Deprotonation-induced structural changes in SNS-pincer ruthenium complexes with secondary thioamide groups

Article abstract of DOI:10.1021/om400969p

The reaction of [Ru(CO)₂Cl₂]_n with a SNS-pincer ligand (^PhSNS·2H) containing two secondary thioamide (-CSNH-) groups afforded a cationic Ru complex with a Cl^- counteranion, [RuCl(CO)₂(^PhSNS·2H)]Cl. The stepwise deprotonation of the two secondary thioamide groups of the above complex afforded neutral mononuclear [RuCl(^PhSNS·1H)(CO)₂] and dinuclear [Ru(^PhSNS)(CO)₂]₂ complexes, with the successive elimination of two HCl molecules. The SNS-pincer ligand functions as a mono- or dianionic ligand with iminothiolate groups after the successive deprotonation steps. The metal-bridging ability of the iminothiolate groups enables the formation of the dinuclear complexes. The IR spectra of the complexes show that the deprotonation of the ligand increases the electron density at the Ru center. The substituents on the secondary thioamide groups in the SNS-pincer ligand influence the deprotonation properties and redox potentials of the complexes; for example, a change in the substituents from a phenyl to a benzyl group decreased the deprotonation ability and oxidation potential of the Ru center.

Full text of DOI:10.1021/om400969p

Article
pubs.acs.org/Organometallics
Deprotonation-Induced Structural Changes in SNS-Pincer Ruthenium
Complexes with Secondary Thioamide Groups
Yoko Komiyama, Junpei Kuwabara,* and Takaki Kanbara*
Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), Graduate School of Pure and Applied Sciences, University
of Tsukuba, 1-1-1, Tennodai, Tsukuba, 305-8573, Japan
S
* Supporting Information
ABSTRACT: The reaction of [Ru(CO)2Cl2]n with a SNS-pincer
ligand (PhSNS·2H) containing two secondary thioamide (−CSNH−)
groups afforded a cationic Ru complex with a Cl− counteranion,
[RuCl(CO)2(PhSNS·2H)]Cl. The stepwise deprotonation of the two
secondary thioamide groups of the above complex afforded neutral
mononuclear [RuCl(PhSNS·1H)(CO)2] and dinuclear [Ru(PhSNS)-
(CO)2]2 complexes, with the successive elimination of two HCl
molecules. The SNS-pincer ligand functions as a mono- or dianionic
ligand with iminothiolate groups after the successive deprotonation
steps. The metal-bridging ability of the iminothiolate groups enables
the formation of the dinuclear complexes. The IR spectra of the
complexes show that the deprotonation of the ligand increases the
electron density at the Ru center. The substituents on the secondary thioamide groups in the SNS-pincer ligand influence the
deprotonation properties and redox potentials of the complexes; for example, a change in the substituents from a phenyl to a
benzyl group decreased the deprotonation ability and oxidation potential of the Ru center.
complex is an intriguing and promising target for investigating
the reactivities and properties of secondary thioamide
complexes. Therefore, the study of a six-coordinate complex
containing secondary thioamide ligands may lead to the
discovery of new catalysts. Herein, we report novel Ru
complexes bearing a SNS-pincer ligand and their trans-
formations via the deprotonation of secondary thioamide
groups. The effects of substituents on the ligand are also
evaluated in terms of reactivity, structure, and physical
properties of the complexes.
