Complexation of tetrakis(acetato)chloridodiruthenium with naphthyridine-2,7-dicarboxylate - Characterization and catalytic activity

Article abstract of DOI:10.1002/ejic.201403156

The reaction of calcium naphthyridine-2,7-dicarboxylate (Cadcnp) with Ru₂(OAc)₄Cl in water resulted in the formation of Ca[Ru₂(dcnp)(OAc)₃]₂ (3). X-ray crystal structural analysis of 3 confirmed its molecular structure and showed that the calcium ion binds to the lateral carboxylate groups of four neighboring anionic units of [Ru₂(dcnp)(μ-OAc)₃] and two acetone molecules to form a two-dimensional framework. The Ru^II-Ru^II valence state of the diruthenium core was supported by superconducting quantum interference device (SQUID) magnetometry [μ_eff (300 K) = 2.77 μ_B]. Complex 3 appears to be an efficient catalyst for the oxidative cleavage of olefins in aqueous media under mild conditions. Typically, the reaction of pulegone with NaIO₄ in water catalyzed by 3 (1 mol-%) at 45 C afforded 3-methyladipic acid quantitatively. The reaction of calcium naphthyridine-2,7-dicarboxylate (Cadcnp) with Ru₂(OAc)₄Cl provides Ca[Ru₂(dcnp)(OAc)₃]₂ as the exclusive product. The complex is catalytically active for the oxidative cleavage of olefins in aqueous media.

Full text of DOI:10.1002/ejic.201403156

FULL PAPER
DOI:10.1002/ejic.201403156
Complexation of Tetrakis(acetato)chloridodiruthenium
with Naphthyridine-2,7-dicarboxylate – Characterization
and Catalytic Activity
Chia-Han Lee,[a] Cai-Ling Wu,[a] Shao-An Hua,[a] Yi-Hung Liu,[a]
Shie-Ming Peng,[a] and Shiuh-Tzung Liu*[a]
Keywords: Dimetallic complexes / Ruthenium / Carboxylate ligands / Cleavage reactions
The reaction of calcium naphthyridine-2,7-dicarboxylate
(Cadcnp) with Ru2(OAc)4Cl in water resulted in the
formation of Ca[Ru2(dcnp)(OAc)3]2 (3). X-ray crystal struc-
tural analysis of 3 confirmed its molecular structure and
showed that the calcium ion binds to the lateral carboxylate
groups of four neighboring anionic units of [Ru2(dcnp)(μ-
OAc)3] and two acetone molecules to form a two-dimensional
framework. The RuII–RuII valence state of the diruthenium
core was supported by superconducting quantum inter-
ference device (SQUID) magnetometry [μeff (300 K)
=
2.77 μB]. Complex 3 appears to be an efficient catalyst for the
oxidative cleavage of olefins in aqueous media under mild
conditions. Typically, the reaction of pulegone with NaIO4 in
water catalyzed by 3 (1 mol-%) at 45 °C afforded 3-methyl-
adipic acid quantitatively.
and co-workers reported that sodium 1,8-naphthyridine-
2,7-dicarboxylate (Na2dcnp) reacted with Ru2(OAc)4Cl un-
der an argon atmosphere to yield a neutral species,
[Ru2(dcnp)(OAc)3] (1), in which the diruthenium core was
revealed to be a “Ru25+” species.[8b]
In this work, we reinvestigated the complexation of
Ru2(OAc)4Cl with the calcium salt of dcnp to yield
Ca[Ru2(dcnp)(OAc)3]2 (3), which is an ionic species, in con-
trast to the neutral nature of 1. Complex 3 was fully charac-
terized by spectroscopic, X-ray crystallographic, and super-
conducting quantum interference device (SQUID) analyses.
In addition, the catalytic activity of the diruthenium com-
plex in the oxidative cleavage of olefinic substrates in
aqueous media was explored.
