Synthesis and catalytic properties of novel ruthenium N-heterocyclic-carbene complexes

Article abstract of DOI:10.1016/j.jorganchem.2009.08.030

The reaction of [RuCl₂(p-cymene)]₂ with 1,3-dialkylimidazolinium salts 1a-f in the presence of a small excess of cesium carbonate yields chelated η⁶-arene, η¹-carbene ruthenium complexes 2a-f. All synthesised co

Full text of DOI:10.1016/j.jorganchem.2009.08.030

Journal of Organometallic Chemistry 694 (2009) 4025–4031
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and catalytic properties of novel ruthenium
N-heterocyclic-carbene complexes
b
Serpil Demir a, Ismail Özdemir a, , Bekir Çetinkaya
*
a Inönü University, Faculty of Science and Art, Department of Chemistry, 44280 Malatya, Turkey
Ege University, Faculty of Science, Department of Chemistry, 35100 Bornova-Izmir, Turkey
b
_
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 6 May 2009
Received in revised form 19 August 2009
Accepted 22 August 2009
Available online 27 August 2009
The reaction of [RuCl2(p-cymene)]2 with 1,3-dialkylimidazolinium salts 1a–f in the presence of a small
excess of cesium carbonate yields chelated
ised compounds were characterized by elemental analysis, NMR spectroscopy. The catalytic activity of
RuCl2(
6-arene, 1-imidazolinylidene) complexes 2a–f was evaluated in the direct arylation of 2-phen-
ylpyridine with chlorobenzene derivatives.
g g
6-arene, 1-carbene ruthenium complexes 2a–f. All synthes-
g
g
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Ruthenium
Imidazolinium salts
N-heterocyclic carbene
C–H bond activation
Arylation
1. Introduction
plexation of substrates during the catalytic cycle, at the same time
the strong donor moiety remains connected to the metal center.
We have shown the route to metal complexes containing mixed
arene and carbene ligands providing 8 electrons to the metal,
and that the natural orientation of the carbene in the complex is
significantly modified [16].
The development of N-heterocyclic carbene (NHC) complexes in
the 1960s [1] was followed by Lappert in the early 1970s [2], then
eventual isolation and crystallographic characterization of a stable
metal-free NHC by Arduengo group in 1991 [3]. N-heterocyclic
carbenes have proven an alternative to tertiary phosphines in
In recent years, transition metal-catalyzed C–H activation has
emerged as a powerful tool to transform otherwise unreactive C–
H bonds into carbon–carbon or carbon–heteroatom bonds [17].
Metal catalyzed direct arylation, through C–H bond activation
has consequently received considerable attention as an efficient
method of biaryl synthesis [18]. In recent years, significant pro-
gress has been made in direct arylation using complexes palladium
[19], rhodium [20], ruthenium [21] and other metals [22].
homogeneous catalysis, because of the strong
r-donating and neg-
ligible -accepting character, NHCs can form stable bonds with
p
various metals from main group to transition metals in different
oxidation states and stabilize catalytically active intermediates
[4]. Today, N-heterocyclic carbenes play a major role as ligands
in organometallic chemistry. They make metal complexes suitable
for a broad spectrum of catalytic applications [5]. For example,
ruthenium complexes catalyze olefin metathesis [6] transfer
hydrogenation [7], furan synthesis [8], palladium catalyzed cross-
coupling reaction and related transformation [9,10] and rhodium
catalyzed hydrosilylation [11] and hydroformylation [12]. It is ex-
pected that when the NHC orientation is perturbed in space, the
catalytic activity of the linked metal site should be largely modi-
fied. This influence is leading to the design of new chelating NHC
complexes. Examples of bis-NHC carbenes [13], mixed pyridine–
carbene [14] and oxazoline–carbene [15] complexes have already
been reported. The hemilable arm in such ligands is capable of
reversible dissociation from the metal center. Such dynamic
behaviour will produce vacant coordination sites that allow com-
We now report new 8 electron bridged
g g
6-arene, 1-carbene
ruthenium complexes from related electron-rich olefins bis-[1,3-
imidazolin-2-ylidene] containing at least one arylmethylene group
linked to a nitrogen atom. We also show that the resulting (g6
arene,
-
g
1-carbene)RuCl2 complexes can be used to for direct aryla-
tion of 2-phenylpyridine with chlorobenzene derivatives.
2. Results and discussion
1,3-Dialkylimidazolinium chlorides, (1a–f) are conventional
NHC precursors. The preparation of 1,3-dialkylimidazolinium
chloride was carried out according to the reported procedures
(Scheme 1) [23]. The salts are air- and moisture-stable both in
the solid state and in solution.
