The intramolecular sp2 and sp3 C-H bond activation of (p-cymene)ruthenium(ii) N-heterocyclic carbene complexes

Article abstract of DOI:10.1039/b818091a

The intramolecular sp² and sp³ C-H activated products, as well as the monometalated products, based on the "(p-cymene)Ru(NHC)" framework were synthesised by treatment of a series of NHCs (1-R-3-methylimidazol-2-ylidene [R = Ph (1), Bn (2), t-Bu (3), i-Pr (4), Mes (5), Cy (6)] and 1,3-bis(isopropyl)imidazol-2-ylidene (7)) with [(p-cymene)RuCl₂]₂ under mild conditions. A new NHC precursor (1-tert-butyl-3-phenyl-4,5-dihydro-imidazol-2-ylidene) was also designed to compare the reactivity of sp² C-H and sp³ C-H bonds upon cyclometalation, and only the sp³ C-H activated product (8) was observed. The factors that possibly determine the selectivity of intramolecular sp² or sp³ C-H activation are elucidated by a series of experiments. In the cases where activation of both sp² C-H and sp³ C-H is possible, steric factors overrode the others to dominate the regioselectivity of activation. All complexes were characterised by ¹H NMR, ¹³C NMR and HRMS spectra. The molecular structures of 1, 3, 5, 6, 7, and 8 were confirmed by X-ray diffraction.

Full text of DOI:10.1039/b818091a

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PAPER
www.rsc.org/dalton | Dalton Transactions
The intramolecular sp2 and sp3 C–H bond activation of
(p-cymene)ruthenium(II) N-heterocyclic carbene complexes†
Congying Zhang,a Yang Zhao,a Bin Li,a Haibin Song,a Shansheng Xua and Baiquan Wang*a,b
Received 14th October 2008, Accepted 30th March 2009
First published as an Advance Article on the web 13th May 2009
DOI: 10.1039/b818091a
The intramolecular sp2 and sp3 C–H activated products, as well as the monometalated products, based
on the “(p-cymene)Ru(NHC)” framework were synthesised by treatment of a series of NHCs
(1-R-3-methylimidazol-2-ylidene [R = Ph (1), Bn (2), t-Bu (3), i-Pr (4), Mes (5), Cy (6)] and
1,3-bis(isopropyl)imidazol-2-ylidene (7)) with [(p-cymene)RuCl2]2 under mild conditions. A new NHC
precursor (1-tert-butyl-3-phenyl-4,5-dihydro-imidazol-2-ylidene) was also designed to compare the
reactivity of sp2 C–H and sp3 C–H bonds upon cyclometalation, and only the sp3 C–H activated
product (8) was observed. The factors that possibly determine the selectivity of intramolecular sp2 or
sp3 C–H activation are elucidated by a series of experiments. In the cases where activation of both sp2
C–H and sp3 C–H is possible, steric factors overrode the others to dominate the regioselectivity of
activation. All complexes were characterised by 1H NMR, 13C NMR and HRMS spectra. The
molecular structures of 1, 3, 5, 6, 7, and 8 were confirmed by X-ray diffraction.
ety of imidazolylidene ligand.31 These discoveries suggest great
Introduction
potential for development in this new area of organometallic
chemistry. Furthermore, Ir(III) NHC complexes were also found
to furnish intramolecular C–H activation products. Considering
that the electronic configurations of Ir(III) complexes are close
to those of Ru(II) complexes, intramolecular C–H activations of
Ru(II)(NHC) complexes are expected.32–38 Therefore, more details
about the structures and reactivities of interesting cyclometalated
Ru(II)(NHC) complexes are required.
On the basis of previous observations and our experiments, we
now report the preparation and reactivity of a series of alkyl- and
aryl-functionalised imidazolylidene complexes of Ru(II), including
several interesting cyclometalated products. In all cases, the
cyclometalation process takes place under mild conditions—
room temperature and absence of any base. The ability of these
complexes to activate the aliphatic or aromatic C–H bond is also
generally studied.
Over the past decades, the activation of unreactive bonds by transi-
tion metal complexes has emerged as a new field of organometallic
chemistry.1–3 Recently, the major interest of this area has focused
on the development of new procedures for catalytic activation
processes.2,4–7
The extensive studies of N-heterocyclic carbenes (NHCs) and
the corresponding organometallic derivatives have been carried
out since the first convenient preparation method of NHC
precursors was reported by Arduengo and co-workers in 1991.8
Due to the great s-electron-donating capability of NHC ligands,
the corresponding complexes have been proven to be very effective
in a variety of metal-catalysed organic reactions, such as olefin
metathesis reactions,9 Suzuki–Miyaura coupling,10 Heck-type
C–C coupling reactions10,11 etc.9,10,12–14 Recently, various interest-
ing reactions with intramolecular aromatic and aliphatic C–H
activation of NHC complexes have been published by several
pioneers.15–24 According to these discoveries, certain NHC-based
ruthenium complexes could undergo intramolecular C–H activa-
tion processes and generate the stable cyclometalated species.11–17
In last decade, normal carbene complexes with the backbone of
[(p-cymene)Ru(NHC)X2] have been widely studied.18–30 Recently,
Dixneuf and co-workers reported an unexpected cyclometalated
(p-cymene)Ru(NHC) species which resulted from plausible in-
tramolecular metal insertion to C–H bond on the vinyl moi-
Results and discussion
The sp2 C–H Activation
According to the published method,31 1-phenyl-3-methylimida-
zolium iodide as the imidazolylidene precursor was deprotonated
at 0 ◦C with n-BuLi, followed by addition of [(p-cymene)RuCl2]2
at room temperature, and directly achieved the aromatic C–H
activation (Scheme 1). The iodine atom attached to the Ru centre
may originate from the imidazolium iodide through halogen
exchange (complex 1). This reaction procedure took place at room
temperature with no presence of any base and was monitored
by thin-layer chromatography (TLC), obtaining only the C–H
activated species. Therefore, the intramolecular sp2 C–H activation
might be an extremely feasible process. This experimental result is
consistent with what Dixneuf et al. had reported.31
aState Key Laboratory of Elemento-Organic Chemistry, College of
Chemistry, Nankai University, Tianjin, People’s Republic of China.
E-mail: bqwang@nankai.edu.cn
bState Key Laboratory of Organometallic Chemistry, Shanghai Institute
of Organic Chemistry, Chinese Academy of Sciences, Shanghai, People’s
Republic of China
† Electronic supplementary information (ESI) available: 1H NMR and 13
C
NMR spectra of all compounds. CCDC reference numbers 675611 (for 3),
675612 (for 5), 675613 (for 6), 705186 (for 1), 705187(for 7), and 705188
(for 8). For ESI and crystallographic data in CIF or other electronic format
see DOI: 10.1039/b818091a
However, complex 2 was obtained as a normally monometalated
species under the same experimental conditions (Scheme 2).
5182 | Dalton Trans., 2009, 5182–5189
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Scheme 1 Synthesis of complex 1.
Fig. 1 ORTEP diagram of 1. All the hydrogen atoms are omitted for clar-
ity for clarity. Thermal ellipsoids are shown at the 30% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(11) 2.060(9), Ru(1)–C(19) 2.007(8),
Ru(1)–I(1) 2.7217(12), Ru(1)–centroid (arene) 1.731, average of Ru–C
in the arene ligand 2.234, C(11)–Ru(1)–C(19) 76.3(4), C(11)–Ru(1)–I(1)
87.8(2), C(19)–Ru(1)–I(1) 87.4(2), C(11)–Ru(1)–centroid (arene) 128.71,
C(19)–Ru(1)–centroid (arene) 132.62, I(1)–Ru(1)–centroid (arene) 127.00.
Scheme 2 Synthesis of complex 2.
is practically identical with the reported vinyl cyclometalated
31
˚
complex [2.071(5) A].
Similar to the five-membered ruthenacycle in complex 1, a
six-membered ruthenacycle might have formed as a result of
subsequent intramolecular sp2 C–H activation of complex 2.
Actually, the larger ring size (six-membered or larger) may not
be favoured by (p-cymene)Ru(II) species, which is contrary to the
Ir(III) complexes where many cyclometalated six-membered ring
examples have been reported to form under similar conditions.33,37
The 1H NMR spectra of complexes 1 and 2 show conspicuous
differences in signals of phenyl protons. Complex 1 has a signal of
four protons at d 8.04–6.92 ppm, while complex 2 has a signal of
five protons at d 7.34–7.24 ppm. The differences unambiguously
The sp3 C–H Activation
By analogy to the Cp*Ir(III) analogues,24 the sp3 C–H activation of
Ru(II)(NHC) complexes might be also achieved. Therefore, 1-tert-
butyl-3-methylimidazolium iodide was synthesised and utilised as
a NHC precursor. This imidazolium salt was allowed to react
with n-BuLi at 0 ◦C in THF, then with [(p-cymene)RuCl2]2 at
room temperature to provide complex 3, and cyclometalation of
the NHC ligand upon one of C–H bonds in tert-butyl group was
observed (Scheme 3).
1
reveal the orthometalation in complex 1. Moreover, the 13C{ H}
NMR spectra of complexes 1 and 2 show the signals of the carbene
carbons at 160.9 and 171.5 ppm, respectively, while the metalated
phenyl carbon of complex 1 appears at 124.0 ppm.
The structure of complex 1 was further confirmed by X-ray
diffraction analysis. The ORTEP diagram of complex 1 is
illustrated in Fig. 1, with the most representative bond distances
and angles shown. It clearly shows that orthometalation on
the phenyl substituent of the NHC ligand has been achieved,
with formation of a five-membered ruthenacycle in coplanar
conformation. The plane of the imidazole moiety shares the same
plane with that of both ruthenacycle and Ph ring. The chelate
bite angle [C(11)–Ru(1)–C(19)] is 76.3(4)◦, similar to that◦for
the previously reported cyclometalated complex [76.59(18) ].31
˚
The Ru–Ccarbene bond distance of 2.007(8) A lies in the range
of other (p-cymene)Ru(NHC) complexes.16,25–30. The Ru–C bond
˚
distance for the cyclometalated phenyl ring is 2.060(9) A, which
Scheme 3 Synthesis of complex 3.
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As with what has been already described for the preparation
of complex 1, the presence of the monometalated species (C)
was not detected, although the reaction was carried out at room
temperature—a considerably mild condition. Utilisation of the
transmetalation reagent Ag2O as an alternative in preparing the
normally coordinated complex (C) merely obtained the cyclomet-
alation product 3, possibly suggesting the monometalated species
Three other substituted imidazolium iodides were also used as
NHC precursors to react with [(p-cymene)RuCl2]2 under the same
reaction conditions mentioned. Unfortunately, no C–H activated
cyclometalated product was observed either under room temper-
ature or under solvent reflux. Only normally coordinated prod-
ucts [(p-cymene)Ru(L)I2] [L = 1-isopropyl-3-methylimidazol-2-
ylidene (4), 1-(2,4,6-trimethylphenyl)-3-methylimidazol-2-ylidene
(5) (Fig. 3), and 1-cyclohexyl-3-methylimidazol-2-ylidene (6)
(Fig. 4)] were obtained for these ligands (Scheme 4).
1
[(p-cymene)Ru(NHC)X2] is too reactive to exist. The H NMR
spectrum of 3 shows the signals of the non-equivalent geminal
protons of the metalated CH2 group at 3.14 and 3.06 ppm
(2JH–H = 9.35 Hz). The other two methyl groups of the tert-
butyl group are diastereotopic and appear as two singlets at 1.42
1
and 1.11 ppm. The 13C{ H} NMR spectrum shows the signals
of carbene carbon and metalated methylene carbon at 181.5 and
24.4 ppm, respectively. Single crystal X-ray diffraction analysis
confirms that complex 3 is also a cyclometalated five-membered
ruthenacycle species (Fig. 2).
Fig. 3 ORTEP diagram of 5. All the hydrogen atoms and solvent are omit-
ted for clarity. Thermal ellipsoids are shown at the 30% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(14) 2.103(3), Ru(1)–I(1) 2.7492(6),
Ru(1)–I(2) 2.7381(5), Ru(1)–centroid (arene) 1.720, average of Ru–C
in the arene ligand 2.227, C(14)–Ru(1)–I(1) 95.83(8), C(14)–Ru(1)–I(2)
85.68(8), I(1)–Ru(1)–I(2) 86.748(12), C(16)–Ru(1)–centroid (arene)
130.27, I(1)–Ru(1)–centroid (arene) 121.08, I(2)–Ru(1)–centroid (arene)
125.03.
Fig. 2 ORTEP diagram of 3. All the hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 30% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(11) 2.023(3), Ru(1)–C(16) 2.134(3),
Ru(1)–I(1) 2.7423(4), Ru(1)–centroid (arene) 1.737, average of Ru–C in
the arene ligand 2.237, C(11)–Ru(1)–C(16) 77.24(11), C(11)–Ru(1)–I(1)
86.92(8), C(16)–Ru(1)–I(1) 87.49(10), C(11)–Ru(1)–centroid (arene)
134.09, C(16)–Ru(1)–centroid (arene) 127.78, I(1)–Ru(1)–centroid (arene)
126.45.
This structure can be regarded as a distorted three-legged piano
stool, with a planar five-membered imidazolylidene–methylene
chelating ligand. The plane of imidazole moiety shares the same
plane with that of ruthenacycle. The Ru–Ccarbene bond distance
˚
of 2.023(3) A, which is practically the same as in complex 1
Scheme 4 Synthesis of complexes 4–6.
˚
[2.007(8) A], and still lies in the range of Ru–Ccarbene lengths
observed from other (p-cymene)Ru(NHC) complexes.16,25–30 The
distance of Ru–CH2 [2.134(3) A] is longer than those for complex
1 [2.060(9) A] and the vinyl cyclometalated complex [2.071(5) A],
possibly due to the different hybridisation of the carbon atoms. The
bite angle of the chelate ligand [C(11)–Ru(1)–C(16)] is 77.24(11)◦,
similar to that for complex 1 [76.3(4)◦].
In particular, we also attempted to utilise 1,3-bis(isopropyl)-
imidazol-2-ylidene for the cyclometalation process. However,
the normally coordinated complex 7 (Fig. 5) instead of the
cyclometalated product was observed (Scheme 5).
In the molecular structure of complex 5 (Fig. 3), the mesityl
plane is nearly perpendicular to the NHC plane (dihedral
˚
31
˚
˚
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Scheme 5 Synthesis of complex 7.
According to the observation of t-Bu substituted NHC ligand,
we assume that, besides the ruthenacycle size, the steric repulsion
between the NHC substituents and the metal centre might
influence or even dominate the feasibility of cyclometalation.
Competition of sp2 vs. sp3 C–H Activation
In order to determine the relative activity between sp2 and sp3
C–H activation, a straightforward synthesis of 1-tert-butyl-3-
phenyl-imidazol-2-ylidene or its analogues is thus required. Two
candidates for synthetic methodology are available according to
the literature published by the groups of Furstner39 and Grubbs.40
The synthesis of 1-phenyl-3-tert-butyl-4,5-dihydro-imidazolium
chloride was finally chosen because of the efficiency of Grubbs’
protocol.
According to the phenomena observed in the previous sections
of this work, both activation processes (sp2/sp3 C–H bond) are
possible in the current issue. The aromatic and aliphatic C–H
activations and formations of complexes 8 and 9 were both
originally expected. However, the reaction of 1-phenyl-3-tert-
butyl-4,5-dihydro-imidazol-2-ylidene with [(p-cymene)RuCl2]2 se-
lectively proceeded to the cyclometalated species 8, without any
detectable formation of complex 9 (Scheme 6).
Fig. 4 ORTEP diagram of 6 shows only one molecule of the two
in the asymmetric unit. All the hydrogen atoms are omitted for clar-
ity. Thermal ellipsoids are shown at the 10% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(4) 2.03(4), Ru(1)–I(1) 2.782(4),
Ru(1)–I(2) 2.784(4), Ru(1)–centroid (arene) 1.712, average of Ru–C
in the arene ligand 2.23, C(4)–Ru(1)–I(1) 94.9(9), C(4)–Ru(1)–I(2)
92.5(9), I(1)–Ru(1)–I(2) 83.71(13), C(4)–Ru(1)–centroid (arene) 124.70,
I(1)–Ru(1)–centroid (arene) 122.73, I(2)–Ru(1)–centroid (arene) 127.25.
Fig. 5 ORTEP diagram of 7. All the hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 30% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(11) 2.101(2), Ru(1)–I(1) 2.7521(6),
Ru(1)–I(2) 2.7431(6), Ru(1)–centroid (arene) 1.711, average of Ru–C
in the arene ligand 2.219, C(11)–Ru(1)–I(1) 93.77(7), C(11)–Ru(1)–I(2)
93.61(6), I(1)–Ru(1)–I(2) 83.660(17), C(11)–Ru(1)–centroid (arene)
126.30, I(1)–Ru(1)–centroid (arene) 125.11, I(2)–Ru(1)–centroid (arene)
123.00.
Scheme 6 Synthesis of complex 8.
As predicted, the monometalated species D was not detected.
The 1H NMR spectrum of 8 shows the signal of the two protons
in the metalated CH2 at 3.20 ppm as a singlet, which is different
from that of complex 3 in which the metalated CH2 protons are
non-equivalent and split. The methyl protons of the tert-butyl
group appear at 1.34 and 1.10 ppm. The signals of the CH in
p-cymene groups are diastereotopic because of asymmetry after
angle = 84.4◦). The methyl groups of the mesityl substituent are
away from the ruthenium atom, accounting for the absence of
C–H activation. As the only consequence of cyclometalation which
failed to occur, the mesityl-substituted NHC might have formed
the disfavoured six-membered ring.
1
the cyclometalation. The 13C{ H} NMR spectrum of 8 confirms
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cyclometalation, with significant signals shown at 162.3 (carbene
carbon) and 24.2 ppm (metalated CH2). The molecular structure
of 8 was further confirmed by X-ray diffraction analysis (Fig. 6).
ylidene is less bulky than 1-tert-butyl-3-methylimidazol-2-ylidene,
it is considered that the experimental consequence might result
from the steric factor and support the former discussion. In all
processes discussed in this paper, six-membered ruthenacycles
from the cyclometalation did not form at all, indicating that
five-membered ruthenacycle is more stable for (p-cymene)Ru(II)-
centred organometallic complexes.
Experimental section
General
Solvents were dried over sodium diphenyl ketyl (THF, hydro-
carbons), or calcium hydride (dichloromethane) and distilled
under argon prior to use. The reactions were carried out under
argon, using Schlenck vacuum line techniques. [(Me)(Ph)ImH]+I-,
[(Me)(t-Bu)ImH]+I-, [(Me)(Mes)ImH]+I-, [(Me)(iPr)ImH]+I- and
[(Me)(Cy)ImH]+I- were prepared by treating the corresponding
N-substituted imidazoles with methyl iodide.41 [(Me)(Bn)ImH]+I-
was prepared by treating N-methylimidazole with benzyl iodide.
[(iPr)2ImH]+Cl- was prepared by a previous literature method.42
NMR spectra were recorded on a Bruker AV300 or VARIAN
AS-400 at room temperature with TMS as internal standard.
Elemental analyses were performed on a Perkin-Elmer 240C
analyzer. HR ESI mass spectra were performed on a Varian
7.0 T FTICR-Mass Spectrometer. Crystal structure and X-ray
data collection data are given in Table 1.
Fig. 6 ORTEP diagram of 8. All the hydrogen atoms are omitted for
clarity. Thermal ellipsoids are shown at the 60% level. Selected bond
◦
˚
distances (A) and angles ( ): Ru(1)–C(7) 2.010(2), Ru(1)–C(13) 2.128(2),
Ru(1)–I(1) 2.7408(9), Ru(1)- centroid (arene) 1.725, average of Ru–C
in the arene ligand 2.232, C(7)–Ru(1)–C(13) 77.54(9), C(7)–Ru(1)–I(1)
87.42(7), C(13)–Ru(1)–I(1) 86.48(7), C(7)–Ru(1)–centroid (arene) 132.85,
C(13)–Ru(1)–centroid (arene) 128.96, I(1)–Ru(1)–centroid (arene) 126.68.
Synthesis of 1-tert-butyl-3-phenyl-4,5-dihydro-imidazolium
chloride
This structure can also be regarded as a distorted three-
legged piano stool, with a five-membered dihydroimidazolylidene–
methylene chelating ligand. The plane of imidazole moiety shares
the same plane with that of ruthenacycle. The Ru–Ccarbene bond
This synthesis is a modification from the published protocol by
Waltman and Grubbs.40
˚
˚
The tert-butylamine (100 mmol, 7.32 g) and triethylamine
(100 mmol, 10.2 g) were dissolved in dry THF (150 mL) and cooled
to 0 ◦C, ethyl chlorooxoactetate (100 mmol, 15.3 g) was added
slowly. The mixture was allowed to warm to room temperature and
stirred overnight. After filtration, the solvent was removed under
reduced pressure to give N-tert-butyloxanilic acid ethyl ester as a
yellowish liquid. Then aniline (100 mmol, 9.31 g), toluene (50 mL),
triethylamine (200 mmol, 20.24 g) were added. The mixture was
heated under reflux overnight, the product precipitated while
being cooled to room temperature. Ethyl acetate was added until
the solid redissolved. The solution was washed with 2 M HCl
solution (2 ¥ 100 mL). The aqueous layer was then extracted with
ethyl acetate, and the combined organic layers were washed with
brine (100 mL), and dried over MgSO4. The solvents were then
removed under reduced pressure, leaving a yellowish solid. This
product was directly used for reduction with LiAlH4 (400 mmol,
15.18 g) in THF (100 mL) under reflux overnight. A saturated
aqueous solution of NaOH was then added very carefully to the
mixture. After filtration the solid was washed several times with
ethyl acetate. The organic layers were combined and dried with
MgSO4. Removal of the solvents in vacuum gave an orange oil,
to which was added 10 mL of concentrated HCl with vigorously
stirring. Then 150 mL of triethylorthoformate and several drops
of HCO2H were added. The mixture was heated under 120 ◦C for
12 h. After it was cooled to room temperature, the solvent was
removed in vacuum and the resulting residue was washed with
distance is 2.010(2) A, the Ru–CH2 distance is 2.128(2) A, and the
bite angle of the chelate ligand [C(7)–Ru(1)–C(13)] is 77.54(9)◦.
Conclusions
We have demonstrated that (p-cymene)Ru(NHC) complexes can
undergo facile intramolecular sp2 and sp3 C–H activation with
certain NHC precursors. In the cases of the formation of
cyclometalated complexes 2 and 4, C–H activation is so favoured
that we could not even trap the noncyclometalated intermediate
species (A and C in Schemes 1 and 3). The same result was also
obtained for the reaction of transmetalation (Scheme 3). Only
the sp3 C–H activation was observed in the case of N-phenyl-N¢-
tert-butyl-4,5-dihydro-imidazol-2-ylidene, although the favoured
five-membered ruthenacycle can be formed either via sp3 or sp2
C–H activation process. Herein, we believe that steric repulsion
should be the dominant factor for C–H activation.33 The presence
of the tert-butyl group in complex C (Scheme 3) and D (Scheme 6)
provides the structures in which one of the methyl groups is closely
oriented toward the Ru centre. This steric bulk between methyl
group and Ru may trigger the cyclometalation, which seems to be
the only way to release the hindrance around the metal centre. The
case of 1,3-bis(isopropyl)imidazol-2-ylidene (complex 7) strongly
supports this point of view. Under similar experimental conditions,
only monometalated species was obtained without any trace
of cyclometalated product. Since 1,3-bis(isopropyl)imidazol-2-
5186 | Dalton Trans., 2009, 5182–5189
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Table 1 Crystal data and summary of X-ray data collection for complexes 1, 3, 5, 6, 7 and 8a
1
3
5·CH2Cl2
6
7
8
Formula
Fw
C20H23IN2Ru
519.37
113(2)
0.71070
Orthorhombic
Pna21
7.729(3)
14.184(6)
17.532(8)
90
C18H27IN2Ru
499.39
294(2)
0.71073
Monoclinic
P21/c
13.331(2)
8.5497(15)
17.376(3)
90
102.401(3)
90
1934.2(6)
4
1.715
2.406
C24H32Cl2I2N2Ru
774.29
113(2)
0.71070
Triclinic
¯
P1
C20H30I2N2Ru
653.33
294(2)
0.71073
Orthorhombic
Pna21
18.958(6)
24.186(8)
10.345(4)
90
90
90
4743(3)
8
1.830
C19H30I2N2Ru
641.32
113(2)
0.71073
Monoclinic
P21/n
8.7376(17)
14.070(3)
17.591(4)
90
99.91(3)
90
2130.4(7)
4
2.000
3.638
C23H31IN2Ru
563.47
113(2)
0.71073
Monoclinic
P2/c
14.538(3)
9.827(2)
15.987(3)
90
101.10(3)
90
2241.2(8)
4
1.670
2.087
T/K
˚
l/A
Cryst. Syst.
Space group
˚
a/A
8.8274(17)
11.8707(18)
14.782(3)
67.695(8)
83.695(10)
70.037(7)
1346.6(4)
2
1.910
3.088
748
0.18 ¥ 0.16 ¥ 0.16
1.96–25.01
12 738
4754/0.0354
287
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
90
90
3
˚
V/A
1922.0(15)
4
1.795
2.425
1016
0.04 ¥ 0.03 ¥ 0.02
1.85–27.86
22 777
4572/0.1006
223
Z
Dc/g cm-3
m/mm-1
3.270
2512
0.22 ¥ 0.20 ¥ 0.16
1.36–25.02
18 648
F(000)
984
1232
1120
Cryst. size/mm
0.30 ¥ 0.24 ¥ 0.20
1.56–26.40
10 851
3944/0.0295
206
0.08 ¥ 0.06 ¥ 0.04
1.86–27.88
15 091
5063/0.0320
224
0.14 ¥ 0.12 ¥ 0.08
2.45–27.48
25 938
5133/0.0494
249
q range/◦
No. of reflns collected
No. of indep. reflns/Rint
No. of params
Goodness-of-fit on F2
R1, wR2 (I > 2s(I))
R1, wR2 (all data)
Flack parameter
8095/0.1413
460
1.150
1.024
1.044
1.036b
1.020
1.031
0.0570, 0.1242
0.0633, 0.1277
0.34(4)
0.0264, 0.0599
0.0365, 0.0643
n/a
0.0233, 0.0551
0.0277, 0.0568
n/a
0.0948, 0.1629
0.2499, 0.2366
-0.02(8)
0.0192, 0.0445
0.0236, 0.0455
n/a
0.0263, 0.0571
0.0316, 0.0586
n/a
a Single crystals of complexes 1, 3, 5, 6, 7 and 8 suitable for X-ray diffraction were obtained from hexane–CH2Cl2 or hexane–THF solution. Data
collection was performed on a BRUKER SMART 1000 (for 3 and 6) or a Rigaku Saturn 70 (for 1, 5, 7 and 8) equipped with a rotating anode system,
˚
using graphite-monochromated Mo-Ka radiation (w-2q scans, l = 0.71073 or 0.71070 A). Semiempirical absorption corrections were applied for all
complexes. The structures were solved by direct methods and refined by full-matrix least-squares. All calculations were using the SHELXTL-97 program
system. b Due to poor quality of the single crystal of 6, some atoms’ thermal parameters (C23, C37, N4, C18, C14, C15, C17, C33, C16) were restrained
to be isotropic.
THF. Subsequent suction filtration afforded the desired 1-tert-
butyl-3-phenyl-4,5-dihydroimidazolium chloride as white powder.
Total yield is 23%. Mp: 210–212 ◦C. 1H NMR (400 MHz, 293 K,
d6-DMSO): d = 9.42 (s, 1H, NCHN), 7.64 (d, J = 7.95 Hz, 2H,
Ph-CH), 7.45 (t, J = 7.36 Hz, J = 7.18 Hz, 2H, Ph-CH), 7.27
(t, J = 7.36 Hz, J = 7.18 Hz, 1H, Ph-CH), 4.38 (t, J = 9.79 Hz,
J = 10.99 Hz, 2H, NCH2), 4.18 (t, J = 10.99 Hz, J = 9.79 Hz,
5.38 (d, J = 5.97 Hz, 1H, p-cymene-CH), 4.05 (s, 3H, N(CH3)),
2.34 (m, 1H, p-cymene-CH(CH3)2), 2.30 (s, 3H, p-cymene-CH3),
0.92 (d, J = 6.89 Hz, 3H, p-cymene-CH(CH3)2) 0.80 (d, J =
1
6.89 Hz, 3H, p-cymene-CH(CH3)2). 13C{ H} NMR (100 MHz,
293 K, CDCl3): d = 160.9 (C–Ru carbene), 142.7 (Ph), 124.0
(Ph), 121.8 (Ph), 114.1 (NCH), 110.8 (NCH), 91.3 (p-cymene-C),
89.2 (p-cymene-C), 88.0 (p-cymene-C), 84.5 (p-cymene-C), 38.2
(NCH3), 31.4 (p-cymene-CH(CH3)2), 23.0 (p-cymene-CH3), 21.7
(p-cymene-CH(CH3)2), 20.8 (p-cymene-CH(CH3)2). HRMS (ESI,
m/z): calcd for C20H23N2Ru+ (M - X) 393.0903, found 393.0906.
1
2H, NCH2), 1.47 (s, 9H, C(CH3)3). 13C{ H} NMR (100 MHz,
293 K, d6-DMSO): d = 136.6 (NCHN), 129.3 (Ph), 125.7 (Ph),
117.7 (Ph), 57.4 (NCH2), 47.6 (NCH2), 45.4 (N(C(CH3)3), 27.4
(N(C(CH3)3). Anal. Calcd. for C13H19ClN2: C, 65.40, H, 8.02, N,
11.73. Found: C, 65.42, H, 8.03, N, 11.76%.
Synthesis of complex 2
Using a procedure similar to that as described for 1, reaction
of [(Me)(Bn)ImH]+I- (1 mmol) with n-BuLi (1 mmol) and
[(p-cymene)RuCl2]2 (0.5 mmol) gave complex 2 in 40% yield as
black red crystals. Mp: 165–167 ◦C. 1H NMR (400 MHz, 293 K,
CDCl3): d = 7.34 (m, 4H, Ph-CH), 7.24 (m, 1H, Ph-CH), 7.04
(s, 1H, NCH), 6.85 (s, 1H, NCH), 5.87 (m, 1H p-cymene-CH),
5.65 (m, 2H p-cymene-CH), 5.54 (m, 1H p-cymene-CH), 5.27
(m, 1H, Bn-CH2), 4.84 (m, 1H, Bn-CH2), 4.14 (s, 3H, N(CH3)),
3.26 (m, 1H, p-cymene-CH(CH3)2), 1.98 (s, 3H, p-cymene-CH3),
Synthesis of complex 1
A mixture of [(Me)(Ph)ImH]+I- (286 mg, 1 mmol) and n-BuLi
(1 mmol) was stirred in THF (30 mL) for 5 h under 0 ◦C. Powdered
[(p-cymene)RuCl2]2 (306 mg, 0.5 mmol) was then added and the
mixture was stirred at room temperature over night. After removal
of solvents in vacuum, the residue was extracted with CH2Cl2 and
filtered through Celite. CH2Cl2 was afterwards removed in vacuum
and a red solid was obtained. After recrystallisation from hexane–
THF complex 1 was obtained (198 mg, 38%) as orange red crystals.
Mp: 208–210 ◦C. 1H NMR (400 MHz, 293 K, CDCl3): d = 8.04
(m, 1H, Ph-CH), 7.34(d, J = 1.56 Hz, 1H, NCH), 7.08 (m, 1H, Ph-
CH), 6.97 (d, J = 1.56 Hz, 1H, NCH), 6.92 (m, 2H, Ph-CH), 5.50
(d, J = 5.97 Hz, 1H, p-cymene-CH), 5.46 (m, 2H, p-cymene-CH),
1
1.25 (m, 6H, p-cymene-CH(CH3)2). 13C{ H} NMR (100 MHz,
293 K, CDCl3): d = 171.5 (C–Ru carbene), 137.2 (Ph), 128.8
(Ph), 128.0 (Ph), 127.7 (Ph), 123.9 (Ph), 123.2 (Ph), 109.9 (NCH),
99.0 (p-cymene-C), 58.7 (PhCH2), 45.1 (NCH3), 45.1 (p-cymene-
CH(CH3)2), 31.6 (p-cymene-CH3), 19.1 (p-cymene-CH(CH3)2).
This journal is
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Dalton Trans., 2009, 5182–5189 | 5187
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HRMS (ESI, m/z): calcd for C21H26N2IRu+ (M - X) 535.0183,
found 534.9977.
(NCH), 107.3 (p-cymene-C), 100.2 (p-cymene-C), 89.6 (p-cymene-
C), 88.8 (p-cymene-C), 83.3 (p-cymene-C), 82.2 (p-cymene-C),
45.6 (NCH3), 45.2 (p-cymene-CH(CH3)2), 31.8 (Mes-CH3), 31.2
(p-cymene-CH3), 23.4 (p-cymene-CH(CH3)2). HRMS (ESI, m/z):
calcd for C23H30N2IRu+ (M - X) 563.0497, found 563.0490.
Synthesis of complex 3
Using a procedure similar to that as described for 1, reac-
tion of [(Me)(t-Bu)ImH)]+I- (1 mmol) with n-BuLi (1 mmol)
and [(p-cymene)RuCl2]2 (0.5 mmol) gave complex 3 in 30% as
orange red crystals. Mp: 142–144 ◦C. 1H NMR (400 MHz,
293 K, CDCl3): d = 6.87 (s, 1H, NCH), 6.65 (s, 1H, NCH),
5.36 (m, 2H, p-cymene-CH), 5.22 (d, J = 5.72 Hz, 1H,
p-cymene-CH), 4.79 (d, J = 5.72 Hz, 1H, p-cymene-CH), 3.92
(s, 3H, N(CH3)), 3.14 (d, J = 9.35 Hz, 1H, C(CH3)2(CH2Ru)),
3.06 (d, J = 9.35 Hz, 1H, C(CH3)2(CH2Ru)), 2.66 (m, 1H,
p-cymene-CH(CH3)2), 1.95 (s, 3H, p-cymene-CH3), 1.42 (s,
3H, C(CH3)2(CH2Ru)), 1.12 (d, J = 7.20 Hz, 3H, p-cymene-
Synthesis of complex 6
Using a procedure similar to that as described for 1, reaction
of [(Me)(Cy)ImH]+I- (1 mmol) with n-BuLi (1 mmol) and
[(p-cymene)RuCl2]2 (0.5 mmol) gave complex 6 in 37% yield as
black red crystals. Mp: 201–203 ◦C. 1H NMR (400 MHz, 293 K,
CDCl3): d = 7.07 (d, J = 1.95 Hz, 1H, NCH), 7.04 (d, J = 1.95 Hz,
1H, NCH), 5.70 (d, J = 30.3 Hz, 2H, p-cymene-CH), 5.24 (m,1H,
NCH-Cy), 4.96 (d, J = 30.3 Hz, 2H, p-cymene-CH), 4.10 (s, 3H,
N(CH3)), 3.30 (m, 1H, CH(CH3)2), 1.91 (s, 3H, p-cymene-CH3),
1.78–1.75 (m, 4H, Cy-CH2), 1.58 (m, 2H, Cy-CH2), 1.30–1.27 (m,
CH(CH3)2), 1.11 (s, 3H, C(CH3)2(CH2Ru)), 1.05 (d, J
=
7.20 Hz, 3H, p-cymene-CH(CH3)2). 13C{ H} NMR (100 MHz,
293 K, CDCl3): d = 181.5 (C–Ru carbene), 122.6 (NCH),
121.8 (NCH), 115.8 (p-cymene-C), 104.6 (p-cymene-C), 86.7
(p-cymene-C), 81.7(p-cymene-C), 64.7 (C(CH3)2(CH2Ru)), 32.1
(NCH3), 31.1 (p-cymene-CH(CH3)2), 30.7 (p-cymene-CH3), 28.3
(C(CH3)2(CH2Ru)), 24.4 (C(CH3)2(CH2Ru)), 21.4 (p-cymene-
CH(CH3)2). HRMS (ESI, m/z): calcd for C18H27N2Ru+ (M - X)
373.1216, found 373.1216.
1
1
10H, Cy-CH2+p-cymene-CH(CH3)2). 13C{ H} NMR (100 MHz,
293 K, CDCl3): d = 169.1 (C–Ru carbene), 124.1 (NCH), 119.7
(NCH), 109.7 (p-cymene-C), 108.9 (p-cymene-C), 99.6 (p-cymene-
C), 88.2 (p-cymene-C), 87.0 (p-cymene-C), 81.0 (p-cymene-C),
62.1 (NCH3), 44.9 (NCH-Cy), 31.5 (p-cymene-CH(CH3)2), 25.2
(CH2-Cy), 19.0 (p-cymene-CH(CH3)2). HRMS (ESI, m/z): calcd
for C20H30N2IRu+ (M - X) 527.0496, found 527.0494.
Synthesis of complex 7
Synthesis of complex 4
A mixture of [(iPr)2ImH]+Cl- (189 mg, 1 mmol) and n-BuLi
(1 mmol) was stirred in THF (30 mL) for 5 h under 0 ◦C. Powdered
[(p-cymene)RuCl2]2 (306 mg, 0.5 mmol) and excess NaI (300 mg,
2 mmol) was then added and the mixture was stirred at room
temperature overnight. After removal of solvents in vacuum, the
residue was extracted with CH2Cl2 and filtered through Celite.
CH2Cl2 was removed in vacuum and red solid was obtained. After
recrystallisation from hexane–CH2Cl2 complex 7 (192 mg, 30%)
Using a procedure similar to that as described for 1, reaction
of [(Me)(iPr)ImH]+I- (1 mmol) with n-BuLi (1 mmol) and
[(p-cymene)RuCl2]2 (0.5 mmol)◦gave complex 4 in 44% yield
1
as black red crystals. Mp: 176 C (dec). H NMR (400 MHz,
293 K, CDCl3): d = 7.07 (s, 2H, NCH), 5.69 (m, 2H,
p-cymene-CH), 5.45 (m,1H, NCH(CH3)2), 5.23 (m, 1H, p-
cymene-CH), 5.00 (m, 1H, p-cymene-CH), 4.08 (s, 3H, NCH3),
3.27 (m, 1H, p-cymene-CH(CH3)2), 1.90 (s, 3H, p-cymene-
CH3), 1.43 (d, J = 6.41 Hz, 6H, NCH(CH3)), 1.26 (m,
◦
1
was obtained as black red crystals. Mp: 189–191 C. H NMR
(300 MHz, 293 K, CDCl3): d = 7.19 (s, 1H, NCH), 7.06 (s,
1H, NCH), 5.70 (d, J = 5.82 Hz, 2H, p-cymene-CH), 5.52 (m,
2H, (CH3)2CHN), 5.06 (d, J = 5.82 Hz, 2H, p-cymene-CH), 3.29
(m, 1H, p-cymene-CH(CH3)2), 1.92 (s, 3H, p-cymene-CH3), 1.39
(d, J = 5.01 Hz, 12H, (CH3)2CHN), 1.26 (d, J = 6.92 Hz, 6H,
1
6H, p-cymene-CH(CH3)2). 13C{ H} NMR (100 MHz, 293 K,
CDCl3): d = 168.7 (C–Ru carbene), 124.4 (NCH), 119.0
(NCH), 108.8 (p-cymene-C), 99.6 (p-cymene-C), 87.9 (p-cymene-
C), 86.7 (p-cymene-C), 81.2 (p-cymene-C), 80.7 (p-cymene-C),
54.8 (NCH(CH3)2), 44.9 (NCH3), 44.9 (p-cymene-CH(CH3)2),
31.5 (p-cymene-CH3), 25.0 (NCH(CH3)), 19.0 (p-cymene-
CH(CH3)2). HRMS (ESI, m/z): calcd for C17H26N2IRu+ (M -
X) 487.0182, found 487.0189.
1
p-cymene-CH(CH3)2). 13C{ H} NMR (75 MHz, 293 K, CDCl3):
d = 167.4 (C–Ru carbene), 119.5 (NCH), 108.0 (p-cymene-
C), 99.8 (p-cymene-C), 87.5 (p-cymene-C), 81.1 (p-cymene-C),
54.7 (NCH(CH3)2), 31.5 (p-cymene-CH(CH3)2), 25.5 (p-cymene-
CH3), 24.9 (NCH(CH3)2), 23.2 (NCH(CH3)2), 22.7 (p-cymene-
CH(CH3)2), 19.6 (p-cymene-CH(CH3)2). HRMS (ESI, m/z): calcd
for C19H34O2N2NaRu+ (M - 2I + 2H2O + Na+) 447.1560, found
447.1570.
Synthesis of complex 5
Using a procedure similar to that as described for 1, reaction
of [(Me)(Mes)ImH]+I- (1 mmol) with n-BuLi (1 mmol) and
[(p-cymene)RuCl2]2 (0.5 mmol) gave complex 5 in 35% yield
as black red crystals. Mp: 189–191 ◦C. 1H NMR (400 MHz,
293 K, CDCl3): d = 7.23(s, 1H, NCH), 6.86 (s, 2H, Mes-
CH), 6.77 (s,1H, NCH), 5.71 (d, J = 5.74 Hz, 2H, p-cymene-
CH), 5.10 (d, J = 5.74 Hz, 2H, p-cymene-CH), 4.19 (s, 3H,
N(CH3)), 3.27(m, 1H, p-cymene-CH(CH3)2), 2.32 (s, 3H, p-
cymene-CH3), 2.05 (s, 3H, Mes-CH3), 2.00 (s, 6H, Mes-CH3), 1.24
(s, 3H, p-cymene-CH(CH3)2), 1.23 (s, 3H, p-cymene-CH(CH3)2).
Synthesis of complex 8
Using a procedure similar to that as described for 7, reaction
of [(Ph)(t-Bu)dihydroImH]+Cl- (1 mmol) with n-BuLi (1 mmol),
[(p-cymene)RuCl2]2 (0.5 mmol) and excess NaI (300 mg, 2 ◦mmol)
1
gave 8 in 32% yield as orange red crystals. Mp: 160–161 C. H
NMR (300 MHz, 293 K, CDCl3): d = 7.97 (d, J = 7.49 Hz,
1H, Ph-CH), 7.42 (t, J = 7.41 Hz, J = 8.06 Hz, 2H, Ph-CH),
7.29 (d, J = 7.29 Hz, 1H, Ph-CH), 4.87 (d, J = 5.93 Hz, 1H,
p-cymene-CH), 4.71 (d, J = 5.63 Hz, 1H, p-cymene-CH), 5.55
1
13C{ H} NMR (100 MHz, 293 K, CDCl3): d = 169.3 (C–Ru
carbene), 139.1 (Mes-Ph), 136.6 (Mes-Ph), 129.4 (Mes-Ph), 128.8
(Mes-Ph), 125.8 (Mes-Ph), 125.5 (Mes-Ph), 125.3 (NCH), 123.8
5188 | Dalton Trans., 2009, 5182–5189
This journal is
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©

View Article Online
(d, J = 5.93 Hz, 1H, p-cymene-CH), 4.24 (m, 1H, NCH2), 3.89
(m, 1H, NCH2), 3.57 (m, 1H, NCH2), 3.46 (m, 1H, NCH2), 3.20
(s, 2H, C(CH3)2(CH2Ru)), 2.57 (m, 1H, p-cymene-CH(CH3)2),
1.94 (s, 3H, p-cymene-CH3), 1.34 (s, 3H, C(CH3)2(CH2Ru)), 1.10
(s, 3H, C(CH3)2(CH2Ru)), 1.06 (d, J = 6.90 Hz, 3H, p-cymene-
CH(CH3)2) 1.00 (d, J = 6.90 Hz, 3H, p-cymene-CH(CH3)2).
14 S. H. Hong, M. W. Day and R. H. Grubbs, J. Am. Chem. Soc., 2004,
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1
13C{ H} NMR (75 MHz, 293 K, CDCl3): d = 162.3 (C–Ru car-
bene), 128.5 (Ph), 126.98 (Ph), 125.97 (Ph), 103.6 (p-cymene-C),
97.2 (p-cymene-C), 90.1 (p-cymene-C), 88.5 (p-cymene-C), 86.7
(p-cymene-C), 84.2 (p-cymene-C), 62.7 (NCH2), 52.2 (NCH2),
43.6 (C(CH3)2(CH2Ru)), 30.7 (p-cymene-CH(CH3)2), 29.9
(p-cymene-CH3), 27.6 (C(CH3)2(CH2Ru)), 26.3 (C(CH3)2-
(CH2Ru)), 24.2 (C(CH3)2(CH2Ru)), 21.2 (p-cymene-CH(CH3)2),
20.0 (p-cymene-CH(CH3)2). HRMS (ESI, m/z): calcd for
C23H31N2Ru+ (M - I) 437.1530, found 473.1537.
23 L. Jafarpour, J. K. Huang, E. D. Stevens and S. P. Nolan,
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Acknowledgements
We are grateful to the National Natural Science Foundation of
China (20672058, 20872066, 20721062), the Research Fund for the
Doctoral Program of Higher Education of China (20070055020),
the 111 Project (B06005), and the Program for New Century
Excellent Talents in University (NCET-04-0229) for financial
support.
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The Royal Society of Chemistry 2009
Dalton Trans., 2009, 5182–5189 | 5189
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