Heterobimetallic iridium-ruthenium assemblies through an ambidentate triazole-diylidene ligand: Electrochemical properties and catalytic behavior in a cascade reaction

Article abstract of DOI:10.1021/om300675p

The preparation in high yield of a (p-cymene)Ru^II(triazolium- ylidene) complex allows the synthesis of an heterobimetallic Ir ^III-Ru^II complex with a triazole-diylidene bridge. The same complex can also be prepared by starting from the previously reported complex Cp*Ir^III(triazolium-ylidene). A full electrochemical study of the heterobimetallic complex has been performed, and the results have been compared with those for the related homobimetallic triazole-diylidene bridged complexes of ruthenium and iridium, where a weak metal-metal interaction (class II, according to the Robin and Day classification) has been detected. The Ir-Ru complex and some other related (p-cymene)Ru(NHC) complexes have been tested in a new tandem process, implying the chelation-assisted arylation of arylpyridines with 1-(4-halophenyl)ethanol. The arylation is accompanied by the transformation of the alcohol into a ketone, in the presence of acetone, through an Oppenauer oxidation process.

Full text of DOI:10.1021/om300675p

Article
pubs.acs.org/Organometallics
Heterobimetallic Iridium−Ruthenium Assemblies through an
Ambidentate Triazole-Diylidene Ligand: Electrochemical Properties
and Catalytic Behavior in a Cascade Reaction
Sara Sabater, Jose A. Mata,* and Eduardo Peris*
a
́
́ ́ ́
Departamento de Quımica Inorganica y Organica, Universitat Jaume I, Avda. Sos Baynat s/n, 12071, Castellon, Spain
S
* Supporting Information
ABSTRACT: The preparation in high yield of a (p-cymene)-
RuII(triazolium-ylidene) complex allows the synthesis of an
heterobimetallic IrIII−RuII complex with a triazole-diylidene
bridge. The same complex can also be prepared by starting
from the previously reported complex Cp*IrIII(triazolium-
ylidene). A full electrochemical study of the heterobimetallic
complex has been performed, and the results have been
compared with those for the related homobimetallic triazole-
diylidene bridged complexes of ruthenium and iridium, where
a weak metal−metal interaction (class II, according to the
Robin and Day classification) has been detected. The Ir−Ru complex and some other related (p-cymene)Ru(NHC) complexes
have been tested in a new tandem process, implying the chelation-assisted arylation of arylpyridines with 1-(4-
halophenyl)ethanol. The arylation is accompanied by the transformation of the alcohol into a ketone, in the presence of
acetone, through an Oppenauer oxidation process.
Scheme 1
INTRODUCTION
■
Synthesis by means of catalytic processes is one of the most
rapidly evolving research areas in chemistry. Natural catalysts
are known to be far more efficient than those developed by
chemists. While the mechanism of action of enzymes often
benefits from the mutual cooperation provided by two or more
metals, man-made catalysts rarely exploit this approach. In the
past few years, many sophisticated metal-based multicatalyst
systems have been reported and reviewed.1−3 In most of the
cases, the action of the one-pot cocatalyst refers to (i) two
catalysts that carry out sequential organic transformations (each
step carried out by one catalyst) or (ii) cooperative catalytic
actions on substrates by suitable catalysts occurring in a
substrate-selective manner, followed by the coupling of the
resulting activated substrates.2 In order to avoid the use of two
different catalysts, the preparation of dinuclear complexes
containing two metals in close proximity has become the
subject of extensive investigations in order to design efficient
bimetallic catalysts.3 The bottleneck for such research is finding
convenient synthetic routes to afford stable bimetallic
structures, a goal that is far more complicated to achieve
when heterobimetallic species are pursued.
types of heterobimetallic complexes allowed us to study several
catalyzed tandem reactions in which each of the metal
fragments facilitates a mechanistically different cycle6,7 and,
more importantly, allowed us to find clear experimental
evidence for catalytic cooperativity between the metals
comprised in the bimetallic unit.7,8 Due to the easy stepwise
deprotonation of a dicationic 1,2,4-triazolium salt, we found a
convenient method for the preparation of a monometallic
complex containing a Cp*Ir fragment bound to a triazolium-
ylidene, which still contains a C−H bond that can be used to
generate a second carbene center (1; Scheme 1).8 On the basis
of this Cp*Ir(triazolium-ylidene), we obtained several hetero-
metallic complexes in which the Cp*Ir fragment remained
constant.7−9 Until now, the preparation of monometallic
complexes with the same triazolium-ylidene ligand but with
metals other than iridium remained elusive.