Introduction
Owing to unique metal–metal interactions between the
mixed-valence ruthenium ions, tetrakis(acetato)chloridodi-
ruthenium, Ru2(OAc)4Cl,[1] and related coordination com-
pounds represent an important class of dimetallic com-
plexes, which have drawn much attention in many aspects
including coordination studies[2–4] and biological,[5] materi-
als,[6] and catalysis applications.[7] The diruthenium centers
of Ru2(OAc)4Cl are coordinated to four carboxylate groups
to form a paddle-wheel shape and are linked by the axial
chloride ligand into a polymeric chain. Thus, the axial
ligands dramatically affect the electronic, spectroscopic,
electrochemical, and magnetic properties.[1–9] Furthermore,
there are many reports concerning the electronic structures
of the diruthenium cores, including “Ru24+” in the neutral
species [Ru2(O2CR)4]0 and “Ru25+” in the cationic species
[Ru2(O2CR)4]+ with two and three unpaired electrons,
respectively.[9]
Results and Discussion
Preparation and Characterization of Ruthenium Complexes
The replacement of the bridging carboxylate ligands with
other multidentate ligands to modify the properties of the
The desired ligand, 1,8-naphthyridine-2,7-dicarboxylic
resulting complexes is another interesting subject in this acid [dcnpH2] (2), was prepared according to the method
area of research. Among various bridging ligands, 1,8- reported previously.[10] The deprotonation of
2
with
naphthyridine-based donors are considered as “masked Ca(OH)2 was performed at ambient temperature in aqueous
carboxylates”, as the nitrogen donor atoms can bind to two medium for 12 h. The treatment of the calcium salt with
metal ions in a syn,syn mode, similarly to a carboxylate Ru2(OAc)4Cl in air resulted in the formation of deep purple
group. Few diruthenium complexes with bridging naphthyr- crystalline solid 3. The synthetic procedure for 3 is different
idinyl ligands have been reported.[8] Among them, Sauvage from that for 1 (Scheme 1). The obtained complex 3 is
stable in air and soluble in water, methanol, and other
[a] Department of Chemistry, National Taiwan University,
highly polar solvents. The electronic absorption spectrum
of 3 in water shows intensive bands at λ = 207 (logε = 4.6)
and 269 nm (logε = 4.03), attributed to the π–π* transitions
1, Sec. 4, Roosevelt Road, Taipei, Taiwan 106
E-mail: stliu@ntu.edu.tw
http://www.ch.ntu.edu.tw/
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of the ligand, and λ = 716 nm (logε = 3.32) owing to metal- Table 1. Selected bond lengths [Å] and angles [°] for 3.
to-ligand charge transfer (MLCT). In addition, a weak ab-
Bond lengths
Bond angles
sorption at λ = 891 nm is due to a δ–δ* transition in the
“Ru24+” paddle-wheel structure.[8d] The absorptions of 3 are
essentially similar to those of 1, the MLCT band of which
appears at λ =710 nm (logε = 3.22).
Ru(1)–Ru(2)
Ru(1)–N(1)
Ru(1)–O(1)
Ru(2)–N(2)
Ru(2)–O(3)
2.2706(3)
2.022(2)
2.287(2)
2.015(2)
2.251 (2)
O(1)–Ru(1)–Ru(2) 165.25(5)
N(1)–Ru(1)–O(7) 179.11(8)
O(5)–Ru(1)–O(9) 177.68(7)
N(1)–Ru(1)–O(1) 75.41(8)
O(3)–Ru(2)–Ru(1) 166.39(5)
N(2)–Ru(2)–O(8) 178.64(8)
O(6)–Ru(2)–O(10) 177.74(8)
N(2)–Ru(2)–O(3) 75.76(8)
N(1)–Ru(1)–O(7) 179.11(8)
Ca(1)–O(11)(acetone) 2.379(2)
Ca(1)–O(2)#
Ca(1)–O(4)
Ru(1)–O(7)
2.313(2)
2.275(2)
2.074(2)
Scheme 1. Preparation of ruthenium complexes 1 and 3.
Figure 1. ORTEP plot of 3.
The ESI-MS spectra of the complex in negative-ion
mode showed the highest mass peak at m/z = 596.8658,
which corresponds to the mass of the anion
[C16H13N2O10Ru2]– with two ruthenium ions, three acetato
ligands, and the dcnp ligand. To unambiguously character-
ize this compound, the crystal structure of 3 was deter-
mined.