INTRODUCTION
■
Protonation and deprotonation of ligands in transition-metal
complexes result in significant structural changes in the
complexes,1 and these processes are involved in catalytic
reactions such as dehydrogenation and hydroamination.2
Milstein reported PNN- and PNP-pincer Ru catalysts that
promote the dehydrogenative oxidation of alcohols via
protonation and deprotonation of the methylene group of the
ligand, thus assisting smooth O−H bond cleavage.3 Similar
ligand-assisted N−H, S−H, and C−H bond cleavages have
been reported.4 Moreover, deprotonation of the ligands
influences the properties of the metal center, such as the
redox potential.5 Recently, several groups have studied
transition-metal complexes containing secondary thioamide
groups as the ligands because a thioamide group has strong
coordination ability and enables the formation of a stable
deprotonated state.6−9 In these complexes, the secondary
thioamide group forms thioamidate and iminothiolate reso-
nance structures upon deprotonation (eq 1).10 Because the S
RESULTS AND DISCUSSION
■
A SNS-pincer ligand containing secondary thioamide groups,
2,6-bis(anilinothiocarbonyl)pyridine (PhSNS·2H), was synthe-
sized in one step from 2,6-pyridinedicarboxyaldehyde, aniline,
and elemental S via the Willgerodt−Kindler reaction.8b,11 The
reaction of the ligand with [Ru(CO)2Cl2]n afforded a cationic
Ru complex with a Cl− counterion, [RuCl(CO)2(PhSNS·2H)]
Cl (Scheme 1). The structure of the complex was established
on the basis of its elemental analysis, as well as 1H NMR and IR
spectral studies. The 1H NMR spectrum of [RuCl-
(CO)2(PhSNS·2H)]Cl supported its structure (Figure 1a);
however, the signal for the thioamide N−H group was not
observed.
While attempting to crystallize [RuCl(CO)2(PhSNS·2H)]Cl
from CHCl3/hexane in air, the crystals of [RuCl(PhSNS·
atom in iminothiolate functions as a bridging group, several
multinuclear complexes can be formed via deprotonation of the
secondary thioamide group;7j,9 for example, square-planar Pd
and Pt complexes with secondary thioamide groups have been
extensively investigated.6−9 Alternatively, a six-coordinate
Received: October 3, 2013
© XXXX American Chemical Society
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1H)(CO)2] were obtained (Scheme 1). The structure of
[RuCl(PhSNS·1H)(CO)2] was established by a single-crystal X-
ray diffraction study (Figure 2a). In this structure, the two
carbonyl ligands are located cis to each other. The S1−C3 bond
length is 1.691(3) Å, and it is shorter than that of S2−C4
(1.751(3) Å) (Table 1). The short S1−C3 bond corresponds
to double-bond character (i.e., SC) in the thioamide group,
while the long S2−C4 bond corresponds to single-bond
character (i.e., S−C) in the iminothiolate group, which is the
deprotonated form.7j,9 The N2−C3 (1.322(4) Å) and N3−C4
(1.280(5) Å) bond lengths are also in agreement with the
thioamide and iminothiolate structures, respectively. The
existence of the iminothiolate structure indicates that
deprotonation occurred during the crystallization process. In
the case of pincer ligands with amide instead of the thioamide
groups, N atoms in the amide coordinate to a Ru center rather
than O atoms at their deprotonated state.12 The coordination
mode at the deprotonated state is the characteristic difference
between amide and thioamide groups. Despite the asymmetry
Scheme 1
1
of the crystal structure, the H NMR spectrum of [RuCl-
(PhSNS·1H)(CO)2] indicated a symmetrical structure in
solution; that is, equivalent signals corresponding to the
protons at the 3 and 5 positions in the central pyridine unit
were observed at δ 8.72 ppm (Figure 1b), indicating that
proton transfer between the thioamide and iminothiolate
groups occurs faster than the NMR time scale.
Treatment of [RuCl(CO)2(PhSNS·2H)]Cl or [RuCl(PhSNS·
1H)(CO)2] with Al2O3 via column chromatography using a
mixture of CHCl3 and ethanol (50:1) as the eluent afforded a
new dinuclear complex, [Ru(PhSNS)(CO)2]2 (Scheme 1). As
shown in Figure 2b, the single-crystal X-ray diffraction study of
[Ru(PhSNS)(CO)2]2 reveals a dimeric structure with the pincer
complexes forming a four-membered ring comprising a Ru1−
S1−Ru2−S3 unit. Each of the pincer fragments has a dianionic
SNS-pincer ligand and two carbonyl ligands, while no Cl ligand
is observed. The vacant site, generated by the liberation of the
Cl ligand, is bridged with the iminothiolate S atoms, i.e., S1 or
Figure 1. 1H NMR spectra of complexes (a) [RuCl(CO)2(PhSNS·
2H)]Cl, (b) [RuCl(PhSNS·1H)(CO)2], and (c) [Ru(PhSNS)(CO)2]2
(CDCl3, 400 MHz).
Figure 2. ORTEP drawings of (a) [RuCl(PhSNS·1H)(CO)2], (b) [Ru(PhSNS)(CO)2]2, (c) [Ru(PhSNS)(CO)(PPh3)2], (d) [RuCl(CO)2(BnSNS·
2H)]Cl, (e) anti-[Ru(BnSNS)(CO)2]2, and (f) [Ru(BnSNS)(CO)(PPh3)2] with the thermal ellipsoids at the 50% probability level. Solvent molecules
and hydrogen atoms except for the thioamide groups are omitted for clarity.
B
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Table 1. Selected Bond Lengths (Å) of the Complexes
S1−C3
1.691(3)
S2−C4
N2−C3
1.322(4)
N3−C4
1.280(5)
Ru1−N1
2.096(2)
[RuCl(PhSNS·1H)(CO)2]
[Ru(PhSNS)(CO)2]2
[Ru(PhSNS)(CO)(PPh3)2]
[RuCl(CO)2(BnSNS·2H)]Cl
anti-[Ru(BnSNS)(CO)2]2
[Ru(BnSNS)(CO)(PPh3)2]
1.751(3)
1.808(7)
1.749(7)
1.263(9)
1.291(9)
2.091(5)
2.138(3)
1.738(4)
1.739(4)
1.295(5)
1.293(5)
a
1.684(8), 1.688(12)
1.8066(13)
1.743(3)
1.687(8), 1.691(13)
1.7666(12)
1.755(3)
1.319(10), 1.364(11)
1.2626(19)
1.289(3)
1.312(11), 1.292(11)
1.2779(18)
1.282(4)
2.087(7), 2.083(9)
2.1039(10)
2.1342(19)
a
Bond lengths of two crystallographically independent molecules are shown.
S3. The larger bond lengths of S1−C3 (1.808(7) Å) and S2−
C4 (1.749(7) Å) support the fact that both secondary
thioamide groups are deprotonated and converted into
the dimer structure requires long reaction time in the 2-fold
protonation process.
The IR spectra of [RuCl(CO)2(PhSNS·2H)]Cl, [RuCl-
(PhSNS·1H)(CO)2], and [Ru(PhSNS)(CO)2]2 exhibit two
strong νCO bands around 2000 cm−1, corresponding to the
two carbonyl ligands (Table 2 and Figure S1). The wave-
iminothiolate groups (Table 1).7j,9 The H NMR spectrum of
1
[Ru(PhSNS)(CO)2]2 shows two nonequivalent signals at δ 8.54
and 8.65 ppm, corresponding to the protons at the 3 and 5
positions of the central pyridine unit (Figure 1c); therefore, it is
evident that the dimeric structure of [Ru(PhSNS)(CO)2]2 is
maintained in solution.
Table 2. Absorption Wavenumber of the Carbonyl Ligands
of the Complexes
The sequential deprotonation process occurred via crystal-
lization and column chromatography as shown in Scheme 1.
The details of the spontaneous deprotonation and possibility of
reprotonation on the iminothiolate moieties were investigated.
Upon washing [RuCl(CO)2(PhSNS·2H)]Cl with H2O, [Ru-
(PhSNS)(CO)2]2 was obtained in 97% yield (Scheme 2; see
νCO (cm−1
)
[RuCl(CO)2(PhSNS·2H)]Cl
[RuCl(PhSNS·1H)(CO)2]
[Ru(PhSNS)(CO)2]2
[Ru(PhSNS)(CO)(PPh3)2]
[RuCl(CO)2(BnSNS·2H)]Cl
anti-[Ru(BnSNS)(CO)2]2
[Ru(BnSNS)(CO)(PPh3)2]
2069, 2008
2058, 1993
2047, 1991
1938
2068, 2006
2042, 1998
1938
Scheme 2
number corresponding to νCO decreases in the order
[RuCl(CO)2(PhSNS·2H)]Cl > [RuCl(PhSNS·1H)(CO)2] >
[Ru(PhSNS)(CO)2]2, indicating that deprotonation of the
thioamide group increases the electron density at the Ru center.
The reactivity of [Ru(PhSNS)(CO)2]2 was evaluated by
treating the complex with 4 equiv of PPh3 in THF. The
addition of PPh3 resulted in the dissociation of the dimeric
structure to afford a mononuclear complex, [Ru(PhSNS)(CO)-
(PPh3)2], in 68% yield (Scheme 3). As shown in Figure 2c, the
Scheme 3
Experimental Section). Because 2-fold deprotonation occurred
in the absence of a base, it is expected that the high polarity of
water promotes deprotonation and is able to disperse liberated
HCl. For obtaining the monodeprotonated species [RuCl-
(PhSNS·1H)(CO)2], weakly acidic water was required for
washing to suppress the second deprotonation; washing of
[RuCl(CO)2(PhSNS·2H)]Cl with an aqueous solution of
NH4Cl gave [RuCl(PhSNS·1H)(CO)2] in 84% yield. Treat-
ment of [RuCl(PhSNS·1H)(CO)2] with H2O induced the
second deprotonation, which formed [Ru(PhSNS)(CO)2]2 in
96% yield. In the inverse way, protonation on the iminothiolate
moiety is possible by addition of HCl in Et2O (Scheme 2). The
reaction of [Ru(PhSNS)(CO)2]2 with a slight excess (3 equiv
per Ru center) of HCl in Et2O for 36 h at 50 °C gave
[RuCl(CO)2(PhSNS·2H)]Cl in a quantitative fashion. The
protonation of [RuCl(PhSNS·1H)(CO)2] with HCl was a
rather fast process, which immediately occurred at room
temperature. These observations indicate that dissociation of
crystal structure of [Ru(PhSNS)(CO)(PPh3)2] reveals that one
of the carbonyl ligands is liberated from [Ru(PhSNS)(CO)2]2
and that the two PPh3 ligands are located trans to each other.
Analysis of the S1−C3 and S2−C4 bond lengths reveals that
the SNS-pincer ligand maintains the iminothiolate structure
during the reaction (Table 1). The 31P{1H} NMR spectrum of
[Ru(PhSNS)(CO)(PPh3)2] shows a single resonance peak at δ
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35.4 ppm, indicating that a single isomer is present in the
solution state (Figure S3). To establish whether the reaction
shown in Scheme 3 proceeds in a stepwise fashion via a
monophosphine complex, [Ru(PhSNS)(CO)2]2 was treated
1
with 2 equiv of PPh3, i.e., one PPh3 per Ru center. The H
NMR spectrum of the reaction mixture revealed the existence
of a mixture of the starting material [Ru(PhSNS)(CO)2]2 and
the final product [Ru(PhSNS)(CO)(PPh3)2] (Figure S4). Thus,
1
the monophosphine complex was not observed in the H or
31P{1H} NMR spectra. These results indicate that the reaction
of the unobserved monophosphine complex [Ru(PhSNS)-
(CO)2(PPh3)] with PPh3 is much faster than the reaction of
[Ru(PhSNS)(CO)2]2 with PPh3 because of the strong trans
effect of PPh3 (Scheme 3).13 In contrast, the reaction of
[Ru(PhSNS)(CO)2]2 with 4-methylbenzylamine instead of
PPh3 afforded a monosubstituted complex, [Ru(PhSNS)-
(CO)2(NH2CH2-4-tolyl)] (Figure S5), further supporting
that the trans effect of PPh3 strongly influences the second
substitution onto the Ru center, because the trans effect of PPh3
is known to be stronger than that of an amine ligand.13
To evaluate the effects of substituents in the thioamide group
on the properties of Ru complexes, a SNS-pincer ligand with a
benzyl group, instead of a phenyl group, was prepared. The
reaction of 2,6-bis(benzylaminothiocarbonyl)pyridine (BnSNS·
2H) with [Ru(CO)2Cl2]n afforded a cationic Ru complex,
[RuCl(CO)2(BnSNS·2H)]Cl (Scheme 4, Figure 3a). The
1
Figure 3. H NMR spectra of (a) [RuCl(CO)2(BnSNS·2H)]Cl, (b) a
mixture of syn- and anti-[Ru(BnSNS)(CO)2]2, (c) anti-[Ru(BnSNS)-
(CO)2]2, and (d) [Ru(BnSNS)(CO)(PPh3)2] (400 MHz in CDCl3).
[RuCl(CO)2(BnSNS·2H)]Cl with either organic or inorganic
bases because the reactions resulted in a complex mixture of
products.
The treatment of [RuCl(CO)2(BnSNS·2H)]Cl with Al2O3 via
column chromatography afforded a mixture of two isomers, syn-
[Ru(BnSNS)(CO)2]2 and anti-[Ru(BnSNS)(CO)2]2 (Scheme
4). The structures of the products were established by the
1
following analysis. The H NMR spectrum of the reaction
Scheme 4
mixture showed eight doublet signals for the methylene protons
in the benzyl group, at δ 4.5−5.5 ppm (Figure 3b).15 The
reaction mixture contained two types of products, and one of
the products could be isolated by crystallization. The structure
of the isolated product was established by a single-crystal X-ray
diffraction study (Figure 2e). The crystal structure showed a
dinuclear complex, anti-[Ru(BnSNS)(CO)2]2, whose structure
was similar to that of [Ru(PhSNS)(CO)2]2. The H NMR
1
spectrum of isolated anti-[Ru(BnSNS)(CO)2]2 showed four
doublet signals for the diastereotopic methylene protons
(Figure 3c), indicating that a dinuclear complex having four
nonequivalent methylene protons was maintained in the
solution state. The structure of the other product was
presumably similar to that of anti-[Ru(BnSNS)(CO)2]2 owing
to the similar four doublet NMR signals for the methylene
protons (Figure S7). Possible candidates for the structure are
(i) a dinuclear complex whose geometry differs from that of
anti-[Ru(BnSNS)(CO)2]2 and (ii) a multinuclear complex larger
than the dinuclear complex.7j,9 In order to confirm the
structure, the product mixture was analyzed by diffusion-
ordered NMR spectroscopy (DOSY). The result of DOSY
experiments showed that the two products have almost the
same diffusion constants (Figure S8). Because the diffusion
constant is correlated to the hydrodynamic radius,16 the two
products should have similar molecular weights. Therefore, the
formation of a dinuclear complex with a different geometry is
more reasonable than the formation of a multinuclear complex
such as a tri- or tetranuclear complex. On the basis of these
studies, it can be concluded that the deprotonation of
[RuCl(CO)2(BnSNS·2H)]Cl resulted in a mixture of syn- and
anti-[Ru(BnSNS)(CO)2]2 complexes (Scheme 4). A similar syn-
type dimer structure of an Ir complex with a SNS pincer ligand
was reported in the literature.15 In the case of the complex with
a phenyl substituent, [RuCl(CO)2(PhSNS·2H)]Cl, deprotona-
tion provided the anti isomer as the single product, presumably
because of the steric hindrance of the phenyl substituent.
product of this reaction is similar to the phenyl-substituted
ligand (PhSNS·2H). Although [RuCl(CO)2(PhSNS·2H)]Cl was
observed to be deprotonated during the crystallization process,
the crystallization of [RuCl(CO)2(BnSNS·2H)]Cl did not
promote the deprotonation of the secondary thioamide
group. Figure 2d shows the crystal structure of [RuCl-
(CO)2(BnSNS·2H)]Cl, which is one of the crystallographically
independent molecules. The bond lengths between the S and C
atoms are in the range 1.684−1.691 Å (Table 1), corresponding
to the SC double bonds in the thioamide structure,
indicating that no deprotonation occurred in both the
thioamide groups. The difference in the deprotonation behavior
is presumably attributed to the lower acidity of the N−H group
in the BnSNS·2H ligand than that in the PhSNS·2H ligand. This
is because an alkylthioamide has lower acidity than an
arylthioamide.14 It was difficult to isolate the monodeproto-
nated species, [RuCl(BnSNS·1H)(CO)2], by the reaction of
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The reaction of a mixture of syn- and anti-[Ru(BnSNS)-
(CO)2]2 with PPh3 afforded a single product of the PPh3
adduct, [Ru(BnSNS)(CO)(PPh3)2] (Scheme 5). Owing to the
CONCLUSION
■
The stepwise deprotonation of the secondary thioamide groups
in [RuCl(CO)2(PhSNS·2H)]Cl afforded neutral mononuclear
[RuCl(PhSNS·1H)(CO)2] and dinuclear [Ru(PhSNS)(CO)2]2
complexes. The SNS-pincer ligand functions as a mono- or
dianionic ligand upon successive deprotonation. The trans-
formations of the ligand influence the electron density at the Ru
center. The metal-bridging ability of the iminothiolate groups is
important for the formation of the dinuclear complex. The
deprotonation properties and redox potentials of the Ru
complexes could be modulated by changing the substituents on
the thioamide group. Dinuclear complexes [Ru(PhSNS)-
(CO)2]2 and [Ru(BnSNS)(CO)2]2 possess a latent vacant site
for further coordination of a substrate.18 These features of Ru
complexes containing the SNS-pincer ligand may lead to the
development of new catalysts that exhibit dynamic behavior, via
simple protonation and deprotonation steps.
Scheme 5
EXPERIMENTAL SECTION
■
General, Measurement, and Materials. 1H, 13C{1H}, and
31P{1H} NMR spectra were recorded using a JEOL ESC-400, Bruker
1
dissociation of the dinuclear structure, the H NMR signal of
AVANCE-400, or Bruker AVANCE-600 NMR spectrometer. IR
spectra were recorded on a JASCO FT/IR-300 spectrophotometer.
ESI mass spectra were recorded using an Applied Biosystems Qstar
Pulsar I. Elemental analyses were carried out using a Perkin-Elmer
2400 CHN elemental analyzer. 2,6-Pyridinedicarboxyaldehyde,
[RuCl3]·3H2O, triphenylphosphine, and other chemicals were used
as received from commercial suppliers. Anhydrous dimethoxyethane,
methanol, and THF were purchased from Kanto Chemical and used as
dry solvents. [Ru(CO)2Cl2]n was prepared using a previously reported
method.19
Crystal Structure Determination. Intensity data were collected
on a Bruker SMART APEX II ULTRA with Mo Kα radiation. A full
matrix least-squares refinement was used for non-hydrogen atoms with
anisotropic thermal parameters using the SHELXL-97 program.
Hydrogen atoms, except for the N-H hydrogen in thioamide groups,
were placed at the calculated positions and were included in the
structure calculation without further refinement of the parameters.
CCDC 913631, 913632, 913633, 962583, 962584, and 962585 contain
the supplementary crystallographic data for compounds [RuCl(PhSNS·
1H)(CO)2], [Ru(PhSNS)(CO)2]2, and [Ru(PhSNS)(CO)(PPh3)2],
[RuCl(BnSNS·2H)(CO)2]Cl, anti-[Ru(BnSNS)(CO)2]2, and [Ru-
(BnSNS)(CO)(PPh3)2], respectively. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html or
from the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
the methylene proton appears as a singlet at δ 4.43 ppm
(Figure 3d), which is shifted upfield by δ 0.66 ppm as
compared to that of [RuCl(CO)2(BnSNS·2H)]Cl (δ 5.09 ppm),
presumably because of the shielding effect of the aromatic rings
in PPh3. The crystal structure of [Ru(BnSNS)(CO)(PPh3)2]
supports this hypothesis (Figure 2f).
