Synthesis and characterization of nickel inverse 9-metallacrown-3, palladium-silver, and dinuclear platinum complexes containing pyrazole-functionalized NHC ligands

Article abstract of DOI:10.1021/ic2012233

Three metallacrown nickel complexes [Ni₃(μ-OH)(L1) ₃](PF₆)₂ (1, L1 = 3-((N-methylimidazolylidenyl) methyl)-5-methylpyrazolate), [Ni₃(μ-OH)(L2)₃](PF ₆)₂ (2, L2 = 3-((N-mesitylimidazolylidenyl)methyl)-5- methylpyrazolate), and [Ni₃(μ-OH)(L3)₃](PF ₆)₂ (3, L3 = 3-((N-pyrimidin-2-ylimidazolylidenyl)methyl)- 5-methylpyrazolate) were obtained by the reactions of corresponding silver-NHC complexes with Raney nickel powder at 45 °C. The same reaction at 80 °C afforded [Ni₃(L2)₄](PF₆)₂ (4). The carbene-transfer reaction of the silver-carbene complex with [(η³-C₃H₅)PdCl]₂ yielded the heterotrimetallic complex [AgPd₂(η³-C ₃H₅)₂(L2)₂](PF₆) (5), whereas the carbene-transfer reaction with Pt(cod)Cl₂ gave [Pt ₂(L3)₂](PF₆)₂ (6). All of these complexes have been fully characterized by ESI-MS, NMR spectroscopy, and elemental analysis. The molecular structures of 1-6 were also studied by X-ray diffraction analysis. In 1-3, three nickel centers are bridged together by three pyrazole-NHC ligands and a hydroxide group, forming a 9-metallacrown-3 topology. Complex 4 is paramagnetic, consisting of two square-planar nickel(II) ions and one tetrahedral nickel ion in which three Ni ions are bridged by four pyrazolate units. In the mixed Pd-Ag complex 5, two palladium and one silver centers are bridged by two pyrazole-NHC ligands. Complex 5 showed good catalytic activity in the Sonogashira coupling reaction of aryl bromides and phenylacetylene under mild conditions typically catalyzed by Pd-Cu systems.

Full text of DOI:10.1021/ic2012233

ARTICLE
pubs.acs.org/IC
Synthesis and Characterization of Nickel Inverse 9-Metallacrown-3,
PalladiumꢀSilver, and Dinuclear Platinum Complexes Containing
Pyrazole-Functionalized NHC Ligands
Chao Chen,†,‡ Huayu Qiu,*,‡ and Wanzhi Chen*,†
†Department of Chemistry, Zhejiang University, Xixi Campus, Hangzhou 310028, People’s Republic of China
‡College of Materials, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036,
People’s Republic of China
S Supporting Information
b
ABSTRACT: Three metallacrown nickel complexes [Ni3(μ-
OH)(L1)3](PF6)2 (1, L1 = 3-((N-methylimidazolylidenyl)-
methyl)-5-methylpyrazolate), [Ni3(μ-OH)(L2)3](PF6)2 (2,
L2 = 3-((N-mesitylimidazolylidenyl)methyl)-5-methylpyrazo-
late), and [Ni3(μ-OH)(L3)3](PF6)2 (3, L3 = 3-((N-pyrimidin-
2-ylimidazolylidenyl)methyl)-5-methylpyrazolate) were obtained
by the reactions of corresponding silverꢀNHC complexes with
Raney nickel powder at 45 °C. The same reaction at 80 °C
afforded [Ni3(L2)4](PF6)2 (4). The carbene-transfer reaction
of the silverꢀcarbene complex with [(η3-C3H5)PdCl]2 yielded
the heterotrimetallic complex [AgPd2(η3-C3H5)2(L2)2](PF6) (5), whereas the carbene-transfer reaction with Pt(cod)Cl2 gave
[Pt2(L3)2](PF6)2 (6). All of these complexes have been fully characterized by ESI-MS, NMR spectroscopy, and elemental analysis.
The molecular structures of 1ꢀ6 were also studied by X-ray diffraction analysis. In 1ꢀ3, three nickel centers are bridged together by
three pyrazoleꢀNHC ligands and a hydroxide group, forming a 9-metallacrown-3 topology. Complex 4 is paramagnetic, consisting
of two square-planar nickel(II) ions and one tetrahedral nickel ion in which three Ni ions are bridged by four pyrazolate units. In the
mixed PdꢀAg complex 5, two palladium and one silver centers are bridged by two pyrazoleꢀNHC ligands. Complex 5 showed good
catalytic activity in the Sonogashira coupling reaction of aryl bromides and phenylacetylene under mild conditions typically
catalyzed by PdꢀCu systems.
’ INTRODUCTION
cations and anions in their cavities.8 A few well-defined pyrazole-
based metallacrown complexes have been reported, and their
physical properties have been studied.9 However, the metalla-
crown complexes involving N-heterocylic carbene ligands have
not been known so far.
Pyrazole derivatives have adjacent nitrogen atoms that could
incorporate more than one reactive metal atom in close proxi-
mity, thus facilitating potentially unique chemical reactivity and
physical properties. Many homo- or heterometallic complexes
of pyrazole derivatives containing short metalꢀmetal distances
have found wide applications in material science,1 bioinorganic
chemistry,2 and homogeneous catalysis.3 Although many poly-
nuclear complexes with pyrazoles or pyrazolates are known,4 the
most notable examples are the trinuclear cyclic complexes of
coinage metals. For example, the triangular pyrazole-based copper
complexes with a Cu3(μ-X)2 core (X = Cl, Br) may relate to the
active sites of particulate methane monooxygenase.5 The analo-
gous [Cu3(μ-OH)(μ-pz)3] complex (Hpz = pyrazole) acts as a
valuable catalyst or catalyst precursor in the peroxidative oxida-
tion of cyclohexane and cyclopentane to the corresponding
ketones and alcohols.6 Moreover, the macrocyclic structure has
a topology of metallacrown, which can be considered as analo-
gous of crown ethers with the repeat unit of ꢀ[metalꢀNꢀN]ꢀ
in which the metal atoms are oriented toward the center of the
cavity.7 Metallacrowns of different sizes are a new class of
molecular recognition agents that can selectively encapsulate
N-Heterocylic carbenes (NHCs) have been extensively stu-
died as ligands in organometallic chemistry and homogeneous
catalysis due to their strong σ-donor properties and ease
of preparation.10 Multidentate NHCs containing additional
nitrogen functionalities may significantly improve catalyst stabi-
lity, and their potential hemilability make ease of generation of
vacant coordination sites and catlytically active species. Multi-
dentate NHCs have been used for construction of multinuclear
metal complexes showing interesting optophysical properties.11
Transition-metal complexes of multidentate ligangs have found
wide applications in CꢀC coupling,12 hydrosilylation,13
polymerization,14 and hydrogenation reactions.15 Our interest
in this area involves the design and synthesis of metalꢀNHC
complexes bearing various functional groups, such as pyridine,
Received: June 7, 2011
Published: July 27, 2011
r
2011 American Chemical Society
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|

Inorganic Chemistry
ARTICLE
Scheme 1. Synthesis of Ligand Precursors
[Ni3(μ3ꢀOH)(L1)3](PF6)2 (1), [Ni3(μ3ꢀOH)(L2)3](PF6)2,
(2), and [Ni3(μ3ꢀOH)(L3)3](PF6)2 (3) were isolated as yellow
solids in 22ꢀ51% yields (Scheme 2). We have previously
reported the synthesis and structure of nickel hydroxide com-
plexes of NHC ligands, and the hydroxide ion is assumed to come
from water in solvent.18 In the case of [H2L2](PF6), another
trinuclear complex [Ni3(L2)4](PF6)2 (4) was also obtained
simultaneously. Complexes1 and 3 could alsobeobtained through
typical carbene-transfer reactions of silver complexes with Ni-
(PPh3)2Cl2, as we previously described in comparable yields.16
Interestingly, when we applied the same procedure to
[H2L2](PF6), we found that, at 25 °C, complex 2 was exclusively
afforded, whereas at 80 °C, complex 4 was obtained as the sole
product. However, we were not able to prepare analogous
[Ni3(L1)4](PF6)2 and [Ni3(L3)4](PF6)2 even at higher tem-
perature by the carbene-transfer route, and only 1 and 3 could be
obtained. Moreover, 2 is stable at 80 °C and could not convert to
4 upon heating. Complexes 1ꢀ4 have been fully characterized by
elemental analysis, NMR, and ESI spectroscopy.
pyrimidine, triazole, and naphthyridine, because such mixed C∧N
ligands would allow a further fine-tuning of the metal coor-
dination.16 We have reported that pyrazole-linked bis(NHC)
ligands were able to construct multinuclear silver and gold clusters
displaying luminescence.17 The dinuclear nickel complexes con-
taining pyrazole-functionalized bis(NHC) ligands showed re-
markable enhancement of catalytic activities in homogeneous
catalysis compared to corresponding mononuclear nickel com-
plexes.18 Other related dinuclear and multinuclear pyrazolate
NHC complexes have also been described.19 In this paper, we
describe the synthesis and characterization of a few pyrazole-
functionalized NHC ligands, the corresponding three trinuclear
metallacrown nickel complexes, [Ni3(μ-OH)(L1)3](PF6)2
(1, L1 = 3-((N-methylimidazolylidenyl)methyl)-5-methylpyra-
zolate), [Ni3(μ-OH)(L2)3](PF6)2 (2, L2 = 3-((N-mesitylimida-
zolylidenyl)methyl)-5-methylpyrazolate), and [Ni3(μ-OH)(L3)3]-
(PF6)2 (3, L3 = 3-((N-pyrimidin-2-ylimidazolylidenyl)methyl)-
5-methylpyrazolate), and a linear trinuclear nickel complex
[Ni3(L2)4](PF6)2 (4). Dinuclear palladium and platinum com-
plexes [AgPd2(η3-C3H5)2(L2)2](PF6) (5) and [Pt2(L3)2](PF6)2
(6) are also detailed.
The 1HNMR spectra of complexes 1 and 3 in dmso-d6 and 2 in
acetone-d6 show three singlet signals at 7.62, 7.39, and 6.01
ppm for 1; 7.85, 7.54, and 5.81 ppm for 2; and 8.08, 7.87, and 5.56
ppm for 3, which can be assigned to the imidazolylidene back-
bone and pyrazole CH protons. The resonance signals of the
methylene protons appear as doublets at 5.59 and 5.33 ppm for 1,
5.65 and 5.37 ppm for 2, and 5.61 and 5.19 ppm for 3,
respectively, illustrating that the rotation of the methylenes in
1ꢀ3 is prohibited. The resonances of hydroxide groups are
observed at 2.08 and 2.34 ppm for 1 and 3, respectively. However,
the hydroxide group of complex 2 is found at 0.79 ppm. The 13C
NMR spectra of 1ꢀ3 exhibit resonance peaks at 152, 154, and
158 ppm, which are ascribed to the carbenic carbon atoms.20 In
the ESI-MS spectra (positive ions in CH3CN), the peaks at
866.89, 1176.65, and 1054.74 amu are ascribed to [Ni3(μ-OH)-
(L)3(PF6)]+ and the peaks at 717.24, 1029.15, and 909.03 amu
are ascribed to [Ni3(μ-OH)(L)3]2+ fragments. The existence of
hydroxide ions is also supported by their IR spectra with broad
absorptions at 3398, 3431, and 3422 cmꢀ1 for 1ꢀ3. Complex 4
shows unusual 1H NMR and 13C NMR spectra. Although all the
1H NMR peaks are sharp and their intensities are consistent with
the formulation of 4, they appeared in the range of ꢀ3.44
to 10.69 ppm, whereas 13C NMR resonances appear in the range
of 12.0ꢀ200.2 ppm due to its paramagnetic nature induced by
the tetrahedral nickel(II) ion. In the ESI-MS spectrum (positive
ions, CH3CN) of 4, the peaks at 1347.12 and 646.45 amu are
ascribed to [Ni3(L2)4(PF6)]+ and [Ni3(L2)4]2+ fragments.
The structures of 1ꢀ3 were identified by X-ray single-crystal
diffraction analysis. The single crystals suitable for X-ray diffrac-
tion were grown by slow diffusion of Et2O into their CH3CN and
DMSO solutions. The three complexes have the same structures
consisting of a triangular Ni3 core in which three nickel ions are
linked by three NHC ligands and a μ3-OH group, and therefore,
only the structure of 1 is shown in Figure 1. The structures of 2
and 3 are given in the Supporting Information. In the structure of
1, each two nickel(II) ions are bridged by a pyrazolate ion,
forming a nine-membered ring capped by a hydroxide. Each
nickel(II) center is coordinated by two pyrazolates, one NHC,
and one OH group, displaying typical square-planar geometry.
Two pyrazolates coordinated to the same metal are trans-
arranged. The hydroxide ion is equally bonded to the three
metals in η3 fashion with an average NiꢀO distance of 1.93 Å and
is 0.620 Å out of the plane defined by three metal centers.
’ RESULTS AND DISCUSSION
Synthesis of Ligand Precursors. As shown in Scheme 1,
3-(chloromethyl)-5-methylpyrazole hydrochloride salt was synthe-
sized from reduction of ethyl 5-methyl-1H-pyrazole-3-carboxylate
and subsequent chlorination. Further reaction of 3-(chloromethyl)-
5-methyl-1-(tetrahydro-pyran-2-yl)pyrazole with N-alkylimidazole
after removal of tetrahydropyran and anion exchange with NH4PF6
gave the corresponding imidazolium salts, 3-(N-methylimidazoli-
umylmethyl)-5-methyl-1H-pyrazole ([H2L1](PF6)), 3-(N-mesity-
limidazoliumylmethyl)-5-methyl-1H-pyrazole ([H2L2](PF6)), and
3-(N-pyrimidin-2-ylimidazoliumylmethyl)-5-methyl-1H-pyra-
zole ([H2L3](PF6)) as white solids. The three imidazolium salts
have been characterized by NMR and elemental analysis. The 1H
NMR spectra of these imidazolium salts in dmso-d6 exhibit their
acidic imidazolium protons at 9.12, 9.70, and 10.22 ppm as
singlets and pyrazole NH protons at 12.67, 12.69, and 12.67
ppm as broad singlets, respectively.
Synthesis and Characterization of [Ni3(μ3ꢀOH)(L)3](PF6)2.
Direct reaction of metal powders with imidazolium salts is the
most convenient procedure for the synthesis of metalꢀNHC
complexes.16e A solution of silverꢀNHC complexes, resulted
from 5-(N-alkylimidazoliumylmethyl)-3-methyl-1H-pyrazole
salts in acetonitrile with an equivalent of Ag2O at 45 °C, was
treated with an excess of Raney nickel powder overnight and
yielded yellow solutions, and the trinuclear nickel complexes
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Inorganic Chemistry
ARTICLE
Scheme 2. Synthesis of the NickelꢀCarbene Complexes
Figure 2. Cationic structure of 4 representedbythermal ellipsoids at30%
probability. Hydrogen atoms have been omitted for clarity. Selected bond
distances (Å) and angles (deg): Ni(1)ꢀN(5) 1.954(5), Ni(1)ꢀN(9)
1.969(5), Ni(1)ꢀN(13) 1.971(5), Ni(1)ꢀN(1) 1.977(5), Ni(2)ꢀ
C(23) 1.861(6), Ni(2)ꢀC(6) 1.869(6), Ni(2)ꢀN(2) 1.922(5), Ni-
(2)ꢀN(6) 1.930(5), Ni(3)ꢀC(40) 1.860(6), Ni(3)ꢀC(57) 1.865(6),
Ni(3)ꢀN(14) 1.927(4,) Ni(3)ꢀN(10) 1.927(5), N(5)ꢀNi(1)ꢀ
N(9) 116.6(2), N(5)ꢀNi(1)ꢀN(13) 107.3(2), N(9)ꢀNi(1)ꢀN(13)
102.47(19), N(5)ꢀNi(1)ꢀN(1) 102.81(19), N(9)ꢀNi(1)ꢀN(1)
112.84(19), N(13)ꢀNi(1)ꢀN(1) 115.16(19), C(23)ꢀNi(2)ꢀC(6)
89.4(2), C(23)ꢀNi(2)ꢀN(2) 156.2(2), C(6)ꢀNi(2)ꢀN(2) 89.4(2),
C(23)ꢀNi(2)ꢀN(6) 87.8(2), C(6)ꢀNi(2)ꢀN(6) 156.0(2), N(2)ꢀNi-
(2)ꢀN(6) 102.51(19), C(40)ꢀNi(3)ꢀC(57) 89.8(2), C(40)ꢀNi(3)ꢀ
N(14) 157.9(2), C(57)ꢀNi(3)ꢀN(14) 88.3(2), C(40)ꢀNi(3)ꢀ
N(10) 88.4(2), C(57)ꢀNi(3)ꢀN(10) 156.0(2), N(14)ꢀNi(3)ꢀN(10)
101.92(19).
Figure 1. Cationic structure of 1 represented by thermal ellipsoids at 30%
probability. Hydrogen atoms have been omitted for clarity. Selected bond
distances (Å) and angles (deg): Ni(1)ꢀN(10) 1.852(7), Ni(1)ꢀN(1)
1.855(8), Ni(1)ꢀC(15) 1.862(9), Ni(1)ꢀO(1) 1.938(6), Ni(2)ꢀO(1)
1.929(6), Ni(2)ꢀN(2) 1.833(8), Ni(2)ꢀN(5) 1.869(8), Ni(2)ꢀC(24)
1.879(12), Ni(3)ꢀN(9) 1.857(8), Ni(3)ꢀN(6) 1.858(9), Ni(3)ꢀC(6)
1.871(12), Ni(3)ꢀO(1) 1.933(6), Ni(2)ꢀO(1)ꢀNi(3) 110.9(3), Ni-
(2)ꢀO(1)ꢀNi(1) 110.0(3), Ni(3)ꢀO(1)ꢀNi(1) 110.2(3), N(10)ꢀNi-
(1)ꢀN(1) 169.7(4), N(2)ꢀNi(2)ꢀN(5) 169.9(4), N(9)ꢀNi(3)ꢀN(6)
170.0(4), C(15)ꢀNi(1)ꢀO(1) 168.2(4), C(24)ꢀNi(2)ꢀO(1)
168.9(4), C(6)ꢀNi(3)ꢀO(1) 169.8(4).
The NiꢀNi distance is 3.174 Å, showing no metalꢀmetal
interaction. The NiꢀC and NiꢀN bond distances fall in the
ranges of 1.862ꢀ1.879 and 1.833ꢀ1.869 Å, respectively, which
are normal for square-planar nickel(II)ꢀNHC complexes.20 The
distances between the three nickel ions and μ3-OH are similar
[Ni(1)ꢀO(1) = 1.938(6), Ni(2)ꢀO(1) = 1.929(6), and Ni-
(3)ꢀO(1) = 1.933(6)] and longer than those reported for other
triangular complexes containing the [Ni3(μ3-O)] core.21 The
three pyrazole rings extend to the same side of the Ni3 plane with
dihedral angles between the pyrazole rings and the Ni3 plane
being 16.46, 13.51, and 15.85°, respectively, whereas the three
NHC moieties extend to the other side of the Ni3 plane.
Complexes 1ꢀ3 represent rare examples of inverse 9-metalla-
crown-3 with three repeating ꢀ[NiꢀNꢀN]ꢀ units supported
by NHC ligands. The center of the metallacycle accommodated a
triply bridging hydroxide. The most common metallacrown
structures containing three [MꢀNꢀN] units rely on the group
11 elements copper, silver, and gold.7,22 The tetracoordinated
nickel(II) complex with a pyramidal μ3-OH core is hard to
achieve considering the square-planar framework compared with
other hexacoordinated nickel(II) compounds with the similar
structure.
The molecular structure of 4 is shown in Figure 2. X-ray
analysis reveals that 4 contains a linearly arranged trinuclear
nickel moiety supported by four pyrazolateꢀNHC ligands. The
central Ni(II) ion is linked to each terminal Ni(II) ion through
two pyrazolate groups, forming a Ni2N4 ring with a twisted chair
conformation. The two terminal nickel(II) ions are coordinated
by two nitrogen atoms of pyrazoles and two carbon atoms of
imidazolylidenes, respectively, forming a distorted square-planar
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Inorganic Chemistry
ARTICLE
Scheme 3. Synthesis of 5
Scheme 4. Synthesis of [Pt2(L3)2](PF6)2 (6)
complexes from the pyrazole-imidazolium salts with Pd(cod)Cl2
or Pd(CH3CN)2Cl2 yielded pale-yellow solutions after removal
of AgCl. Unfortunately, we were not able to isolate PdꢀNHC
complexes because they quickly decomposed to palladium black.
When [(η3-C3H5)PdCl]2 was used, a mixed palladiumꢀsilver
complex 5 was obtained (Scheme 3). The complex was char-
1
acterized by H and 13C NMR spectra, elemental analysis, and
ESI spectroscopy. In its 1H NMR spectrum, the imidazolylidene
backbone and pyrazole CH protons appear at 7.78, 7.45, and
6.18 ppm as three singlets. The 13C NMR spectrum exhibits a
resonance peak at 175 ppm ascribed to the carbenic carbon
atoms. In the ESI-MS spectrum (positive ions, CH3CN), the
peaks at 962.99 and 427.21 amu were ascribed to [AgPd2(η3-
C3H5)2(L2)2]+ and [Pd(η3-C3H5)L2]+ fragments.
Single crystals of 5 were obtained by slow evaporation of its
acetonitrile solution. As shown in Figure 3, the structure of 5
consists of two tetracoordinated Pd(II) and one bicoordinated
Ag(I) atom. The coordination geometry around Pd is distorted
square-planar with one carbene, one pyrazole, and an ally group.
The Pd(1)ꢀC(6) distance (2.052(6)) is normal as compared to
those of known palladiumꢀNHC complexes (1.8ꢀ2.1 Å).23 The
Ag atom is linked by two pyrazoles in linear geometry with a
NꢀAgꢀN of 176.1(3)°. The AgꢀN distance (2.081(5) Å) is
also in the normal range of other silver complexes.24
Synthesis and Characterization of[Pt2(L3)2](PF6)2. As shown
in Scheme 4, the carbene-transfer reaction with [Pt(cod)Cl2] in
acetonitrile gave [Pt2(L3)2](PF6)2 (6) as a yellow solid. The
cationic section of 6 is depicted in Figure 4. The two platinum(II)
ions were linked by two pyrazolates, forming a Pt2N4 ring with a
boat conformation, and themolecule asa whole displays a beautiful
saddle-like conformation. Each Pt(II) ion is coordinated by two
pyrazoles, onepyrimidine, andoneNHCcarbon ina square-planar
geometry. The dihedral angle between the two pyrazole planes is
40.9°. The pyrimidine, pyrazole, and imidazolylidene rings of the
same ligand are roughly coplanar. In the ESI-MS spectrum
(positive ions, CH3CN), the peaks at 1012.85 and 434.61 amu
were ascribed to [Pt2(L3)2](PF6)+ and [PtL3]+ fragments.
Catalytic Studies. Transition metalꢀNHC complexes have
proven to be useful catalysts in various CꢀC coupling reactions.
The mixed PdꢀAg complex offers us an opportunity to examine
its efficiency for Sonogashira coupling. Although the PdꢀCu
system is more frequently used, the PdꢀAg system is also a
choice.25 The well-defined PdꢀAg catalyst would be superior to
the commonly used two-component catalysts taking account of
practical convenience. Under the conditions we previously
used,26 we examined the catalytic activity of 5. A brief investiga-
tion showed that 5 alone is inefficient for the coupling reaction of
p-acetylphenyl bromide and phenylacetylene. Activation of the
PdꢀAg catalyst was achieved by addition of 1 mol % of PPh3.
Phosphine is believed to stabilize low valent palladium species,
which is the actual catalyst. A survey of the reaction of aryl halides
with phenylacetylene using 1 mol % of 5 in the presence of
Cs2CO3 at 80 °C was done, and the results are given in Table 1.
The palladiumꢀsilver complex was found to be good for the
Figure 3. Structure of 5 represented by thermal ellipsoids at 30%
probability. Hydrogen atoms have been omitted for clarity. Selected
bond distances (Å) and angles (deg): Pd(1)ꢀC(6) 2.052(6), Pd(1)ꢀ
N(2) 2.086(5), Pd(1)ꢀC(18) 2.112(7), Pd(1)ꢀC(19) 2.144(7), Pd-
(1)ꢀC(20) 2.206(7), Ag(1)ꢀN(1) 2.081(5), C(6)ꢀPd(1)ꢀN(2)
86.5(2), C(6)ꢀPd(1)ꢀC(18) 100.2(2), N(2)ꢀPd(1)ꢀC(18) 172.9(2),
C(6)ꢀPd(1)ꢀC(19) 132.3(3), N(2)ꢀPd(1)ꢀC(19) 137.1(2), C(18)ꢀ
Pd(1)ꢀC(19) 37.9(3), C(6)ꢀPd(1)ꢀC(20) 168.8(2), N(2)ꢀPd(1)ꢀ
C(20) 104.7(2), C(18)ꢀPd(1)ꢀC(20) 68.6(3), C(19)ꢀPd(1)ꢀC(20)
37.8(3), N(1)ꢀAg(1)ꢀN(1)#1 176.1(3). Symmetry code: #1 ꢀx + 2,
y, ꢀz + 1/2.
geometry. The bond distances of NiꢀC [1.860(6)ꢀ1.869(6) Å]
and NiꢀN [1.922(5)ꢀ1.930(5) Å] and the bond angles between
adjacent donating atoms (within the bond angles from 87.8° to
102.51° for Ni(2) and 88.3° to 101.92° for Ni(3)) are in the
normal range as compared to many known nickelꢀNHC com-
plexes having a square-planar geometry.20 The central Ni(II) ion
is coordinated by four pyrazolate nitrogen atoms. Unlike the two
terminal nickel ions, the central nickel ion adopts a distorted
tetrahedral geometry with NꢀNi1ꢀN bond angles of 102.47ꢀ
116.59°. The steric hindrance of methyl groups on the pyrazole
rings prevents a typical square-planar structure. The tetrahedral
coordination geometry of nickel ion confirmed its paramagnetic
nature due to the presence of two unpaired electrons. The bond
distances of Ni(1)ꢀN are in the range of 1.954(5)ꢀ1.977(5) Å,
which are significantly longer than other NiꢀN distances around
the square-planar Ni(II) ions.
Synthesis and Characterization of [AgPd2(η3-C3H5)2-
(L2)2](PF6). The reactions of the in situ generated silverꢀNHC
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Inorganic Chemistry
ARTICLE
Table 1. Sonogashira Coupling Reactions Catalyzed by 5a
entry
R
X
R0
time (h)
yield %
1
2
P-C(O)CH3
H
Br
Br
Br
Br
Br
Br
Br
Br
Br
Br
Cl
phenyl
phenyl
phenyl
phenyl
phenyl
phenyl
phenyl
phenyl
1-butyl
1-hexyl
phenyl
8
8
100 (95)
95
3
P-CH3
8
97 (92)
100
4
P-OCH3
8
5
P-Cl
8
100
6
2-bromothiophene
2-bromothiophene
2-bromopyridine
P-C(O)CH3
P-C(O)CH3
P-C(O)CH3
8
79
7
16
16
24
24
24
98 (90)
100 (87)
80 (76)
75
8
9
10
Figure 4. Molecular structure of 6 represented by thermal ellipsoids at a
30% level. Selected bond lengths (Å) and angles (deg): Pt(1)ꢀC(18)
1.915(14), Pt(1)ꢀN(8) 1.982(10), Pt(1)ꢀN(11) 2.074(10), Pt(1)ꢀ
N(1) 2.096(10), Pt(2)ꢀC(6) 1.912(13), Pt(2)ꢀN(2) 1.970(10), Pt-
(2)ꢀN(5) 2.049(11), Pt(2)ꢀN(7) 2.061(10), C(18)ꢀPt(1)ꢀN(8)
86.7(5), C(18)ꢀPt(1)ꢀN(11) 79.0(5), N(8)ꢀPt(1)ꢀN(11) 164.2(4),
C(18)ꢀPt(1)ꢀN(1) 170.5(5), N(8)ꢀPt(1)ꢀN(1) 95.2(4,) N(11)ꢀ
Pt(1)ꢀN(1) 100.1(4), C(6)ꢀPt(2)ꢀN(2) 88.2(5), C(6)ꢀPt(2)ꢀ
N(5) 78.7(5), N(2)ꢀPt(2)ꢀN(5) 164.7(4), C(6)ꢀPt(2)ꢀN(7)
170.3(4), N(2)ꢀPt(2)ꢀN(7), 95.4(4) N(5)ꢀPt(2)ꢀN(7) 98.8(4).
11
60 (44)
a Reaction conditions: aryl halide, 1.0 mmol; alkyne, 1.2 mmol; complex
5, 1.0 mol %; PPh3, 1.0 mol %; Cs2CO3, 1.2 mmol; DMF, 3 mL; 80 °C.
GC yields and isolated yields are given in parentheses.
3-(Chloromethyl)-5-methylpyrazole hydrochloride. The
compound was synthesized from ethyl 3-methyl-pyrazole-5-carboxylate
1
according to the literature method.30 Yield: 11.0 g, 66%. H NMR
(CDCl3): 13.20 (br, NH, 2H), 6.40 (s, pyrazole CH, 1H), 4.73 (s, CH2,
2H), 2.54 (s, CH3, 3H). 13C NMR (CDCl3): 145.2, 144.5, 106.6, 33.6,
11.1. HRMS (TOF MS EI+) m/z: [M ꢀ HCl] calcd for C5H7ClN2
130.0298. Found 130.0299.
coupling of aryl bromides bearing electron-withdrawing or
electron-donating substituents and phenylacetylene in good-
to-excellent yields (entries 1ꢀ5). The catalyst system is also
efficient for the coupling reaction of heteroaryl bromides, and
the target products could be obtained in nearly quantita-
tive yields (entries 6ꢀ8), although the reaction time is longer.
Aliphatic alkynes show lower activity than aromatic alkynes
(entries 9ꢀ10). The Sonogashira reaction of 4-chloroacetophene
is also successful, giving a moderate yield within 24 h (entry 11).
In summary, we have synthesized and fully characterized a few
nickelꢀ, palladiumꢀ, and platinumꢀNHC complexes of pyr-
azoleꢀNHC ligands. Nickel complexes 1ꢀ3 have a topology of
inverse 9-metallacrown-3 with three repeated [NiꢀNꢀN] units,
and the metallacycles host a triply bridging hydroxide represent-
ing the first examples of metallacrown complexes supported by
NHC ligands. A linearly arranged Ni3 complex was obtained at
higher temperature. The same ligand forms a dinuclear platinum
complex showing versatile coordination behavior of pyrazoleꢀ
NHC ligands. The heterobimetallic complex 5 contains palladium
and silver ions and shows good catalytic activity in Sonogashira
coupling reactions of aryl bromides and phenylacetylene.
3-(Chloromethyl)-5-methyl-1-(tetrahydro-pyran-2-yl)-
pyrazole. 1,2-Dihydropyran (9.22 g, 110 mmol) was added to a solution
of 3-(chloromethyl)-5-methylpyrazole hydrochloride (8.3 g, 50 mmol) in
500 mLofdichloromethane at roomtemperature. Afterstirring overnight,
the mixture was concentrated to 100 mL and washed with a solution of
25 g of sodium bicarbonate in 400 mL of water, and the separated
organic phase was dried over MgSO4. The solvent was evaporated, and
the residue was recrystallized from petroleum ether to give a white solid.
Yield: 9.4 g, 88%. 1H NMR (CDCl3): 6.11 (s, pyrazole CH, 1H), 5.20
(dd, J = 2.0 and 10 Hz, thp CH, 1H), 4.57 (d, J = 12 Hz, CH2, 1H), 4.53
(d, J = 12 Hz, CH2, 1H), 4.03 (d, J = 7.2 Hz, thp CH, 1H), 3.62 (m, thp
CH2, 1H), 2.39 (m, thp CH2, 1H), 2.31 (s, CH3, 3H), 2.08 (m, thp CH2,
1H), 1.90 (m, thp CH2, 1H), 1.68 (m, thp CH2, 2H) 1.56 (m, thp CH2,
H). 13C NMR (CDCl3): 148.3, 140.6, 105.7, 84.5, 67.9, 39.3, 29.5, 24.9,
22.8, 11.0. HRMS (TOF MS EI+) m/z: calcd for C10H15ClN2O
214.0873. Found 214.0870.
3-(N-Methylimidazoliumylmethyl)-5-methyl-1H-pyrazole
hexafluorophosphate ([H2L1](PF6)). A solution of 3-(chloro-
methyl)-5-methyl-1-(tetrahydro-pyran-2-yl)pyrazole (2.14 g, 10 mmol)
and N-methylimidazole (1.23 g, 15 mmol) in toluene (10 mL) was
refluxed overnight. The resulting solid was dissolved in ethanol (25 mL)
and filtered. To the filtrate was added concentrated hydrochloric acid
(1.5 mL), and it was stirred for 3 h. The solvent was removed, the residue
was redissolved in water (25 mL), and then a saturated NH4PF6 aqueous
solution (30 mL) was added dropwise. The resulting precipitate was
washed with water, ethanol, and ether. Yield: 2.51 g, 78%. Anal. Calcd for
C9H13F6N4P: C, 33.55; H, 4.07; N, 17.39. Found: C, 33.86; H, 4.06; N,
17.31. 1H NMR (dmso-d6): 12.67 (s, NH, 1H), 9.12 (s, NCHN, 1H),
7.71, 7.67 (both s, NCHCHN, each 1H), 6.09 (s, pyrazole CH, 1H),
5.31 (s, CH2, 2H), 3.65 (s, CH3, 3H), 2.22 (s, CH3, 3H). 13C NMR
(dmso-d6): 145.7, 140.7, 136.9, 124.1, 122.9, 103.8, 46.7, 36.2, 10.9.
3-(N-Mesitylimidazoliumylmethyl)-5-methyl-1H-pyrazole
hexafluorophosphate ([H2L2](PF6)). According to the same
’ EXPERIMENTAL SECTION
General Procedures. All chemicals were of reagent grade quality
obtained from commercial sources and used as received. Ethyl 3-methyl-
pyrazole-5-carboxylate,27 [(η3-C3H5)PdCl]2,28 and Pt(cod)Cl229 were
synthesized according to the reported methods. NMR spectra were
recorded on a Bruker Avance-400 (400 MHz) spectrometer, 400 MHz
for 1H and 100 MHz for 13C. Chemical shifts (δ) were expressed in parts
per million downfield to TMS at δ = 0 ppm, and coupling constants (J)
were expressed in Hz. ESI-mass spectral data were acquired using a
Waters Micromass ZQ mass spectometer (+ mode, ESI source).
Elemental analyses were performed on a Flash EA 1112 instrument.
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Inorganic Chemistry
ARTICLE
Table 2. Summary of X-ray Crystallographic Data for 1 and 4ꢀ6
1 2CH3CN DMSO
4 2CH3CN
5 CH3CN
6 2CH3CN
3
3
3
3
3
formula
C
31H43F12N13Ni3P2O2S
C72H82F12N18Ni3P2
1665.63
C44H54AgF6N10Pd2P
1188.61
C28H28F12N14Pt2P2
1240.76
fw
1127.91
crystal system
space group
a/Å
triclinic
triclinic
monoclinic
C2/c
triclinic
P1
P1
P1
10.9545(12)
15.3178(18)
15.4704(19)
106.440(2)
2360.5 (5)
2
13.2854(14)
19.085(2)
19.144(2)
92.2230(10)
3958.2(7)
2
20.3269(8)
22.2835(8)
11.0602(5)
107.703(4)
4772.5(3)
4
9.7764(9)
12.1843(16)
16.3997(19)
86.770(2)
1862.7(4)
2
b/Å
c/Å
β/deg
V/Å3
Z
D/g cmꢀ3
cryst size/mm
reflns collected
ind reflns, Rint
goodness of fit on F2
R1, wR2 [I > 2σ(I)]
R1, wR2 (all data)
1.587
1.398
1.654
2.212
0.22 ꢁ 0.17 ꢁ 0.10
12 510
0.41 ꢁ 0.38 ꢁ 0.35
20 735
0.32 ꢁ 0.25 ꢁ 0.23
16 103
0.37 ꢁ 0.30 ꢁ 0.21
9742
8193, 0.1097
1.057
13 765, 0.0232
1.044
4168, 0.0716
1.032
6474, 0.0323
1.035
0.0948, 0.2265
0.1882, 0.2614
0.0638, 0.1727
0.1152, 0.2238
0.0645, 0.1708
0.0705, 0.1794
0.0495, 0.1159
0.0868, 0.1396
procedure as for compound [H2L1](PF6), [H2L2](PF6) was obtained
as a white solid. Yield: 3.54 g, 83%. Anal. Calcd for C17H21F6N4P: C,
47.89; H, 4.96; N, 13.14. Found: C, 47.41; H, 4.92; N, 12.75. 1H NMR
(dmso-d6): 12.69 (br, NH, 1H), 9.50 (s, NCHN, 1H), 8.00, 7.91 (both
d, J = 1.6 Hz, NCHCHN, each 1H), 7.15 (s, mesityl CH, 2H), 6.12 (s,
pyrazole CH, 1H), 5.45 (s, CH2, 2H), 2.33 (s, CH3, 3H), 2.24 (s,
mesityl CH3, 3H), 2.01 (s, mesityl CH3, 6H). 13C NMR (dmso-d6):
145.8, 141.0, 137.6, 134.7, 131.4, 130.0, 129.7, 124.5, 123.63, 103.7,
65.4, 20.9, 17.3, 10.8.
3-(N-Pyrimidin-2-ylimidazoliumylmethyl)-5-methyl-1H-
pyrazole hexafluorophosphate ([H2L3](PF6)). [H2L3](PF6)
was prepared similarly as [H2L1](PF6). Yield: 3.54 g, 83%. Anal.
Calcd for C12H13F6N6P: C, 37.32; H, 3.39; N, 21.76. Found: C, 37.01;
H, 3.34; N, 20.46. 1H NMR (dmso-d6): 12.67 (br, NH, 1H), 10.22 (s,
NCHN, 1H), 9.03 (d, J = 5.2 Hz, o-C4H3N, 2H), 8.43, 7.92 (both s,
NCHCHN, each 1H), 7.74 (t, J = 4.8 Hz, m-C4H3N, 1H), 6.16 (s,
pyrazole CH, 1H), 5.48 (s, CH2, 2H), 2.21 (s, CH3, 3H). 13C NMR
(dmso-d6): 160.4, 152.4, 144.9, 141.0, 135.9, 124.2, 122.9, 119.8,
104.2, 47.3, 10.8.
9H), 1.93 (s, mesityl CH3, 9H), 1.81 (s, mesityl CH3, 9H), 0.79 (s, OH,
1H). 13C NMR (dmso-d6): 154.0 (NiꢀC), 147.4, 146.6, 137.4, 134.3,
134.1, 132.8, 129.1, 128.9, 126.7, 123.5, 103.4, 47.7, 23.1, 20.6, 18.3, 15.9.
For 4: tan-yellow solid. Yield: 65 mg, 41%. Anal.Calcd for
C68H76F12N16Ni3P2: C, 51.58; H, 4.84; N, 14.15. Found: C, 51.64; H,
4.85; N, 14.33. The compound is paramagnetic. 1H NMR (acetone-d6):
10.69 (s, 4H), 6.62 (s, 4H), 5.14 (s, 4H), 4.96 (s, 4H), 4.82 (s, 4H), 2.89
(s, 8H), 2.06 (s, 24H), ꢀ1.72 (s, 12H), ꢀ3.44 (s, 12H). 13C NMR
(acetone-d6): 200.2, 138.6, 132.8, 130.5, 129.5, 129.4, 127.5, 127.1,
123.0, 122.8, 65.2, 19.5, 13.5, 12.0.
Synthesis of [Ni3(μ-OH)(L3)3](PF6)2 (3). Complex 3 was pre-
pared similarly as for 1 and isolated as a yellow soild. Yield: 48 mg, 30%.
Anal. Calcd for C36H34F12N18Ni3OP2: C, 36.01; H, 2.85; N, 21.00.
Found: C, 35.79; H, 2.79; N, 20.86. 1H NMR (dmso-d6): 8.95
(d, J = 5.2 Hz, o-C5H4N2, 6H), 8.08, 7.87 (all s, NCHCHN, each
3H), 6.95 (d, J = 4.8 Hz, m-C5H4N2, 3H), 5.56 (s, pyrazole CH, 3H),
5.61, 5.19 (both d, J = 16.4 Hz, CH2, 6H), 2.34 (s, OH, 1H), 1.43
(s, CH3, 9H). 13C NMR (dmso-d6): 158.3 (NiꢀC), 156.0, 151.2, 145.4,
141.7, 135.2, 124.1, 122.7, 103.3, 47.5, 14.6.
Synthesis of [Ni3(μ-OH)(L1)3](PF6)2 (1). A solution of [H2L1]-
(PF6) (128 mg, 0.4 mmol) in CH3CN (5 mL) was treated with Ag2O
(96 mg, 0.4 mmol). After the mixture was stirred at 45 °C for 2 h, an excess
of Raney nickel powder (ca. 100 mg) was added and stirred for 24 h. After
filtration through a plug of Celite, the solution was concentrated to ca.
1.0 mL. Addition of diethyl ether (10 mL) afforded 1as a yellow solid. Yield:
78 mg, 51%. Anal. Calcd for C27H37F12N12Ni3OP2: C, 32.15; H, 3.40; N,
Synthesis of [AgPd2(η3-C3H5)2(L2)2](PF6) (5). A solution of
[H2L2](PF6) (170 mg, 0.4 mmol) in CH3CN (5 mL) was treated
with Ag2O (96 mg, 0.4 mmol). The mixture was stirred at 45 °C for 2 h.
[(η3-C3H5)PdCl]2 (74 mg, 0.2 mmol) was then added to the solution at
room temperature and stirred for another 2 h. After filtration through a
plug of Celite, the filtrate was concentrated to ca. 2 mL. Addition of
diethyl ether (30 mL) gave 5 as a white solid. Yield: 169 mg, 76%. Anal.
1
16.66. Found: C, 32.41; H, 3.44; N, 16.17. H NMR (dmso-d6): 7.61
Calcd for C40H48AgF6N8Pd2P H2O: C, 42.72; H, 4.48; N, 9.96. Found:
1 3
(s, NCHCHN, 3H), 7.39 (s, NCHCHN, 3H), 6.01 (s, pyrazole CH, 3H),
5.59, 5.32 (both d, J = 16.8 Hz, CH2, 6H), 3.23 (s, CH3, 9H), 2.08 (s, OH,
1H), 1.51 (s, CH3, 9H). 13CNMR(dmso-d6): 152.3 (NiꢀC), 145.8, 125.2,
124.1, 104.5, 47.0, 36.7, 13.6.
C, 42.21; H, 4.24; N, 9.50. H NMR (dmso-d6): 7.78, 7.74 (both s,
NCHCHN, each 2H), 7.02 (s, mesityl CH, 2H), 6.94 (s, mesityl CH,
2H), 6.18 (s, pyrazole CH, 2H), 5.31 (d, J = 15.6 Hz, CH2, 4H), 5.14 (m,
CH2 + C3H5, 4H), 4.20 (d, J = 7.6 Hz, C3H5, 2H), 3.30 (s, C3H5, 2H),
3.17 (d, J = 13.6 Hz, C3H5, 2H), 2.60 (br, C3H5, 2H), 2.32 (s, CH3, 6H),
2.29 (s, mesityl CH3, 6H), 1.92 (s, mesityl CH3, 6H), 1.85 (s, mesityl
CH3, 6H). 13C NMR (dmso-d6): 175.4 (PdꢀC), 148.9, 145.2, 138.8,
136.8, 135.3, 134.9, 129.2, 129.0, 123.3, 122.3, 118.1, 102.5, 68.8, 65.3,
47.5, 21.0, 18.5, 17.9, 15.6, 14.5.
Synthesis of [Ni3(μ-OH)(L2)3](PF6)2 Et2O (2) and [Ni3-
3
(L2)4](PF6)2 (4). According to the same procedure as described for
1, complexes 2 and 4 were obtained simultaneously and isolated by
fractional crystallization. For 2: yellow solid. Yield: 38 mg, 22%. Anal.
Calcd for C55H68F12N12Ni3O2P2: C, 47.35; H, 4.91; N, 12.05. Found:
C, 47.29; H, 5.18; N, 12.30. 1H NMR (acetone-d6): 7.85, 7.54 (both s,
NCHCHN, each 3H), 7.09 (s, mesityl CH, 3H), 6.65 (s, mesityl CH,
3H), 5.81 (s, pyrazole CH, 3H), 5.65, 5.37 (both d, J = 18.0 Hz, CH2,
6H), 4.01 (s, CH3, 9H), 2.12 (s, mesityl CH3, 9H), 2.12 (s, mesityl CH3,
Synthesis of [Pt2(L3)2](PF6)2 (6). A solution of [H2L3](PF6)
(154 mg, 0.4 mmol) in CH3CN (5 mL) was treated with Ag2O (96 mg,
0.4 mmol) at 45 °C for 2 h. Pt(cod)Cl2 (114 mg, 0.4 mmol) was
then added to the solution at room temperature and stirred for 2 h.
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Inorganic Chemistry
ARTICLE
The resulting mixture was filtered through a plug of Celite to remove
AgCl, and the filtrate was concentrated to ca. 2 mL. Compound 6 was
obtained as a pale yellow solid after addition of 20 mL of diethyl ether.
Yield: 129 mg, 56%. Anal. Calcd for C24H22F12N12Pt2P2: C, 24.88; H,
1.91; N, 14.51. Found: C, 24.63; H, 2.21; N, 14.63. 1H NMR (dmso-d6):
9.19 (d, J = 4.8 Hz, m-C5H4N2, 2H), 8.38, 7.98 (both s, NCHCHN, each
2H), 8.17 (d, J = 5.6 Hz, m-C5H4N2, 2H), 7.68 (t, J = 5.2 Hz, o-C5H4N2,
2H), 6.75 (s, pyrazole CH, 2H), 5.92, 5.85 (both d, J = 17.6 Hz, CH2,
4H), 2.31 (s, CH3, 6H). 13C NMR (dmso-d6): 161.9 (PtꢀC), 159.5,
157.8, 152.0, 146.5, 143.5, 123.5, 121.1, 108.3, 48.7, 14.7.
I. O. Inorg. Chem. 2009, 48, 6960. (b) Contaldi, S.; Nicola, C. D.; Garau,
F.; Karabach, Y. Y.; Martins, L. D. R. S.; Monari, M.; Pandolfo, L.;
Pettinari, C.; Pombeiro, A. J. L. Dalton Trans. 2009, 4928. (c) Sachse, A.;
Demeshko, S.; Dechert, S.; Daebel, V.; Langeb, A.; Meyer, F. Dalton
Trans. 2010, 3903. (d) Kashiwame, Y.; Kuwata, S.; Ikariya, T. Chem.—
Eur. J. 2010, 16, 766.
(4) For reviews, see: (a) Sadimenko, A. P.; Basson, S. S. Coord. Chem.
Rev. 1996, 147, 247. (b) Klingele, J.; Dechert, S.; Meyer, F. Coord. Chem.
Rev. 2009, 253, 2698. (c) Kuwata, S.; Ikariya, T. Chem.—Eur. J. 2011,
17, 3542.
(5) Boꢁca, R.; Dlhꢀaꢁn, L.; Mezei, G.; Ortiz-Pꢀerez, T; Raptis, R. G.;
X-ray Diffraction Analysis. Single-crystal X-ray diffraction data
for 1ꢀ4 and 6 were collected at 298(2) K on a Siemens Smart/CCD
area-detector diffractometer with a Mo KR radiation (λ = 0.71073 Å),
and 5 was measured at 153(2) K on a Gemini Ultra Atlas/CCD area-
detector diffractometer with Cu KR radiation (λ = 1.54184 Å) by using
an ω-2θ scan mode. Unit-cell dimensions were obtained with least-
squares refinement. Data collection and reduction were performed using
the SMART and SAINT software or Oxford Diffraction CrysAlisPro
software.31 All structures were solved by direct methods and refined
against F2 by the full-matrix least-squares techniques.32 All non-hydro-
gen atoms were refined anisotropically. Hydrogen atoms were intro-
duced in their calculated positions. Details of the X-ray experiments and
crystal data are summarized in Table 2.
Telser, J. Inorg. Chem. 2003, 42, 5801.
(6) Nicola, C. D.; Karabach, Y. Y.; Kirillov, A. M.; Monari, M.;
Pandolfo, L.; Pettinari, C.; Pombeiro, A. J. L. Inorg. Chem. 2007, 46, 221.
(7) Mezei, G.; Zaleski, C. M.; Pecoraro, V. L. Chem. Rev. 2007,
107, 4933.
(8) (a) Kayser, L.; Pattacini, R.; Rogez, G.; Braunstein, P. Chem.
Commun. 2010, 46, 6461. (b) Zhang, J.; Teo, P.; Pattacini, R.; Kermagoret,
A.; Welter, R.; Rogez, G.; Hor, T. S. A.; Braunstein, P. Angew. Chem., Int.
Ed. 2010, 49, 4443. (c) Angaridis, P. A.; Baran, P.; Boꢁcꢁa, R.; Cervantes-
Lee, F.; Haase, W.; Mezei, G.; Raptis, R. G.; Werner, R. Inorg. Chem. 2002,
41, 2219.
(9) (a) Casarin, M.; Cingolani, A.; Nicola, C. D.; Falcomer, D.;
Monari, M.; Pandolfo, L.; Pettinari, C. Cryst. Growth Des. 2007, 7, 677.
(b) Halcrow, M. A. Dalton Trans. 2009, 2059. (c) Pꢀerez, J.; Riera, L. Eur.
J. Inorg. Chem. 2009, 4913. (d) Jones., L. F.; Kilner, C. A.; Halcrow, M. A.
Chem.—Eur. J. 2009, 15, 4667. (e) Jones, L. F.; Barrett, S. A.; Kilner,
C. A.; Halcrow, M. A. Chem.—Eur. J. 2008, 14, 223. (f) Viciano-
Chumillas, M.; Tanase, S.; de Jongh, L. J.; Reedijk, J. Eur. J. Inorg. Chem.
2010, 3403.
’ ASSOCIATED CONTENT
S
Supporting Information. Structural parameters for 1ꢀ6
b
as CIF files and the structural drawings of 2 and 3. This material is
(10) Hahn, F. E.; Jahnke, M. C. Angew. Chem., Int. Ed. 2008, 47, 3122.
(11) (a) Catalano, V. J.; Malwitz, M. A.; Etogo, A. O. Inorg. Chem.
2004, 43, 5714. (b) Catalano, V. J.; Malwitz, M. A. Inorg. Chem. 2003,
42, 5483. (c) Hu, X.; Tang, Y.; Gantzel, P.; Meyer, K. Organometallics
2003, 22, 612. (d) Rit, A.; Pape, T.; Hepp, A.; Hahn, F. E. Organome-
tallics 2011, 30, 334.
(12) (a) Liu, A.; Zhang, X.; Chen, W. Organometallics 2009,
28, 4868. (b) Ellul, C. E.; Reed, G.; Mahon, M. F.; Pascu, S. I.;
Whittlesey, M. K. Organometallics 2010, 29, 4097. (c) Chiu, P. L.; Lai,
C.-L.; Chang, C.-F.; Hu, C.-H.; Lee, H. M. Organometallics 2005,
24, 6169.
(13) (a) Poyatos, M.; Maisse-Franc-ois, A.; Bellemin-Laponnaz, S.;
Gade, L. H. Organometallics 2006, 25, 2634. (b) Lv., C.; Gu, S.; Chen,
W.; Qiu, H. Dalton Trans. 2010, 39, 4198.
(14) Li, W.; Sun, H.; Chen, M.; Wang, Z.; Hu, D.; Shen, Q.; Zhang,
Y. Organometallics 2005, 24, 5925.
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: chenwzz@zju.edu.cn. Fax: 0086-571-88273314.
’ ACKNOWLEDGMENT
We gratefully acknowledge the financial support of the
National Natural Science Foundation of China (20872129 and
21072170) and the Fundamental Research Fund for the Central
Universities (2010QNA3004) for financial support.
’ REFERENCES
(15) Fogler, E.; Balaraman, E.; Ben-David, Y.; Leitus, G.; Shimon,
L. J. W.; Milstein, D. Organometallics 2011, 30, 3826.
(1) (a) Rawashdeh-Omary, M. A.; Rashdan, M. D.; Dharanipathi, S.;
Elbjeirami, O.; Ramesh, P.; Dias, H. V. R. Chem. Commun. 2011,
47, 1160. (b) Hou, L.; Shi, W.-J.; Wang, Y.-Y.; Wang, H.-H.; Cui, L.;
Chen, P.-X.; Shi, Q.-Z. Inorg. Chem. 2011, 50, 261. (c) Jozak, T.; Sun, Y.;
Schmitt, Y.; Lebedkin, S.; Kappes, M.; Gerhards, M.; Thiel, W. R. Chem.
—Eur. J. 2011, 17, 3384. (d) Fujisawa, K.; Ishikawa, Y.; Miyashita, Y.;
Okamoto, K. Inorg. Chim. Acta 2010, 363, 2977. (e) Wang, K.-W.; Chen,
J.-L.; Cheng, Y.-M.; Chung, M.-W.; Hsieh, C.-C.; Lee, G.-H.; Chou,
P.-T.; Chen, K.; Chi, Y. Inorg. Chem. 2010, 49, 1372.
(2) (a) Frensch, L. K.; Pr€opper, K.; John, M.; Demeshko, S.;
Br€uckner, C.; Meyer, F. Angew. Chem., Int. Ed. 2011, 50, 1420.
(b) Dougan, S. J.; Melchart, M.; Habtemariam, A.; Parsons, S.; Sadler,
P. J. Inorg. Chem. 2006, 45, 10882. (c) Kelly, M. E.; Dietrich, A.; Gꢀomez-
Ruiz, S.; Kalinowski, B.; Kaluderoviꢀc, G. N.; M€uller, T.; Paschke, R.;
Schmidt, J.; Steinborn, D.; Wagner, C.; Schmidt, H. Organometallics
2008, 27, 4917. (d) Kennedy, A. R.; Florence, A. J.; McInnes, F. J.;
Wheate, N. J. Dalton Trans. 2009, 7695. (e) Sun, R. W.-Y.; Ng, M. F.-Y.;
Wong, E. L.-M.; Zhang, J.; Chui, S. S.-Y.; Shek, L.; Lau, T.-C.; Che, C.-M.
Dalton Trans. 2009, 10712.
(16) (a) Xi, Z.; Zhang, X.; Chen, W.; Fu, S.; Wang, D. Organometallics
2007, 26, 6636. (b) Zhang, X.; Liu, A.; Chen, W. Org. Lett. 2008, 10, 3849.
(c) Liu, B.; Zhang, Y.; Xu, D.; Chen, W. Chem. Commun. 2011, 47, 2883.
(d) Gu, S.; Xu, H.; Zhang, N.; Chen, W. Chem.—Asian. J. 2010, 5, 1677.
(e) Liu, B.; Xia, Q.; Chen, W. Angew. Chem., Int. Ed. 2009, 48, 5513.
(17) Zhou, Y.; Chen, W. Organometallics 2007, 26, 2742.
(18) (a) Zhou, Y.; Xi, Z.; Chen, W.; Wang, D. Organometallics
2009, 27, 5911. (b) Xi, Z.; Zhou, Y.; Chen, W. J. Org. Chem. 2008,
73, 8497.
(19) (a) Scheele, U. J.; John, M.; Dechert, S.; Meyer, F. Eur. J. Inorg.
Chem. 2008, 373. (b) Jeon, S.-J.; Waymouth, R. M. Dalton Trans.
2008, 437. (c) Scheele, U. J.; Georgiou, M.; John, M.; Dechert, S.;
Meyer, F. Organometallics 2008, 27, 5146. (d) Zhou, Y.; Zhang, X.;
Chen, W.; Qiu, H. J. Organomet. Chem. 2008, 693, 205. (e) Liu, B.; Liu,
B.; Zhou, Y.; Chen, W. Organometallics 2010, 29, 1457.
(20) (a) Li, F.; Hu, J. J.; Koh, L. L.; Hor, T. S. A. Dalton Trans.
2010, 5231. (b) Ray, S.; Shaikh, M. M.; Ghosh, P. Eur. J. Inorg. Chem.
2009, 13, 1932. (c) Zhang, C.; Wang, Z. Organometallics 2009, 28, 6507.
(e) Berding, J.; van Dijkman, T. F.; Lutz, M.; Spekb, A. L.; Bouwman, E.
Dalton Trans. 2009, 6948. (f) Zhang, X.; Liu, B.; Liu, A.; Xie, W.; Chen,
(3) (a) Penkova, L. V.; Maciag, A.; Rybak-Akimova, E. V.; Haukka,
M.; Pavlenko, V. A.; Iskenderov, T. S.; Kozzowski, H.; Meyer, F.; Fritsky,
8677
dx.doi.org/10.1021/ic2012233 |Inorg. Chem. 2011, 50, 8671–8678

Inorganic Chemistry
ARTICLE
W. Organometallics 2009, 28, 1336. (g) Varonka, M. S.; Warren, T. H.
Organometallics 2010, 29, 717.
(21) Biswas, B.; Pieper, U.; Weyherm€uller, T.; Chaudhuri, P. Inorg.
Chem. 2009, 48, 6781.
(22) (a) Mohamed, A. A. Coord. Chem. Rev. 2010, 254, 1918.
(b) Tsupreva, V. N.; Titov, A. A.; Filippov, O. A.; Bilyachenko, A. N.;
Smol’yakov, A. F.; Dolgushin, F. M.; Agapkin, D. V.; Godovikov, I. A.;
Epstein, L. M.; Shubina, E. S. Inorg. Chem. 2011, 50, 3325.
(23) (a) Frey, G. D.; Sch€utz, J.; Herdtweck, E.; Herrmann, W. A.
Organometallics 2005, 24, 4416. (b) Li, F. W.; Bai, S.; Andy Hor, T. S.
Organometallics 2008, 27, 672. (c) Dyson, G.; Frison, J.; Simonovic, S.;
Whitwood, A. C.; Douthwaite, R. E. Organometallics 2008, 27, 281.
(d) Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan, S. P. Organome-
tallics 2004, 23, 3752.
(24) Garrison, J. C.; Youngs, W. J. Chem. Rev. 2005, 11, 105.
(25) Chinchilla, R.; Nꢀajera, C. Chem. Rev. 2007, 107, 874.
(26) Gu, S.; Chen, W. Organometallics 2009, 28, 909.
(27) Skinner, P. J.; Cherrier, M. C.; P. Webb, J.; Shin, Y.-J.;
Gharbaoui, T.; Lindstrom, A.; Hong, V.; Tamura, S. Y.; Dang, H. T.;
Pride, C. C.; Chen, R.; Richman, J. G.; Connolly, D. T.; Semple, G.
Bioorg. Med. Chem. Lett. 2007, 17, 5.
(28) Dent, W. T.; Long, R.; Wilkinson, A. J. J. Chem. Soc. 1964, 1585.
(29) McDermott, J. X.; White, J. F.; Whitesides, J. M. J. Am. Chem.
Soc. 1976, 98, 6521.
(30) Schenck, T. G.; Downes, J. M.; Milne, C. R. C.; Mackenzie, P. B.;
Boucher, T. G.; Whelan, J.; Bosnich, B. Inorg. Chem. 1985, 24, 2334.
(31) (a) SMART-CCD Software, version 4.05; Siemens Analytical
X-ray Instruments: Madison, WI, 1996. (b) CrysAlisPro; Oxford Diffrac-
tion Ltd.: Oxford, U.K., 2008.
(32) Sheldrick, G. M. SHELXTL, version 5.1; Bruker AXA Inc.:
Madison, WI, 1998.
8678
dx.doi.org/10.1021/ic2012233 |Inorg. Chem. 2011, 50, 8671–8678