ESI-MS observations. This part of the structure is quite
similar to the previously reported crystal structure of 1,
which is a “Ru25+” complex.[8b] Each Ru ion in 3 exhibits
an octahedral coordination sphere with a metal–metal bond
[2.2706(3) Å]. A comparison of some structural parameters
of 1 and 3 is shown in Scheme 2. Compared with a Ru–Ru
bond length of 2.273(4) Å in 1, the metal–metal distance in
3 is slightly shorter by ca. 0.002 Å. All other bond lengths
and angles in 3 are in the normal range and comparable to
those in 1, except for the C–O bond length of the dcnp
ligand. The coordination of the CaII ion to the carbonyl
The solid-state structure of 3, crystallized from water,
tetrahydrofuran (THF), and acetone, was determined by X-
ray crystallography. The detailed structure is discussed with
its structural features, and the selected bond lengths and
angles are presented in Table 1. The coordination character-
istics of 3 are depicted in Figure 1. Complex 3 shows a con-
tinuous interaction throughout the crystal lattice, wherein
the calcium ion binds to the lateral carboxylate groups of
four different neighboring [Ru2(dcnp)(μ-OAc)3] units and
two acetone molecules. The calcium ion is hexacoordinate
with two acetone molecules in a trans arrangement. The
terminal carboxylate groups of [Ru2(dcnp)(μ-OAc)3] adopt
a bridging mode and connect the CaII centers to construct
a two-dimensional framework. The bond lengths between
the calcium ion and the carboxylate O atoms, Ca–O(4) and
Ca–O(2)#, are 2.313(2) and 2.275(2) Å, respectively,
whereas the bond length between the calcium ion and the
acetone O atom is 2.379(2) Å. The O(4)–Ca(1)–O(2)# and
O(4)–Ca(1)–O(2)#2 angles are 84.96(7) and 95.04(8)°,
respectively; presumably, the deviation from 90° is due to
the crystal packing.
The diruthenium portion in 3 is shown in Figure 2 and
reveals a dimetallic core bridged by the dcnp ligand and
three acetato ligands; this structure is consistent with the ability level).
Figure 2. ORTEP plot of the diruthenium portion in 3 (30% prob-
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Scheme 2. Comparison of bond lengths [Å] in 1 and 3.
moieties does not affect the lengths of the C=O bonds. electron oxidation processes [RuIIIRuII/RuII = 0.51 V and
2
There is no significant difference between the C(10)–O(4) RuII2/RuIIRuI = –1.01 V], which are quite different from
and C(10)–O(3) bond lengths in 3, but a difference (ca. those of 1. The cyclic voltammogram of 3 in a 5% water/
0.05 Å) appears between these two bonds in 1.
DMF solution is essentially similar to that in anhydrous
Crystallographic analysis shows the empirical formula of DMF; therefore, the substitution of the acetato ligands by
3 to be Ca0.5[C22H25N2O12Ru2]. On the basis of charge water proceeds very slowly at ambient temperature.[12c]
balance, the [Ru2(dcnp)(μ-OAc)3] fragment should be a
“–1” ion, which implies that the diruthenium core is a
“RuII–RuII” species. This is supported by magnetism mea-
Catalytic Oxidative Cleavage of Alkenes
surements. The temperature dependence of the magnetiza-
tion has been measured for 3 with a SQUID magnetometer.
The temperature-dependent data were transformed to the
effective magnetic moment. The effective magnetic moment
carboxylic acids and ketones, and various methods have
The oxidative cleavage of C=C bonds is an important
methodology for the conversion of olefinic substrates into
(μeff) of 3 at room temperature is ca. 2.77 μB (Figure 3),
which is consistent with the theoretical value of 2.83 μB for
a “Ru24+” species with two unpaired electrons. This obser-
vation is consistent with the structure revealed by
crystallography. According to the zero-field-splitting (ZFS)
been developed.[11] Diruthenium carboxylate complexes are
potential catalysts for the oxidation of several organic sub-
strates.[7,12] To minimize the environmental impact of the
use of organic solvents, aqueous reactions are required in
the development of new catalytic reactions. It occurred to
us that the water-soluble nature of 3 should make it possible
to cleave carbon–carbon double bonds in an aqueous
system.
3
model,[9b] the D value of A2g splitting was estimated to be
226 cm–1.
To obtain information on the catalytic system, we first
examined the oxidation of cyclohexene catalyzed by 3 in the
presence of various oxidants. The standardized protocol
was performed with cyclohexene (0.25 mmol), NaIO4
(1 mmol), and 3 (2.5ϫ10–3 mmol) in water (1 mL) at ambi-
ent temperature for 16 h (Scheme 3). In this reaction, adipic
acid was obtained as the product, as determined by NMR
spectroscopic analysis. The optimization results are summa-
rized in Table 2.
Scheme 3. Oxidative cleavage of cyclohexene.
Figure 3. SQUID data for 3.
Among the various oxidants used in this study, most gave
poor results, except NaIO4 and PhI(OAc)2. The use of
The potentials of the RuIII2/RuIIIRuII and RuIIIRuII/RuII
2
redox couples of 1 are +0.33 V and –1.11 V, respectively. NaIO4 provided the best yield of the desired product
The redox behavior of 3 in anhydrous N,N-dimethylform- (Table 2, Entry 1). The reaction proceeded more quickly at
amide (DMF) has been studied by cyclic voltammetry. The an elevated reaction temperature (Table 2, Entries 2 and 3).
cyclic voltammogram of 3 consists of two reversible one- In addition to the above factors, we investigated the solvent
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Table 2. Oxidative cleavage of cyclohexene catalyzed by 3 under catalyst precursors exhibited some activity (Table 3, En-
various conditions.[a]
tries 2–6) but were not as active as 3. It is quite clear that
Entry Solvent
Oxidant (c, mmol)
T [°C] Yield [%][b]
the ligand plays an important role in the catalysis. To vali-
date the ligand effect on the catalysis, the oxidative cleavage
of norbornene catalyzed by 3, 5, and Ru2(OAc)4Cl was
monitored by NMR spectroscopy, and the yields of the de-
sired products are plotted in Figure 4. The oxidation of nor-
bornene catalyzed by diruthenium complex 3 proceeded
smoothly, and the yield of cyclopentanedicarboxylic acid
reached 62% within 1 h. A moderate yield was achieved
when Ru2(OAc)4Cl was employed as the catalyst, but the
diminished activity after ca. 50 min indicates the effect of
the ligand on the stabilization of the active metal species.
Complex 5, a mononuclear species stabilized by a pyridine-
carboxylato ligand, showed a similar initial rate as that for
3, but the activity decreased gradually. These observations
demonstrate the advantage of diruthenium complex 3 in the
catalytic reaction.
1
2
3
4
5
6
7
8
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
NaIO4 (1)
NaIO4 (1)
NaIO4 (1)
H2O2 (2.5)
tBuO2H (1)
oxone (1)
PhI(OAc)2 (1)
benzoquinone (1)
NaClO (1)
30
45
60
30
30
30
30
30
30
30
30
30
30
30
30
72
85
86
trace
10
8
58
trace
trace
trace
25
9
10
11
12
13
14
15
NaClO (1)/NaIO4 (0.05)
H2O/acetone (1:1) NaIO4 (1)
H2O/THF (1:1) NaIO4 (1)
H2O/CH3CN (1:1) NaIO4 (1)
H2O/CH3CN(3:1) NaIO4 (1)
H2O/CH3CN (4:1) NaIO4 (1)
[c]
–
71
56
24
[a] Reaction conditions: cyclohexene (0.25 mmol), oxidant, and Ru
complex (2.5ϫ10–3 mmol) in solvent (1 mL) for 16 h. [b] Yield de-
termined by NMR spectroscopy. [c] A complex mixture of prod-
ucts.
effect on the catalysis. As shown in the Table 2, the activity
of the catalyst was remarkably influenced by the solvent.
Water appears to be the best choice of solvent for 3 as the
catalyst; therefore, the process meets the environmental
criterion. Complex 3 loses its catalytic selectivity in a mix-
ture of water/THF (Table 2, Entry 12), in which a complex
mixture of products was produced. We cannot fully inter-
pret the differences in various solvents, but it seems clear
that ligand 2 is a good choice for water-soluble catalyst
design.
A series of experiments was performed to evaluate the
suitability of various ruthenium sources for the oxidation
process (Table 3). Clearly, complex 3 has the best activity
for this oxidation. The other ruthenium complexes tested as
Figure 4. Oxidation of norbornene with several catalysts.