* Corresponding author.
E-mail address: iozdemir@inonu.edu.tr (I. Özdemir).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.08.030

4026
S. Demir et al. / Journal of Organometallic Chemistry 694 (2009) 4025–4031
N
+
N
+
Cl-
Cl-
N
N
OMe
1f
1a
Rn
N
+
Cl-
N
OMe
OMe
OMe
N
N
Cl-
R = CH3
n = 4 or 5
+
N
N
1
1e
+
R'Cl
1b
N
+
Cl-
N
N
+
Cl-
N
OMe
OMe
OMe
1d
1c
Scheme 1. Synthesis of substituted imidazolinium salts.
The structures of 1a–f were determined by their characteristic
spectroscopic data and elemental analyses. 13C NMR chemical
shifts were consistent with the proposed structure, the imino car-
bon appeared as a typical singlet in the 1H-decoupled mode in the
157.3, 157.9, 158.4, 157.9 158.7 and 158.2 ppm, respectively for
imidazolinium chlorides 1a–f. The 1H NMR spectra of the imidazo-
linium salts further supported the assigned structures; the reso-
nances for C(2)–H were observed as sharp singlets in the 9.39,
9.85, 10.38, 9.67, 10.49 and 9.32 ppm, respectively for 1a–f. The
IR data for imidazolinium salts 1a–f clearly indicate the presence
of the –C@N– group with a v(C@N) vibration at 1630, 1629,
1661, 1630, 1653 and 1653 cmÀ1, respectively for 1a–f. The NMR
values are similar to those found for other 1,3-dialkylimidazolini-
um salts [24].
Several general methods have been utilized for the preparation
of transition metal–NHC complexes. They are based on (i) in situ
deprotonation of the azolium salts, (ii) complexation of the free,
or protected form of the NHC carbene, (iii) thermal cleavage of
electron-rich olefin (NHC)2 resulting from the dimerization of
non-sterically hindered NHC, and formal insertion of the metal in
a C@C bond, (iv) transmetallation from a silver–NHC complex, (v)
direct oxidative addition to the metal center or (vi) the nucleo-
philic attack at the carbon atom of a coordinated isocyanide [25].
It has recently been shown that the heating in toluene of
[RuCl2(p-cymene)]2, imidazolinium salt, and Cs2CO3 afforded an
in situ prepared catalyst for enyne or alkene metathesis more ac-
tive that the isolated complex RuCl2(imidazolinylidene)(p-cymene)
complex [26]. It was suggested that the catalyst resulted from the
coordination of the in situ formed carbene, on imidazolium salt
deprotonation with Cs2CO3, with concommittant displacement of
the (p-cymene) ligand. Thus the imidazolinium salts 1a–f in the
presence of a small excess of cesium carbonate was heated with
[RuCl2(
2a–f with the aryl group
g
6-p-cymene)]2 in toluene at 110 °C for 6 h. The complexes
g
6-coordinated to the ruthenium atom
was obtained in good yields (Scheme 2). This result shows that
Cs2CO3 is able to generate a ruthenium coordinated imidazolinylid-
ene group in refluxing toluene and that the p-cymene ligand can be
intramolecularly displaced by an aryl group to generate a bidentate
ligand.
All products 2a–f were obtained as orange-brown crystalline
complexes in 65–88% yields. The air and moisture-stable ruthe-
nium carbene complexes (2a–f) were soluble in halogenated sol-
vents and insoluble in non-polar solvents. The ruthenium
complexes 2a–f have been characterized by analytical and spectro-
scopic techniques. Ruthenium complexes exhibit a characteristic
t(NCN) band typically at 1500–1669 cmÀ1 [8,27]. 13C chemical
shifts, which provide a useful diagnostic tool for metal carbene
complexes, show that Ccarb is substantially deshielded. Values of
13
d(
C
carb
) are in the 198.5–201.5 ppm range and are similar to
those found for other carbene complexes. These complexes show
typical spectroscopic signatures, which are in line with those re-
cently reported for other [RuCl2(mono-NHC)(arene)] complexes
[28].
We have recently shown that NHC–ruthenium(II) species in situ
generated from of [RuCl2(p-cymene)]2 and monoazolium salts un-
der basic conditions were able to catalyze the direct arylation of

S. Demir et al. / Journal of Organometallic Chemistry 694 (2009) 4025–4031
4027
N
Cl
Ru
Cl
N
2a
N
N
N
N
Cl
Cl
Cl
Ru
Ru
Cl
OMe
2f
2b
Rn
N
+
Cl-
N
R'
1a-1f
+
Cs2CO3
+
N
N
1/2
Cl
Cl
OMe
OMe
OMe
Ru
RuCl2
2
toluene/reflux
2e
N
N
Cl
Cl
OMe
Ru
OMe
N
N
OMe
Cl
Cl
Ru
2c
2d
Scheme 2. Synthesis of chelated
g
6-arene,
g
1-carbene ruthenium(II) complexes.
R
R
2-phenylpyridine by aryl bromides [29]. The mechanism study
showed that the first step of the reaction deals with the orthomet-
allation of the 2-phenylpyridine-ruthenium(II) adduct via a coop-
erative action of both the ruthenium(II) site and the coordinated
carbonate. We have found that the (dicarbene)ruthenium com-
plexes 2a–f can also act as catalyst precursors for the direct diary-
lation of 2-phenylpyridine, used as model substrate, directed in
ortho-position by the N-atom of the pyridine group according to
Scheme 3.
N
2a-2f /0.025 mmol
N
+
+
N
Cs2CO3, NMP,
120 oC, 10 h
Cl
2.2
R
R
4
3
R= COCH3; OCH3; CH3
The importance of the coordination of the required base in the
catalyst intermediate [29,30] led us to explore first the influence
of Cs2CO3, K2CO3, and KOBut in the presence of a precatalyst 2.
We found that Cs2CO3 in NMP at 120 °C provided the best condi-
Scheme 3. Direct arylation of 2-phenylpyridine with aryl chlorides.
Control experiments indicated that the arylation of 2-phenyl-
tions, and that initial treatment of the chelated
g
6-arene,
g
1-car-
pyridine with chlorobenzene reaction did not occur in the absence
of 2a. Under the optimum reaction conditions, the chlorobenzene
substrates reacted with 2-phenylpyridine to selectively afford the
major di-ortho-arylated products in excellent yields (Table 1 en-
tries 5, 10 and 16). It is worth noting that these new catalytic sys-
tems based on (carbene)ruthenium precursors in the presence of
cesium carbonate make possible the arylation with chloroarene
bene ruthenium(II) complexes. We first investigated the arylation
of 2-phenylpyridine with 4-chloroacetophenone in the presence
of [(g g
6-arene, 1-carbene)RuCl2] (2a–f) as catalyst precursor, and
extended the scope of the reaction to the para-substituted
methoxy-, and methylchorobenzenes. The results are reported in
Table 1.

4028
S. Demir et al. / Journal of Organometallic Chemistry 694 (2009) 4025–4031
Table 1
umn chromatography was performed using silica gel 60 (70-230
Direct arylation of chloro benzene derivatives with 2-phenylpyridine.a
mesh). Elemental analyses were carried out by analytical service
_
R
of TÜBITAK with
apparatus.
a Carlo Erba Strumentaziona Model 1106
R
N
4.2. General synthesis of imidazolinium salts
2a-2f /0.025 mmol
N
+
+
N
Cs2CO3, NMP,
120 oC, 10 h
To a solution of N-substituted imidazoline (1) (5.0 mmol) in
DMF (10 mL) was added slowly alkyl or aryl halide (5.0 mmol)
and the resulting mixture was stirred at 70 °C for 10 h. Diethyl-
ether (10 mL) was added to obtain a white crystalline solid which
was filtered off. The solid was washed with diethylether
(3 Â 10 mL) dried under vacuum and the crude product was
recrystallized from ethanole/diethylether.
2.2
R
Cl
R
4
3
R= COCH3; OCH3; CH3
Entry
[Ru–NHC]
Ar
Yield 3/4 (%)b
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
2a
2b
2c
2d
2e
2f
4-MeCOC6H4
4-MeCOC6H4
4-MeCOC6H4
4-MeCOC6H4
4-MeCOC6H4
4-MeCOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeOC6H4
4-MeC6H4
25/75
30/70
17/83
12/88
10/90
28/72
37/63
31/69
19/81
13/87
24/76
35/65
20/80
15/85
13/87
7/93
4.2.1. 1,3-Bis(2,3,4,5,6-pentamethylbenzyl)imidazolinium chloride, 1a
Yield: 3.93 g (92%), m.p.: 332–333 °C,
t
(CN): 1630 cmÀ1. Anal.
Calc. for C27H39N2Cl: C, 75.93; H, 9.20; N, 6.56. Found: C, 75.98;
H, 9.15; N, 6.62%. 1H NMR (399.9 MHz, CDCl3) d = 9.39 (s, 1H,
NCHN), 4.93 (s, 4H, CH2C6(CH3)5-2,3,4,5,6), 3.78 (s, 4H, NCH2CH2N),
2.26, 2.22 and 2.19 (s, 30H, CH2C6(CH3)5-2,3,4,5,6). 13C NMR
(100.5 MHz, CDCl3) d = 157.3 (NCHN), 136.4, 133.5, 133.2 and
125.6 (CH2C6(CH3)5-2,3,4,5,6), 47.8 (NCH2CH2N), 47.4 (CH2-
C6(CH3)5-2,3,4,5,6), 17.2, 16.9 and 16.8 (CH2C6(CH3)5-2,3,4,5,6).
9
10
11
12
13
14
15
16
17
18
4-MeC6H4
4-MeC6H4
4-MeC6H4
4-MeC6H4
4.2.2. 1-(2,3,4,5,6-Pentamethylbenzyl)-3-(2,4,6-trimethylbenzyl)
imidazolinium chloride, 1b
25/75
28/72
4-MeC6H4
Yield: 3.71 g (93%), m.p.: 298–299 °C,
t
(CN): 1629 cmÀ1. Anal.
a
Reaction conditions: ruthenium complex 2 (0.025 mmol), 2-phenylpyridine
Calc. for C25H35N2Cl: C, 75.25; H, 8.84; N, 7.02. Found: C, 75.19;
H, 8.86; N, 7.06%. 1H NMR (399.9 MHz, CDCl3) d = 9.85 (s, 1H,
NCHN), 6.87 (s, 2H, CH2C6H2(CH3)3-2,4,6), 4.97 (s, 2H,
CH2C6H2(CH3)3-2,4,6), 4.90 (s, 2H, CH2C6(CH3)5-2,3,4,5,6), 3.79–
3.64 (m, 4H, NCH2CH2N), 2.33, 2.29, 2.25, 2.23 and 2.21 (s, 24H,
CH2C6(CH3)5-2,3,4,5,6 and CH2C6H2(CH3)3-2,4,6). 13C NMR
(100.5 MHz, CDCl3) d = 157.9 (NCHN), 136.5, 133.6, 133.3 and
125.5 (CH2C6(CH3)5-2,3,4,5,6), 139.0, 137.8, 129.8 and 125.4
(0.5 mmol), ArCl (1.25 mmol), Cs2CO3 (1.5 mmol), NMP as solvent, 120 °C, 10 h.
Conversion of 2-phenylpyridine and 3/4 ratio determined by 1H NMR and by
b
GC.
derivatives that are more easily available than bromoarenes, but
much less reactive than the corresponding bromides, as the second
step of the catalytic reaction involves an oxidative addition to the
orthometallated ruthenium(II) intermediate [29].
(CH2C6H2(CH3)3-2,4,6),
47.5
(CH2C6H2(CH3)3-2,4,6),
47.4
(NCH2CH2N), 46.3 (CH2C6(CH3)5-2,3,4,5,6), 20.9 (CH2C6H2(CH3)3-
2,4,6), 20.1 (CH2C6H2(CH3)3-2,4,6), 17.2, 16.9 and 16.8
(CH2C6(CH3)5-2,3,4,5,6).
3. Conclusion
The above results show that imidazolinylidene ligands contain-
ing an arylmethyl-N group on reaction with [RuCl2(p-cymene)]2 al-
4.2.3. 1-(2,3,4,5,6-Pentamethylbenzyl)-3-(3,4,5-trimethoxybenzyl)
ways displace the p-cymene to give (g g
1-carbene, 6-arene)RuCl2
imidazolinium chloride, 1c
Yield: 4.02 g (90%), m.p.: 256–257 °C,
t
(CN): 1661 cmÀ1. Anal.
complexes. We have investigated the arylation of 2-phenylpyridine
with aryl chlorides in the presence of the Ru–NHC complexes
resulting in the formation of the corresponding arylated pyridine
derivatives and further applications of the present catalytic system
are ongoing and will be reported in due course.
Calc. for C25H35N2O3Cl: C, 67.17; H, 7.89; N, 6.27. Found: C,
67.21; H, 7.93; N, 6.25%. 1H NMR (399.9 MHz, CDCl3) d = 10.38 (s,
1H, NCHN), 6.74 (s, 2H, CH2C6H2(OCH3)3-3,4,5), 4.97 (s, 2H,
CH2C6H2(OCH3)3-3,4,5), 4.80 (s, 2H, CH2C6(CH3)5-2,3,4,5,6), 3.89
(s, 6H, CH2C6H2(OCH3)3-3,4,5), 3.82 (s, 3H, CH2C6H2(OCH3)3-3,4,5),
3.79-3.62 (m, 4H, NCH2CH2N), 2.29, 2.23 and 2.20 (s, 15H,
CH2C6(CH3)5-2,3,4,5,6). 13C NMR (100.5 MHz, CDCl3) d = 158.4
(NCHN), 153.8, 138.4, 128.4 and 106.2 (CH2C6H2(OCH3)3-3,4,5),
136.6, 133.6, 133.3 and 125.5 (CH2C6(CH3)5-2,3,4,5,6), 60.8
(CH2C6H2(OCH3)3-3,4,5), 56.6 (CH2C6H2(OCH3)3-3,4,5), 52.5
(CH2C6H2(OCH3)3-3,4,5), 47.5 and 47.4 (NCH2CH2N), 47.3
(CH2C6(CH3)5-2,3,4,5,6), 17.2, 16.9 and 16.8 (CH2C6(CH3)5-
2,3,4,5,6).
4. Experimental
4.1. General procedures
All reactions for the preparation imidazolinium salts (1) and
ruthenium(NHC) complexes (2) were carried out under argon in
flame-dried glassware using standard Schlenk techniques. Com-
plex 1f was synthesized according to known procedure [31]. The
solvents used were purified by distillation over the drying agents
indicated and were transferred under Ar:Et2O (Na/K alloy), CH2Cl2
(P4O10), hexane, toluene (Na). Melting points were determined in
glass capillaries under air with an Electrothermal-9200 melting
point apparatus. FT-IR spectra were recorded as KBr pellets in
the range 400–4000 cmÀ1 on a ATI UNICAM 1000 spectrometer.
1H NMR and 13C NMR spectra were recorded using a Varian AS
400 Merkur spectrometer operating at 400 MHz (1H), 100 MHz
4.2.4. 1,3-Bis(2,3,5,6-tetramethylbenzyl)imidazolinium chloride, 1d
Yield: 3.39 g (85%), m.p.: 337–338 °C,
t
(CN): 1630 cmÀ1. Anal.
Calc. for C25H35N2Cl: C, 75.25; H, 8.84; N, 7.02. Found: C, 75.29;
H, 8.80; N, 7.09%. 1H NMR (399.9 MHz, CDCl3) d = 9.67 (s, 1H,
NCHN), 7.01 (s, 2H, CH2C6H(CH3)4-2,3,5,6), 4.97 (s, 4H,
CH2C6H(CH3)4-2,3,5,6), 3.73 (s, 4H, NCH2CH2N), 2.25 and 2.24 (s,
24H, CH2C6H(CH3)4-2,3,5,6). 13C NMR (100.5 MHz, CDCl3)
d = 157.9 (NCHN), 134.6, 133.8, 132.8 and 128.2 (CH2C6H(CH3)4-
(
13C) in CDCl3 with tetramethylsilane as an internal reference. Col-

S. Demir et al. / Journal of Organometallic Chemistry 694 (2009) 4025–4031
4029
2,3,5,6), 47.6 (NCH2CH2N), 46.9 (CH2C6H(CH3)4-2,3,5,6), 20.5 and
15.9 (CH2C6H(CH3)4-2,3,5,6).
(s, 2H, CH2C6(CH3)5-2,3,4,5,6), 3.57 and 3.23 (t, 4H, J = 9.3 Hz,
NCH2CH2N), 2.21 (s, 6H, CH2C6H2(CH3)3-2,4,6), 2.17 (s, 3H,
CH2C6H2(CH3)3-2,4,6), 2.07, 2.01 and 1.97 (CH2C6(CH3)5-2,3,4,5,6).
13C NMR (100.5 MHz, CDCl3) d = 201.2 (Ru–Ccarbene), 138.3, 136.8,
129.6 and 129.1 (CH2C6H2(CH3)3-2,4,6), 106.0, 99.3, 94.3 and 86.2
(CH2C6(CH3)5-2,3,4,5,6), 48.4 (CH2C6H2(CH3)3-2,4,6), 48.8 and 47.5
(NCH2CH2N), 47.3 (CH2C6(CH3)5-2,3,4,5,6), 20.9 (CH2C6H2(CH3)3-
2,4,6), 20.5 (CH2C6H2(CH3)3-2,4,6), 15.6, 14.9 and 14.8
(CH2C6(CH3)5-2,3,4,5,6).
4.2.5. 1-(2,3,5,6-Tetramethylbenzyl)-3-(3,4,5-trimethoxybenzyl)
imidazolinium chloride, 1e
Yield: 3.85 g (89%), m.p.: 247–248 °C,
t
(CN): 1653 cmÀ1. Anal.
Calc. for C24H33N2O3Cl: C, 66.57; H, 7.68; N, 6.47. Found: C,
66.65; H, 7.72; N, 6.45%. 1H NMR (399.9 MHz, CDCl3) d = 10.49 (s,
1H, NCHN), 6.99 (s, 1H, CH2C6H(CH3)4-2,3,5,6), 6.75 (s, 2H,
CH2C6H2(OCH3)3-3,4,5), 4.98 (s, 2H, CH2C6H2(OCH3)3-3,4,5), 4.80
(s, 2H, CH2C6H(CH3)4-2,3,5,6), 3.90 (s, 6H, CH2C6H2(OCH3)3-3,4,5),
3.83 (s, 3H, CH2C6H2(OCH3)3-3,4,5), 3.79–3.62 (m, 4H, NCH2CH2N),
2.26 and 2.23 (s, 12H, CH2C6H(CH3)4-2,3,5,6). 13C NMR (100.5 MHz,
CDCl3) d = 158.7 (NCHN), 153.8, 138.4, 128.4 and 106.2
(CH2C6H2(OCH3)3-3,4,5), 134.8, 133.8, 132.8 and 128.1
4.3.3. RuCl2[
(OCH3)3-3,4,5)], 2c
Yield: 513 mg (88%), m.p.: 281–282 °C,
g
1-CN{CH2(
g
6-C6(CH3)5-2,3,4,5,6)}CH2CH2N(CH2C6H2-
t
(CN): 1515 cmÀ1. Anal.
Calc. for C25H34N2O3RuCl2: C, 51.55; H, 5.88; N, 4.81. Found: C,
51.62; H, 5.85; N, 4.84%. 1H NMR (399.9 MHz, CDCl3) d = 6.76 (s,
2H, CH2C6H2(OCH3)3-3,4,5), 4.74 (s, 2H, CH2C6H2(OCH3)3-3,4,5),
4.15 (s, 2H, CH2C6(CH3)5-2,3,4,5,6), 3.82 (s, 6H, CH2C6H2(OCH3)3-
3,4,5), 3.80 (s, 3H, CH2C6H2(OCH3)3-3,4,5), 3.74–3.67 and 3.55–
3.48 (m, 4H, NCH2CH2N), 2.13, 2.05 and 2.02 (s, 15H,
CH2C6(CH3)5-2,3,4,5,6). 13C NMR (100.5 MHz, CDCl3) d = 200.7
(Ru–Ccarbene), 152.9, 137.1, 132.2 and 106.9 (CH2C6H2(OCH3)3-
3,4,5), 107.2, 98.3, 94.7 and 85.7 (CH2C6(CH3)5-2,3,4,5,6), 60.8
(CH2C6H2(OCH3)3-3,4,5), 56.3 (CH2C6H2(OCH3)3-3,4,5), 53.8
(CH2C6H2(OCH3)3-3,4,5), 49.2 and 48.5 (NCH2CH2N), 47.7
(CH2C6(CH3)5-2,3,4,5,6), 15.6, 14.9 and 14.8 (CH2C6(CH3)5-
2,3,4,5,6).
(CH2C6H(CH3)4-2,3,5,6),
60.8
(CH2C6H2(OCH3)3-3,4,5),
56.6
(CH2C6H2(OCH3)3-3,4,5), 52.5 (CH2C6H2(OCH3)3-3,4,5), 47.5 ve
47.4 (NCH2CH2N), 46.8 (CH2C6H(CH3)4-2,3,5,6), 20.5 and 16.0
(CH2C6H(CH3)4-2,3,5,6).
4.2.6. 1-(2,3,4,5,6-Pentamethylbenzyl)-3-(2-methoxyethyl)
imidazolinium chloride, 1f
Yield: 2.76 g (85%), m.p.: 149–150 °C,
t
(CN): 1653 cmÀ1. Anal.
Calc. for C18H29N2OCl: C, 66.54; H, 9.00; N, 8.62. Found: C, 66.57;
H, 9.05; N, 8.59%. 1H NMR (399.9 MHz, CDCl3) d = 9.32 (s, 1H,
NCHN), 4.89 (s, 2H, CH2C6(CH3)5-2,3,4,5,6), 4.06 (t, 2H, J = 8.0 Hz,
NCH2CH2OCH3), 3.86–3.78 (m, 4H, NCH2CH2N), 3.63 (t, 2H,
J = 8.0 Hz, NCH2CH2OCH3), 3.33 (s, 3H, CH2CH2OCH3), 2.28, 2.23
and 2.20 (s, 15H, CH2C6(CH3)5-2,3,4,5,6). 13C NMR (100.5 MHz,
CDCl3) d = 158.2 (NCHN), 136.5, 133.6 133.4 and 125.5
(CH2C6(CH3)5-2,3,4,5,6), 69.2 (NCH2CH2OCH3), 58.9 (CH2CH2OCH3),
49.4 (CH2C6(CH3)5-2,3,4,5,6), 48.1 (NCH2CH2OCH3), 48.0 and 47.3
(NCH2CH2N), 17.2 and 16.9 (CH2C6(CH3)5-2,3,4,5,6).
4.3.4. RuCl2[
(CH3)4-2,3,5,6)], 2d
Yield: 363 mg (68%), m.p.: 381–382 °C,
g
1-CN{CH2(
g
6-C6H(CH3)4-2,3,5,6)}CH2CH2N(CH2C6H-
t
(CN): 1500 cmÀ1. Anal.
Calc. for C25H34N2RuCl2: C, 56.17; H, 6.41; N, 5.24. Found: C,
56.15; H, 6.48; N, 5.19%. 1H NMR (399.9 MHz, CDCl3) d = 8.33 (s,
1H, coord. CH2C6H(CH3)4-2,3,5,6), 7.04 (s, 1H, free CH2C6H(CH3)4-
2,3,5,6), 4.68 (s, 2H, coord. CH2C6H(CH3)4-2,3,5,6), 3.71 (s, 2H, free
CH2C6H(CH3)4-2,3,5,6), 3.61 and 3.08 (t, 4H, J = 10.5 Hz,
NCH2CH2N), 2.21 and 2.15 (s, 24H, free and coord. CH2C6H(CH3)4-
2,3,5,6). 13C NMR (100.5 MHz, CDCl3) d = 198.5 (Ru–Ccarbene),
134.3, 133.6, 132.6 and 129.4 (free CH2C6H(CH3)4-2,3,5,6), 108.3,
99.0, 90.6 and 84.1 (coord. CH2C6H(CH3)4-2,3,5,6), 48.8 and 48.3
(NCH2CH2N), 47.7 (free CH2C6H(CH3)4-2,3,5,6), 47.2 (coord.
CH2C6H(CH3)4-2,3,5,6), 20.6 and 16.1 (free CH2C6H(CH3)4-2,3,5,6),
18.0 and 13.7 (coord. CH2C6H(CH3)4-2,3,5,6).
4.3. General synthesis of
complexes
g g
6-arene, 1-carbene ruthenium(II)
A suspension of imidazolinium salt (1a–1f) (2.10 mmol), Cs2CO3
(2.14 mmol) and [RuCl2(p-cymene)]2 (0.82 mmol) was heated
under reflux in degassed toluene (20 mL) for 6 h. The reaction mix-
ture was then filtered while hot, and the volume was reduced to
about 10 mL before addition of n-hexane (15 mL). The precipitate
formed was crystallized from CH2Cl2/hexane (5:15 mL) to give of
orange-brown crystals.
4.3.5. RuCl2[
(OCH3)3-,3,4,5)], 2e
Yield: 426 mg (75%), m.p.: 335–336 °C, t
g
1-CN{CH2(
g
6-C6H(CH3)4-2,3,5,6)}CH2CH2N(CH2C6H2-
4.3.1. RuCl2[
g
1-CN{CH2(
g
6-C6(CH3)5-2,3,4,5,6)}CH2CH2N-
(CN): 1507 cmÀ1. Anal.
(CH2C6(CH3)5-2,3,4,5,6)], 2a
Calc. for C24H32N2O3RuCl2: C, 50.70; H, 5.67; N, 4.93. Found: C,
50.75; H, 6.63; N, 4.98%. 1H NMR (399.9 MHz, CDCl3) d = 6.72 (s,
2H, CH2C6H2(OCH3)3-3,4,5), 5.49 (s, 1H, CH2C6H(CH3)4-2,3,5,6),
4.77 (s, 2H, CH2C6H2(OCH3)3-3,4,5), 4.19 (s, 2H, CH2C6H(CH3)4-
2,3,5,6), 3.84 (s, 6H, CH2C6H2(OCH3)3-3,4,5), 3.81 (s, 3H,
CH2C6H2(OCH3)3-3,4,5), 3.74–3.68 and 3.56–3.50 (m, 4H, NCH2-
CH2N), 2.08 and 2.03 (s, 12H, CH2C6H(CH3)4-2,3,5,6). 13C NMR
(100.5 MHz, CDCl3) d = 199.7 (Ru–Ccarbene), 152.9, 137.1, 132.4
and 106.7 (CH2C6H2(OCH3)3-3,4,5), 109.9, 98.1, 90.7 and 83.8
Yield: 478 mg (85%), m.p.: 337–338 °C, t
(CN): 1507 cmÀ1. Anal.
Calc. for C27H38N2RuCl2: C, 57.67; H, 6.81; N, 4.98. Found: C,
57.69; H, 6.88; N, 4.93%. 1H NMR (399.9 MHz, CDCl3) d = 5.19 (s,
2H, free CH2C6(CH3)5-2,3,4,5,6), 4.14 (s, 2H, coord. CH2C6(CH3)5-
2,3,4,5,6), 3.59 and 3.27 (t, 4H, J = 9.6 Hz, NCH2CH2N), 2.22, 2.17,
2.12, 2.07 and 2.03 (s, 30H, CH2C6(CH3)5-2,3,4,5,6). 13C NMR
(100.5 MHz, CDCl3) d = 200.9 (Ru–Ccarbene), 134.2, 134.1, 133.4
and 129.9 (free CH2C6(CH3)5-2,3,4,5,6), 105.9, 99.2, 94.2 and 88.2
(coord. CH2C6(CH3)5-2,3,4,5,6), 48.9 (serbest CH2C6(CH3)5-
2,3,4,5,6), 48.5 and 48.1 (NCH2CH2N), 47.4 (coord. CH2C6(CH3)5-
2,3,4,5,6), 17.0 and 16.8 (free CH2C6(CH3)5-2,3,4,5,6), 15.6, 14.9
and 14.8 (coord. CH2C6(CH3)5-2,3,4,5,6).
(CH2C6H(CH3)4-2,3,5,6),
60.8
(CH2C6H2(OCH3)3-3,4,5),
56.3
(CH2C6H2(OCH3)3-3,4,5), 53.9 (CH2C6H2(OCH3)3-3,4,5), 49.2 and
47.9 (NCH2CH2N), 47.6 (CH2C6H(CH3)4-2,3,5,6), 18.3 and 13.7
(CH2C6H(CH3)4-2,3,5,6).
4.3.2. RuCl2[
(CH3)3-2,4,6)], 2b
Yield: 465 mg (87%), m.p.: 313–314 °C,
g
1-CN{CH2(
g
6-C6(CH3)5-2,3,4,5,6)}CH2CH2N(CH2C6H2-
4.3.6. RuCl2[
(CH2CH2OCH3)], 2f
Yield: 299 mg (65%), m.p.: 153–154 °C,
g
1-CN{CH2(
g
6-C6(CH3)5-2,3,4,5,6)}CH2CH2N
t
(CN): 1506 cmÀ1. Anal.
t
(CN): 1669 cmÀ1. Anal.
Calc. for C25H34N2RuCl2: C, 56.17; H, 6.41; N, 5.24. Found: C,
56.21; H, 6.38; N, 5.23%. 1H NMR (399.9 MHz, CDCl3) d = 6.71 (s,
2H, CH2C6H2(CH3)3-2,4,6), 5.04 (s, 2H, CH2C6H2(CH3)3-2,4,6), 4.11
Calc. for C18H28N2ORuCl2: C, 46.96; H, 6.13; N, 6.08. Found: C,
47.01; H, 6.15; N, 6.04%. 1H NMR (399.9 MHz, CDCl3) d = 4.15 (s,
2H, CH2C6(CH3)5-2,3,4,5,6), 3.84 (t, 2H, J = 4.2 Hz, NCH2CH2OCH3),

4030
S. Demir et al. / Journal of Organometallic Chemistry 694 (2009) 4025–4031
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NCH2CH2OCH3), 3.27 (s, 3H, CH2CH2OCH3), 2.12, 2.03 and 1.99 (s,
15H, CH2C6(CH3)5-2,3,4,5,6). 13C NMR (100.5 MHz, CDCl3)
d = 201.5 (Ru–Ccarbene), 107.6, 97.6, 95.3 and 85.0 (CH2C6(CH3)5-
2,3,4,5,6), 74.7 (NCH2CH2OCH3), 58.5 (CH2CH2OCH3), 51.8
(CH2C6(CH3)5-2,3,4,5,6), 49.5 (NCH2CH2OCH3), 48.5 and 48.1
(NCH2CH2N), 15.6, 14.9 and 14.8 (CH2C6(CH3)5-2,3,4,5,6).
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Ruthenium complex (2a–f) (0.025 mmol), 2-phenylpyridine
(0.5 mmol), aryl chloride (1.25 mmol) and Cs2CO3 (1.50 mmol)
were stirred in NMP (2 mL) at 120 °C for 10 h. H2O and EtOAc were
added to the cold reaction mixture. The organic phase was dried
over MgSO4 and concentrated under vacuum. The remaining resi-
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This work was financially supported by the Technological and
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