Synthesis and photochromic studies of η6-mesitylene ruthenium(ii) complexes bearing N-heterocyclic carbene ligands with the dithienylethene moiety

Article abstract of DOI:10.1039/c1nj20161a

A series of half-sandwich type ruthenium(ii) complexes, [(η⁶-mesitylene)Ru(NHC-L)Cl]PF₆ (NHC = N-heterocyclic carbene, L = azole and imine ligand), containing the dithienylethene moiety has been synthesized and characterized by

Full text of DOI:10.1039/c1nj20161a

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PAPER
Synthesis and photochromic studies of g6-mesitylene ruthenium(II)
complexes bearing N-heterocyclic carbene ligands with the
dithienylethene moietywz
Gongping Duan, Wing-Tak Wong and Vivian Wing-Wah Yam*
Received (in Victoria, Australia) 25th February 2011, Accepted 7th June 2011
DOI: 10.1039/c1nj20161a
A series of half-sandwich type ruthenium(II) complexes, [(Z6-mesitylene)Ru(NHC-L)Cl]PF6
(NHC = N-heterocyclic carbene, L = azole and imine ligand), containing the dithienylethene
1
moiety has been synthesized and characterized by H NMR, X-ray crystallography and electronic
absorption spectroscopy. These complexes show photochromic properties upon UV photo-
irradiation to generate the closed forms of the dithienylethene moiety.
dependence of the photochromic behaviours on the metal
Introduction
center and its coordination sphere. Following these works, a
Since the early reports in 1970s,1 half-sandwich type ruthenium(II)
series of half-sandwich type ruthenium(II) complexes bearing
complexes with the formula of [(Z6-arene)RuLn] have been
dithienylethene-containing chelating NHC ligands, with the
formula of [(Z6-mesitylene)Ru(NHC-L)Cl]PF6 (L = azole or
imine ligand), has been synthesized and their electrochemical
extensively studied due to their rich coordination chemistry,2
photochemistry,3 electrochemistry,4 and especially their
wide applications in catalysis.5 Due to the presence of a
and photochromic behaviours have been explored and
p-coordinating arene ligand, this class of complexes generally
have lower-lying ligand field (LF) excited states and thereby
reported in this paper. This work may also open up an
interesting class of half-sandwich ruthenium(II) compounds
become photochemically reactive.3a,d,f,g On the other
that may find potential photo-switchable catalytic properties.
hand, both the electrochemical4c,e,g,5c and photochemical
properties3h–j of these complexes could be tuned by structural
modification of ligand L. Recently, N-heterocyclic carbene
Results and discussion
(NHC) ligands have been introduced into this type of
complexes and the catalytic activities towards various
reactions have been investigated.5e–g The introduction of the
strongly s-donating NHC ligand would also offer an oppor-
tunity to increase the photostability of the complexes by
increasing the LF excited state energy, and allows for the
study of the photoreactivity of this class of compounds other
than those of photosubstitution reactions. Dithienylethene
type photochromic molecules have drawn large interest for
their pronounced thermal irreversibility and fatigue resistance
as a potential candidate in optical data storage and molecular
photoswitching.6 Recently, NHC metal complexes with the
dithienylethene moiety have been reported.6b,7 Photophysical
and photochemical studies of these compounds have shown a
Synthesis and characterization
The 4,5-dithienylimidazoles with the pyridyl N-substituent
have been synthesized through copper(I)-catalyzed cross-
coupling reactions, while the N-alkyl analogues are obtained
by nucleophilic substitution reactions. Selective methylation of
the imidazole ring has led to the imidazolium iodide ligand
precursors (Scheme 1). Coordination of the NHC ligand to
ruthenium(II) is found to take place smoothly through
Ag(I)–carbene complex-mediated transmetallation (Scheme 2).6c,8
Complexes 3–9 are characterized by 1H NMR spectroscopy
and are found to show broad signals at room temperature.
Variable-temperature 1H NMR studies are performed on
complexes 3, 6, 8 and 9. The signals are found to broaden at
elevated temperatures; on the other hand, the signals become
more sharpened and better resolved upon lowering of the
temperature with some slight changes of the intensity ratio
between signals. These observations indicate the slow inter-
conversion among conformations at ambient temperature,
probably due to the restricted rotation of the thiophene rings
that leads to the parallel and anti-parallel conformations.9 In
all the cases studied, according to the signals of the protons
on the thiophene rings, four distinct sets of peaks can be
Institute of Molecular Functional Materialsy, and Department of
Chemistry, The University of Hong Kong, Pokfulam Road,
Hong Kong, P. R. China. E-mail: wwyam@hku.hk
w Dedicated to Professor Didier Astruc on the occasion of his 65th
birthday.
z Electronic supplementary information (ESI) available: CCDC
reference numbers 814059 (for 6) and 814060 (for 3). For ESI and
crystallographic data in CIF or other electronic format see DOI:
10.1039/c1nj20161a
y Areas of Excellence Scheme, University Grants Committee (Hong Kong).
c
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Scheme 1 Synthetic route to imidazolium ligand precursors.
distinguished at a sufficiently low temperature (typically 243 K),
at which the interconversions may be almost frozen (Fig. S1
in ESIw). For peaks corresponding to the other protons,
generally less than four sets of signals can be distinguished
due to the smaller differences in the chemical shifts among the
signals. These observations suggest the involvement of four
interconvertible conformations due to the orientation of
the two thiophene rings and the unsymmetric coordination
environment of the metal center (Fig. S2 in ESIw).
Complexes 3 and 6 have been characterized by X-ray
crystallography (Tables S1 and S2 in ESIw) and are
representative of the structures of the other complexes. In
these structures (Fig. 1), the ruthenium(II) metal centers
adopt a pseudo-octahedral coordination geometry with all
the Ccarbene–Ru–Cl, N–Ru–Cl and Ccarbene–Ru–N angles in
the range of 84.3(2)1–89.5(3)1. The only exception is observed
in complex 6, in which the Ccarbene–Ru–N bite angle is 75.8(4)1
due to the geometrical restraint of the ligand. The Ru–Ccarbene
bond distance is 2.055(4) A for 3 and 2.029(10) A for 6, typical
of those observed in other related complexes,10 indicating that
the bonds have essentially single bond character.10a In both
structures, the two thiophene rings in the ligand adopt an
anti-parallel conformation.
Electronic absorption studies
The electronic absorption spectrum of complex 1 shows a
strong absorption at 290–320 nm with a less intense broad
band at around 350–390 nm (Fig. 2). The lower-energy
absorption band is tentatively assigned as metal-to-ligand
charge transfer (MLCT) transition according to its relatively
c
2268 New J. Chem., 2011, 35, 2267–2278
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Scheme 2 Synthetic route to complexes 1–9.
low energy and its molar extinction coefficient in the order of
103 molꢀ1 dm3 cmꢀ1, as well as on the basis of literature
reports on other related complexes.11 The higher-energy band
is assigned as mainly intra-ligand, IL(bpy), in character
in comparison to other ruthenium complexes bearing the
2,20-bipyridyl ligand.12 Compared to that of 1, the MLCT
band of 2 appears as a shoulder at around 320 nm, which is
significantly hypsochromically shifted. This is probably due to
the smaller extent of p-conjugation of the NHC-py ligand than
that of the 2,20-bipyridine ligand. A similar observation
in the lower-energy region of the spectra shows a progressive
red shift, which turns from an absorption that is almost totally
masked in 3 (o280 nm) to a shoulder at 300 nm in 6, and
further to a broad, but distinct band at 320 nm in 9. This trend
is in accordance with the lowering of the p* orbital energy of
the chelating ligand through the series, and thus leading to the
assignment of this band as dp(Ru) - p*(NHC-L) MLCT
transition.
A weak band at around 400 nm with small extinction
coefficient (e = 300–800 molꢀ1 dm3 cmꢀ1) is typically
observed for all the complexes bearing N-heterocyclic carbene
ligands, and is tentatively assigned as metal-centered (MC)
transition, probably with mixing of some ligand character.3d,15
In the series from 3 to 9, upon altering from a non-conjugated
ligand to a conjugated ligand, this band shows little shift.