With the optimized conditions in hand, the generality of
the oxidative cleavage of C=C bonds catalyzed by 3 was
investigated (Table 4). We performed the reactions with a
variety of cycloalkenes and styrene derivatives. All cycloalk-
enes underwent oxidative cleavage to afford the respective
dicarboxylic acids in good-to-excellent yields. The oxidation
of norbornene proceeded smoothly under the optimized
conditions to yield cis-cyclopentanedicarboxylic acid in
80%. However, the yield was improved to 99% by the ad-
dition of acetone to the reaction mixture as the cosolvent
owing to the poor solubility of the substrate in water. Vinyl-
benzene derivatives were also reactive under the oxidation
conditions and afforded the corresponding benzoic acids in
high yields even for 4-vinylpyridine and trans-stilbene.
Moreover, the oxidation of cinnamates was accomplished
in excellent yields (Table 4, Entries 12, and 13). This system
was successfully applied to the oxidation of pulegone to
quantitatively provide 3-methyladipic acid. However, the
oxidative cleavage of cyclohexenone led to the production
of pentanedioic acid (33%), presumably via the α-
dicarbonyl intermediate followed by decarboxylation.
Table 3. Oxidation of cyclohexene catalyzed by various Ru com-
plexes.[a]
Entry Ru complex
Amount of catalyst [mmol] Yield [%][b]
1
2
3
4
5
6
Complex 3
Ru2(OAc)4Cl
Complex 4
Complex 5
Complex 6
RuCl3·3H2O
2.5ϫ10–3 (1 mol-%)
5ϫ10–3 (2 mol-%)
0.01 (4 mol-%)
0.01 (4 mol-%)
0.01 (4 mol-%)
72
52
45
42
36
38
0.01 (4 mol-%)
[a] Reaction conditions: cyclohexene (0.25 mmol), NaIO4
(1 mmol), and Ru complex in H2O (1 mL) at 30 °C for 16 h. [b]
Yields determined by NMR spectroscopy.
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Table 4. Oxidative cleavage of olefins catalyzed by 3.[a]
nance spectra were recorded with a 400 MHz spectrometer. Chemi-
cal shifts are given in parts per million relative to Me4Si for 1H
and 13C NMR spectroscopy. Infrared spectra were recorded with
samples as KBr pallets. The ligand dcnpH2,[10] dicarbonyl{(P, P Ј,N-
1,9-diphenyl-2,3,4,5,6,7,8,9-octahydro-1H-5,1,9-
benzazadiphosphacycloundecine)}chlororuthenium (4),[13] (N,O-2-
pyridinecarboxylato)(η6-p-cymene)chlororuthenium (5),[14] and
(N,N-bipyridine)(η6-benzene)chlororuthenium chloride (6)[15] were
prepared according to the reported methods. Cyclic voltammetry
measurements were performed with a CH instruments 750A po-
tentiostat with a graphite working electrode and Pt wire auxiliary
electrode at ambient temperature. The potentials were measured
versus the saturated sodium chloride calomel electrode (SSCE).
Complex
3 in DMF [0.1 m tert-butylammonium perchlorate
(TBAP]) was determined at a scan rate of 100 mV/s.
Complex 3: To a mixture of H2dcnp (100 mg, 0.46 mmol) and
Ca(OH)2 (34 mg, 0.46 mmol) in a 25 mL flask was added water
(10 mL), and the mixture was stirred at ambient temperature for
12 h. Ru2(OAc)4Cl (196 mg, 0.46 mmol) was then added to the
above solution, and the resulting mixture was heated at 60 °C for
5 h. After removal of the water, the residue was dissolved in meth-
anol (20 mL), and the solution was filtered to remove salts. After
concentration, the desired complex was obtained as a deep purple
solid (191 mg, 68%). Recrystallization from water/THF/acetone
gave 1 as a deep purple crystalline solid, suitable for X-ray crystal-
lography. HRMS (ESI–): calcd. for C16H13N2O10Ru2 [Ru2(dcnp)(μ-
OAc)3]– 596.8669; found 596.8658.
Complex 5:[14] A mixture of 2-picolinic acid (100 mg, 0.81 mmol)
and [RuCl(p-cymene)]2 (248.9 mg, 0.41 mmol) in isopropyl alcohol
(5 mL) was stirred at ambient temperature for 48 h. The solution
slowly turned bright orange. Filtration of the mixture gave an
orange solid, which was washed with water, methanol, and ether.
The desired complex was obtained as an orange solid (212.8 mg,
1
60%): H NMR (400 MHz, CDCl3): δ = 8.94 (m, 1 H, Py-H), 8.00
(d, J = 7.6 Hz, 1 H, Py-H), 7.91 (t, J = 7.6 Hz, 1 H, Py-H), 7.55
(m, 1 H, Py-H), 5.60 (d, J = 6 Hz, 1 H, Ar-H), 5.57 (d, J = 6 Hz,
1 H, Ar-H), 5.45 (d, J = 5.2 Hz, 1 H, Ar-H), 5.36 (d, J = 5.2 Hz,
1 H, p-Ar-H), 2.85 (m, J = 6.8 Hz, 1 H, CH), 2.27 (s, 3 H, CH3),
1.20 [d, J = 6.8 Hz, 6 H, CH(CH3)2] ppm. 13C NMR (100 MHz):
δ = 171.3, 152.8, 150.9, 139.3, 128.3, 126.7, 102.5, 98.9, 83.0, 82.7,
81.6, 80.9, 77.5, 77.2, 76.9, 31.3, 22.6, 22.5, 19.1 ppm.
[a] Reaction conditions: olefin (0.25 mmol), NaIO4 (1 mmol), H2O
(1 mL), and Ru complex 3 (2.5ϫ10–3 mmol) at 45 °C for 16 h. [b]
Isolated yield. [c] Cosolvent (water/acetone 3:1). [d] Acetone as the
side product.
Typical Procedure for Oxidative Cleavage of Olefins: An olefinic
substrate (0.25 mmol), Ru complex (1 mol-%), and NaIO4
(1.025 mmol) in water (1 mL) were loaded in a reaction vessel with
Conclusions
We have prepared and characterized the diruthenium
complex Ca[Ru2(dcnp)(OAc)3]2 (3), in which the diruth- a stirring bar. The mixture was heated at 45 °C for 16 h. After the
enium core is a “RuII–RuII” species. The crystal structure
completion of the reaction, brine (4 mL) was added to the reaction
mixture, which was then extracted with diethyl ether (5 mLϫ3).
of 3 clearly shows that the anionic unit of [Ru2(dcnp)(μ-
OAc)3]– coordinates to the Ca2+ ion to form a two-dimen-
The combined organic extracts were dried and concentrated. The
residue was analyzed by NMR spectroscopy. Recrystallization pro-
sional framework. The utilization of the diruthenium com-
vided the desired compounds in pure form. The spectroscopic data
plex 3 as the catalyst for the oxidative cleavage of alkenes
of the organic products are essentially identical to those reported
previously.
in water led to the corresponding carboxylic acids. Complex
3 is an excellent catalyst for the oxidation of olefins to carb-
oxylic acids under mild conditions. More catalytic activity
studies involving 3 for other transformations are in pro-
Adipic Acid: 1H NMR {400 Hz, [D6]dimethyl sulfoxide ([D6]-
DMSO)}: δ = 1.47 (m, 4 H), 2.17 (m, 4 H), 11.97 (br, 2 H, CO2H)
ppm. 13C NMR (100 Hz): δ = 174.4, 33.4, 24.1 ppm.
gress.
1
Glutaric Acid: H NMR (400 Hz, [D3]acetonitrile): δ = 1.81 (m, J
= 7.4 Hz, 2 H), 2.33 (t, J = 7.4 Hz, 4 H) ppm. 13C NMR (100 Hz):
δ = 175.4, 33.7, 21.3 ppm.
Experimental Section
1
Octanedioic Acid: H NMR (400 Hz, [D6]DMSO): δ = 1.26 (m, 4
General Information: Chemicals and solvents of analytical grade
H), 1.48 (m, 4 H), 2.18 (m, 4 H), 11.95 (br, 2 H, CO2H) ppm. 13C
were used without further purification. Nuclear magnetic reso-
NMR (100 Hz): δ = 174.2, 38.9, 28.3, 24.4 ppm.
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Succinic Acid: 1H NMR (400 Hz, [D6]DMSO): δ = 2.40 (s, 4 H),
11.6–13.4 (br, 2 H) ppm. 13C NMR (100 Hz): δ = 173.7, 28.8 ppm.
