An unexpected semi-hydrogenation of a ligand in the complexation of 2,7-bispyridinyl-1,8-naphthyridine with Ru3(CO)12

Article abstract of DOI:10.1039/c3dt53029a

Thermal reaction of 2,7-bis(2-pyridinyl)-l,8-naphthyridine (bpnp) with Ru₃(CO)₁₂ in the presence of moisture resulted in the formation of a formate-bridged diruthenium complex [(bpnp-H₃)Ru ₂(μ-HCOO)(CO)₄] (1), in which the ligand was partially hydrogenated. Complex 1 was fully characterized by spectroscopic analyses and X-ray single crystal determination. Regarding the partially reduced ligand in 1, it occurs through a water-gas shift type reduction. The bridging formate ligand can be substituted by other carboxylate ligands. Physical and chemical properties of the newly prepared complexes were investigated.

Full text of DOI:10.1039/c3dt53029a

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An unexpected semi-hydrogenation of a ligand
in the complexation of 2,7-bispyridinyl-1,8-
naphthyridine with Ru3(CO)12†
Cite this: Dalton Trans., 2014, 43,
3557
Bei-Sih Liao,a Yi-Hung Liu,a Shie-Ming Peng,a K. Rajender Reddy,*b Shin-Hung Liu,a
Pi-Tai Chou*a and Shiuh-Tzung Liu*a
Thermal reaction of 2,7-bis(2-pyridinyl)-l,8-naphthyridine (bpnp) with Ru3(CO)12 in the presence of
moisture resulted in the formation of a formate-bridged diruthenium complex [(bpnp-H3)Ru2(μ-HCOO)-
(CO)4] (1), in which the ligand was partially hydrogenated. Complex 1 was fully characterized by spectro-
scopic analyses and X-ray single crystal determination. Regarding the partially reduced ligand in 1, it
occurs through a water–gas shift type reduction. The bridging formate ligand can be substituted by other
carboxylate ligands. Physical and chemical properties of the newly prepared complexes were investigated.
Received 28th October 2013,
Accepted 6th December 2013
DOI: 10.1039/c3dt53029a
www.rsc.org/dalton
Introduction
Since the discovery of diruthenium tetracarbonyl complexes by
Lewis and co-workers in 1969,1 the diruthenium(I,I) derivatives
containing a “Ru2(CO)4” backbone have appeared as an attrac-
tive class of dinuclear compounds in the study of coordination
chemistry,2a,3 catalysis,2b–d,4 and biological activity.2e,5 These
studies clearly illustrate the importance of the bridging
ligands, particularly the carboxylates, in stabilization of these
complexes and in governing the catalytic activities.2–5 However,
the coordination chemistry of “Ru2(CO)4” toward 2,7-bis(2-
pyridyl)-1,8-naphthyridine (bpnp), which is known to be a
good tetradentate ligand in the stabilization of metal–metal
bonding in the complexes, has not been disclosed. Since bpnp
is a crescent shaped tetra-donor, coordination of four nitrogen
donors toward a dinuclear species would in principle have
both axial positions capped, which is expected to affect the
properties of the resulting metal complex. We describe here
the thermal reaction of bpnp with Ru3(CO)12 in the presence
Results and discussion
Heating a mixture of Ru3(CO)12 and bpnp in chlorobenzene
in the presence of moisture at 140 °C for 4 h gave [(bpnp-H3)-
Ru2(μ-HCOO)(CO)4] (1) in 90% yield based on the ligand.
Carrying out the reaction under extreme dry conditions
resulted in the formation of a mixture of complicated pro-
ducts, but not complex 1, indicating that water plays an impor-
tant role in the formation of this complex. Complex 1 was
characterized by spectroscopic techniques and crystallographic
analysis. The characteristic IR stretching at 1579 cm−1 is attrib-
uted to the bridging formate group. Bands appearing at 2057,
2012, 1958 and 1925 cm−1 are assigned to the terminal CO
stretching vibrations. The most significant 1H NMR signals for
the complex are the protons corresponding to the naphthyri-
dine framework. Due to the partial hydrogenation of the
ligand, five sets of 1H NMR signals of 1 (δ 5.13, 3.01, 2.76,
2.68 and 1.75) appear in the region of C(sp3)–H, which is corre-
lated to three signals (δ 69.2, 28.3 and 28.2) of 13C NMR shifts.