Assuming the assignment of a lowest-lying d–d excited state,
the lack of emission at room temperature in all complexes
studied can be readily rationalized.16
has been reported in a study on [Ru(NHC-py)3]2+ 13
The
.
relatively intense band at 265 nm is assigned as IL(NHC-py)
transition, with some mixing of a dp(Ru) - p*(mesitylene)
MLCT character.14
Compared to its counterpart without the dithienylethene
moiety, the electronic absorption spectrum of complex 8
shows much higher extinction coefficient at around 240 nm
(Fig. 2). The difference may be ascribed to the p - p* and
n - p* IL transition of the two thiophene rings if the
absorption spectra are considered to be additive. This strong
absorption masks most of the details of other bands (IL and
MLCT), which makes further assignment difficult. The
electronic absorption data of complexes 1–9 are summarized
in Table 1.
Electrochemical studies
The electrochemical properties of complexes 1–9 have been
studied by cyclic voltammetry in acetonitrile with 0.1 M
n-Bu4NPF6 as the supporting electrolyte (Table 2). Complex
5 represents a typical example in the series as shown in Fig. 3.
An irreversible cathodic wave is observed at around
ꢀ1.31 V vs. SCE. According to literature reports,4a–c,14,17 this
can tentatively be assigned as a one-step two-electron reduction
Complexes 3–9 show intense absorptions in the ultra-violet
region with a less intense band tailing to 300–350 nm which
accounts for the orange-yellow color of the solid. On going
through the series, from complex 3 to 9, the absorption band
c
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Fig. 2 (a) Overlaid electronic absorption spectra of 1 (––) and 2 (---)
in acetonitrile; (b) overlaid electronic absorption spectra of 2 (---) and
8 (––) in acetonitrile.
Fig. 1 Perspective views of complex cations of 3 (top) and 6 (bottom)
at 30% thermal ellipsoid probability. All hydrogen atoms and water
molecules of crystallization are omitted for clarity.
to be strongly dependent on the structure of the ligands, with
complexes 3–5 containing an unconjugated NHC-ligand
showing more negative potentials of reduction while complexes
6–9 containing a conjugated NHC-ligand are easier to be
reduced. This is indicative of the involvement of the ligand
p* orbital in the reduction.14 The redox potentials of the
chloride-dissociated complexes [(Z6-mes)Ru(L)] (E2) show
almost the same trend as E1.
of the metal center, probably with some mixing of ligand
character. An oxidation peak at the potential (E2) about 0.3 V
less negative is observed in the reverse scan, probably due to
the oxidation of the less electron-rich chloride-dissociation
product [(Z6-mes)Ru(Ph-NHCT-CH2ox)] that is formed upon
population of electron density on the ds* orbital.4c,14
Complex 5 displays an anodic peak at +1.41 V vs. SCE,
which is typical for the RuIII/II redox couple in related
compounds.4c,5c The oxidation is irreversible due to the
dissociation of the arene ligand. An additional anodic wave
is observed for complex 5 at a more positive potential
(+1.64 V vs. SCE), which can be ascribed to the irreversible
oxidation of the dithienylethene (DTE) moiety when considering
the presence of this wave in the cyclic voltammograms of all
the DTE-containing complexes 3–9, and its absence in that of
complexes 1 and 2.
As discussed previously, both the first oxidation and
reduction of [(Z6-mes)Ru(L)Cl]+ are mainly metal-centered,
and thus the lowest energy excited state of these complexes is
most probably metal-centered (d–d) in nature with a slight
mixing of a MLCT character. This is in accordance with
studies reported previously (vide infra). Moreover, the
transition energies estimated from the electrochemical data
(E3 ꢀ E1 = 2.6–2.8 V) match well with that observed in the
electronic absorption spectra (420–430 nm).
Other complexes show similar electrochemical behaviour as
that of complex 5, with some trends observed through the
series. It is found that the potential of the RuIII/II redox couple
(E3 in Table 2) increases in the order of 7 (NHCT-pyOEt) o 8
(NHCT-py) o 9 (NHCT-pym) o 1 (2,20-bpy) with decreasing
ease of oxidation, in accordance with the decreasing
s-donating and increasing p-accepting ability of the ligands.
The potentials of the metal-centered reduction (E1) are found
Photochromic studies
Complexes 3–9 are found to undergo reversible photo-
cyclization to form the closed form species in methanol and
acetonitrile (Scheme 3). Table 1 summarizes the electronic
absorption data of the closed forms. The closed forms of 3–5
have essentially the same electronic absorption spectra with
two bands at 340 and 550 nm that closely resemble the closed
c
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Table 1 Electronic absorption data of complexes 3–9 at room temperaturea,b
Complex
l )
max/nm (e/molꢀ1 dm3 cmꢀ1
1c
233 (14700), 291 (15700), 315 (8900), 353 (2800), 393 sh (1800)
213 (31700), 265 (8100), 314 sh (4600), 397 (500)
232 (30600), 424 (300)
324 sh (14300), 342 (19400), 548 (10400)
244 (25600), 426 (300)
286 (16400), 304 (16100), 342 (21200), 546 (11100)
232 sh (35500), 274 sh (12600), 426 (400)
300 sh (13700), 344 (20000), 550 (10300)
234 (23400), 302 sh (7400), 400 (400)
282 (10880), 346 (22500), 538 (9810)
306 sh (8000), 406 (700)
2c
3 (open form)
(closed form)
4 (open form)
(closed form)
5 (open form)
(closed form)
6 (open form)
(closed form)
7 (open form)
(closed form)
8 (open form)
(open form)c
(closed form)
9 (open form)
(closed form)
354 (20000), 534 (4500)
228 sh (36300), 320 sh (5500), 400 (700)
230 sh (35800), 320 sh (5600), 394 sh (700)
272 sh (15900), 360 (20000), 532 (5100)
226 sh (32400), 318 (5200), 398 sh (800)
246 (19400), 272 sh (13300), 378 (20100), 526 (7000)
a
The molar extinction coefficients of the closed forms of 3, 4 and 6 are determined by a combination of 1H NMR and UV-vis spectroscopic
studies; while for that of complexes 5 and 7–9, the signals corresponding to the closed forms cannot be observed in the 1H NMR spectra due to very
low conversion, and the values are estimated by artificially making the extinction coefficient at the band maxima at around 340–380 nm to be 2.0 ꢁ
b
104 molꢀ1 dm3 cmꢀ1, which is the average value of 3, 4 and 6. All data derived from this estimation are shown in italics. All data are measured in
c
methanol unless otherwise specified. Measured in acetonitrile.
Table 2 Electrochemical data of complexes 1–9 in acetonitrile with
0.1 M n-Bu4NPF6 as the supporting electrolyte (V vs. SCE)
a
b
c
d
Complex
E1
E2
E3
E4
E3 ꢀ E1
e
e
1
2
3
4
5
6
7
8
9
ꢀ0.97
ꢀ1.23
ꢀ1.38
ꢀ1.35
ꢀ1.31
ꢀ1.23
ꢀ1.27
ꢀ1.27
ꢀ1.18
ꢀ0.76
ꢀ0.85
ꢀ1.07
ꢀ1.02
ꢀ1.03
ꢀ0.91
ꢀ0.90
ꢀ0.81
ꢀ0.77
+1.56
+1.37
+1.43
+1.45
+1.41
+1.38
+1.32
+1.36
+1.43
—
—
2.53
2.60
2.81
2.80
2.72
2.61
2.59
2.63
2.61
+1.62
+1.62
+1.64
+1.69
+1.71
+1.69
+1.65
Epc of the redox couple [(Z6-mes)RuII(L)Cl]+ + 2eꢀ - [(Z6-mes)-
a
Ru0(L)Cl]ꢀ. Epa of the redox couple [(Z6-mes)RuII(L)]2+ + 2eꢀ
-
+
b
[(Z6-mes)Ru0(L)]. Epa of the redox couple [(Z6-mes)RuIII(L)Cl]2+
c
eꢀ - [(Z6-mes)RuII(L)Cl]+
.
Epa of the redox couple involving the
e
. Not observed.
d
dithienylethene moiety of [(Z6-mes)RuIII(L)Cl]2+
Fig. 3 Cyclic voltammogram of complex 5 in acetonitrile (0.1 M
n-Bu4NPF6). Scan rate = 100 mV sꢀ1
.
forms of the imidazolium cations (Fig. 4(a)).7 Moving on
through the series, from 6 to 9, the closed forms show a red
shift of the absorption band from 340 to 380 nm, while the
band at around 550 nm shows a slight blue shift (Fig. 4(b)).
The lowest energy band is assigned as an IL transition, similar
to those reported previously.7,9b The absorption at 340–380 nm
is likely to have a p(fused-thiophene) - p*(L) intra-ligand
charge transfer (ILCT) character (L = oxazole, pyridine and
pyrimidine) with mixing of an IL, and/or MLCT transition,
which is consistent with the observed trend.
Scheme 3 Representative photochromic reaction of complex 8.
The quantum yield of the photo-cyclization shows a
dramatic decrease through the series 3–9 (Table 3). For
example, complex 3 shows a F280 of 0.044 while complex 9
shows a F280 of 0.0037. However, even the largest value does
not exceed 0.05. The generally small values (o5%) indicate the
existence of an efficient non-radiative deactivation pathway.
Based on previous discussions, this pathway would probably be
proceeding through a lower-lying MC excited state.
For complexes 7–9, photo-cyclization is accessible by
irradiation at 340 nm, mainly corresponding to the absorption
of the MLCT transition. This indicates that the photo-
cyclization pathway via a triplet state is possible in this system,
with the intersystem crossing to the 3MLCT excited state,
which is generally a very fast process in ruthenium(II)
complexes.18 However, due to the relatively high energy of
the absorption band, a substantial admixture of IL character
c
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Conclusion
A
series of half-sandwich type N-heterocyclic carbene–
ruthenium(II) complexes [(Z6-mesitylene)Ru(NHC-L)Cl]PF6
containing the dithienylethene moiety has been synthesized
and characterized by 1H NMR, X-ray crystallography and
electronic absorption spectroscopy. These complexes show
photochromic properties upon photo-irradiation. The low
quantum yield of the photochromic reaction of these com-
plexes has been attributed to the efficient deactivation of the
excited state.
Experimental section
Materials and reagents
2-Chloromethyl-4,5-dimethyloxazole,21 4,5-dimethyloxazol-2-
amine,22 2-bromo-4,5-dimethylthiazole,23 thiazole-2-carbalde-
hyde,24 4,5-dimethyloxazole,25 2-chloro-4,5-dimethyloxazole,26
2-chloropyrimidine27 and 2-bromo-5-ethoxypyridine28 were
synthesized by modification of literature methods. 1,2-
Bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione was synthe-
sized using modification of a reported Cu(I)-mediated coupling
reaction29 between the Grignard reagent of 3-bromo-2,5-
dimethylthiophene30 and oxalyl chloride. 4,5-Bis(2,5-
dimethylthiophen-3-yl)-1H-imidazole (Th2im) was synthesized
from 1,2-bis(2,5-dimethylthiophen-3-yl)ethane-1,2-dione according
to modification of literature reported methods.31 Silver(I)
oxide was synthesized according to a literature method32
and was stored in the dark. [(Z6-Mesitylene)RuCl2]2 was
synthesized by a literature method.33 n-Bu4NPF6 for electro-
chemical studies was recrystallized at least twice from absolute
ethanol. Acetonitrile for photophysical measurements was
distilled over calcium hydride. Methanol for photophysical
measurements was distilled over magnesium. All other
reagents and solvents are commercially available and are used
as received.
Fig. 4 (a) Overlaid electronic absorption spectra of the open (––) and
closed (---) forms of 3 in methanol; (b) overlaid electronic absorption
spectra of the closed forms of 6–9 in methanol.
Table 3 Photochemical quantum yield of 3–9 in MeOH at 293 K
under deareated conditions and in the presence of air
Synthesis
Photochemical quantum yield/F
1-((4,5-Dimethyloxazol-2-yl)methyl)-4,5-bis(2,5-dimethyl-
thiophen-3-yl)-1H-imidazole (im-CH2ox). The reaction was
performed under nitrogen using a standard Schlenk technique.
A mixture of Th2im (387 mg, 1.34 mmol), 2-(chloromethyl)-
4,5-dimethyloxazole (445 mg, 2.98 mmol) and K2CO3 (233 mg,
1.69 mmol) in a MeCN–DMSO mixture (20 mL, 3 : 1 v/v) was
heated to reflux under nitrogen. The reaction was monitored
by TLC. Acetonitrile was then removed under reduced
pressure. The residue was taken up with ethyl acetate, washed
with water several times to remove DMSO, and dried over
anhydrous MgSO4. Purification by flash column chromato-
graphy on silica gel using a chloroform–methanol mixture
(100 : 1 v/v) as eluent gave im-CH2ox as an off-white solid after
removal of the solvent. Yield: 466 mg, 1.17 mmol; 87%.
1H NMR (300 MHz, CDCl3): d = 1.92 (s, 3H; 2-Me), 2.04
(s, 3H; oxazolyl Me), 2.17 (s, 3H; oxazolyl Me), 2.24 (s, 3H; 2-Me),
2.31 (s, 3H; 5-Me), 2.44 (s, 3H; 5-Me), 4.94 (s, 2H; CH2), 6.44
(s, 1H; thienyl), 6.54 (s, 1H; thienyl), 7.68 (s, 1H; imidazolyl
2-H). Positive-ion EI mass spectrum: m/z 397 {M}+, 382
{M–Me}+, 287 {M–Me–C5H5NO}+.
Photo-cyclization
Photo-cycloreversion
F280
F340
F500
Deareated In air Deareated In air Deareated In air
Complex
3a
4a
5c
6a
7c
8c
9c
0.044
0.021
0.029
0.045 —b
0.020 —b
—
—
—
0.094
0.085
0.092
0.090
0.083
0.092
0.058
b
b
b
0.029 —b
b
0.0078
0.0079
0.0043
0.0037
—
—
—
—
0.0077d
0.0088
0.0062
0.0039
0.0071d 0.061
0.0092 0.16e
0.0055 0.08e
0.0030 0.4e
b
b
b
b
—
—
b
b
—
a
b
Data obtained with an estimation of ꢂ20% uncertainty. Not
c
measured. Data obtained with an estimation of ꢂ40% uncertainty.
d
e
Excited at 320 nm. Poor accuracy due to low percentage conversion.
may also be present, which renders the reaction proceeding
mainly through a singlet pathway. On the other hand, although
an obvious decrease of the quantum yield in the presence of
oxygen19 is not observed, the possible involvement of a triplet-
sensitizing pathway cannot be completely excluded.20
c
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1-((4,5-Dimethyloxazol-2-yl)methyl)-4,5-bis(2,5-dimethyl-
thiophen-3-yl)-3-methyl-1H-imidazolium iodide (im-CH2ox+Iꢀ).