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cis-Cyclopentane-1,3-dicarboxylic Acid: 1H NMR (400 Hz, [D6]-
DMSO): δ = 1.72–1.88 (m, 5 H), 2.06–2.11 (m, 1 H), 3.39 (br, 2
H), 12.08 (br, 2 H, CO2H) ppm. 13C NMR (100 Hz): δ = 176.4,
43.4, 33.0, 29.2 ppm.
1
Benzoic Acid: H NMR (400 Hz, [D6]DMSO): δ = 7.50 (dd, J = 8,
4 Hz, 2 H, Ar-H), 7.62 (t, J = 8 Hz, 1 H, Ar-H), 7.94 (d, J = 4 Hz,
2 H, Ar-H), 12.94 (br, 1 H, CO2H) ppm. 13C NMR (100 Hz): δ =
167.3, 132.9, 130.8, 129.3, 128.6 ppm.
1
4-Chlorobenzoic Acid: H NMR (400 Hz, [D6]DMSO): δ = 7.54 (d,
J = 8.4 Hz, 2 H), 7.92 (d, J = 8.4 Hz, 2 H), 13.0 (br, 1 H, CO2H)
ppm. 13C NMR (100 Hz): δ = 166.2, 137.6, 131.0, 129.4, 128.6
ppm.
[3]
1
4-Bromorobenzoic Acid: H NMR (400 Hz, [D6]acetone): δ = 7.95
(d, J = 8.8 Hz, 2 H), 7.69 (d, J = 8.8 Hz, 2 H) ppm. 13C NMR
(100 Hz): δ = 166.6, 132.5, 132.1, 130.5, 128.0 ppm.
1
4-Picolinic Acid: H NMR (400 Hz, D2O): δ = 8.59 (d, J = 4.2 Hz,
2 H), 7.72 (d, J = 4.2 Hz, 2 H) ppm. 13C NMR (100 Hz): δ = 173.2,
149.1, 145.2, 123.1 ppm.
[4]
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1
2-Phenylacetic Acid: H NMR (400 Hz, CDCl3): δ = 7.29–7.36 (m,
5 H, Ar), 3.67 (s, 2 H, CH2) ppm. 13C NMR (100 Hz): δ = 178.2,
133.3, 129.4, 128.7, 127.4, 41.3 ppm.
3-Methylhexanedioic Acid: 1H NMR (400 Hz, CDCl3): δ = 0.98 (d,
J = 6.8 Hz, 3 H, CH3), 1.50–1.58 (m, 1 H), 1.71–1.75 (m, 1 H),
1.98–2.03 (m, 1 H), 2.18–2.23 (m, 1 H), 2.30–2.43 (m, 3 H) ppm.
13C NMR (100 Hz): δ = 180.0, 179.3, 41.4, 31.8, 31.3, 29.8, 19.5
ppm.
Crystallography: Crystals of 3 suitable for X-ray structure determi-
nation were obtained by recrystallization from a solution of water,
THF, and acetone. The cell parameters were determined with a
Siemens SMART CCD diffractometer. Crystal data of 3:
C22H25Ca0.50N2O12Ru2, Mw = 731.62, monoclinic, space group
P21/n; a = 8.2264(2) Å, b = 18.0498(5) Å, c = 17.5389(5) Å, α =
[6]
[7]
90°, β = 92.405(2)°, γ = 90°; V = 2601.97(12) Å3; Z = 4; ρcalcd.
=
1.868 Mgm–3; F(000) = 1460; crystal size: 0.20ϫ0.15ϫ0.10 mm;
reflections collected: 15966; independent reflections: 5795 [R(int) =
0.0311]; θ range 2.92 to 27.50°; goodness-of-fit on F2 0.999; final
R indices [IϾ2σ(I)] R1 = 0.0283, wR2 = 0.0616; R indices (all data)
R1 = 0.0400, wR2 = 0.0665. The structure was solved with the
SHELXS-97 program[16] and refined with the SHELXL-97 pro-
gram[17] by full-matrix least-squares techniques on F2 values.
CCDC-1036945 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[8]
[9]
Acknowledgments
The authors thank the National Science Council, Taiwan for finan-
cial support (grant number MOST103-2113-M-002 -002-MY3).
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Received: December 4, 2014
Published Online: February 3, 2015
Eur. J. Inorg. Chem. 2015, 1417–1423
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© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim