7.47 (t, J =
8.0 Hz, 1 H, Py–H), 7.28–7.32 (m, 4 H, Py–H, Ph–H), 7.08 (d, J =
4.0 Hz, 1 H, CH), 6.86 (d, J = 4.0 Hz, 1 H, NCH), 6.81 (d, J = 4.0 Hz,
intensity data collection and crystal data are given by full-matrix least-
squares procedures based on F2.[10] All the non-hydrogen atoms were
refined anisotropically. The hydrogen atoms in these complexes were
1 H, NCH), 4.74 (s, 1 H, Fc–H), 4.43 (s, 1 H, Fc–H), 4.30 (s, 5 H, all generated geometrically (C–H bond lengths fixed at 0.95 Å), as-
Fc–H), 4.24 (s, 2 H, Fc–H), 2.82–2.93 (m, 2 H, CH), 2.05 (d, J = signed appropriate isotropic thermal parameters, and allowed to ride
1008
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1004–1010

Ferrocenyl-NHC Palladium Complexes
Table 2. Crystallographic data for complexes 2a, 2b, and 2f.
2a
2b
2f
Empirical formula
Formula weight
C21H23Cl2FeN3Pd
550.57
C48H58Cl4Fe2 N6Pd2·CH3CN
1226.36
C32H37Cl2FeN3Pd
696.80
Temperature /K
296(2)
296(2)
296(2)
Crystal system
Space group
orthorhombic
P212121
monoclinic
C2/c
monoclinic
P21/c
Crystal size /mm
a /Å
b /Å
c /Å
0.29ϫ0.27ϫ0.22
7.4163(6)
11.7509(9)
25.1829(19)
90
0.35ϫ0.33ϫ0.25
31.547(5)
10.8116(16)
15.831(2)
90
0.28ϫ0.26ϫ0.20
18.859(5)
10.675(3)
15.679(4)
90
α /°
β /°
90
90
2194.6(3)
4
1.666
90.979(4)
90
5398.6(14)
4
1.509
1.420
104.011(3)
90
3062.6(14)
4
1.511
1.261
γ /°
V /Å3
Z
Dcalcd. /mg·cm–3
Absorption coefficient /mm–1
F(000)
1.735
1104
2488
1424
θ range /°
Reflections collected / unique
1.62–28.01
29398 / 5146
[R(int) = 0.0206]
5146 / 0 / 253
1.145
2.38–26.37
33528 / 5492
[R(int) = 0.0283]
5492 / 78 / 295
1.037
3.59–25.35
20532 / 5547
[R(int) = 0.0595]
5547 / 0 / 357
1.074
Data / restrains / parameters
Goodness-of-fit on F2
Final R indices [I Ͼ 2σ (I)]
R1 = 0.0221
wR2 = 0.0584
R1 = 0.0226
wR2 = 0.0591
R1 = 0.0343
wR2 = 0.0903
R1 = 0.0401
wR2 = 0.0961
R1 = 0.0709
wR2 = 0.2091
R1 = 0.0804
wR2 = 0.2206
R indices (all data)
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on their parent carbon atoms. All the hydrogen atoms were held sta-
tionary and included in the structure factor calculation in the final stage
of full-matrix least-squares refinement. The structure was solved by
directed methods using the SHELXS-97 program and absorption cor-
rection was performed by the SADABS program. Selected crystallo-
graphic data are shown in Table 2. Crystals of complex 2a, 2b, and 2f
suitable for X-ray diffraction analysis were obtained by slow evapora-
tion of a saturated solution of acetonitrile and DCM (15:1) at room
temperature.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies
of the data can be obtained free of charge on quoting the depository
numbers CCDC-922470 (2a), CCDC-922471 (2b), and CCDC-922472
(2f) (Fax: +44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk, http://
www.ccdc.cam.ac.uk).
Acknowledgements
We are grateful to the foundation of National Natural Science Founda-
tion of China (21071121, 21172188 and 21104064), 333 Project for
the Cultivation of High-level Talents (33GC1002) SRF for ROCS,
SEM, PAPD, Graduate Foundation (2012YYB080) and the State Key
Laboratory of Inorganic Synthesis and Preparative Chemistry at Jilin
University (2013–03) for financial support.
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Received: February 18, 2013
Published Online: April 22, 2013
1010
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© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 1004–1010