To a solution of im-CH2ox (0.11 mg, 0.25 mmol) in toluene
(8 mL) was added iodomethane (0.2 mL) and the mixture was
stirred at 40–50 1C for 48 h. The solvent was removed under
reduced pressure. The residue was dissolved in acetone (1 mL),
followed by addition of diethyl ether (15 mL). White precipi-
tate came out gradually. The solid was collected by filtration
the product as an off-white solid. Yield: 0.30 g, 0.51 mmol;
1
74%. H NMR (300 MHz, CDCl3): d = 1.91 (s, 3H; 2-Me),
2.01 (br s, 3H; 2-Me), 2.05 (s, 3H; Me at oxazolyl), 2.22 (s, 3H;
Me at oxazolyl), 2.27 (s, 3H; 5-Me), 2.42 (s, 3H; 5-Me), 5.52
(AB, J = 16.6 Hz; –CHH0–), 5.82 (AB, J = 16.6 Hz;
–CHH0–), 6.19 (s, 1H; thienyl), 6.59 (s, 1H; thienyl),
7.40–7.50 (m, 3H; phenyl), 7.60–7.65 (m, 2H; phenyl), 9.80
(s, 1H; imidazolyl 2-H). Positive-ion FAB mass spectrum: m/z
474 {M–I}+. Elemental analysis, found (%): C, 53.03; H, 4.67;
1
to give im-CH2ox+Iꢀ. Yield: 0.11 mg, 0.21 mmol; 82%. H
1
2
NMR (300 MHz, CDCl3): d = 1.93 (br s, 3H; 2-Me), 2.01
(br s, 3H; 2-Me), 2.02 (s, 3H; oxazolyl Me), 2.20 (s, 3H;
oxazolyl Me), 2.39 (s, 3H; 5-Me), 2.42 (s, 3H; 5-Me), 3.86
(s, 3H; N-Me), 5.42 (br s, 2H; CH2), 6.48 (br s, 1H; thienyl),
6.54 (br s, 1H; thienyl), 10.15 (s, 1H; imidazolyl 2-H). Positive-
ion FAB mass spectrum: m/z 412 {M–I}+. Elemental analysis,
found (%): C, 47.68; H, 4.80; N, 7.28; calcd. for
C22H26N3OS2IꢃH2O (%): C, 47.40; H, 4.06; N, 7.53.
N, 6.64; calcd. for C27H28N3OS2Iꢃ H2O (%): C, 53.11; H, 4.79;
N, 6.88.
1-(4,5-Dimethyloxazol-2-yl)-4,5-bis(2,5-dimethylthiophen-3-yl)-
1H-imidazole (im-ox). The reaction was performed under
nitrogen using a standard Schlenk technique.
A mixture of Th2im (0.45 g, 1.57 mmol), caesium carbonate
(1.05 g, 3.2 mmol), copper(I) iodide (0.025 g, 0.13 mmol) and
1,10-phenanthroline (0.025 g, 0.14 mmol) was placed in a two-
necked round-bottom flask charged with a reflux condenser.
The flask was filled with nitrogen by a pump-fill method for
three times. DMF (30 mL) was degassed by purging with
nitrogen for 10 min, and then added to the mixture, followed
by 2-chloro-4,5-dimethyloxazole (0.45 g, 3.4 mmol). The
mixture was stirred at 110–120 1C. The progress of the
reaction was monitored by TLC. DMF was then removed
under reduced pressure and the residue was treated as
previously reported. Purification by flash column chromato-
graphy on silica gel (pre-treated with 1% triethylamine
in hexane) using a petroleum ether–ethyl acetate mixture
(6 : 1 v/v) as eluent gave the desired product as a yellow solid
after removal of the solvent. Yield: 0.36 g, 0.94 mmol; 60%.
1H NMR (400 MHz, CDCl3): d = 1.94 (s, 3H; 2-Me), 2.08
(s, 3H; Me at oxazolyl), 2.15 (s, 3H; Me at oxazolyl), 2.22
(s, 3H; 2-Me), 2.33 (s, 3H; 5-Me), 2.38 (s, 3H; 5-Me), 6.45
(s, 1H; thienyl), 6.47 (s, 1H; thienyl), 8.05 (s, 1H; thienyl 2-H).
Positive-ion EI mass spectrum: m/z 383 {M}+, 368 {M–Me}+,
299 {M–Me–C4H5O}+, 273 {M–Me–C5H5NO}+. Elemental
analysis, found (%): C, 62.59; H, 5.63; N, 10.46; calcd. for
C20H21N3OS2 (%): C, 62.63; H, 5.52; N, 10.96.
1-((4,5-Dimethylthiazol-2-yl)methyl)-4,5-bis(2,5-dimethyl-
thiophen-3-yl)-1H-imidazole (im-CH2th). Im-CH2th was pre-
pared by a method similar to that for im-CH2ox, except that
2-(chloromethyl)-4,5-dimethylthiazole (0.33 g, 2.0 mmol) was
used in place of 2-(chloromethyl)-4,5-dimethyloxazole to react
with Th2im (0.39 g, 1.3 mmol). Yield: 0.39 g, 0.9 mmol; 73%.
1H NMR (400 MHz, CDCl3): d = 1.91 (s, 3H; 2-Me), 2.22
(s, 3H; 2-Me), 2.28 (s, 6H; two thiazolyl Me), 2.32 (s, 3H;
5-Me), 2.43 (s, 3H; 5-Me), 5.16 (m, 2H; CH2), 6.46 (s, 1H;
thienyl), 6.52 (s, 1H; thienyl), 7.71 (s, 1H; imidazolyl 2-H).
Positive-ion EI mass spectrum: m/z 413 {M}+, 398 {M–Me}+,
287 {M–Me–C5H5NS}+. Elemental analysis, found (%): C,
60.96; H, 5.64; N, 9.79; calcd. for C21H23N3S3 (%): C, 60.98;
H, 5.60; N, 10.15.
1-((4,5-Dimethylthiazol-2-yl)methyl)-4,5-bis(2,5-dimethyl-
thiophen-3-yl)-3-methyl-1H-imidazolium iodide (im-CH2th+Iꢀ).
Im-CH2th+Iꢀ was synthesized using a method similar to that
for im-CH2ox+Iꢀ except that im-CH2th (0.10 g, 0.24 mmol)
was used in place of im-CH2ox. Yield: 0.10 g, 0.18 mmol; 75%.
1H NMR (300 MHz, CDCl3): d = 1.89 (br s, 3H; 2-Me), 2.04
(br s, 3H; 2-Me), 2.32 (s, 3H; thiazolyl Me), 2.36 (s, 3H;
thiazolyl Me), 2.40 (s, 3H; 5-Me), 2.41 (s, 3H; 5-Me), 3.83
(s, 3H; N-Me), 5.53 (br s, 2H; CH2), 6.53 (br s, 1H; thienyl),
6.60 (br s, 1H; thienyl), 10.02 (s, 1H; imidazolyl 2-H). Positive-
ion FAB mass spectrum: m/z 428 {M–I}+. Elemental analysis,
found (%): C, 47.46; H, 4.62; N, 7.02; calcd. for C22H26N3S3I
(%): C, 47.56; H, 4.72; N, 7.56.
1-(4,5-Dimethyloxazol-2-yl)-4,5-bis(2,5-dimethylthiophen-3-yl)-
3-methyl-1H-imidazolium iodide (im-ox+Iꢀ). Im-ox+Iꢀ was
synthesized using a method similar to that for im-pyOEt+ ꢀ
I
except that im-ox (0.10 g, 0.26 mmol) was used in place of
im-pyOEt. Yield: 0.09 g, 0.17 mmol; 66%. 1H NMR (400 MHz,
CDCl3): d = 2.01 (s, 3H; 2-Me), 2.03 (s, 3H; 2-Me), 2.09
(s, 3H; Me at oxazolyl), 2.23 (s, 3H; Me at oxazolyl), 2.35
(s, 3H; 5-Me), 2.45 (s, 3H; 5-Me), 4.07 (s, 3H; N-Me), 6.37
(s, 1H; thienyl), 6.64 (s, 1H; thienyl), 10.48 (s, 1H; imidazolyl
2-H). Positive-ion FAB mass spectrum: m/z 398 {M–I}+.
Elemental analysis, found (%): C, 46.73; H, 4.55; N, 7.40;
calcd. for C21H24N3OS2IꢃH2O (%): C, 46.41; H, 4.82; N, 7.73.
1-((4,5-Dimethyloxazol-2-yl)methyl)-4,5-bis(2,5-dimethyl-
thiophen-3-yl)-3-phenyl-1H-imidazolium iodide (Ph-im-CH2ox+Iꢀ).
To a mixture of Th2im-Ph (0.25 g, 0.68 mmol) and sodium
iodide (0.19 g, 1.3 mmol) in acetone (15 mL) was added
2-(chloromethyl)-4,5-dimethyloxazole (0.13 g, 0.83 mmol),
and the mixture was stirred at 50 1C under nitrogen. After
20 h of reaction, a second batch of 2-(chloromethyl)-4,5-
dimethyloxazole (0.13 g, 0.83 mmol) was added, and the
mixture was further stirred for 20 h. After removal of the
solvent, dichloromethane (10 mL) was added to the residue.
The solid formed was removed by filtration, and the filtrate
was evaporated to dryness. Ethyl acetate (1.5 mL) was added
to the residue, followed by diethyl ether (15 mL) to precipitate
2-(4,5-Bis(2,5-dimethylthiophen-3-yl)-1H-imidazol-1-yl)-4-
ethoxypyridine (im-pyOEt). The reaction was performed under
nitrogen using a standard Schlenk technique.
A mixture of Th2im (0.24 g, 0.8 mmol), caesium carbonate
(0.55 g, 1.7 mmol), copper(I) iodide (0.055 g, 0.29 mmol) and
1,10-phenanthroline (0.055 g, 0.29 mmol) was placed in a
two-necked round-bottom flask charged with a reflux condenser.
c
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The flask was filled with nitrogen by a pump-fill method for
three times. DMSO (15 mL) was degassed by purging with
nitrogen for 10 min, and then added to the mixture followed
by 2-bromo-4-ethoxylpyridine (0.27 g, 1.3 mmol). The mixture
was heated to 120–130 1C under nitrogen. The progress of
the reaction was monitored by TLC. The general work-up
followed by purification with flash column chromatography
on silica gel (pre-treated with 1% triethylamine in hexane)
using a petroleum ether–ethyl acetate mixture (1 : 1 to 3 : 7 v/v)
as eluent gave the pure product as an off-white solid after
removal of the solvent. Yield: 0.14 g, 0.33 mmol; 40%.
1H NMR (300 MHz, CDCl3): d = 1.31 (t, 2H, J = 7.0 Hz;
–OCH2CH3), 1.92 (s, 3H; 2-Me), 2.25 (s, 3H; 2-Me), 2.34
(s, 3H; 5-Me), 2.36 (s, 3H; 5-Me), 3.78 (q, 2H, J = 7.0 Hz;
–OCH2CH3), 6.24 (d, 1H, J = 2.3 Hz; pyridyl 3-H), 6.38
(s, 1H; thienyl), 6.48 (s, 1H; thienyl), 6.71 (dd, 1H, J = 5.8,
2.3 Hz; pyridyl 5-H), 8.26 (d, 1H, J = 5.8 Hz; pyridyl 6-H),
8.29 (s, 1H; imidazolyl 2-H). Positive-ion EI mass spectrum:
m/z 409 {M}+, 394 {M–Me}+, 273 {M–Me–C7H7NO}+.
Elemental analysis, found (%): C, 64.34; H, 5.77; N, 10.01;
calcd. for C22H23N3OS2 (%): C, 64.51; H, 5.66; N, 10.26.
using a method similar to that for im-pyOEt+ ꢀ
I
except that
im-py (0.19 g, 0.50 mmol) was used in place of im-pyOEt. Yield:
1
0.24 g, 0.46 mmol; 93%. H NMR (300 MHz, CDCl3): d =
1.95 (s, 3H; 2-Me), 2.05 (br s, 3H; 2-Me), 2.28 (s, 3H; 5-Me),
2.45 (s, 3H; 5-Me), 3.99 (s, 3H; NMe), 6.24 (s, 1H; thienyl),
6.76 (s, 1H; thienyl), 7.45 (dd, 1H, J = 7.5, 4.9 Hz; pyridyl
5-H), 7.57 (d, 1H, J = 8.1 Hz; pyridyl 3-H), 7.84 (td, 1H, J =
7.8, 1.7 Hz; pyridyl 4-H), 9.91 (s, 1H; imidazolyl 2-H),
8.52–8.54 (m, 1H; pyridyl 6-H). Positive-ion FAB mass
spectrum: m/z 380 {M–I}+. Elemental analysis, found (%):
1
2
C, 48.99; H, 4.37; N, 7.81; calcd. for C21H22N3S2Iꢃ H2O (%):
C, 48.84; H, 4.49; N, 8.14.
2-(4,5-Bis(2,5-dimethylthiophen-3-yl)-1H-imidazol-1-yl)-
pyrimidine (im-pym). Im-pym was synthesized using a method
similar to that for im-pyOEt except that 2-chloropyrimidine
(0.35, 5.6 mmol) was used in place of 2-bromo-4-ethoxyl-
pyridine to react with Th2im (0.8 g, 2.8 mmol). The progress
of the reaction was monitored by TLC. Purification by flash
column chromatography on silica gel (pre-treated with 1%
triethylamine in hexane) using a petroleum ether–ethyl acetate
mixture (1 : 1 to 1 : 2 v/v) as eluent gave the desired product as
an off-white solid after removal of the solvent. Yield: 0.74 g,
2.0 mmol; 72%. 1H NMR (400 MHz, CDCl3): d = 1.90 (s, 3H;
2-Me), 2.26 (s, 3H; 2-Me), 2.34 (s, 3H; 5-Me), 2.38 (s, 3H;
5-Me), 6.42–6.43 (m, 2H; thienyl), 7.17 (t, 1H, J = 4.8 Hz;
pyrimidyl 5-H), 8.52 (s, 1H; imidazolyl 2-H), 8.63 (d, 2H, J =
4.8 Hz; pyrimidyl 4,6-H). Positive-ion EI mass spectrum: m/z
366 {M}+, 351 {M–Me}+, 273 {M–Me–C4H2N2}+. Elemental
analysis, found (%): C, 61.97; H, 5.02; N, 14.93; calcd. for
C19H18N4S2 (%): C, 62.26; H, 4.95; N, 15.29.
4,5-Bis(2,5-dimethylthiophen-3-yl)-1-(4-ethoxypyridin-2-yl)-3-
methyl-1H-imidazolium iodide (im-pyOEt+Iꢀ). Im-pyOEt+ ꢀ
I
was synthesized using
a method similar to that for
im-CH2ox+Iꢀ except that im-pyOEt (0.12 g, 0.35 mmol) was
used in place of im-CH2ox and the reaction was performed at
60–70 1C. Yield: 0.13 g, 0.24 mmol; 68%. 1H NMR (300 MHz,
CDCl3): d = 1.39 (t, 2H, J = 7.0 Hz; –OCH2CH3), 1.97
(s, 3H; 2-Me), 2.06 (s, 3H; 2-Me), 2.29 (s, 3H; 5-Me), 2.44
(s, 3H; 5-Me), 3.96 (s, 3H; N-Me), 4.14 (q, 2H, J = 7.0 Hz;
–OCH2CH3), 6.30 (s, 1H; thienyl), 6.73 (s, 1H; thienyl), 6.89
(dd, 1H, J = 5.8, 2.2 Hz; pyridyl 5-H), 7.32 (d, 1H, J =
2.2 Hz; pyridyl 3-H), 8.21 (d, 1H, J = 5.8 Hz; pyridyl 6-H),
9.87 (s, 1H; imidazolyl 2-H). Positive-ion FAB mass spectrum:
m/z 424 {M–I}+. Elemental analysis, found (%): C, 49.53; H,
1-Methyl-3-(2-pyrimidyl)-4,5-bis(2,5-dimethylthiophen-3-yl)-
1H-imidazolium iodide (im-pym+Iꢀ). Im-pym+Iꢀ was synthe-
sized using a method similar to that for im-pyOEt+ ꢀ
I
except
that im-pym (0.11 g, 0.31 mmol) was used in place of im-pyOEt
.
Yield: 0.11 g, 0.22 mmol; 70%. 1H NMR (300 MHz, CDCl3):
d = 1.97 (s, 3H; 2-Me), 2.06 (br s, 3H; 2-Me), 2.33 (s, 3H;
5-Me), 2.45 (s, 3H; 5-Me), 4.10 (s, 3H; N-Me), 6.32 (s, 1H;
thienyl), 6.62 (br s, 1H; thienyl), 7.47 (t, 1H, J = 4.8 Hz;
pyrimidyl 5-H), 8.78 (d, 2H, J = 4.8 Hz; pyrimidyl 4,6-H),
10.83 (s, 1H; imidazolyl 2-H). Positive-ion FAB mass
spectrum: m/z 381 {M–I}+. Elemental analysis, found (%):
1
2
4.75; N, 7.05; calcd. for C23H26N3OS2Iꢃ H2O (%): C, 49.28; H,
4.86; N, 7.50.
2-(4,5-Bis(2,5-dimethylthiophen-3-yl)-1H-imidazol-1-yl)pyridine
(im-py). Im-py was prepared by a method similar to that for
im-pyOEt, except that 2-bromopyridine (0.55 g, 3.5 mmol) was
used in place of 2-bromo-4-ethoxylpyridine to react with
Th2im (0.81 g, 2.8 mmol). Purification with flash column
chromatography on silica gel (pre-treated with 1% triethyl-
amine in hexane) using a petroleum ether–ethyl acetate mixture
(2 : 1 v/v) as eluent gave the desired product as an off-white
solid. Yield: 0.83 g, 2.3 mmol; 65%. 1H NMR (300 MHz,
CDCl3): d = 1.89 (s, 3H; 2-Me), 2.22 (s, 3H; 2-Me), 2.35
(s, 6H; two 5-Me), 6.31 (s, 1H; thienyl), 6.49 (s, 1H; thienyl),
6.75 (d, 1H, J = 8.2 Hz; pyridyl 3-H), 7.23 (dd, 1H, J = 7.4,
5.0 Hz; pyridyl 5-H), 7.61 (td, 1H, J = 7.8, 1.9 Hz; pyridyl
4-H), 8.27 (s, 1H; imidazolyl 2-H), 8.53–8.51 (m, 1H; pyridyl
6-H). Positive-ion EI mass spectrum: m/z 365 {M}+,
350 {M–Me}+, 273 {M–Me–C5H3N}+. Elemental analysis,
found (%): C, 64.55; H, 5.20; N, 11.00; calcd. for C20H19N3S2ꢃ
13H2O (%): C, 64.66; H, 5.34; N, 11.31.
1
2
C, 46.53; H, 4.16; N, 10.42; calcd. for C20H21N4S2Iꢃ H2O (%):
C, 46.42; H, 4.29; N, 10.83.
[(g6-Mesitylene)Ru(2,20-bpy)Cl]PF6 (1). 2,20-Bipyridine (41 mg,
0.24 mmol) was refluxed with the [(Z6-mesitylene)RuCl2]2
dimer (65 mg, 0.22 mmol based on ruthenium) in degassed
absolute ethanol (20 mL) for two hours. The reaction mixture
was cooled down and filtered. After evaporation to dryness,
the residue was dissolved in methanol (1 mL), and a saturated
solution of NH4PF6 in methanol (1 mL) was added. The
product which appeared as a yellow precipitate was filtered
and washed with methanol and diethyl ether successively.
Recrystallization by slow evaporation of diethyl ether vapor
into a concentrated solution of the crude product in aceto-
nitrile gave analytically pure 2 as orange red crystals. Yield:
112 mg, 0.20 mmol; 91%. 1H NMR (400 MHz, CD3CN): d =
2.11 (s, 9H, Me at mesitylene), 5.33 (s, 3H; mesitylene), 7.70
4,5-Bis(2,5-dimethylthiophen-3-yl)-3-methyl-1-(pyridin-2-yl)-
1H-imidazolium iodide (im-py+Iꢀ). Im-py+Iꢀ was synthesized
c
2274 New J. Chem., 2011, 35, 2267–2278
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(ddd, 2H, J = 7.3, 5.7, 1.4 Hz; pyridyl 5-H), 8.16 (td, 2H, J =
7.8, 1.4 Hz; pyridyl 4-H), 8.29 (d, 2H, J = 8.0 Hz; pyridyl
3-H), 9.18 (dd, 2H, J = 5.7, 0.7 Hz; pyridyl 6-H). Positive-ion
FAB mass spectrum: m/z 413 {M–PF6}+.
(m, 1H; –CHH0–), 5.30 (s, 3H; mesitylene), 5.30–5.56 (br, 1H;
–CHH0–), 6.06 (s, 0.18H; thienyl), 6.20 (s, 0.25H; thienyl), 6.35
(s, 0.18H; thienyl), 6.50 (s, 0.66H; thienyl), 6.94 (s, 0.13H;
thienyl), 7.08 (s, 0.54H; thienyl). Positive-ion FAB mass
spectrum: m/z 668 {M–PF6}+. Elemental analysis, found
(%): C, 45.62; H, 5.14; N, 5.08; calcd. for C31H37N3OS2-
[(g6-Mesitylene)Ru(NHC-py)Cl]PF6 (2). A mixture of silver(I)
oxide (14 mg, 0.059 mmol) and 1-methyl-3-(2-pyridyl)-1H-
imidazolium iodide (30 mg, 0.11 mmol) in dichloromethane
(10 mL) was stirred in the dark for 3–4 h, followed by addition
of the [(Z6-mesitylene)RuCl2]2 dimer (32 mg, 0.11 mmol based
on ruthenium). The mixture was stirred for another 4 h in the
dark and filtered through Celite. The filtrate was evaporated to
dryness under reduced pressure. To the residue was added
methanol (20 mL). After standing for about 1 h, the
methanolic solution was filtered through a pad of Celite.
The pad of Celite was washed several times with methanol.
To the combined filtrates was added NH4PF6 (100 mg), and
the solvent was removed under reduced pressure. The residue
was purified by passing through a short column of alumina
(neutral) using acetone and then acetone–methanol mixture
(10 : 1 v/v) as eluent. The desired product was obtained as an
orange solid after removal of the solvent. Recrystallization by
slow evaporation of diethyl ether vapor into a concentrated
solution of the crude product in methanol gave analytically
pure 2 as brown crystals. Yield: 11 mg, 0.020 mmol; 18%.
1H NMR (400 MHz, acetone-d6): d = 2.31 (s, 9H; Me at
mesitylene), 4.26 (s, 3H; N-Me), 5.62 (s, 3H; mesitylene), 7.57
(ddd, 1H, J = 7.5, 5.8, 1.2 Hz; pyridyl 5-H), 7.71 (d, 1H, J =
2.3 Hz; imidazoyl), 8.07 (d, 1H, J = 8.3 Hz; pyridyl 3-H), 8.24
(ddd, 1H, J = 8.3, 7.5, 1.5 Hz; pyridyl 4-H), 8.25 (d, 1H, J =
2.3 Hz; imidazoyl), 9.19 (d, 1H, J = 5.8 Hz; pyridyl 6-H).
Positive-ion FAB mass spectrum: m/z 416 {M–PF6}+.
1
RuClPF6 H2O (%): C, 45.28; H, 4.66; N, 5.11.
2
[(g6-Mesitylene)Ru(NHCT-CH2th)Cl]PF6 (4). Complex 4
was synthesized using a method similar to that for 3 except
that im-CH2th+Iꢀ (61 mg, 0.11 mmol) was used in place of
im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2 dimer
(32 mg, 0.11 mmol based on ruthenium). The analytically pure
product was obtained as orange crystals after recrystallization
from
a MeOH–diethyl ether mixture. Yield: 37 mg,
0.044 mmol; 40%. 1H NMR (400 MHz, CDCl3, 297 K):
d = 1.74 (s, 1.8H; 2-Me), 1.87 (br s, 2.25H; 2-Me), 2.03 (s,
5.4H; Me at mesitylene), 2.06 (s, 3.6H; Me at mesitylene), 2.17
(br s, 1.4H; 2-Me), 2.30–2.45 (m, 7.7H, 5-Me, 2-Me and Me at
thiazolyl), 2.50 (s, 1.85H; 5-Me), 2.84 (s, 3H; Me at thiazolyl),
3.80 (s, 3H; N-Me), 5.28 (s, 3H; mesitylene), 5.40–5.50 (m, 2H;
–CHH0–), 6.06 (s, 0.19H; thienyl), 6.25 (s, 0.15H; thienyl), 6.28
(s, 0.15H; thienyl), 6.32 (s, 0.19H; thienyl), 6.49 (s, 0.48H;
thienyl), 6.56 (s, 0.12H; thienyl), 6.85 (s, 0.12H; thienyl), 7.05
(s, 0.48H; thienyl). Positive-ion FAB mass spectrum: m/z 684
{M–PF6}+. Elemental analysis, found (%): C, 44.18; H, 4.48;
N, 4.78; calcd. for C31H37N3S3RuClPF6H2O (%): C, 43.94; H,
4.64; N, 4.96.
[(g6-Mesitylene)Ru(Ph-NHCT-CH2ox)Cl]PF6 (5). Complex
5 was synthesized using a method similar to that for 3 except
that Ph-im-CH2ox+Iꢀ (60 mg, 0.10 mmol) was used in place
of im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2
dimer (32 mg, 0.11 mmol based on ruthenium). The analyti-
cally pure product was obtained as bright orange crystals after
recrystallization from a MeOH–diethyl ether mixture. Yield:
59 mg, 0.067 mmol; 68%. 1H NMR (400 MHz, CDCl3,
[(g6-Mesitylene)Ru(NHCT-CH2ox)Cl]PF6 (3). A mixture of
silver(I) oxide (14 mg, 0.059 mmol) and im-CH2ox+Iꢀ (52 mg,
0.10 mmol) in dichloromethane (10 mL) was stirred in the dark
for 3–4 h, followed by addition of the [(Z6-mesitylene)RuCl2]2
dimer (32 mg, 0.11 mmol based on ruthenium). The mixture
was stirred for another 4 h in the dark and filtered through
Celite. The filtrate was evaporated to dryness under reduced
pressure. To the residue was added methanol (20 mL). After
standing for about 1 h, the methanolic solution was filtered
through a pad of Celite. The pad of Celite was washed several
times with methanol. To the combined filtrates was added
NH4PF6 (100 mg), and the solvent was removed under
reduced pressure. The residue was purified by passing through
a short column of alumina (neutral) using acetone and then
acetone–methanol mixture (50 : 1 v/v) as eluent. The desired
product was obtained as an orange solid after removal of the
solvent. Recrystallization by slow evaporation of diethyl ether
vapor into a concentrated solution of the crude product in
methanol gave analytically pure 3 as orange crystals. Yield:
40 mg, 0.049 mmol; 51%. 1H NMR (400 MHz, CDCl3,
297 K): d = 1.74 (s, 1.65H; 2-Me), 1.78 (br s, 0.45H; 2-Me),
1.84 (s, 1.5H; 2-Me), 1.93 (br s, 0.7H; 2-Me), 2.05 (s, 6H; Me at
mesitylene), 2.09 (s, 3H; Me at mesitylene), 2.11 (br s, 1.15H;
Me), 2.27 (br s, 3H; Me at oxazolyl), 2.33–2.43 (m, 4.55H;
5-Me and 2-Me), 2.45 (s, 3H; Me at oxazolyl), 2.49 (s, 2H;
5-Me), 3.80 (s, 1H; N-Me), 3.84 (s, 2H; N-Me), 5.00–5.20
297 K):
d = 1.60–1.75 (m, 2.66H; 2-Me), 1.75–1.95
(m, 2.54H; 2-Me), 1.90 (s, 9H; Me at mesitylene), 2.05–2.20
(m, 2.8H; 5-Me and 2-Me), 2.29 (s, 3H; Me at oxazolyl), 2.34
(s, 1H; 5-Me), 2.44 (s, 1H; Me at oxazolyl), 2.46 (s, 2H; Me at
oxazolyl), 2.52 (s, 3H; 5-Me), 4.81 (br, 2H; mesitylene), 4.88
(s, 1H; mesitylene), 5.15 (d, 0.29H, J = 16.9 Hz; –CHH0–),
5.31 (d, 0.71H, J = 16.9 Hz; –CHH0–), 5.40–5.55 (br, 0.29H;
–CHH0–), 5.66 (d, 0.71H, J = 16.9 Hz; –CHH0–), 5.78
(s, 0.5H; thienyl), 6.01 (s, 0.5H; thienyl), 6.19 (br, 0.25H;
phenyl 5-H), 6.88–6.95 (m, 0.75H; phenyl 5-H), 7.03 (br s,
1H; thienyl), 7.30–7.35 (m, 1H; phenyl 4-H), 7.40–7.44 (m, 1H;
phenyl 3-H), 7.48–7.53 (m, 1H; phenyl 2-H), 8.33 (br, 0.3H;
phenyl 1-H), 8.40 (br, 0.52H; phenyl 1-H), 8.64 (br, 0.18H;
phenyl 1-H). Positive-ion FAB mass spectrum: m/z 730
{M–PF6}+. Elemental analysis, found (%): C, 49.43; H,
4.90; N, 4.62; calcd. for C36H39N3OS2RuClPF6 (%): C,
49.40; H, 4.49; N, 4.80.
[(g6-Mesitylene)Ru(NHCT-ox)Cl]PF6 (6). Complex 6 was
synthesized using a method similar to that for 3 except that
im-ox+Iꢀ (49 mg, 0.09 mmol) was used in place of
im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2 dimer
(30 mg, 0.10 mmol based on ruthenium). Recrystallization by
c
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slow evaporation of diethyl ether vapor into a concentrated
solution of the crude product in acetone gave analytically pure
6 as a bright yellow crystalline solid. Yield: 61 mg, 0.076
[(g6-Mesitylene)Ru(NHCT-pym)Cl]PF6 (9). Complex 9 was
synthesized using a method similar to that for 3 except that
im-pym+Iꢀ (50 mg, 0.10 mmol) was used in place of
im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2 dimer
(31 mg, 0.11 mmol based on ruthenium). Recrystallization by
slow evaporation of diethyl ether vapor into a concentrated
solution of the crude product in acetone gave analytically pure
9 as reddish orange crystals. Yield: 60 mg, 0.077 mmol; 79%.
1H NMR (400 MHz, CDCl3–CD3CN 10 : 1 v/v, 297 K): d =
1.84 (s, 2H; 2-Me), 1.96 (s, 2H; 2-Me), 2.19 (s, 2H; 2-Me),
2.29–2.30 (m, 9H; Me at mesitylene), 2.35–2.39 (m, 3H; 5-Me),
2.45 (s, 3H; 5-Me), 3.92 (s, 1.72H; N-Me), 3.97 (s, 1.28H;
N-Me), 5.47 (s, 3H; mesitylene), 6.23 (s, 0.26H; thienyl), 6.44
(s, 0.60H; thienyl), 6.60–6.70 (m, 0.75H; thienyl), 6.89
(s, 0.39H; thienyl), 7.35–7.41 (m, 1H; pyrimidyl 5-H),
8.55–8.59 (m, 1H; pyrimidyl 4-H), 9.15–9.18 (m, 1H; pyrimidyl
6-H). Positive-ion FAB mass spectrum: m/z 637 {M–PF6}+.
Elemental analysis, found (%): C, 44.45; H, 4.18; N, 6.89;
calcd. for C29H32N4S2RuClPF6 (%): C, 44.53; H, 4.12;
N, 7.16.