In addition, the 13C NMR shift at δ 174.3 is assigned to be the
carbon of the bridging formate. The detailed structure of 1 was
confirmed by X-ray diffraction analysis of its single crystal.
The solid-state structure of 1 crystallized from dichloro-
methane and diethyl ether was determined by single crystal
of moisture to yield
a formate-bridged diruthenium(I,I)
complex containing a partial reduction of the naphthyridine
ligand.
aDepartment of Chemistry, National Taiwan University, 1, Sec. 4, Roosevelt Road,
Taipei 106, Taiwan. E-mail: stliu@ntu.edu.tw; Fax: +(8862)23636359
bInorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical
Technology, Tarnaka, Hyderabad-500 607, India. E-mail: rajender@iict.res.in;
Fax: +91-040-27160921
†CCDC 942976 for 1. For crystallographic data in CIF or other electronic format
see DOI: 10.1039/c3dt53029a
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Scheme 1 Formation of diruthenium complex 1.
Fig. 1 ORTEP plot of 1 at the 30% probability level. Labels of some
aromatic carbons are omitted for clarity.
Table 1 Selected bond distances (Å) and angles (°) of 1
Ru(1)–N(1)
Ru(1)–N(2)
Ru(1)–C(1)
Ru(1)–C(2)
2.159(2)
2.118(2)
1.856(3)
1.838(3)
2.148(2)
2.6616(3)
1.370(4)
1.359(5)
1.483(4)
1.374(3)
1.364(3)
177.5(1)
157.36(6)
171.79(11)
160.21(7)
88.23(13)
Ru(2)–N(3)
Ru(2)–N(4)
Ru(2)–C(3)
Ru(2)–C(4)
Ru(2)–O(6)
N(3)–C(17)
C(11)–C(12)
C(13)–C(14)
C(16)–C(17)
N(3)–C(14)
2.104(2)
2.176(2)
1.858(3)
1.827(3)
2.168(2)
1.476(4)
1.391(5)
1.452(4)
1.514(5)
1.325(4)
Ru(1)–O(5)
Ru(1)–Ru(2)
C(10)–C(11)
C(12)–C(13)
C(13)–C(15)
N(2)–C(10)
Scheme 2 Pathway for the formation of the metal-hydride and the
formate ligand.
N(2)–C(14)
N(2)–Ru(1)–C(1)
N(1)–Ru(1)–Ru(2)
N(3)–Ru(2)–C(3)
N(4)–Ru(2)–Ru(1)
C(1)–Ru(1)–C(2)
O(5)–Ru(1)–C(2)
N(1)–Ru(1)–N(2)
O(6)–Ru(2)–C(4)
N(3)–Ru(2)–N(4)
C(3)–Ru(2)–C(4)
176.7(1)
77.49(9)
174.1(1)
77.1(1)
bipyridine metal complexes. No significant discrepancies in
the other bond lengths and angles are noticed in complex 1. It
was noticed that the Ru–Ru distance (2.6616(3) Å) is relatively
shorter than that of complexes with “Ru2(CO)4”,4 indicating
that geometrically constraining this tetradentate ligand shortens
91.5(1)
analysis. An ORTEP diagram of the molecular structure of 1 is the metal–metal bond.
shown in Fig. 1 and relevant bond distances and angles are
Notably, complex 1 could be prepared from the hydrogen-
collected in Table 1. The structure of this newly prepared di- ated ligand directly (Scheme 1). Thus, with Pd/C as a catalyst,
ruthenium(I,I) displays a dinuclear core of “Ru2(CO)4”, similar hydrogenation of bpnp gave the partially reduced compound
to that in previously reported compounds.6 Two ruthenium bpnp-H4 in 83% yield, which when treated with Ru3(CO)12 in
centers are cis-bridged by the bpnp-H4 ligand and a formate. the presence of formic acid provided 1 in practically quantitat-
Two axial sites of the diruthenium core are capped by the pyri- ive yield. Apparently, the formation of 1 from bpnp requires
dinyl nitrogen atoms of bpnp-H4. Each ruthenium center in 1 the addition of H2. The addition of hydrogen to bpnp resulting
is in an octahedral coordination geometry with two carbonyl in the formation of complex 1 is believed to occur via ruthe-
groups occupying it in a cis fashion. A slightly distorted nium-catalyzed transfer hydrogenation. This was proved by a
eclipsed conformation is adopted about the Ru(1)–Ru(2) bond separate experiment. Treatment of bpnp with isopropanol and
as evidenced by the torsional angle: N(2)–Ru(1)–Ru(2)–N(3) Cs2CO3 in the presence of [RuCl2(THF)(CO)3] (5 mol%) as the
10.54(9)° and C(2)–Ru(1)–Ru(2)–C(4) 17.96(13)°. The Ru–C dis- catalyst under refluxing conditions readily yielded bpnp-H4 in
tances trans to nitrogen donors are slightly longer (1.856(3)– 75% yield.
1.858(3) Å) than those trans to oxygen donors (formate)
As illustrated in the crystal structure, a formate ligand acts
(1.827(3)–1.838(3) Å) due to the trans influence. Analysis of as a bridging ligand in complex 1. Quite likely, the formate is
bond distances along the naphthyridine rings (Table 1) tells formed by the deprotonation of formic acid, which is gener-
one of naphthyridine rings remaining as an aromatic system, ated from CO and H2O under the reaction conditions.
but not the other, consistent with the spectroscopic data. Nakahara and co-workers disclosed that formic acid is an
Both bite angles of the bipyridinyl fragment toward the intermediate in the water–gas-shift process as evidenced by
metal centers [N(1)–Ru(1)–N(2) 77.49(9)° and N(3)–Ru(2)–N(4) the NMR study.8 A mechanistic rationalization is illustrated in
77.1(1)°] deviate from 90°, which are quite similar to those of Scheme 2. The initial step involves the nucleophilic attack of
3558 | Dalton Trans., 2014, 43, 3557–3562
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water or hydroxide to the coordinated carbonyl ligand. It is
known that the carbonyl carbon center of “Ru(CO)n” is suscep-
tible to nucleophilic attack,4a,7 which leads to the formation of
the hydroxycarbonyl species I. Elimination of the hydroxy-
carbonyl ligand generates the metal-hydride species II
accompanied by the formation of carbon dioxide. Indeed, the
generation of CO2 from the reaction was identified. This
process is in agreement with the typical pathway for a WGS
reaction catalyzed by transition-metal complexes.9 The ligand
bpnp was partially reduced by the metal-hydride followed by
the protonation. Replacement of water with D2O gave the deut-
erated product 1, clearly confirming the hydrogen atoms from
H2O molecules. Protonation of the ruthenium hydroxycarbonyl
may give the intermediate III. Subsequently, the reductive
elimination of hydride and hydroxycarbonyl ligands results in
the formation of formic acid, acting as a bridging ligand for
the di-ruthenium core (Scheme 2).
Fig. 3 HOMO (a) and LUMO (b) calculated for complex 1.
The oxidation and reduction potentials of 1 were deter-
mined by cyclic voltammetry in acetonitrile (Fig. 2). The cyclic
voltammogram of complex 1 exhibits two 1e− irreversible
ligand-based oxidations at −0.7, 0.65 and 1.25 V, whereas the
free bpnp-H4 shows irreversible oxidation potentials at −0.86
and −1.6 V. This irreversible behaviour is different from the
related “Ru2(CO)4” species coordinated by other 1,8-naphthyri-
dine-based ligands.6
The electronic spectra of complexes and bpnp-H4 were
recorded in acetonitrile in the range of 200–700 nm. The λmax
values of all compounds are given in Table 2. Three major
transitions that appeared for complex 1 in acetonitrile are at
290, 372 and 455 nm with the extinction coefficients of 2240,
4680 and 19 950, respectively. The intra-ligand transition
(π→π*) is observed at 372 nm, which is red-shifted (ca. 30 nm)
compared with the free ligand bpnp-H4. The broad absorption
in the visible region at 455 nm is assigned as a metal–ligand
to ligand charge transfer band.
We have carried out a DFT calculation based on the X-ray
crystal structure. This shows that the HOMO (highest occupied
molecular orbital) is located mostly along the Ru–Ru vector
and one of the pyridinyl rings within the complex (Fig. 3a). On
the other hand, the LUMO (lowest unoccupied molecular
orbital) is located in the unsaturated part of naphthyridine and
the other pyridinyl ring (Fig. 3b). The calculated absorption for
the HOMO–LUMO transition is at 464.5 nm, which is in agree-
ment with the experimental data.
In order to understand the coordination chemistry of the
diruthenium complex, ligand substitutions of 1 toward various
donors were investigated. Treatment of 1 with an equimolar
amount of triphenylphosphine gave a mixture of various sub-
stituted products as evidenced by a complicated 31P NMR spec-
trum, indicating that the substitution is not regio-selective.
However, reaction of 1 with excess of triphenylphosphine
readily caused decomposition of 1 to give the free ligand
bpnp-H4. The bidentate dppe (dipehenylphosphinoethane)
also did the similar reaction. These observations indicate that
the chelation stabilization of bpnp-H4 toward “Ru2(CO)4” is not
comparable to that of the phosphine ligands. On the other
hand, the bridging formate was replaced by other carboxylates
(eqn (1)). Complex 1 was treated with excess acetic acid in
acetone at 50 °C to give the acetate bridged complex 2a,
whereas benzoic acid provided the substituted product 2b
accordingly. Both complexes 2a and 2b were characterized by
NMR, UV-Vis and elemental analysis. 1H-NMR shifts of the
tetradentate in both 2a and 2b are quite similar to those in 1,
whereas the absorption spectra for 2a and 2b are also similar to
that of 1 (Table 2).
Fig. 2 Cyclic voltammogram for 1 with 0.1 M [Bu4N][PF6] as the sup-
porting electrolyte at a scanning rate of 100 mV s−1
.
Table 2 UV-vis data for complexes 1–2 and bpnp-H4
Compound
λmax/nm (log ε)a
bpnp-H4
1
339 (3.86), 250 (4.16), 218 (4.16)
455 (3.35), 372 (3.67), 290 (4.3)
ð1Þ
2a
2b
455 (3.36), 368 (3.75), 286 (4.35)
455 (3.75), 372 (3.67), 287 (4.37), 231 (4.61)
a In CH3CN, at 25 °C.
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To highlight the application of the formation of a formate, 8 Hz, 1 H), 7.57 (t, J = 6.4 Hz, 1 H), 7.5 (t, J = 6.4 Hz, 1 H), 7.05
we set out to catalytically prepare formic acid from CO and (d, J = 6.4 Hz, 1 H), 6.99 (d, J = 6.4 Hz, 1 H), 5.13 (m, 1 H), 3.01
H2O. Quite disappointingly, complex 1 did not show any cata- (m, 1 H), 2.76 (m, 1 H), 2.68 (m, 1 H), 1.75 (m, 1 H); 13C NMR
lytic activity towards this preparation. However, with the use of (200 MHz): δ 207.6, 206.6, 205.3, 202.1, 174.3, 166.8, 165.7,
an in situ generated catalytic system from bpnp and Ru3(CO)12, 158, 153.6, 152.3, 152.2, 138.8, 138.7, 133.3, 125.9, 124.5,
reactions of water under pressurized CO (100 psi) gave formic 124.2, 122.5, 106.8, 69.2, 28.3, 28.2. ESI-MS (TOF): m/z calcd
acid in a turnover number of 98 (mol of product per mol of for [M − HCOO]+ = 602.92, found 603.10. Anal. calcd for
catalyst), indicating that some intermediates from the C23H16N4O6Ru2: C, 42.73; H, 2.49; N, 8.67. Found: C, 42.43;
complexation of bpnp with Ru3(CO)12 might play the role of H, 2.38; N, 8.43.
catalysts.
Chlorobenzene containing 1% water as the solvent gave 1 in
90% yield. A solution of chlorobenzene saturated with water
also provided a similar result.
Method b. A mixture of bpnp-H4 (57 mg, 0.2 mmol),
Ru3(CO)12 (130 mg, 0.18 mmol) and formic acid (0.08 ml,
1.7 mmol) in benzene (1.0 mL) was placed in a reaction tube.
The resulting mixture was stirred at 100 °C for 12 h. The reac-
tion mixture was then cooled to room temperature, and filtered
through Celite with the eluent of EtOAc–acetone. The filtrate
was concentrated and the residue was re-precipitated from
CH2Cl2–toluene to give pure 1 as orange solids (0.18 mmol,
91%).
Conclusions
In summary, we have reported the synthesis and the character-
ization of the carboxylate-bridged diruthenium complex
[(bpnp-H3)Ru2(μ-HCOO)(CO)4] that resulted from the com-
plexation of Ru3(CO)12 with bpnp. The structure of 1 was con-
firmed by X-ray single crystal analyses. Interestingly, the ligand
was partially hydrogenated during the complexation. This
study provides an insight into the ligand effect on “Ru2(CO)4”
complexes, particularly for the species with both axial posi-
tions capped. Studies on the catalytic reactivity of these com-
plexes are currently under investigation.
Preparation of bpnp-H4
Method a. A solution of bpnp (0.12 g, 0.42 mmol) and Pd/C
(20 mg) in ethanol (10 mL) was placed in an autoclave. Hydro-
gen gas (100 psi) was pressurized. The mixture was heated at
100 °C for 24 h. The mixture was filtered through Celite, and
washed with acetone and methanol. The filtrate was concen-
trated to give the pure compound as yellow solids (0.11 g,
0.35 mmol, 83%). 1H (400 MHz, d6-acetone): δ 8.57–8.60 (m,
2 H), 8.37 (d, J = 8 Hz, 1 H), 7.67–7.84 (m, 3 H), 7.54 (d, J =
7.6 Hz, 1 H), 7.46 (d, J = 8 Hz, 1 H), 7.24–7.41 (m, 2 H), 6.45 (s,
1 H), 4.77–4.8 (m, 1 H), 2.77–2.84 (m, 1 H), 2.56–2.63 (m, 1 H),
2.14–2.28 (m, 1 H), 2.08–2.12 (m, 1 H). 13C (100 MHz, CDCl3):
δ 162.3, 156.6, 155.2, 152.6, 149.2, 148.9, 136.9, 136.7, 136.6,
122.9, 122.2, 120.6, 120.4, 116.5, 110.8, 56.7, 27.8, 24.6. Anal.
calcd for C18H16N4: C, 74.98; H, 5.59; N, 19.43. Found:
C, 74.47; H, 5.39; N, 19.18.
Experimental
General information
All reactions and manipulation steps were performed under a
dry nitrogen atmosphere. Tetrahydrofuran was distilled under
nitrogen from sodium benzophenone ketyl. Dichloromethane
and chlorobenzene were dried over CaH2 and distilled under
nitrogen. Other chemicals and solvents were of analytical
grade and were used after degassing (degassed process).
Nuclear magnetic resonance spectra were recorded in CDCl3
on a Bruker AVANCE 400 spectrometer. Chemical shifts are
given in parts per million relative to Me4Si for 1H and 13C
NMR. Infrared spectra were measured on a Varian 640-IR
spectrometer. The ligand bpnp was prepared according to a
reported procedure.10
Method b. In a sealed tube was placed a mixture of bpnp
(20 mg, 0.07 mmol), RuCl2(THF)(CO)3 (3 mg) and Cs2CO3
(10 mg, 0.03 mmol) in isopropanol (1 mL). This mixture was
heated at 110 °C with stirring for 12 h. After cooling, the
mixture was filtered through Celite to remove metal salt and
Preparation of complex 1
Method a. To a mixture of bpnp (28.4 mg, 0.1 mmol) and the filtrate was concentrated to give the desired product
Ru3(CO)12 (57.5 mg, 0.09 mmol) was added chlorobenzene (15.2 mg, 75%).
(1.0 mL) and H2O (0.1 mL) under nitrogen. The mixture was
heated at 140 °C with stirring for 4 h. During the reaction, the
Preparation of complex 2a
gas generated was bubbled into a solution of CaCl2 and a A solution of complex 1 (20 mg, 0.031 mmol) and acetic acid
white solid of CaCO3 was formed. The reaction solution was (0.31 mmol) in acetone (1.0 mL) was heated at 50 °C for 12 h.
then cooled to room temperature, filtered through Celite, and The reaction mixture was cooled, filtered through Celite, and
washed with EtOAc and acetone. The solution was recovered washed with acetone. The combined organic solutions were
and concentrated and the residue was recrystallized from dried over anhydrous Na2SO4 and concentrated. The residue
dichloromethane and toluene to give 1 as orange solids was re-precipitated from methanol–ether to give the product as
(58.1 mg, 0.09 mmol, 90%). 1H NMR (400 MHz, d6-acetone): a red solid (16.5 mg, 80%): 1H NMR (400 MHz, acetone-d6):
δ 8.99 (d, J = 5.2 Hz, 1 H), 8.95 (d, J = 4.4 Hz, 1 H), 8.17 (d, J = δ 8.97 (d, J = 4.4 Hz, 1 H), 8.93 (d, J = 6 Hz, 1 H), 8.17 (d, J =
8.4 Hz, 1 H), 8–8.05 (m, 2 H), 7.8 (s, 1 H, H-COO), 7.73 (d, J = 8.4 Hz, 1 H), 7.97–8.03 (m, 2 H), 7.7 (d, J = 7.6 Hz, 1 H), 7.54
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(t, J = 7.6 Hz, 1 H), 7.5 (t, J = 6.8 Hz, 1 H), 7.02 (d, J = 7.2 Hz, formalisms were adopted in the singlet and triplet geometry
1 H), 6.97 (d, J = 7.2 Hz, 1 H), 5.15–5.19 (m, 1 H), 3.01–3.08 (m, optimization, respectively. “double-ζ” quality basis set
A
1 H), 2.8–2.87 (m, 1 H), 2.74–2.79 (m, 1 H), 1.65–1.73 (m, 1H), consisting of Hay and Wadt’s effective core potentials
1.47 (s, 3 H, –Me); 13C NMR (100 MHz): δ 207.5, 206.5, 205.6, (LANL2DZ)14 was employed for the Ru metal atom, and a
197.87, 183.5, 166.6, 165.3, 157.8, 153.4, 152.1, 152, 138.6, 6-31G* basis set15 for the rest of the atoms. Time-dependent
138.4, 133.1, 125.7, 124.3, 123.9, 122.4, 122.3, 106.6, 69.3, 28.6, DFT (TDDFT) calculations using the B3LYP functional were
28.4, 23.3. Anal. calcd C24H18N4O6Ru2: C, 43.64; H, 2.75; then performed based on the optimized structures at ground
N, 8.48. Found: C, 43.34; H, 2.48; N, 8.13.
states.16
Preparation of complex 2b
Production of formic acid
1
The procedure was similar to that for 2a. H NMR (400 MHz,
acetone-d6): δ 9.11 (d, J = 5.2 Hz, 1 H), 9.06 (d, J = 4.8 Hz, 1 H),
8.17 (d, J = 8.4 Hz, 1 H), 8.04–8.08 (m, 2 H), 7.74 (d, J = 7.6 Hz,
1 H), 7.63 (t, J = 5.6 Hz, 1 H), 7.57 (t, J = 6.4 Hz, 1 H), 7.45 (d,
J = 7.6 Hz, 2 H), 7.3 (t, J = 7.6 Hz, 1 H), 7.12 (t, J = 7.6 Hz, 2 H),
6.97 (d, J = 7.6 Hz, 1 H), 6.9 (d, J = 6.8 Hz, 1 H), 5.2–5.24 (m,
1 H), 2.98–3.01 (m, 1 H), 2.84–2.87 (m, 1 H), 2.73–2.77 (m,
1 H), 1.63–1.67 (m, 1H); 13C NMR (100 MHz): δ207.5, 206.6,
205.8, 205.3, 178.4, 166.7, 165.4, 157.9, 153.5, 152.2, 138.7,
138.5, 134.8, 133.1, 132.6, 131.7, 130.3, 129.7, 128.3, 125.8,
124.4, 123.9, 122.3, 106.6, 69.3, 28.6, 28.3. Anal. calcd
C29H20N4O6Ru2: C, 48.20; H, 2.79; N, 7.75. Found C 47.89;
H, 2.65; N, 7.43.
A mixture of bpnp (0.02 mmol), Ru3(CO)12 (0.02 mmol) and
water (5 mmol) in C6H5Cl (1 mL) was placed in a 20 mL auto-
clave. The system was flashed with nitrogen three times, and
then pressurized with CO (100 psi). The mixture was heated at
100 °C for 24 h. The reaction mixture was cooled to 4 °C with
an ice-water bath. After releasing all gases, the solution was
analysed by 1H NMR and GC.
Acknowledgements
This work was funded by the National Science Council, Taiwan
(NSC-100-2113-M002-001-MY3) and the India–Taiwan program
of cooperation in science and technology (NSC-100-2923-
M-002-004-MY3). K.R.R thanks GITA/CII (India) for support
under the India–Taiwan S&T cooperation programme.
Crystallography
Crystals suitable for X-ray determination were obtained for 1
by recrystallization from dichloromethane and toluene at room
temperature. Cell parameters were determined using
a
Siemens SMART CCD diffractometer. Crystal data of 1:
C23H16N4O6Ru2, Mw = 646.54, monoclinic, space group P2(1)/n;
a = 9.3648(5) Å, b = 15.1336(7) Å, c = 16.4997(11) Å, α = 90°, β =
104.020(6)°, γ = 90°; V = 2268.7(2) Å3; Z = 4; ρcalcd. = 1.893 Mg
m−3; F(000) = 1272; crystal size: 0.20 × 0.15 × 0.10 mm3; reflec-
tions collected: 14 611; independent reflections: 5061 [R(int) =
0.0224]; θ range 2.88 to 27.50°; goodness-of-fit on F2 1.013;
final R indices [I > 2σ(I)] R1 = 0.0277, wR2 = 0.0641; R indices
(all data) R1 = 0.0335, wR2 = 0.0679. The structure was solved
using the SHELXS-97 program11 and refined using the
SHELXL-97 program12 by full-matrix least-squares on F2
values.
Notes and references
1 G. R. Crooks, B. F. G. Johnson, J. Lewis, I. G. Williams and
G. Gamlen, J. Chem. Soc. A, 1969, 2761.
2 Reviews: (a) B. Therrien and G. Süss-Fink, Coord. Chem.
Rev., 2009, 253, 2639; (b) J. L. Roizen, M. E. Harvey and
J. Du Bois, Acc. Chem. Res., 2012, 45, 911; (c) Y. Arikawa and
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Physical measurement
Infrared spectra were recorded on a Varian 640-IR spectro-
meter on KBr pellets. Electronic absorptions were measured
on a Shimatzu PC 2100 spectrometer. Cyclic voltammograms
were obtained in acetonitrile with 0.1 M tetrabutylammonium
hexafluorophosphate (TBAPF6) as the supporting electrolyte. A
glassy carbon disk was used as the working electrode and a
platinum wire functioned as the auxiliary electrode. All
voltammograms were recorded versus a Ag/AgCl electrode at a
scanning rate of 100 mV s−1
.
Computation
Calculations on the electronic states of all title complexes
were carried out using the density functional theory (DFT)
with B3LYP hybrid functional.13 Restricted and unrestricted
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3562 | Dalton Trans., 2014, 43, 3557–3562
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