The electrochemical properties of the complexes were
studied by cyclic voltammetry (CV). The voltammograms of
the chloro-substituted and dinuclear complexes exhibited
irreversible oxidation waves. In contrast, the voltammograms
of [Ru(PhSNS)(CO)(PPh3)2] and [Ru(BnSNS)(CO)(PPh3)2]
exhibited a reversible redox couple at 0.148 and 0.119 V versus
the ferrocene/ferrocenium couple, respectively (Figure 4). The
Electrochemical Measurement. Electrochemical measurements
were performed with a BAS ALS1200a hand-held electrochemical
analyzer. A conventional three-electrode configuration was used, with
glassy carbon working (BAS electrode) and platinum wire auxiliary
electrodes and a 0.10 M AgNO3/Ag reference (BAS RE-5). Cyclic
voltammograms were recorded at a scan rate of 100 mV s−1 in CH2Cl2
with (Et4N)PF6. After each experiment, a small amount of ferrocene
was added as an internal reference, and all data reported herein are
reported versus the Fc/Fc+ couple.
Figure 4. Cyclic voltammograms of [Ru(PhSNS)(CO)(PPh3)2] and
[Ru(BnSNS)(CO)(PPh3)2] in CH2Cl2 (1 × 10−3 M) containing
Bu4NPF6 (0.1 M). Sweep rate = 100 mV s−1.
Synthetic Methods. Synthesis of 2,6-Bis(anilinothiocarbonyl)-
pyridine (PhSNS·2H) (ref 7b). A mixture of aniline (413 μL, 4.5 mmol)
and sulfur (80 mg, 2.5 mmol as elemental sulfur) was stirred in
anhydrous dimethoxyethane (2 mL) for 30 min at 82 °C under a
nitrogen atmosphere. Na2S·9H2O (103 mg, 0.43 mmol) was then
added at 82 °C, and the mixture was cooled to room temperature. 2,6-
Pyridinedicarboxyaldehyde (135 mg, 1.0 mmol) was then added, and
the mixture was stirred at 82 °C for 12 h under a nitrogen atmosphere.
After cooling to room temperature, a saturated aqueous solution of
NH4Cl was added to the mixture. The resulting mixture was extracted
with CHCl3 and washed with water and a saturated aqueous solution
redox couple was assigned to a RuII/III redox couple on the basis
of the reported electrochemical property of Ru complexes
bearing a similar pincer-type ligand.7i,17 The lower redox
potential of [Ru(BnSNS)(CO)(PPh3)2] indicates that the Ru
center in [Ru(BnSNS)(CO)(PPh3)2] is slightly electron rich in
comparison with [Ru(PhSNS)(CO)(PPh3)2] presumably due to
the stronger electron-donating ability of the BnSNS-pincer
ligand than that of the PhSNS-pincer ligand.
E
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of NH4Cl. After drying over Na2SO4, the solution was filtered and
evaporated in vacuo. The product was isolated by column
chromatography on silica gel using CHCl3 as an eluent (186 mg,
for C42H26N6O4Ru2S4: C, 49.99; H, 2.60; N, 8.33. Found: C, 49.93; H,
2.88; N, 8.14.
Synthesis of [RuCl(CO)2(BnSNS·2H)]Cl. A mixture of [Ru(CO)2Cl2]n
(114 mg, 0.50 mmol) and BnSNS·2H (189 mg, 0.50 mmol) was stirred
in anhydrous methanol (5 mL) for 3 days at room temperature under
a nitrogen atmosphere. The solution was evaporated in vacuo.
Recrystallization from CHCl3 and hexane gave [RuCl(CO)2(BnSNS·
1
53%). H NMR (400 MHz, CDCl3): δ 11.15 (s, 2H, NH), 8.94 (d,
2H, pyridine-H3, 5, J = 7.6 Hz), 8.06 (t, 1H, pyridine-H4, J = 8.0 Hz),
7.97 (d, 4H, