A Y-shaped tris-N-heterocyclic carbene for the synthesis of simultaneously chelate-monodentate dipalladium complexes

Article abstract of DOI:10.1021/om200820s

A Y-shaped tris-NHC ligand has been obtained and coordinated to palladium, affording metal complexes with novel topological properties. The tris-NHC ligand is capable of coordinating the two metals, affording two different coordination environments. The X

Full text of DOI:10.1021/om200820s

ARTICLE
pubs.acs.org/Organometallics
A Y-Shaped Tris-N-Heterocyclic Carbene for the Synthesis of
Simultaneously Chelate-Monodentate Dipalladium Complexes
Sergio Gonell, Macarena Poyatos,* Josꢀe A. Mata, and Eduardo Peris*
Departamento de Química Inorgꢀanica y Orgꢀanica, Universitat Jaume I, Avenida Vicente Sos Baynat s/n, 12071 Castellꢀon, Spain
S Supporting Information
b
ABSTRACT: A Y-shaped tris-NHC ligand has been obtained and coordi-
nated to palladium, affording metal complexes with novel topological proper-
ties. The tris-NHC ligand is capable of coordinating the two metals, affording
two different coordination environments. The X-ray molecular structure of
two of the complexes are reported. The three new Pd complexes provide good
activity in the hydroarylation of alkynes, although we did not find any clear
evidence about the benefits of using the dimetallic palladium species in the
catalytic outcomes.
’ INTRODUCTION
of bridging two metals in two different coordination environ-
ments while facilitating a higher stability and providing access to
potential stereoelectronic versatility. With this in mind, we now
describe the preparation of a Y-shaped tris-NHC ligand and its
coordination to Pd.
With the obvious restricted number of transition metals for
the preparation of new metal complexes, the advance in the
preparation of efficient homogeneous catalysts relies on the
design of new ligands with improved stereoelectronic properties.
In the field of homogeneous catalysis, the main advances refer
to improvements of known reactions, especially aiming for
environmentally benign and economically attractive synthetic
procedures.1 Sophisticated ligands are now being designed
that do far more than just fulfill their traditional spectator roles
by binding to the metal and providing a sterically defined binding
pocket for the substrate in homogeneous transition-metal
catalysis.2 In this context, N-heterocyclic carbenes have emerged
as a very useful type of ligands for homogeneous catalyst design,
due to their high topological and electronic versatility, combined
with a great coordination capability.3 The library of known N-
heterocyclic carbene ligands now covers an extraordinary wide set
of architectures, and every year, new NHC-based ligands with
novel topologies are designed in order to afford homogeneous
catalysts and materials with improved properties.
We have recently been interested in the preparation of multi-
functional catalysts for their use in tandem catalytic processes.4 In
this regard, the use of 1,2,4-trimethyltriazolyl-diylidene (ditz),5
as a bridging ligand for the preparation of homo- and hetero-
dimetallic complexes, was extraordinarily useful in the develop-
ment of a wide set of tandem catalytic reactions.6 Although ditz
has constituted an excellent starting point for the development of
catalysts with excellent applications in tandem catalysis, it may
not be stable enough to allow its use under the harsh conditions
required for some catalytic reactions and also does not allow for
the modification of its stereoelectronic properties. Within this
context, we decided to design a new ligand that may overcome
the two mentioned limitations, but keeping the coordination
versatility shown by ditz. The new ligand should thus be capable
’ RESULTS AND DISCUSSION
The triazolium salt 1 (Scheme 1) can be prepared by a four-
step procedure starting from 5-chloro-1-methyl-4-nitroimida-
zole. All four steps provided high yields in the formation of all
the reaction intermediates, so the overall yield in the formation of
1 was moderate (ca. 50%). The triazolium salt 1 was specifically
designed for the generation of a Y-shaped tris-NHC ligand
capable of simultaneously binding to two metals in a bis-chelat-
ing/monodentate coordination form.
The tetramethyl-trisimidazolium salt 1 generated a tris-NHC
ligand that was coordinated to palladium by the procedure
shown in Scheme 2. The reaction of 1 with an equimolecular
amount of Pd(OAc)2 in refluxing acetonitrile in the presence of
KI afforded complex 2 (yield 90%), in which the ligand is
chelating the Pd(II) center. Complex 2 is an interesting scaffold
for the preparation of dimetallic complexes, because it contains a
remaining imidazolium unit, which can be used for the coordina-
tion of a second complex fragment. In fact, the reaction of 2 with
an equivalent of Pd(OAc)2 in refluxing acetonitrile and KI affords
the dipalladium complex 3 in a 50% yield. This relatively low
yield may be due to loss of the product during the purification
1
procedure (column chromatography), because the H NMR
spectrum of the reaction products suggests that a much higher
yield is obtained in the synthetic reaction. Complex 3 can also be
obtained by direct reaction of the trisimidazolium salt 1 with
Received: September 1, 2011
Published: October 19, 2011
r
2011 American Chemical Society
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Scheme 1
2 equiv of Pd(OAc)2 in refluxing acetonitrile and in the presence
of KI. Complex 3 contains two palladium fragments, in which
the two metal centers are in two different coordination environ-
ments. The reaction of 3 with pyridine affords the pyridine adduct
4 in 73% yield. All complexes 2À4 were characterized by means of
NMR and high-resolution mass spectroscopies. Complexes 2 and
4 gave satisfactory elemental analyses, whereas complex 3 failed to
give a satisfactory one probably due to the presence of a persistent
amount of solvent or moisture.
and a monodentate form. The monocarbene palladium fragment
completes its coordination sphere with two trans iodide ligands,
and a pyridine. The complex fragment with the chelate ligand
completes its pseudosquare planar sphere with two cis iodide
ligands. The average PdÀC distance in the chelate fragment is
1.98 Å, similar to the analogue distance shown by 2. The PdÀC
distance in the monocarbene fragment is 1.960 Å. The coordina-
tion plane of the palladium monocarbene is quasiperpendicular
with respect to the plane of the coordinated azole ring (85.5°).
The chelating imidazolylidenes are at an angle of 63° with respect
to the metal coordination plane of the biscarbene unit. Interest-
ingly, the coordination plane of the chelate palladium fragment is
quasiperpendicular with respect to the plane of the monocarbene
azole ring that is coordinated to the other palladium center
(88.4°), thus implying that the dimetallic complex 4 depicts a
lower “chair angle” compared with that shown by the mono-
metallic complex 2 (97.4°), as depicted in Figure 3. This sharper
angle of the ligand brings the two metal atoms at a close distance
of 6.7 Å.
To explore the catalytic properties of 2À4, we thought that the
Fujiwara hydroarylation of acetylenes7 would be a good model
reaction because a number of Pd(II)ÀNHC complexes have shown
good activity toward this high atom-economy CÀH activation
process.8À10 For a first catalyst screening, we performed the
reaction of pentamethylbenzene with ethyl propiolate at 80 °C in
a mixture of trifluoroacetic acid and 1,2-dichoroethane (4:1 in
volume), using a 0.1 or 0.05 mol % catalyst loading. We also used
Pd(OAc)2 for comparative purposes. As can be seen from the
data shown in Table 1, catalyst 3 is the one that provides better
activities in terms of conversions, although all three PdÀNHC
catalysts provided low selectivity. In terms of conversion, catalyst
1
The H NMR spectrum of 2 is consistent with the 2-fold
symmetry of the complex. A distinct signal at δ 9.6 is attributed to
the proton at the azolium ring. The 13C NMR shows the signal
due to the carbene carbon atoms at 167 ppm. The dipalladium
complexes 3 and 4 also show NMR spectra that confirm their
2-fold symmetry. The most significant signals in the 13C NMR
spectra are those due to the carbene carbon atoms at 166.9
(chelate) and 142.3 (monodentate) ppm for 3, and 167.0
(chelate) and 148.6 (monodentate) ppm for 4.
The molecular structures of 2 and 4 were confirmed by means
of X-ray diffractometry. Figures 1 and 2 show the plot of the
molecular structures of complexes 2 and 4, respectively.
The molecular structure of 2 consists of a palladium center
with a chelating bis-NHC ligand. Two iodide ligands in a cis
disposition complete the coordination sphere about the metal
center. The average PdÀCcarbene distance is 1.993 Å. The two
coordinated imidazolylidenes lie at an angle of 65.3° relative to
the metal coordination plane. The molecule has a chair con-
formation, with the azolium ring at an angle of 97.4° (“chair
angle”, Figure 3) with respect to the metal coordination plane.
The molecular structure of 4 consists of a dipalladium complex
in which the ligand is bridging the two metal centers in a bis-chelating
Scheme 2
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Figure 3. Side-on view of complexes 2 and 4 with “chair angle”.
Figure 1. Plot of the molecular structure of compound 2. Hydrogen
atoms and the counterion (BF4À) are omitted for clarity. Selected bond
lengths (Å) and angles (°): Pd(1)ÀC(4) 1.993(4), Pd(1)ÀC(7)
1.992(5), Pd(1)ÀI(1) 2.642(4), Pd(1)ÀI(2) 2.666(5); C(4)ÀPd-
(1)ÀC(7) 85.17(18).
Table 1. Hydroarylation of Pentamethylbenzene with Ethyl
Propiolatea
entry
cat. (mol %)
conv. (%)b
yield (%)b
a
b
c
1
2
3
4
5
6
2 (0.1)
48
65
56
40
33
34
30
48
45
35
29
28
18
17
11
5
0
0
0
0
0
0
3 (0.1)
4 (0.1)
Pd(OAc)2 (0.1)
3 (0.05)
4 (0.05)
4
6
Figure 2. Plot of the molecular structure of compound 4. Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles (°):
Pd(1)ÀC(4) 1.997(8), Pd(1)ÀC(7) 1.972(8), Pd(1)ÀI(1) 2.642(8),
Pd(1)ÀI(2) 2.650(8), Pd(2)ÀC(1) 1.960(7), Pd(2)ÀI(3) 2.590(8),
Pd(2)ÀI(4) 2.593(8), Pd(2)ÀN(7) 2.106(6), Pd(1)ÀPd(2) 6.722(8);
C(4)ÀPd(1)ÀC(7) 85.4(3).
a Reactions conditions: 2.65 mmol of pentamethylbenzene, 2.65 mmol
of ethyl propiolate, 4 mL of trifluoroacetic acid (TFA), 1 mL of 1,2-di-
chloroethane (DCE) at 80 °C. Reaction time = 5 h. b Conversions (referred
to pentamethylbenzene) and yields determined by 1H NMR spectroscopy
using diethyl phthalate (2.65 mmol) as an internal standard.
3 compares well with the bisbenzymidazolylidene-palladium(II)-
dibromide described by Basato and co-workers,8,9 but their
catalyst was far more selective in the formation of the Z product
(a). As in their studies,9 alkyne polymerization and hydration by
traces of water are found to be serious competitive reactions, as
confirmed by the detection of such a byproduct by 1H NMR.
Compound 3 was tested toward other substrates (Table 2). As
can be seen from the data shown in Table 2, 3 provided good
activity in the conversion of all combinations of arenes and
acetylenes used, affording better performances than previously
reported catalysts for the same reaction (similar yields were
obtained for other systems, but for longer reaction times).8,9
Interestingly, catalyst 3 is able to provide good catalytic activity
even when the reactions are carried out at room temperature
(entries 5À8), a result that is even more remarkable if we take
into account the low catalyst loading used for these reactions
(0.1 mol %). As expected, the catalyst outcome is improved by
removing the iodide ligands with the addition of AgOAc
(compare entries 5 and 6, and also 9 and 10).
’ CONCLUSIONS
In summary, we have obtained a new trisimidazolium salt that
generates a tris-NHC ligand with unusual topological properties.
The ligand is able to bind two palladium fragments, affording two
different coordination environments. The new complexes have
provided good activity in the hydroarylation of alkynes, but we
have not been able to provide clear evidence about the benefits of
using the dimetallic species in the outcome of this catalytic
reaction. Further studies in order to obtain other homo- and
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Table 2. Hydroarylation of Alkynes Using Catalyst 3a,c
a Reactions conditions: 0.1 mol % of catalyst 3, 2.65 mmol of alkyne, 2.65 mmol of arene, reaction time = 5 h, 4 mL of trifluoroacetic acid (TFA), 1 mL
of 1,2-dichloroethane (DCE). b With addition of 5.3 Â 10À3 mmol of AgOAc. c Yields determined by 1H NMR spectroscopy using diethyl phthalate
(2.65 mmol) as an internal standard.
heterodimetallic complexes based on this ligand are underway.
We believe that the use of this ligand can provide interesting
catalytic consequences in the near future.
were recorded on a Varian Innova 300 and 500 MHz, using MeOD-d4 and
DMSO-d6 as solvents. Exact mass analysis was realized using a Q-TOF
premier mass spectrometer with an electrospray source (Waters, Manchester,
U.K.) operating at a resolution of ca. 16 000 (fwhm). Elemental analyses
were carried out on a EuroEA3000 Eurovector analyzer.
Synthesis of Compound A. 5-Chloro-1-methyl-4-nitroimidazole
(5 g, 30.35 mmol) and imidazole (1.74 g, 25.3 mmol) were dissolved in
75 mL of acetonitrile, and then KOH (3.2 g, 50.6 mmol) was added. The
resulting mixture was refluxed for 2 h. Afterward, the reaction was
’ EXPERIMENTAL SECTION
General Procedures. All operations were carried out by using
standard Schlenk techniques under a nitrogen atmosphere. All other
reagents were used as received from commercial suppliers. NMR spectra
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filtered and the solvent was removed under vacuum, giving a dark brown
solid. Compound A was obtained as a brown solid after purification by
sublimation in vacuum at 120 °C. Yield: 4.7 g, 96%. 1H NMR (500 MHz,
MeOD-d4): δ 8.01 (s, 1H, CHimid), 7.86 (s, 1H, CHimid), 7.45 (s, 1H,
CHimid), 7.27 (s, 1H, CHimid), 3.58 (s, 3H, NCH3). 13C NMR (75 MHz,
MeOD-d4): δ 140.3 (CHimid), 136.4 (CHimid), 130.5 (CHimid), 125.4
(Cq), 122.38 (CHimid), 122.2 (Cq), 32.3 (NCH3). Anal. Calcd for
C7H7N5O2 (193.16): C, 43.53; H, 3.65; N, 36.26. Found: C, 43.40; H,
3.40; N, 36.15. Electrospray MS (20 V, m/z): 194.1 [M + H]+.
Synthesis of Compound B. A mixture of compound A (1 g, 5.18
mmol) and Raney Nickel (2 mL, activated catalyst 50% slurry in water)
in methanol (50 mL) was stirred at room temperature under a H2
atmosphere (1 atm) for 4 h. Afterward, the suspension was filtered
through a pad of Celite and the solvent was removed under vacuum,
giving the desired product as a brown oil. The oil so isolated was used in
the next step without further purification. Yield: 804 mg, 95%. 1H NMR
(300 MHz, MeOD-d4): δ 7.8 (s, 1H, CHimid), 7.3 (s, 1H, CHimid), 7.2 (s,
1H, CHimid), 7.1 (s, 1H, CHimid), 3.4 (s, 3H, NCH3). 13C NMR (75
MHz, MeOD-d4): δ 141.4 (CHimid), 136.5 (Cq), 133.8 (CHimid), 130.0
(CHimid), 128.2 (Cq), 123.8 (CHimid), 31.1 (NCH3). Electrospray MS
(20 V, m/z): 186.1 [M + Na]+.
30.6 (NCH3).). Anal. Calcd for C13H17BF4I2N6Pd (704.34): C, 22.17;
H, 2.43; N, 11.93. Found: C, 22.20; H, 2.52; N, 11.84. Electrospray MS
(20 V, m/z): 616.8 [M]+.
Synthesis of Compound 3. A mixture of Pd(OAc)2 (100 mg,
0.446 mmol), 1 (115.7 mg, 0.223 mmol), and KI (150 mg, 0.87 mmol) in
acetonitrile (20 mL) was refluxed overnight under an inert atmosphere.
Afterward, the mixture was filtered through a pad of Celite and the
solvent was removed under vacuum. The crude solid was purified by
column chromatography. Elution with a mixture of 7:3 dichloro-
methane/acetone afforded the separation of an orange band that con-
tained compound 3. Removal of the volatiles afforded 3 as a brown-
orange solid. Yield: 114 mg, 50%. Complex 3 can also be obtained from
2. A mixture of Pd(OAc)2 (50 mg, 0.223 mmol), 2 (157 mg, 0.223
mmol), and KI (74 mg, 0.446 mmol) in acetonitrile (20 mL) was
refluxed overnight under an inert atmosphere. After removal of the
volatiles, the crude solid was purified as described above. Yield: 112 mg,
50%. 1H NMR (300 MHz, DMSO-d6): δ 8.2 (s, 2H, CHimid), 7.8 (s, 2H,
CHimid), 3.9 (s, 6H, NCH3), 3.8 (s, 6H, NCH3). 13C NMR (75 MHz,
DMSO-d6): δ 179.4 (NC), 166.9 (Pd-Ccarbene), 142.3 (Pd-Ccarbene),
126.2 (CHimid), 123.9 (CHimid), 122.3 (Cq), 40.1 (NCH3), 36.7
(NCH3), 30.7 (NCH3). Electrospray MS (20 V, m/z): 932.6 [M À I +
CH3CN]+.
Synthesis of Compound 4. Compound 3 (50.4 mg, 0.05 mmol)
was dissolved in 0.5 mL of pyridine. The mixture was heated for 30 min
at 80 °C. During this time, the desired product precipitated as a yellow
solid. The excess of pyridine was removed under vacuum, and the yellow
solid was washed several times with diethyl ether and dried under
vacuum. Suitable crystals for X-ray diffraction studies were obtained by
slow diffusion of diethyl ether into a solution of 4 in acetonitrile. Yield:
38 mg, 73%. 1H NMR (500 MHz, DMSO-d6): δ 9.0 (d, 3JHÀH = 4.4 Hz,
2H, Py), 8.2 (s, 2H, CHimid), 8.0 (t, 3JHÀH = 6.9 Hz, 1H, Py), 7.8 (s, 2H,
CHimid), 7.6 (d, 3JHÀH = 7.0 Hz, 2H, Py), 4.0 (s, 6H, NCH3), 3.9 (s, 6H,
NCH3). 13C NMR (75 MHz, DMSO-d6): δ 167.0 (Pd-Ccarbene), 153.2,
124.9 (Py), 122.3 (Py), 148.6 (Pd-Ccarbene), 136.6 (Cq), 126.1 (CHimid),
123.4 (CHimid), 40.0 (NCH3), 36.7 (NCH3). Anal. Calcd for
Synthesis of Compound C. The amine B (804 mg, 4.93 mmol) in
methanol (10 mL) was treated with 40% aq glyoxal (0.6 mL, 5.2 mmol)
for 16 h at room temperature. NH4Cl (560 mg, 10.4 mmol) was added,
followed by 37% aq formaldehyde (0.8 mL, 10.2 mol). The mixture was
diluted with methanol (50 mL) and the resulting mixture refluxed for
1 h. After this time, H3PO4 was added until pH 2. The resulting mixture
was then stirred at reflux for an additional 8 h. After removal of the
solvent, the dark residue was poured into ice (150 g) and treated with an
aq 40% KOH solution until pH 9. The resulting mixture was extracted
with dichloromethane (5 Â 50 mL). The organic phases were combined
and dried over Na2SO4 and the solvent was removed under vacuum,
giving compound C as a brown solid. The solid so obtained was used
1
in the next step without further purification. Yield: 448 mg, 46%. H
NMR (500 MHz, MeOD-d4): δ 7.9 (s, 1H, CHimid), 7.8 (s, 1H, CHimid),
7.7 (s, 1H, CHimid), 7.5 (s, 1H, CHimid), 7.3 (s, 1H, CHimid), 7.1 (s, 1H,
CHimid), 7.0 (s, 1H, CHimid), 3.6 (s, 3H, NCH3). 13C NMR (75 MHz,
MeOD-d4): δ 141.0 (CHimid), 137.1 (Cq), 136.4 (CHimid), 132.1
(CHimid), 131.0 (CHimid), 130.4 (Cq), 129.9 (CHimid), 129.6 (CHimid),
123.4 (CHimid), 31.6 (NCH3). Electrospray MS (20 V, m/z): 214.9
[M + H]+.
C18H21I4N7Pd2 (1055.86) 0.5 Et2O: C, 20.48; H, 2.00; N, 9.29. Found:
3
C, 20.62; H, 2.32; N, 10.06. Electrospray MS (20 V, m/z): 1079.5
[M + Na]+.
’ CATALYTIC EXPERIMENTS
Synthesis of Compound 1. A mixture of C (484 mg, 2.26 mmol)
and (CH3)3OBF4 (1.4 g, 9.5 mmol) was refluxed in degassed acetonitrile
overnight under an inert atmosphere. During this time, the desired
product precipitated as a light brown solid. The product was collected by
filtration and washed with cold acetonitrile and diethyl ether. Yield:
550 mg, 47%. 1H NMR (300 MHz, DMSO-d6): δ 9.7 (s, 1H, NCHN),
9.4 (s, 2H, NCHN), 8.1 (s, 2H, CHimid), 8.0 (s, 2H, CHimid), 4.0
(s, 6H, NCH3), 3.9 (s, 6H, NCH3). 13C NMR (75 MHz, DMSO-d6):
δ 140.3 (NCHN), 135.5 (Cq), 125.4 (NCHN), 124.0 (CHimid), 121.7
(CHimid), 36.9 (NCH3), 34.3 (NCH3). Electrospray MS (15 V, m/z):
129.1 [M À H]2+.
Typical procedure for catalytic hydroarylation of acetylenes:
The arene (2.65 mmol) and the catalyst (0.00265 or 0.00132
mmol) were placed together in a thick-walled Schlenk tube fitted
with a Teflon cap. The tube was then evacuated and filled with
nitrogen three times. Diethyl phthalate (2.65 mmol), trifluoro-
acetic acid (4 mL), and 1,2-dichloroethane (1 mL) were added
and the resulting mixture stirred at room temperature for 5 min.
After this time, the acetylene (2.65 mmol) was added and the
reaction mixture stirred at the desired temperature (80 °C or
room temperature). Aliquots were taken at the desired times and
analyzed by 1H NMR spectroscopy. The conversion was calcu-
lated referred to the disappearance of pentamethylbenzene.
X-ray Crystal Structure Determinations. Data collection was
performed at room temperature on a Siemens Smart CCD
diffractometer using graphite-monochromated Mo Kα radiation
(λ = 0.71073 Å). The diffraction frames were integrated using the
SAINT package.11
Synthesis of Compound 2. A mixture of Pd(OAc)2 (50 mg,
0.223 mmol), 1 (115.7 mg, 0.223 mmol), and KI (74.7 mg, 0.446 mmol)
in acetonitrile (20 mL) was refluxed for 3 h under an inert atmosphere.
Afterward, the mixture was filtered through a pad of Celite and the
solvent was removed under vacuum. The resulting orange residue was
redissolved in acetone, and the insoluble salts were removed by filtration.
Finally, the solvent was removed under vacuum, obtaining compound 2
as an orange solid. Yield: 145 mg, 92%. 1H NMR (300 MHz, DMSO-d6):
Space group assignment was based on systematic absences, E
statistics, and successful refinementof the structures. The structure
was solved by direct methods with the aid of successive difference
Fourier maps and refined using the SHELXTL 6.1 software
package.12 All non-hydrogen atoms were refined anisotropically,
3
δ 9.6 (s, 1H, NCHN), 8.1 (d, JHÀH = 2.1 Hz, 2H, CHimid), 7.8 (d,
3JHÀH = 2.1 Hz, 2H, CHimid), 4.0 (s, 6H, NCH3), 3.9 (s, 6H, NCH3).
13C NMR (75 MHz, DMSO-d6): δ 167.0 (Pd-Ccarbene), 135.5
(NCHN), 126.7 (CHimid), 123.1 (Cq), 122.4 (CHimid), 34.6 (NCH3),
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and hydrogen atoms were assigned to ideal positions and refined
using a rigid model.
(7) (a) Jia, C. G.; Lu, W. J.; Oyamada, J.; Kitamura, T.; Matsuda, K.;
Irie, M.; Fujiwara, Y. J. Am. Chem. Soc. 2000, 122, 7252. (b) Jia, C. G.;
Piao, D. G.; Oyamada, J. Z.; Lu, W. J.; Kitamura, T.; Fujiwara, Y. Science
2000, 287, 1992.
(8) Biffis, A.; Gazzola, L.; Gobbo, P.; Buscemi, G.; Tubaro, C.;
Basato, M. Eur. J. Org. Chem. 2009, 3189.
Crystal Data and Structure Refinement for Complex 2.
Crystals suitable for X-ray study were obtained by slow diffusion
of diethyl ether into a concentrated solution of the compounds in
acetonitrile. Radiation, λ (Å), 0.71073; crystal system, mono-
clinic; space group, P21/c; a (Å), 9.4486(2); b (Å), 23.6206(6); c
(Å), 9.3608(2); α (°), 90; β (°), 90.187(2); γ (°), 90; Z, 4;
independent reflections, 12 023 [R(int) = 0.0376]; GOF, 1.051;
final R indices [I > 4σ(I)], R1 = 0.0324, wR2 = 0.0712; min/max
res dens (e ÅÀ3), À0.89 and 0.79.
(9) Biffis, A.; Tubaro, C.; Buscemi, G.; Basato, M. Adv. Synth. Catal.
2008, 350, 189.
(10) (a) Buscemi, G.; Biffis, A.; Tubaro, C.; Basato, M. Catal. Today
2009, 140, 84. (b) Buscemi, G.; Biffis, A.; Tubaro, C.; Basato, M.; Graiff,
C.; Tiripicchio, A. Appl. Organomet. Chem. 2010, 24, 285. (c) Gazzola,
L.; Tubaro, C.; Biffis, A.; Basato, M. New J. Chem. 2010, 34, 482.
(d) Saravanakumar, R.; Ramkumar, V.; Sankararaman, S. Organometallics
2011, 30, 1689. (e) Viciu, M. S.; Stevens, E. D.; Petersen, J. L.; Nolan,
S. P. Organometallics 2004, 23, 3752.
(11) SAINT, version 5.0; Bruker Analytical X-ray System: Madison,
WI, 1998.
(12) Sheldrick, G. M. SHELXTL, version 6.1; Bruker AXS, Inc.:
Crystal Data and Structure Refinement for Complex 4.
Crystals suitable for X-ray study were obtained by slow diffusion
of diethyl ether into a concentrated solution of the compounds in
acetonitrile. Radiation, λ (Å), 0.71073; crystal system, orthorhom-
bic; space group, Pccn; a (Å), 15.4313(4); b (Å), 20.7211(7); c (Å),
19.7639(5); α (°), 90; β (°), 90; γ (°), 90; Z, 4; independent
reflections, 32 780 [R(int) = 0.0408]; GOF, 1.049; final R indices
[I > 4σ(I)], R1 = 0.0427, wR2 = 0.1276; min/max res dens
(e ÅÀ3), À1.55 and 2.87.
Madison, WI, 2000.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF data. This material is
b
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: poyatosd@uji.es (M.P.), eperis@uji.es (E.P.).
’ ACKNOWLEDGMENT
We gratefully acknowledge financial support from MEC of
Spain (CTQ2008-04460/BQU) and Bancaixa (P1.1B2010-02,
P1.1A2008-02). We would also like to thank the MICINN for a
Ramꢀon y Cajal program (M.P.) and the Universitat Jaume I for a
fellowship (S.G.). The authors are grateful to the Serveis Centrals
d’Instrumentaciꢀo Científica (SCIC) of the Universitat Jaume I
for providing us with spectroscopic and X-ray facilities.
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dx.doi.org/10.1021/om200820s |Organometallics 2011, 30, 5985–5990