The metal−metal separation in bimetallic catalysts plays a
crucial role in the activity of the designed complexes. It has
been proposed that the optimum separation of the two metals
should be 3.5−6 Å, regardless of the existence of any direct
interaction between the metal centers.3 During the past few
years we have reported an efficient method for the preparation
of homo- and heterobimetallic complexes bound to a 1,2,4-
triazolyl-3,5-diylidene (Scheme 1).4−9 The preparation of such
We herein describe the preparation of a (p-cymene)RuII
complex with a triazolium-ylidene ligand. This compound acts
as an intermediate to the production of other Ru-containing
Received: July 19, 2012
© XXXX American Chemical Society
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Scheme 2
heterobimetallic complexes. We have used this compound for
the preparation of an heterometallic complex of Ru(II) and
Ir(III). The final Ru−Ir complex can be obtained from two
different routes, via the (p-cymene)Ru(triazolium-ylidene) or
the Cp*Ir(triazolium-ylidene) intermediates. The new com-
plexes obtained have been tested in a tandem process, implying
the chelation-assisted arylation of arylpyridines with 1-(4-
halophenyl)ethanol. The arylation is accompanied by the
transformation of the alcohol into a ketone, in the presence of
acetone, through an Oppenauer oxidation process.
RESULTS AND DISCUSSION
■
The reaction of 1,2,4-trimethyltriazolium tetrafluoroborate
([ditzH2](BF4)2) in methanol at 0 °C in the presence of an
equimolecular amount of NaH affords the methanolic adduct
[ditzH-MeOH](BF4),10 which can either be isolated or used in
situ. The reaction of [ditzH-MeOH](BF4) with the corre-
sponding amount of [RuCl2(p-cymene)]2 in refluxing methanol
affords the (p-cymene)Ru(triazolium-ylidene) complex 2 in
high yield (80%). The reaction of 2 with [IrCp*Cl2]2 in
acetone at 50 °C in the presence of NaOAc affords the Ru(II)/
Ir(III) complex 3 in 81% yield. Complex 3 can also be obtained
by starting from the previously reported Cp*Ir(triazolium-
ylidene) complex 1,8 by reaction with [RuCl2(p-cymene)]2 in
acetone at 50 °C in the presence of NaOAc, affording 3 in 70%
yield. Scheme 2 summarizes the two possible routes to
compound 3.
Figure 1. Molecular diagram of complex 2. Ellipsoids are shown at the
50% probability level. Hydrogen atoms of the p-cymene ligand and the
counteranion (BF4 ) are omitted for clarity. Selected bond lengths (Å)
and angles (deg): Ru(1)−Cl(2) = 2.4045(11), Ru(1)−Cl(3) =
2.4172(10), Ru(1)−C(4) = 2.058(4), Ru(1)−Ccentroid = 1.699; C(4)−
Ru(1)−Cl(2) = 90.95(11), C(4)−Ru(1)−Cl(3) = 88.37(10), Cl(2)−
Ru(1)−Cl(3) = 84.91(4), N(5)−C(4)−N(10) = 102.8(3).
−
regarded as a three-legged piano stool, with a p-cymene ligand,
two chlorides, and a triazolium-ylidene completing the
coordination sphere about the Ru(II) center. The cationic
Complexes 2 and 3 were characterized by NMR and mass
spectroscopy. The 1H NMR spectrum of 2 shows the
characteristic signal for the acid NCHN proton at δ 9.54.
The integration of this signal relative to the signals due to the
three methyl groups (at δ 4.38, 4.21, and 4.17) indicates that
only one of the two NCHN protons of the triazolium dicationic
salt was lost upon coordination to the metal. The most relevant
feature of the 13C NMR spectrum is the signal due to the
metalated M−Ccarbene carbon at 192.3 ppm.
−
nature of the complex is confirmed by the presence of a BF4
counterion. The Ru−Ccarbene distance is 2.058(4) Å, in the same
range as for other Ru complexes containing a bridging ditz
ligand.5
Cyclic voltammetric (CV) studies have recently been
proposed as a valuable means to study the electronic properties
of NHC ligands in rhodium and iridium complexes.11 The same
technique has also been used to ascertain whether there is any
metal−metal electronic communication across ditopic bis-
(NHCs).12,13 It has been claimed that the potential MC π-
bonding may stimulate electronic communication between
remote metal centers connected by π-delocalized connecting
ligands.13 We have carried out CV measurements of complex 3
and for comparative purposes also on complexes 4−7 depicted
in Scheme 3. In order to obtain more accurate data about the
peak separation in the dimetallic complexes, we also performed
differential pulse voltammetry (DPV) experiments (Table 1).
The absence of any protic signal in the 1H NMR spectrum of
3 indicates the deprotonation of both NCHN protons of the
initial triazolium salt. The three distinct signals due to the
methyl groups of the azole ring suggest the loss of the 2-fold
symmetry of the ligand, upon coordination to the two different
metal fragments. The 13C NMR spectrum displays two
representative signals due to the Ru−Ccarbene and Ir−Ccarbene
signals at 186.4 and 168.1 ppm, respectively.
The molecular structure of 2 (Figure 1) was unambiguously
determined by X-ray diffraction studies. The molecule can be
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the bis-iridium complex 4 gave an irreversible CV wave; thus,
we could not obtain suitable data for analysis.
Scheme 3
In order to study the catalytic activity of the dimetallic
complexes 3 and 5, we decided to test them in a combination of
two reactions: the chelation-assisted arylation of arylpyridines
with aryl halides (a reaction which is typically catalyzed by
Ru(II) complexes)15 and the Oppenauer oxidation of alcohols.
We wanted to explore the effect of the two metal centers in the
dimetallic complexes on the final outcome of this tandem
reaction. Although this tandem reaction presumably can be
catalyzed by one only metal (Ru), there are no examples of
such tandem reaction reported in the literature; thus, we
believed that the study of this reaction might provide some
interesting results. We first studied one individual step of the
reaction consisting of the arylation of 2-phenylpyridine with
chlorobenzene. For comparative purposes, we also tested the
activity of the monometallic Ru complex 6, a very effective
catalyst for the arylation and also the deuteration of a wide set
of substantially different pyridines.16
As can be seen from the results shown in Table 2, for the
reactions carried out with 5 mol % catalyst loading (entries 1−
3), the diruthenium complex 5 proved to be the most active
catalyst, in terms of both conversion and selectivity toward the
bis-arylated product. Interestingly, 5 provides a better catalytic
outcome than the Ir−Ru complex 3, a fact that may seem rather
logical if we take into account that 5 contains two ruthenium
centers while 3 contains only one. This result indicates not only
that the iridium fragment is formally inactive in this reaction
but also that the two metals in 5 behave as active catalytic
centers, meaning that we can discard a situation in which one
ruthenium is acting as a spectator center while the other is
catalyzing the process. For the reaction carried out with 3, the
reduction of the catalyst loading to 2.5 mol % (entry 4, 5 mol %
based on metal), results in a decrease of conversion and a loss
of selectivity, and the overall catalytic outcome is very similar to
that provided by the monometallic catalyst 6. Also, under these
reaction conditions, catalyst 5 is far more effective than the Ir−
Ru catalyst 3, despite the fact that the reaction was carried out
with the same concentration of Ru.
Table 3 shows the most representative results from a
comparative study of the catalytic behavior of complexes 3−6
in the Oppenauer oxidation of 1-phenylethanol in acetone. For
this reaction, the best catalyst was the monometallic ruthenium
complex 6 (Table 3, entry 1). All the rest of the catalysts
showed less catalytic activity, in terms of both the conversions
achieved and reaction times. The bis-iridium catalyst 4 was the
best catalyst among all the bimetallic complexes tested (entry
4).
Once we proved the activity of our complexes in both the
arylation of arylpyridines and the oxidation of alcohols with
acetone, we decided to combine both processes into a one-pot
tandem reaction; thus, we used catalysts 3−6 in the arylation of
arylpyridines with 1-(4-chlorophenyl)ethanol (or 1-(4-
bromophenyl)ethanol) in a mixture of N-methylpyrrolidine
and acetone, aiming to obtain the arylated pyridines with
carbonyl functionalities. The monitoring of this reaction
allowed us to observe that only the starting substrates and
the final product are detected along all the reaction time course,
indicating that once the oxidation of the alcohol had taken
place, the arylation step is fast. On the other hand, in a parallel
experiment, we decided to perform the reaction in the absence
of acetone; therefore, we avoided the oxidation of the alcohol.
Under these reaction conditions, the arylation of 1-(4-
Table 1. Electrochemical Data from Cyclic Voltammetry
(CV) and Difference Pulse Voltammetry (DPV)
a
E1/2 (V) (ΔE (mV))
entry
complex
ΔE1/2 (mV)
1
2
3
4
5
3
4
5
6
7
1.29 (80)
1.35 (110)
1.46(60)
120
b
1.15
1.34 (−)
1.13 (109)
120
1.17 (112)
a
Measured in CH2Cl2, 0.1 M TBAPF6 electrolyte, calibrated to Fc+/Fc
b
(E1/2 = 0.46 V vs SCE). Irreversible peak measured at 100 mV s−1.
The redox potential of the monometallic Ru compound 6 is
1.13 V, attributed to the E(RuII/RuIII) process. For the Ir
complex 7, the redox potential is 1.17 V and is attributed to an
E(IrIII/IrIV) process. These values can be compared to those
shown by the dimetallic complexes 3−5. The heterobimetallic
complex 3 displays two independent redox processes attributed
to the Ru and Ir centers, at 1.29 and 1.41 V, respectively. These
values confirm that the triazolyl-diylidene ligand in 3 has a
lower electron-donating character than the monocarbenes in 6
and 7. Also, we have to take into account that the redox values
shown for complexes 6 and 7 are very similar (ΔE = 40 mV);
therefore, the fact that we observed the two peaks separated by
120 mV in 3 may be due to the influence of the oxidation of the
Ru center over the oxidation of the Ir center, suggesting that
the two centers are (weakly) electronically coupled.
Both the CV and DPV experiments on complex 5 reveal that
two oxidation bands are present, separated by 120 mV (Figure
2). This separation corresponds to a class II system according
to the Robin and Day classification.14 Although this interaction
can be classified as weak, it has to be taken into account that it
is the highest electronic coupling measured among all other
Janus-type bis-NHC related ligands reported to date, which
have shown weaker couplings, ranging from 60 to 80 mV.12,13
The first oxidation peak in 5 appears at 1.34 V, at a value
slightly higher than the same process attributed to the Ru
center in 3 (1.29 V), indicating that the presence of the Ru(p-
cymene)Cl2 fragment in 5 instead of IrCp*Cl2 reduces the
electron-donating character of the part of the ligand bound to
Ru(p-cymene)Cl2, although this effect is small. Unfortunately,
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Figure 2. Cyclic voltammetry (top) and differential pulse voltammetry (bottom) of complexes 3 (b, d) and 5 (a, c). Deconvolution was performed
by superimposition of multiple DPV signals of 6.
a
Table 2. Chelation-Assisted Arylation of 2-Phenylpyridine
with Chlorobenzene
Table 3. Oppenauer Oxidation of 1-Phenylethanol
a
b
entry
cat.
t (h)
yield (%)
1
2
3
4
5
6
5
3
1
9
9
9
9
99
76
88
94
37
b
b
c
entry
cat.
t (h)
A (%)
B (%)
4
c
5
1
2
3
4
6
5
3
12
5
25
74
99
18
74
a
Reaction conditions: catalyst (0.01 mmol), 1 mmol of phenylethanol,
1.5 mmol of K2CO3, 2 mL of acetone as solvent, 100 °C. Yields and
ratios determined by GC (internal standard anisole). 1 mol % of
b
12
12
56
25
c
c
5
metal.
a
Reaction conditions: KOAc (10 mol %), catalyst (5 mol %), 2 mL of
NMP as solvent, room temperature for 1 h, then 2-phenylpyridine (0.5
mmol), chlorobenzene (1.25 mmol), K2CO3 (1.5 mmol), 120 °C.
homobimetallic complex 5 was also an excellent catalyst and
performed better than the Ir−Ru heterobimetallic complex 3
under the same reaction conditions (compare entries 1 and 2).
The best outcome shown by catalyst 6 may be understood if we
take into account that the oxidation of the alcohol is the rate-
determining step of the process, a step in which 6 is more
active, as seen from the results shown in Table 3. Catalyst 6 was
also active in the bis-arylation of N-phenylpyrazole, when both
1-(4-chlorophenyl)ethanol and 1-(4-bromophenyl)ethanol
were used as arylating agents (Table 4 entries 4−7). The bis
b
Yields and ratios determined by GC (internal standard anisole) and
c
1
by H NMR. 5 mol % of metal.
chlorophenyl)ethanol did not occur, therefore indicating that
the aryl chloride is activated by the oxidation of the alcohol
functionality to the ketone.
As can be seen from the data shown in Table 4, the best
catalyst from all those that we used was compound 6, when a
catalyst loading of 5 mol % (based on metal) was used. The
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b
Table 4. Tandem Oxidation of 1-(4-Halophenyl)ethanols and Arylation of Arylpyridines
a
b
Yields and ratios determined by GC (internal standard anisole) and by 1H NMR. Reaction conditions: KOAc (10 mol %), catalyst (5 mol %), 2
c
mL of NMP/acetone (1/1) as solvent, room temperature for 1 h, then arylpyridine (0.5 mmol), Ar−X (1.25 mmol), K2CO3 (2.5 mmol), 120 °C. 5
mol% of metal.
iridium catalyst 4 was inactive in the overall process, because it
could not facilitate the second step of the reaction (arylation of
the pyridine).
process the arylation is accompanied by the transformation of
the alcohol into a ketone, in the presence of acetone, through
an Oppenauer oxidation process. This tandem process is
unprecedented in the literature.
CONCLUSIONS
■
EXPERIMENTAL SECTION
A new triazolium-ylidene complex of ruthenium (2) has been
prepared. This complex is a useful intermediate in the
formation of ruthenium-containing heterobimetallic complexes
bridged by the triazole-diylidene (ditz) ligand. In this present
work we have prepared a heterobimetallic Ir−Ru complex (3),
which can also be obtained by starting from our previously
reported iridium triazolium-ylidene complex 1.8
Electrochemical studies of complexes 3−5 reveal that there is
an electronic interaction between the two metals bound by the
triazole-diylidene ligand. Although this interaction can be
considered as weak (class II according to the Robin and Day
classification14), it is remarkably stronger than the communi-
cation shown for other related NHC-based Janus type
ligands.12,13
■
General Procedures. All manipulations were carried out under
nitrogen using standard Schlenk techniques and high vacuum, unless
otherwise stated. Compound 1 was prepared according to the
literature procedure.8 Anhydrous solvents were dried using a solvent
purification system (SPS, MBraun) or purchased from Aldrich and
degassed prior to use by purging with dry nitrogen and kept over
molecular sieves. All other reagents were used as received from
commercial suppliers. NMR spectra were recorded on Varian Innova
spectrometers operating at 300 or 500 MHz (1H NMR) and 75 or 125
MHz (13C NMR), respectively, using CDCl3 as solvent at room
temperature unless otherwise stated. Elemental analyses were carried
out in an Carlo Erba EA 1108 CHNS-O analyzer. Electrospray mass
spectra (ESI-MS) were recorded on a MicromassQuatro LC
instrument, and nitrogen was employed as the drying and nebulizing
gas.
Complex 3 and some other related (p-cymene)Ru(NHC)
complexes have been tested in a new tandem process, implying
the chelation-assisted arylation of arylpyridines with 1-(4-
halophenyl)ethanol, where the monometallic (p-cymene)Ru-
(NHC) complex 6 has shown the best activities. In this catalytic
X-ray Studies. Diffraction data were collected on a Agilent
SuperNova diffractometer equipped with an Atlas CCD detector using
Mo Kα radiation (λ = 0.710 73 Å). Single crystals were mounted on a
MicroMount polymer tip (MiteGen) in a random orientation.
Absorption corrections based on the multiscan method were applied.17
E
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The structures were solved by direct methods in SHELXS-97 and
refined by the full-matrix method based on F2 with the program
SHELXL-97 using the OLEX software package.18
placed together in a thick-walled glass tube. The mixture was stirred at
100 °C for the desired time. Yields were determined by GC
chromatography using anisole (1 mmol) as internal standard. Products
were identified according to the spectroscopic data of the
commercially available compounds.
Electrochemical Measurements. The measurements were
carried out using a GPES equipped PGSTAT-30 potentiostat from
Autolab at room temperature. A three-electrode configuration was
used, where two Pt microelectrodes were connected to the working
electrode and counter electrode and a Ag wire was used as the pseudo
reference electrode. The redox potential of ferrocene was used to
calibrate the potential scale. Dichloromethane was used as the solvent
for all experiments. [NBu4]PF6 was used as the supporting electrolyte.
Synthesis of Compound 2. A suspension of sodium hydride
(60% in mineral oil, 15.7 mg, 0.39 mmol) in dry methanol was stirred
at 0 °C under a nitrogen atmosphere until a clear solution of sodium
methoxide was formed. 1,2,4-Trimethyltriazolium tetrafluoroborate
(93.6 mg, 0.32 mmol) was added, and the mixture was stirred at room
temperature for 1 h. After addition of [RuCl2(p-cymene)]2 (100 mg,
0.16 mmol), the mixture was refluxed for 2 h. The suspension was
filtered, and the solution was concentrated under reduced pressure.
Compound 2 was obtained as an orange solid after crystallization from
acetonitrile/methanol. Yield: 129 mg (80%).
1H NMR (300 MHz, CD3CN): δ 9.54 (s, 1H, NCHN), 5.66 (d,
3
3JH,H = 6 Hz, 1H, CHp‑cym), 5.43 (d, JH,H = 6 Hz, 1H, CHp‑cym), 4.38
ASSOCIATED CONTENT
* Supporting Information
■
(s, 3H, NCH3), 4.21 (s, 3H, NCH3), 4.17 (s, 3H, NCH3), 2.94 (sept,
3JH,H = 7.5 Hz, 1H, CHisop p‑cym), 2.10 (s, 3H, CH3 p‑cym), 1.33 (d, 3JH,H
= 6 Hz, 6H, CH3 isop p‑cym). 13C{1H} NMR (75 MHz, CD3CN): δ
192.3 (Ccarbene−Ru), 145.7 (NCHN), 112.6, 99.8 (Cq p‑cym), 88.2, 85.3
(CHp‑cym), 40.1, 39.6, 38.1 (NCH3), 31.6 (CHisop p‑cym), 22.4
(CH3 isop p‑cym), 18.7 (CH3 p‑cym). Anal. Calcd for C15H24N3BCl2F4Ru
(505.15): C, 35.66; H, 4.79; N, 8.32. Found: C, 35.50; H, 5.05; N,
7.99. Electrospray MS (cone 15 V; m/z, fragment): 418.2 [M]+.
HRMS ESI-TOF-MS (positive mode): [M − Cl]+ monoisotopic peak
418.0385, calcd 418.0389, εr = 0.9 ppm.
Synthesis of Compound 3. Method A. Compound 2 (100 mg,
0.198 mmol), NaOAc (17 mg, 0.207 mmol), and [IrCp*Cl2]2 (79 mg,
0.099 mmol) were stirred under nitrogen in deoxygenated acetone (10
mL) at 50 °C for 16 h. The final suspension was filtered, giving an
orange solid, which was extracted with dichloromethane (3 × 10 mL).
Crystallization from dichloromethane/diethyl ether gave compound 3
as an orange crystalline solid. Yield: 130 mg (81%).
S
Text, tables, figures, and a CIF files giving details of the catalytic
experiments, high-resolution mass spectra (HR/MS) of
compounds 2 and 3, electrochemical data including CV and
DPV, 1H and 13C NMR of new complexes, and X-ray
diffraction data for complex 3. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jmata@uji.es (J.A.M.); eperis@uji.es (E.P.). Fax:
(+34) 964728214. Tel: (+34) 964729166.
■
Notes
The authors declare no competing financial interest.
Method B. Compound 1 (150 mg, 0.247 mmol), NaOAc (20.6 mg,
0.247 mmol), and [RuCl2(p-cymene)]2 (75.3 mg, 0.123 mmol) were
stirred under nitrogen in deoxygenated acetone (10 mL) at 50 °C for
16 h. The final suspension was filtered, giving an orange solid, which
was extracted with dichloromethane (3 × 10 mL). Crystallization from
dichloromethane/diethyl ether gave compound 3 as an orange
crystalline solid. Yield: 141 mg (70%).
ACKNOWLEDGMENTS
We are grateful for financial support from the Ministerio de
■
Ciencia e Innovacion
Bancaixa (P1.1B2010-02). We would also thank the “General-
́
of Spain (CTQ2011-24055/BQU) and
itat Valenciana” for a fellowship (S.S.). We are grateful to the
“Serveis Centrals d’Instrumentacio
Universitat Jaume I for providing us with spectroscopic and X-
ray facilities.
́
́
Cientifica (SCIC)” of the
1H NMR (300 MHz, CD3Cl): δ 5.53 (d, 3JH,H = 6 Hz, 1H, CHp‑cym),
3
3
5.49 (d, JH,H = 6 Hz, 1H, CHp‑cym), 5.42 (d, JH,H = 6 Hz, 1H,
3
CHp‑cym), 5.25 (d, JH,H = 6 Hz, 1H, CHp‑cym), 4.37 (s, 3H, NCH3),
4.32 (s, 3H, NCH3), 4.27 (s, 3H, NCH3), 2.93 (m, 1H, CHisop p‑cym),
2.18 (s, 3H, CH3 p‑cym), 1.63 (s, 15H, C5(CH3)5), 1.32 (d, 3JH,H = 6 Hz,
6H, CH3 isop p‑cym). 13C{1H} NMR (75 MHz, CD2Cl2): δ 186.4
(Ccarbene−Ru), 168.1 (Ccarbene−Ir), 109.6, 98.5 (Cq p‑cym), 90.2
(C5(CH3)5), 86.6, 85.4, 84.9, 83.9 (CHp‑cym), 42.1, 39.2, 38.1
(NCH3), 30.8 (CHisop p‑cym), 22.3, 21.9 (CH3isop p‑cym), 18.6 (CH3 p-cym),
8.8 (C5(CH3)5). Anal. Calcd for C25H38N3Cl4RuIr (815.69): C, 36.81;
H, 4.69; N, 5.15. Found: C, 36.76; H, 4.73; N, 4.75. Electrospray MS
(cone 15 V; m/z, fragment): 780.3 [M − Cl]+, 372.5 [M − 2Cl]2+.
HRMS ESI-TOF-MS (positive mode): [M − Cl]+ monoisotopic peak
780.0796, calcd 780.0789, εr = 0.9 ppm.
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