1
mmol; 81%. H NMR (400 MHz, CDCl3, 297 K): d = 1.82
(br s, 1.5H; 2-Me), 2.00 (br s, 4.5H; 2-Me), 2.21 (s, 3H; 5-Me),
2.31 (s, 9H; Me at mesitylene), 2.33 (s, H; Me at oxazolyl), 2.40
(s, 3H; 5-Me), 2.44 (s, 3H; Me at oxazolyl), 3.91 (br s, 3H;
N-Me), 5.44 (s, 3H; mesitylene), 6.65 (br s, 1.51H; thienyl),
7.05 (br s, 0.49H; thienyl). Positive-ion FAB mass spectrum:
m/z 654 {M–PF6}+. Elemental analysis, found (%): C, 45.09;
H, 4.80; N, 5.02; calcd. for C30H35N3OS2RuClPF6 (%): C,
44.75; H, 4.46; N, 5.22.
[(g6-Mesitylene)Ru(NHCT-py4-OEt)Cl]PF6 (7). Complex 7
was synthesized using a method similar to that for 3 except
that im-pyOEt+ ꢀ
(49 mg, 0.09 mmol) was used in place of
I
im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2 dimer
(31 mg, 0.11 mmol based on ruthenium). Recrystallization by
slow evaporation of diethyl ether vapor into a concentrated
solution of the crude product in acetone gave analytically pure
7 as yellowish orange crystals. Yield: 56 mg, 0.068 mmol; 76%.
1H NMR (400 MHz, CDCl3, 297 K): d = 1.93 (s, 2H; 2-Me),
2.05–2.15 (m, 2H; 2-Me), 2.25 (s, 6H; Me at mesitylene), 2.27
(s, 3H; Me at mesitylene), 2.18–2.32 (m, 2H; 2-Me), 2.38–2.44
(m, 6H; 5-Me), 3.75–3.85 (m, 2H; –OCH2CH3), 3.89 (s, 1H;
N–Me), 3.94 (s, 2H; N–Me), 5.35 (s, 2H; mesitylene), 5.39
(s, 1H; mesitylene), 6.36–6.45 (m, 1.65H; pyridyl 3-H and
thienyl), 6.57 (s, 0.56H; thienyl), 6.67 (br s, 0.14H; thienyl),
6.73 (dd, 0.64H, J = 6.7, 2.6 Hz; pyridyl 4-H), 6.76
(dd, 0.36H, J = 6.7, 2.6 Hz; pyridyl 4-H), 7.05 (br, 0.12H;
thienyl), 7.21 (br, 0.52H; thienyl), 8.51 (d, 0.64H, J = 6.7 Hz;
pyridyl 6-H), 8.54 (d, 0.36H, J = 6.7 Hz; pyridyl 6-H).
Positive-ion FAB mass spectrum: m/z 680 {M–PF6}+.
Elemental analysis, found (%): C, 46.44; H, 4.86; N, 4.99;
calcd. for C32H37N3OS2RuClPF6 (%): C, 46.57; H, 4.52;
N, 5.09.
Physical measurements and instrumentation
NMR spectra were recorded either on a Bruker DPX 300
(300 MHz) or on a Bruker AVANCE 400 (400 MHz)
FT-NMR spectrometer. Variable-temperature 1H NMR
spectra were recorded on a Bruker DPX 500 (500 MHz)
FT-NMR spectrometer equipped with a Bruker BVT 2000
temperature controller. Chemical shifts (d/ppm) were reported
relative to tetramethylsilane (Me4Si). Electron impact (EI) and
fast atom bombardment (FAB) mass spectra were recorded on
a Finnigan MAT 95 mass spectrometer. Negative ion electro-
spray ionization (ESI) mass spectra were recorded on a
Finnigan LCQ spectrometer. Elemental analyses of ligands
and metal complexes were performed on a Flash EA 1112
elemental analyzer by the Institute of Chemistry at the
Chinese Academy of Sciences in Beijing. UV-Vis absorption
spectra were recorded on a Hewlett-Packard 8452A diode
array spectrophotometer. Cyclic voltammetric measurements
were performed using a CH Instruments, Inc. model CHI
620 Electrochemical Analyzer. Measurements were performed
in acetonitrile solution with 0.1 M n-Bu4NPF6 as supporting
electrolyte. The AgCl/Ag electrode was used as the reference
electrode, and the glassy carbon electrode (CH Instruments,
Inc.) was used as the working electrode with a platinum wire as
the counter electrode. The glassy carbon electrode was
polished with 1 mm and 0.3 mm a-alumina slurry (Linde) on
a microcloth (Buehler Co.) successively, and then sonicated
and rinsed thoroughly with deionized water.
[(g6-Mesitylene)Ru(NHCT-py)Cl]PF6 (8). Complex 8 was
synthesized using a method similar to that for 3 except that
im-py+Iꢀ (50 mg, 0.10 mmol) was used in place of
im-CH2ox+Iꢀ to react with the [(Z6-mesitylene)RuCl2]2 dimer
(32 mg, 0.11 mmol based on ruthenium). Recrystallization by
slow evaporation of diethyl ether vapor into a concentrated
solution of the crude product in acetone gave analytically pure
8 as orange crystals. Yield: 32 mg, 0.041 mmol; 42%. 1H NMR
(400 MHz, CDCl3, 297 K): d = 1.58 (s, 2H; 2-Me), 1.91
(br s, 2H; 2-Me), 2.26 (s, 6H; Me at mesitylene), 2.28 (s, 3H;
Me at mesitylene), 2.04–2.29 (m, 2H; 2-Me), 2.39–2.45 (m, 6H;
5-Me), 3.91 (s, 1.2H; N-Me), 3.95 (s, 1.8H; N-Me), 5.41 (s, 2H;
mesitylene), 5.45 (s, 1H; mesitylene), 6.31 (s, 0.20H; thienyl),
6.36 (s, 0.32H; thienyl), 6.46 (br s, 0.14H; thienyl), 6.57
(s, 0.52H; thienyl), 6.66 (s, 0.15H; thienyl), 6.90–7.00
(m, 1.15H; pyridyl 3-H and thienyl), 7.14 (s, 0.52H; thienyl),
7.12–7.29 (m, 1H; pyridyl 5-H), 7.68–7.77 (m, 1H; pyridyl
4-H), 8.87–8.92 (m, 1H; pyridyl 6-H). Positive-ion FAB mass
spectrum: m/z 636 {M–PF6}+. Elemental analysis, found (%):
C, 47.14; H, 4.64; N, 5.39; calcd. for C30H33N3S2RuClPF6ꢃ
12C4H10O (%): C, 47.00; H, 4.68; N, 5.14.
X-Ray crystallography
Single crystals of complexes 3 and 6 suitable for X-ray
diffraction structure determination were obtained by slow
diffusion of diethyl ether vapor into an acetone or methanol
solution of the respective complex. Orange and brown block
crystals were formed. Crystals of 3 (0.20 ꢁ 0.30 ꢁ 0.39 mm)
and 6 (0.14 ꢁ 0.15 ꢁ 0.49 mm) mounted on a glass capillary
were used for data collection at 305 K on a Bruker Smart
CCD 1000 using graphite monochromatized Mo-Ka radiation
c
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(l = 0.71073 A). Raw frame data were integrated with SAINT
program.34a Semi-empirical absorption correction with
SADABS34b was applied. The structure was solved by direct
methods employing SHELXS-97 program34c and expanded
using Fourier techniques. All non-H atoms were refined
anisotropically. All of the C-bound H atoms were observable
from a difference Fourier map but were all placed at
geometrical positions with C–H = 0.93, 0.96, 0.97 A for
phenyl, methyl and methylene H-atoms. The positions of H
atoms were calculated based on riding mode with Uiso(H) =
1.2Ueq(Carrier). Details of the restraints used in the refinement
can be found in the ESI.w CCDC reference numbers 814059
(for 6) and 814060 (for 3).
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Acknowledgements
V. W.-W. Y. acknowledges the support from The University
of Hong Kong under the Distinguished Research Achievement
Award Scheme and the URC Strategic Research Theme on
Molecular Materials. This work has been supported by the
University Grants Committee Areas of Excellence Scheme
(AoE/P-03/08). G. D. acknowledges the receipt of a post-
graduate studentship, administrated by The University of
Hong Kong. We are grateful to Dr L. Szeto for her assistance
in X-ray crystal structure data collection and determination.
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