Synthesis and structural characterization of palladacycles with polydentate ligands by a stepwise coupling route - Palladacycles containing halides as efficient catalysts and substrates

Article abstract of DOI:10.1002/ejic.201100617

A series of ferrocenyl palladacycles with polydentate ligands were conveniently prepared by the Suzuki coupling reactions of a halide-containing ferrocenyl palladacycle [PdCl({(ν⁵-C₅H ₅)}Fe{(ν⁵-C₅H

Full text of DOI:10.1002/ejic.201100617

FULL PAPER
DOI: 10.1002/ejic.201100617
Synthesis and Structural Characterization of Palladacycles with Polydentate
Ligands by a Stepwise Coupling Route – Palladacycles Containing Halides as
Efficient Catalysts and Substrates
Chen Xu,*[a] Zhi-Qiang Wang,[a] Ya-Peng Zhang,[b] Xin-Ming Dong,[b] Xin-Qi Hao,[b]
Wei-Jun Fu,[a] Bao-Ming Ji,[a] and Mao-Ping Song[b]
Keywords: Palladium / Sandwich complexes / Homogeneous catalysis / Amination / Halides / Palladacycles
A series of ferrocenyl palladacycles with polydentate ligands
were conveniently prepared by the Suzuki coupling reac-
(DCPAB)] (32), where DCPAB = 2-dicyclohexylphosphanyl-
2Ј-(N,N-dimethylamino)biphenyl. The halide-containing pal-
ladacycles act as efficient catalysts and substrates in the cou-
pling reactions. 37 new examples have been fully charac-
terized by elemental analysis, IR and 1H NMR spectroscopy,
and ESI-MS. Additionally, the molecular structures of eight
compounds were determined by single-crystal X-ray diffrac-
tion, and many types of intermolecular C–H···Cl (O, N, π) in-
teractions and π–π interactions were found in the crystal
structures of these palladacycles.
tions of
a
halide-containing ferrocenyl palladacycle
[PdCl({(η5-C5H5)}Fe{(η5-C5H3)N2C4H2Cl})(PPh3)] (1) and
arylboronic acids without additional palladium catalysis. In
the absence of additional base, amination also occurred in
high yield. This new protocol was successfully applied to the
Suzuki coupling reactions of the analogous halide-contain-
ing palladacycle [PdCl({(η5-C5H5)}Fe{(η5-C5H3)NC5H3Br})-
(PPh3)] (15) and Buchwald–Hartwig amination of the ana-
logous complex [PdCl({(η5-C5H5)}Fe{(η5-C5H3)NC5H3Br})-
have been developed, and they can be mainly divided into
four strategies: C–H activation, oxidative addition, trans-
metalation, and nucleophilic addition.[2c] C–H activation is
the simplest and most direct process (Scheme 1, A), how-
ever, a synthetic limitation has emerged as a serious prob-
lem. First, cyclopalladated complexes with free donor
groups may be difficult to prepare by cyclopalladation be-
cause the precursor polydentate ligand may coordinate to
the Pd center and block C–H activation.[6] Furthermore, in
the direct cyclopalladation protocol by C–H activation, the
regioselectivity of cyclopalladation is not controlled. To
overcome these problems, we planned to develop a stepwise
coupling route (stepwise introduction of the free donor
groups) for the synthesis of palladacycles with polydentate
ligands (Scheme 1, B). These complexes can be used as
metalloligands for the synthesis of cyclopalladated poly-
nuclear complexes.
Introduction
Palladium-catalyzed coupling reactions, such as the Su-
zuki coupling reaction and the Buchwald–Hartwig amin-
ation, have become powerful methods in organic synthe-
sis.[1] A number of Pd catalyst precursors, usually simple
palladium salts or complexes associated with the appropri-
ate ligands, can mediate these reactions under various reac-
tion conditions. Among them, palladacycles are one of the
most developed and studied classes of precatalyst because
of their structural versatility and high catalytic activity.[2]
Since the first report on the use of palladacycles for cou-
pling reactions by Herrmann in 1995,[3] a wide variety of
palladacycles have been successfully used in these reactions.
For instance, monophosphane palladacycles combine the
stability imparted by a palladacycle framework with the
high activity commonly associated with monophosphane li-
gands and are far more active than the corresponding di-
meric palladacycles.[4] In particular, cyclopalladated ferro-
cene derivatives are fascinating as ferrocene is an ideal
framework to which planar chirality can be introduced.[5]
Various methods for the preparation of these complexes
Palladium-catalyzed coupling reactions of cyclomet-
alated halide-containing iridium complexes with aryl-
boronic acids have been reported.[7] To the best of our
knowledge, there are no reports concerning the coupling
reactions of halide-containing palladacycles. In recent
years, part of our research effort has focused on the synthe-
sis and application of cyclometalated complexes.[8] In a pre-
[a] College of Chemistry and Chemical Engineering, Luoyang
Normal University,
liminary communication,[9] we reported
a new tri-
Luoyang, Henan 471022, China
E-mail: xubohan@163.com
phenylphosphane cyclopalladated ferrocenylchloropyrimid-
ine complex 1, which reacted with KOH to provide a Pd4
cluster monophosphane palladacycle by Pd-catalyzed hy-
droxylation. In view of these findings and our continued
[b] Department of Chemistry, Zhengzhou University,
Zhengzhou, Henan 450052, China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201100617.
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Palladacycles as Efficient Catalysts and Substrates
In order to further examine the role and catalytic activity
of 1 in the coupling reaction and to develop a new stepwise
synthetic strategy, we researched the Suzuki coupling of 1
with naphthylboronic acid (Scheme 2, B). Based on our pre-
vious experiments on palladacylic precatalysts for Suzuki
coupling reactions,[4c,10] the reaction was performed under
a nitrogen atmosphere in dioxane in the presence of Cs2CO3
at 110 °C for 16 h, which afforded the coupled product 3 in
93% yield (Table 1, Entry 1) without an additional palla-
dium catalyst. Other reaction conditions such as K2CO3 in
dioxane, K3PO4 in dioxane, K2CO3 in toluene, and K3PO4
in toluene afforded good yields (91, 85, 89, and 83%,
respectively).
Scheme 1. Synthetic strategy for palladacycles with polydentate li-
gands.
Table 1. Effect of 1 on Suzuki coupling reactions.[a]
interest in other coupling reactions of 1 and analogous ha-
lide-containing palladacycles, we examined their role and
catalytic activity in Suzuki and C–N coupling reactions.
Here, we present an efficient method for the synthesis of
palladacycles with polydentate ligands by a stepwise cou-
pling route and the synthesis and structural characteriza-
tion of these palladacycles.
Results and Discussion
Synthesis of Palladacycles with Polydentate Ligands by
Stepwise Suzuki Coupling Reactions
There are two pathways for the synthesis of palladacycles
with a polydentate ligand (Scheme 2, A and B). According
to the traditional method (A), 3 was obtained from Suzuki
coupling, cyclopalladation, and bridge-splitting reactions.
Considering that 1 is a chloride-containing (in the pyrimid-
ine ring) monophosphane palladacycle, we speculate that it
reacted with arylboronic acids both as catalyst and sub-
strate. The new pathway B is contrary to route A in se-
quence, which is particularly attractive because it does not
require an additional palladium catalyst. If it can be suc-
cessfully applied to the coupling reactions, other ligands
could be introduced to the cyclopalladated ligand. This
strategy enabled us to prepare a new class of palladacycles
with polydentate ligands.
Entry Equiv. 1 Equiv. a Equiv. b % Yield of
% Yield of
2[b]
3[b]
1
2
3
4
5
6
7
8
1
0.1
0.5
1
0.01
0.001
1
1
1
1
1
1
1
4
5
0
1
1
1
1
1
1
0
0
93
85
87
88
39
0
73
18
90
0
90
trace
trace
92
1
95
[a] Reaction conditions: b (0.5 mmol), Cs2CO3 (1.0 mmol), dioxane
(5 mL), 110 °C, 16 h. [b] Isolated yield.
We next explored the effect of 1 on Suzuki coupling reac-
tions. Employing a mixture of 1, a, and b, the coupled prod-
uct 3 was obtained in good yields (Table 1, Entries 2–4).
However, the product 2 was not isolated using 1.0 equiv. of
1 (Entry 4). Furthermore, 1 could be present in lower than
1 mol-% without loss of activity (Entry 5), however, the
yield of 2 only reached 18% when 0.1 mol-% of 1 was used
(Entry 6), which revealed that a small percentage (less than
0.1 mol-%) of 1 behaves as the catalyst[11] and the remaining
1 behaves as the substrate. The results indicated that 1 was
an efficient precatalyst.[10c] Loading naphthylboronic acid
(a) to 4.0 equiv. gave 2 and 3 in 90–92% yields, respectively
(Entry 7). Although the reductive ring-opening reactions of
palladacyclic catalysts have been reported in the couplings
of arylboronic acids with palladacycles,[12] 2 was not ob-
tained with 5.0 equiv. of a in this reaction (Entry 8).
Scheme 2. Synthesis of 3.
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Additionally, we also investigated the coupling reaction Table 2. Suzuki coupling reactions of heteroaryl–B(OH)2 with 1.[a]
of 1 with bis(pinacolato)diboron (Scheme 3). Although,
palladium-catalyzed coupling reactions of bis(pinacolato)-
diboron with aryl halides have been extensively studied,[13]
to the best of our knowledge, there are no reports concern-
ing the coupling reactions of halide-containing pallada-
cycles with bis(pinacolato)diboron. The reaction gave 4 in
moderate yield (52%) and its molecular structure is shown
in Figure S1–S2 (see Supporting Information). The corre-
sponding boronate was not observed; a possible reason was
that the ortho-substituted pinacol ester of pyrimidinyl-
boronic acid formed was not stable under the reaction con-
ditions.[14] The results also indicated that 1 was a efficient
catalyst precursor and substrate in reaction.
Scheme 3. Reaction of bis(pinacolato)diboron and 1.
In contrast to arylboronic acids, Suzuki coupling reac-
tions of heteroarylboronic acids have been less reported.[15]
To obtain palladacycles containing more free donor groups,
the Suzuki coupling reactions of a variety of structurally
diverse heteroarylboronic acids with 1 were investigated in
the presence of K2CO3 (Cs2CO3 is more expensive than
K2CO3) in dioxane. The corresponding palladacycles were
isolated in good yields (86–92%) for heteroarylboronic ac-
ids such as 2-furylboronic acid, thiophen-2-boronic acid,
and pyridinylboronic acid (Table 2, Entries 1–4). Next, we
proceeded to examine the substrate scopes with respect to
pyridinylboronic acids. The method proved to be effective
for pyridinylboronic acids bearing a variety of functional
groups, including ethers (Entry 5), esters (Entries 6–7) and
amines (Entry 8). However, for the very sterically hindered
pyridinylboronic acid, the corresponding palladacycle was
obtained in low yield (Entry 9).
In order to extend the scope of this catalyst system to
other halide-containing palladacycles, we synthesized the
analogous 15 according to reported procedures
[a] Reaction conditions:
(0.6 mmol), K2CO3 (1.0 mmol), dioxane (5 mL), 110 °C, 24 h. [b]
1
(0.5 mmol), heteroaryl–B(OH)2
(Scheme 4).[4d,9] The newly developed Suzuki reaction pro-
tocol was also successfully applied to heteroarylboronic ac- Isolated yield.
ids and 15. As shown in (Table 3), a series of heteroaryl-
boronic acids were efficiently transformed to the desired 15 decreased slightly. This may be because the activity of
products in good yields (Entries 1–6). Compared with those the bromine atom in 15 is lower than that of the chlorine
starting from 1, the yields of coupled products starting from atom in 1.
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Palladacycles as Efficient Catalysts and Substrates
the model reaction to evaluate the effectiveness of 1 in diox-
ane without additional base (Scheme 5), and the desired
product 22 was obtained in good yield (88%). When K2CO3
was used as the base, the yield increased slightly to 91%.
However, the hydroxy product was not observed in the reac-
tion. Other solvents such as toluene also afforded good
yield (85%).
Scheme 4. Synthesis of 14 and 15.
Table 3. Suzuki coupling reactions of heteroaryl–B(OH)2 with 15.[a]
Scheme 5. Synthesis of 22.
A variety of electronically and structurally diverse
amines could be coupled efficiently with 1 in the absence of
additional base in dioxane at 110 °C for 24 h (Table 4). Sim-
ilar to the results with aniline, the reactions of p-toluidine
and 4-methoxyaniline with 1 provided high isolated yields
(Entries 1–2). However, for 4-nitroaniline only 30% isolated
yield was obtained under the same conditions (Entry 3).
The reactions of primary aliphatic amines of aryl chlorides
are not common in amination reactions. We also examined
the aminations of aliphatic amines with 1, and, unexpec-
tedly, the yields of aliphatic amines (90–95%) are better
than the yield of aniline in most cases (Entries 4–6). In or-
der to introduce more free donor groups to the pallada-
cycles, we investigated the amination of imidazole with 1
(Entry 7), and the corresponding product was isolated in
good yield (91%).
To further explore the role of 1 in the above coupling
reactions, we performed the parallel coupling reaction of b
and aniline (Scheme 6). The coupled product 30 was also
obtained in moderate yield (53%) in the absence of ad-
ditional base. However, the corresponding product was not
obtained by the reaction of 14 with aniline (Table 5, Entry
1). The result revealed that 1 could only act as a substrate
in the reaction. The C–N bond formation in 22 is due to
the strong activity of the chloride atom (in the pyrimidine
ring).[18] Even when the strong organic base KOtBu was
used, the coupling of the analogous halide-containing palla-
dacycle 15 and aniline was also unsuccessful (Entry 2), indi-
[a] Reaction conditions: 15 (0.5 mmol), heteroaryl–B(OH)2
(0.6 mmol), K2CO3 (1.0 mmol), dioxane (5 mL), 110 °C, 24 h. [b]
Isolated yield.
Synthesis of Palladacycles with Polydentate Ligands by
Stepwise C–N Coupling Reactions
The high activity of 1 in the Suzuki coupling reactions cating that 1 and 15 are inactive in Buchwald–Hartwig ami-
of arylboronic acids encouraged us to examine their activity nations.
towards C–N coupling reactions. It is known that the cata-
Based on our previous experiments on palladacylic pre-
lyst and base are crucial components of the Buchwald– catalysts for Buchwald–Hartwig aminations,[4d,4e] we per-
Hartwig amination.[16] Beller reported transition metal-free formed the aminations of 14 or 15 and aniline catalyzed by
amination of aryl chlorides, which proceed efficiently in the 31[4e] (Figure 1). As expected, the corresponding products
presence of an excess of KOtBu.[17] We have also found that were obtained in good yields (Entries 3–4). To explore the
cyclopalladated complexes are very efficient for the amin- “real” catalyst in the reaction, 32 was also synthesized. Sub-
ation of aryl chlorides in the presence of KOtBu or KOH sequent experiments further proved that 32 was an efficient
as a base.[4d,4e] Considering that 1 is a chloride-containing catalyst precursor for Buchwald–Hartwig aminations (En-
palladacycle, it can react with KOH to provide a hydroxy tries 5–6) suggesting that DCPAB participated in the cata-
product.[9] Thus, we chose the coupling of aniline with 1 as lytic cycle. On the basis of these results, we propose that
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Table 4. C–N coupling reactions of various amines with 1.[a]
Table 5. Effect of 31 or 32 on Buchwald–Hartwig aminations.[a]
En-
try
Equiv. Equiv. 15 Equiv. ani- Equiv. cata- % Yield[b]
14
line
lyst
1
2
3
4
5
6
1
0
1
0
1
0
0
1
0
1
0
1
1.5
1.5
1.5
1.5
1.5
1.5
0
0
33 (0)
34 (0)
33 (91)
34 (94)
33 (90)
34 (92)
31 (0.001)
31 (0.001)
32 (0.001)
32 (0.001)
[a] Reaction conditions: 14 (0.5 mmol) or 15 (0.5 mmol), aniline
(0.75 mmol), KOtBu (1.0 mmol), dioxane (5 mL), 110 °C, 24 h. [b]
Isolated yield.
that the coupling reaction catalyzed by small percentage of
halide-containing palladacycle proceeded through a classi-
cal Pd0/PdII cycle.[11,19]
Figure 1. Ferrocenyl palladacycles 31 and 32.
Finally, this newly developed coupling protocol was also
successfully applied to the synthesis of palladacycles with
polydentate ligands by Buchwald–Hartwig aminations of
32. As shown in Table 6, 32 was very effective in the aryl-
ation of aniline and 4-methoxyaniline (Entries 1–2). How-
ever, the yields of aliphatic amines in this system decreased
slightly (Entries 3–4). For imidazole, the corresponding
product was isolated in good yield (Entry 5).
[a] Reaction conditions: 1 (0.5 mmol), amine (0.75 mmol), dioxane
(5 mL), 110 °C, 24 h. [b] Isolated yield.
Crystal Structures and Intermolecular Interactions
Although many structures of palladacycles have been de-
termined, few reports discuss the intermolecular interac-
tions in these complexes.[20] We systematically investigated
the crystal structures of palladacycles 3, 10, 11, 15, 17, 26,
27, and 32, focusing on their supramolecular interactions.
All the crystals were obtained by recrystallization from
CH2Cl2/petroleum ether solution at room temperature. The
single-crystal X-ray analysis indicates that these pallada-
cycles are trans complexes in the solid state. The Pd atom
Scheme 6. Synthesis of 30.
the phosphane ligand may promote the release of the real in each complex is in a slightly distorted square planar envi-
catalytic species from the palladacycle, and stabilize the ronment bonded to the phosphorus, chloride, pyrimidinyl
active species under the reaction conditions. It is proposed nitrogen, and a carbon atom of the ferrocenyl moiety.
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Palladacycles as Efficient Catalysts and Substrates
Table 6. Buchwald–Hartwig aminations of various amines with
32.[a]
Figure 2. Molecular structure of 3·2CH2Cl2. Thermal ellipsoids are
drawn at 50% probability. H atoms and CH2Cl2 are omitted for
clarity. Selected bond lengths [Å] and angles [°]: Pd(1)–C(16)
1.999(5), Pd(1)–N(1) 2.130(4), Pd(1)–P(1) 2.2402(14), Pd(1)–Cl(1)
2.3842(15) and C(16)–Pd(1)–N(1) 80.80(18), C(16)–Pd(1)–P(1)
92.11(15), P(1)–Pd(1)–Cl(1) 95.30(5), N(1)–Pd(1)–Cl(1) 91.93(12).
Figure 3. 1D chain structure of 3·2CH2Cl2 showing the C–H···N
hydrogen bonds and π–π interactions. Thermal ellipsoids are drawn
at 50% probability. Non-hydrogen bonding H atoms and CH2Cl2
are omitted for clarity.
[a] Reaction conditions: 32 (0.5 mmol), amines (0.75 mmol),
KOtBu (1.0 mmol), dioxane (5 mL), 110 °C, 24 h. [b] Isolated yield.
The molecular structure of 3 is shown in Figure 2. The organometallic compounds.[22] Therefore, C–H···Cl–M hy-
bicyclic system formed by the palladacycle and the C5H3 drogen bonding can be used to assemble transition metal-
moiety is approximately coplanar (dihedral angles of 1.1°). based building blocks into supramolecular structures.[23]
However, the pyrimidine and naphthalene rings are not co- The molecular structures of 10 and 11 were confirmed by
planar and have a dihedral angle of 50.7°. In 3·2CH2Cl2, single-crystal X-ray diffraction analysis (see Figures 4, 5,
there are C–H···N hydrogen bonds and π–π stacking inter- and Figure S5 in the Supporting Information). The crystal
actions between the naphthalene rings,[21] which are attrib- structures of the two complexes are similar, the oxygen
uted to the 1D chain structure (Figure 3). In addition, atom of ester group forms C–H···O hydrogen bonds, how-
CH2Cl2 molecules are present in the two adjacent chains ever, the nitrogen atom in the pyridine ring does not partici-
and form intermolecular C–H···Cl hydrogen bonds (Cl···H pate in hydrogen bonding. In comparison with 3·2CH2Cl2,
2.895 Å) with the chlorine atom of 3 (Figure S3–S4, Sup- the chlorine atom of 10 forms three types of intermolecular
porting Information).
C–H···Cl hydrogen bonds with adjacent C–H groups of the
Hydrogen bonds are considered to be the most powerful Cp and pyridine rings, which give rise to a 1D chain (Fig-
organizing element in molecular assembly due to their ure 4). Like 10, 11 also has a 1D chain structure formed by
highly selective and directional character. In particular, C– C–H···Cl and C–H···O(ester) hydrogen bonds (Figure S6,
H···Cl hydrogen bonds have attracted great interest as the Supporting Information). It is noteworthy that intermo-
H-bonding acceptor capability of terminal metal-bound lecular π–π interactions involving the neighboring pyridine
chlorine (M–Cl) is stronger than their C–Cl analogues in rings (the interplanar distance is 3.659 Å) are also present
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C. Xu et al.
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in 11. Owing to the π–π stacking effects and C–H···Cl(O) gen bonds, whereas the bromine atom on the pyridine ring
hydrogen bonds, the crystal structure of 11 is extended into does not participate in hydrogen bonding. In complex 17
a 2D architecture (Figure 6).
(Figure 8), there are two types of C–H···Cl hydrogen bonds
and C–H···N interactions, which are attributed to the 1D
chain structure. Interestingly, the uncoordinated pyridinyl
nitrogen atom also forms intermolecular C–H···N hydrogen
bonds with the adjacent C–H group of the Cp ring, which
is not found in the structures of 10 and 11. In addition,
CH2Cl2 molecules are present in the two adjacent chains
(Figure 9).
Figure 4. 1D chain structure of 10 showing the C–H···Cl(O) hydro-
gen bonds. Thermal ellipsoids are drawn at 50% probability. Non-
hydrogen bonding H atoms are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–C(13) 1.994(7), Pd(1)–N(1)
2.127(6), Pd(1)–P(1) 2.242(2), Pd(1)–Cl(1) 2.379(2) and C(13)–
Pd(1)–N(1) 80.8(3), C(13)–Pd(1)–P(1) 92.3(2), P(1)–Pd(1)–Cl(1)
95.90(8), N(1)–Pd(1)–Cl(1) 91.79(17).
Figure 7. 1D chain structure of 15 showing the C–H···Cl hydrogen
bonds. Thermal ellipsoids are drawn at 50% probability. Non-hy-
drogen bonding H atoms are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–C(10) 1.988(4), Pd(1)–N(1)
2.140(3), Pd(1)–P(1) 2.2322(11), Pd(1)–Cl(1) 2.3642(2) and C(10)–
Pd(1)–N(1) 81.38(15), C(10)–Pd(1)–P(1) 90.34(12), P(1)–Pd(1)–
Cl(1) 94.81(4), N(1)–Pd(1)–Cl(1) 91.80(9).
Figure 5. Molecular structure of 11 (one of the two independent
molecules). Thermal ellipsoids are drawn at 50% probability. H
atoms are omitted for clarity. Selected bond lengths [Å] and angles
[°] (corresponding values for the second independent molecule are
given in brackets): Pd(1)–C(2) 1.983(4) [1.981(4)], Pd(1)–N(1)
2.127(3) [2.131(3)], Pd(1)–P(1) 2.2442(13) [2.2235(13)], Pd(1)–Cl(1)
2.3740(12) [2.3856(12)] and C(2)–Pd(1)–N(1) 80.70 (15) [81.02(15)],
C(2)–Pd(1)–P(1) 92.28(13) [90.57(13)], P(1)–Pd(1)–Cl(1) 97.01(5)
[95.67(4)], N(1)–Pd(1)–Cl(1) 90.28(10) [94.54(10)].
Figure 8. Molecular structure of 17 (one of the two independent
molecules). Thermal ellipsoids are drawn at 50% probability. H
atoms and CH2Cl2 are omitted for clarity. Selected bond lengths
[Å] and angles [°] (corresponding values for the second independent
molecule are given in brackets): Pd(1)–C(1) 1.990(7) [1.992(7)],
Pd(1)–N(1) 2.150(5) [2.141(5)], Pd(1)–P(1) 2.2454(18) [2.2398(17)],
Pd(1)–Cl(1) 2.4713(13) [2.4213(14)] and C(1)–Pd(1)–N(1) 80.9(2)
[80.9(3)], C(2)–Pd(1)–P(1) 92.3(2) [92.0(2)], P(1)–Pd(1)–Cl(1)
93.80(6) [94.58(6)], N(1)–Pd(1)–Cl(1) 93.06(15) [93.64(15)].
Figure 10 shows that 26 exists as a dimer due to intermo-
lecular N–H···N hydrogen bonds and the chlorine atom that
forms a hydrogen bond with the adjacent C–H group of
CH2Cl2. This is different from the structures of 10, 11, 15,
and 17, which have 1D chain structures formed by C–H···Cl
hydrogen bonds. The molecular structure of 27 is shown in
Figure 11. Unlike 26, 27 also has a 1D chain structure
formed by C–H···Cl hydrogen bonds. It is worth noting that
Figure 6. Two-dimensional lamellar structure of 11 showing the C–
H···Cl(O) hydrogen bonds and π–π interactions. Thermal ellipsoids
are drawn at 50% probability. Non-hydrogen bonding H atoms are
omitted for clarity.
The molecular structure of 15 is shown in Figure S7 the intermolecular C–H···π interactions[20d,24] are present in
(Supporting Information). It can be seen from Figure 7 that 27, resulting in a 2D supramolecular architecture (Fig-
15 also has a 1D chain structure formed by C–H···Cl hydro- ure 12).
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Palladacycles as Efficient Catalysts and Substrates
Figure 9. 2D lamellar structure of 17 showing the C–H···Cl(N) in-
teractions. Thermal ellipsoids are drawn at 50% probability. Non-
hydrogen bonding H atoms are omitted for clarity.
Figure 12. 2D lamellar structure of 27 showing the C–H···Cl(π) in-
teractions. Thermal ellipsoids are drawn at 50% probability. Non-
hydrogen bonding H atoms are omitted for clarity.
Figure 10. The dimeric structure of 26 showing the C–H···N hydro-
gen bonds. Thermal ellipsoids are drawn at 50% probability. Non-
hydrogen bonding H atoms are omitted for clarity. Selected bond
lengths [Å] and angles [°]: Pd(1)–C(2) 1.991(3), Pd(1)–N(1)
2.118(2), Pd(1)–P(1) 2.2407(8), Pd(1)–Cl(1) 2.3818(9) and C(2)–
Pd(1)–N(1) 80.63(11), C(2)–Pd(1)–P(1) 92.75(9), P(1)–Pd(1)–Cl(1)
95.56(3), N(1)–Pd(1)–Cl(1) 91.85(7).
Figure 13. Molecular structure of 32. Thermal ellipsoids are drawn
at 50% probability. H atoms and CH2Cl2 are omitted for clarity.
Selected bond lengths [Å] and angles [°]: Pd(1)–C(1) 1.973(6),
Pd(1)–N(1) 2.156(5), Pd(1)–P(1) 2.2679(15), Pd(1)–Cl(1) 2.3986(15)
and C(1)–Pd(1)–N(1) 79.9(2), C(1)–Pd(1)–P(1) 95.25(17), P(1)–
Pd(1)–Cl(1) 93.28(6), N(1)–Pd(1)–Cl(1) 92.21(13).
Conclusions
We have developed an efficient method for the synthesis
of palladacycles with polydentate ligands by a stepwise cou-
pling route without additional palladium catalysis. A small
percentage of the halide-containing palladacycle acted as a
precatalyst and the remainder behaved as the substrate in
the coupling reaction. The advantages of this method in-
clude good substrate generality, high efficiency, and that ad-
ditional catalysis is not required. A series of new ferrocenyl
palladacycles with polydentate ligands were successfully
Figure 11. Molecular structure of 27. Thermal ellipsoids are drawn
at 50% probability. Non-hydrogen bonding H atoms are omitted
for clarity. Selected bond lengths [Å] and angles [°]: Pd(1)–C(11)
1.987(8), Pd(1)–N(1) 2.114(3), Pd(1)–P(1) 2.2345(9), Pd(1)–Cl(1)
2.3685(2) and C(11)–Pd(1)–N(1) 80.78(12), C(11)–Pd(1)–P(1)
93.18(10), P(1)–Pd(1)–Cl(1) 94.80(4), N(1)–Pd(1)–Cl(1) 91.95(7).
The molecular structure of 32 is shown in Figure 13. In synthesized by Suzuki and C–N coupling reactions. Single-
32, DCPAB replaces PPh3 in 15. The Pd–P [2.2679(15) Å] crystal X-ray analysis confirms that there are many types
bond length in 32 is longer than those in the other seven of intermolecular C–H···Cl (O, N, π) interactions and π–π
complexes [2.2322(11)–2.2454(18) Å] possibly due to the interactions in the structures of these palladacycles. Subse-
steric bulk of DCPAB. Unlike 15, C–H···Cl hydrogen bonds quent work will focus on the synthesis of polynuclear or
are not found in 32.
heteropolymetallic palladacycles by this method.
Eur. J. Inorg. Chem. 2011, 4878–4888
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4885

C. Xu et al.
FULL PAPER
General Procedure for Palladacycles with Polydentate Ligands by
Stepwise Suzuki Coupling Reactions: In a Schlenk tube, a mixture
of halide-containing palladacycle (0.5 mmol), arylboronic acid
(0.5–2.5 mmol), and base (1.0 mmol) in solution (5 mL) was evacu-
ated and charged with nitrogen. The reaction mixture was heated
at 110 °C for 16–24 h, cooled, and quenched with water. The or-
ganic layer was separated, and the aqueous layer was extracted with
dichloromethane. The combined organic layers were washed with
water, dried with MgSO4, filtered, the solvent was removed on a
rotary evaporator, and the products were isolated by flash
chromatography on silica gel. Data for a selected example:
Experimental Section
Materials and Instrumentation: All reactions were carried out under
a dry nitrogen atmosphere using standard Schlenk techniques. Sol-
vents were dried and freshly distilled prior to use. All other chemi-
cals were commercially available except for chloromercuriferro-
cene,[25] b,[9] 1,[9] and 31,[4e] which were prepared according to the
published procedures. Melting points were measured using a WC-
1 microscopic apparatus. Elemental analyses were determined with
a Carlo Erba 1160 Elemental Analyzer. IR spectra were collected
1
with a Bruker VECTOR22 spectrophotometer as KBr pellets. H
NMR spectra were recorded with a Bruker DPX-400 spectrometer
in CDCl3 with TMS as an internal standard. Mass spectra were
measured with a LC-MSD-Trap-XCT instrument.
[PdCl({(η5-C5H5)}Fe{(η5-C5H3)NC5H3NC5H3N(CH3)2})(PPh3)]
(21): Red solid; yield 90%; m.p.: 239–240 °C. C40H35ClFeN3PPd
(786.41): calcd. C 61.09, H 4.49, N 5.34; found C 61.31, H 4.25, N
[(η5-C5H5)]Fe[(η5-C5H3)NC5H3Br] (14): In a flask equipped with a
reflux condenser and gas inlet, chloromercuriferrocene (1 mmol),
2,5-dibromopyridine (1.1 mmol), NaI (2 mmol), Pd(PPh3)4
(0.05 mmol), dry tetrahydrofuran (18 mL), and dry Me2CO
(12 mL) were placed under a N2 atmosphere. The reaction mixture
was heated at 80 °C for 5 h, cooled, and quenched with water. The
organic layer was separated, and the aqueous layer was extracted
with dichloromethane, the combined organic layers were washed
with water, dried with MgSO4, filtered, and the solvent was re-
moved on a rotary evaporator. The product was purified by passing
it through a short column of silica gel with CH2Cl2/petroleum ether
(2:1) as eluent. The second band was collected and afforded 14 as
a red solid; yield 65%; m.p.: 111–112 °C. C15H12BrFeN (342.02):
calcd. C 52.68, H 3.54, N 4.10; found C 52.87, H 3.32, N 4.31. IR
5.55. IR (KBr): ν = 3048, 2935, 1604, 1545, 1498, 1435, 1404, 1380,
˜
1221, 1180, 1155, 1098, 1001, 952, 812, 749, 697 cm–1. ESI+-MS:
1
m/z = 751.1 [M – Cl]+. H NMR (400 MHz, CDCl3): δ = 9.82 (s,
1 H, Ar–H), 8.46 (s, 2 H, Ar–H), 7.83 (m, 8 H, Ar–H), 7.41 (m, 9
H, Ar–H), 7.28 (d, 1 H, Ar–H), 6.58 (d, 1 H, Ar–H), 4.61 (s, 1 H,
C5H3), 4.06 (s, 1 H, C5H3), 3.68 (s, 5 H, C5H5), 3.37 (s, 1 H, C5H3),
3.12 (s, 6 H, CH3) ppm. For other new compounds, see Supporting
Information.
General Procedure for Palladacycles with Polydentate Ligands by
C–N Coupling Reactions: In a Schlenk tube, a mixture of halide-
containing palladacycle (0.5 mmol), amine (0.75 mmol) or base
(1.0 mmol) in solution (5 mL) was evacuated and charged with ni-
trogen. The reaction mixture was heated at 110 °C for 24 h. The
work up was the same as described above for the Suzuki reaction.
Data for a selected example:
(KBr): ν = 3075, 3021, 1569, 1489, 1437, 1388, 1367, 1283, 1375,
˜
1200, 1101, 1026, 1001, 889, 840, 825, 752, 695 cm–1. ESI+-MS:
1
m/z = 342.0 [M + H]+. H NMR (400 MHz, CDCl3): δ = 8.53 (s,
1 H, Ar–H), 7.67 (d, 1 H, Ar–H), 7.28 (d, 1 H, Ar–H), 4.88 (s, 1
H, C5H3), 4.41 (s, 1 H, C5H3), 4.05 (s, 5 H, C5H5) ppm.
[PdCl({(η5-C5H5)}Fe{(η5-C5H3)N2C4H2NHC6H4CH3})(PPh3)]
(23): Red solid; yield 89%; m.p.: 246–247 °C. C39H33ClFeN3PPd
(772.38): calcd. C 60.65, H 4.31, N 5.44; found C 60.91, H 4.12, N
General Procedure for the Synthesis of 15 and 32: A mixture of
14 (1 mmol), Li2PdCl4 (1.1 mmol), and NaOAc (1 mmol) in dry
methanol (20 mL) was stirred for 24 h at room temperature. The
red solids (yield: 85%) were collected by filtration and washed sev-
eral times with methanol, and can be assigned as a dimeric complex
of palladium.[1] Because of its poor solubility in common solvents,
it was treated, without further purification, with the monophos-
phane ligand (PPh3 or DCPBA) (1.1 mmol) in dry CH2Cl2 at room
temp. for 1 h. The product was purified by passing it through a
short column of silica gel with CH2Cl2 as eluent. The first band
was collected and afforded 15 or 32.
5.64. IR (KBr): ν = 3079, 2924, 1602, 1507, 1436, 1398, 1302, 1258,
˜
1184, 1151, 1097, 1022, 997, 813, 748, 695 cm–1. ESI+-MS: m/z =
736.1 [M–Cl]+. 1H NMR (400 MHz, CDCl3): δ = 9.32 (s, 1 H, Ar–
H), 7.81 (m, 6 H, Ar–H), 7.43 (m, 9 H, Ar–H), 7.33 (d, 2 H, Ar–
H), 7.25 (d, 2 H, Ar–H), 6.50 (s, 1 H, Ar–H), 4.54 (s, 1 H, C5H3),
4.13 (s, 1 H, C5H3), 3.71 (s, 5 H, C5H5), 3.34 (s, 1 H, C5H3), 2.39 (s,
1 H,CH3) ppm. For other new compounds, please see Supporting
Information.
X-ray Crystal Structure Determination: Crystallographic data were
collected with a Bruker SMART APEX-II CCD diffractometer
with Mo-Kα radiation (λ = 0.071073 Å) at room temperature. The
data were corrected for Lorentz-polarization factors and absorp-
tion. Structures were solved by direct methods and refined by full-
matrix least-squares methods on F2 with the SHELX-97 pro-
gram.[26] An empirical absorption correction was applied using the
SADABS program. All non-hydrogen atoms were refined aniso-
tropically, and hydrogen atoms were placed in geometrically calcu-
lated positions. The details of crystal structure determination of
the eight complexes discussed are summarized in Table 7.
[PdCl({(η5-C5H5)}Fe{(η5-C5H3)NC5H3Br})(PPh3)] (15): Red solid;
yield 93%; m.p.: 219–220 °C. C33H26BrClFeNPPd (745.15): calcd.
C 53.19, H 3.52, N 1.88; found C 53.32, H 3.26, N 1.99. IR (KBr):
ν = 3120, 1592, 1494, 1433, 1391, 1308, 1238, 1188, 1159, 1099,
˜
1026, 993, 906, 852, 816, 746, 695 cm–1. ESI+-MS: m/z = 708.9
1
[M – Cl]+. H NMR (400 MHz, CDCl3): δ = 9.46 (s, 1 H, Ar–H),
7.78–7.86 (m, 6 H, Ar–H), 7.76 (d, 1 H, Ar–H), 7.27–7.47 (m, 9 H,
Ar–H), 7.16 (d, 1 H, Ar–H), 4.59 (s, 1 H, C5H3), 4.11 (s, 1 H,
C5H3), 3.71 (s, 5 H, C5H5), 3.33 (s, 1 H, C5H3) ppm.
[PdCl({(η5-C5H5)}Fe{(η5-C5H3)NC5H3Br})(DCPAB)] (32): Red so-
lid; yield 85%; m.p.: 192–193 °C. C41H47BrClFeN2PPd (876.41):
calcd. C 56.19, H 5.41, N 3.20; found C 56.33, H 5.22, N 3.38. IR
CCDC-804625 (for 3), -800308 (for 10), -808329 (for 11), -804624
(for 15), -804623 (for 17), -824513 (for 26), -800310 (for 27), and
-804897 (for 32) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(KBr): ν = 3046, 2924, 2849, 1589, 1492, 1444, 1375, 1304, 1259,
˜
1188, 1109, 1042, 1022, 993, 943, 847, 814, 734 cm–1. ESI+-MS:
1
m/z = 840.1 [M – Cl]+. H NMR (400 MHz, CDCl3): δ = 9.42 (s,
1 H, Ar–H), 7.73 (s, 1 H, Ar–H), 7.12–7.32 (m, 9 H, Ar–H), 4.53
(s, 1 H, C5H3), 4.29 (s, 1 H, C5H3), 3.90 (s, 5 H, C5H5), 3.19 (s, 1
H, C5H3), 2.53 (s, 6 H, NMe2), 3.33 (s, 1 H, C5H3), 1.26–2.09 (m,
22 H, PCy2) ppm.
Supporting Information (see footnote on the first page of this arti-
cle): General comments, synthesis and characterization data (melt-
4886
www.eurjic.org
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2011, 4878–4888

Palladacycles as Efficient Catalysts and Substrates
Table 7. Crystallographic data and structure refinement for 3·2CH2Cl2, 10, 11, 15, 17·(CH2Cl2)0.5, 26, 27, and 32·2CH2Cl2.
3·2CH2Cl2
10
11
15
Formula
Mr
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C44H36Cl5FeN2PPd
963.22
C39H31ClFeN3O2PPd
802.34
monoclinic
P21/c
22.989(5)
9.3512(19)
17.663(4)
90
105.97(3)
90
C80H6Cl2Fe2N6O4P2Pd2 C33H26BrClFeNPPd
1632.73
monoclinic
P21/n
11.5196(9)
17.9889(13)
38.505(3)
90
745.13
monoclinic
P21/c
9.3489(9)
16.0727(15)
19.7101(18)
90
triclinic
¯
P1
10.7161(18)
14.179(2)
15.680(3)
69.002(2)
70.677(2)
69.303(2)
2022.9(6)
1.581
α [°]
β [°]
96.2740(10)
90
7931.4(10)
1.367
91.1970(10)
90
2961.0(5)
1.671
γ [°]
V [Å3]
3650.6(13)
1.460
4
Dc [gcm–3]
Z
2
4
4
F(000)
GOF
R1, wR2
[IϾ2σ(I)][a]
R1, wR2
(all data)
972
1.036
0.0520,
0.1478
0.0654,
0.1602
1624
1.071
0.0773,
0.2408
0.0958,
0.2604
3312
1.026
0.0459,
0.0909
0.0910,
0.1010
1480
1.001
0.0363,
0.0764
0.0655,
0.0897
17·(CH2Cl2)0.5
26
27
32·2CH2Cl2
Formula
Mr
Crystal system
Space group
a [Å]
b [Å]
c [Å]
C77H62Cl4Fe2N4P2Pd2
1571.55
orthorhombic
P2(1)2(1)2(1)
9.970(2)
19.760(4)
33.830(7)
90
90
90
6665(2)
1.566
4
C39H39Cl3FeN3PPd
849.30
C37H35ClFeN3PPd
750.35
monoclinic
P21/c
23.912(2)
9.2147(9)
17.5050(17)
90
96.3810(10)
90
C43H51BrCl5FeN2PPd
1046.24
monoclinic
P2(1)
10.1963(9)
19.2579(16)
11.4529(10)
90
98.7990(10)
90
2222.4(3)
1.563
triclinic
¯
P1
10.0708(9)
13.3732(12)
16.1276(14)
89.3420(10)
79.3680(10)
72.5340(10)
2034.1(3)
1.300
α [°]
β [°]
γ [°]
V [Å3]
3833.1(6)
1.300
4
Dc [gcm–3]
Z
2
2
F(000)
GOF
R1, wR2
[IϾ2σ(I)][a]
R1, wR2
(all data)
3176
1.051
0.0491,
0.1390
0.0568,
0.1457
864
1.060
0.0345,
0.0982
0.0422,
0.1029
1528
1.016
0.0377,
0.0914
0.0568,
0.0987
1060
1.022
0.0440,
0.1085
0.0552,
0.1166
[a] R = Σ||Fo| – |Fc||/Σ|Fo|; wR = {Σ[w(Fo – Fc ) /Σ(Fo2)2]}1/2
.
2
2 2
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We are grateful to the National Natural Science Foundation of
China (NSFC) (grant number 20902043) and the Natural Science
Foundation of Henan Province and Henan Education Department,
China (grant numbers 102300410220 and 2009B150019) for finan-
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Received: June 20, 2011
Published Online: September 16, 2011
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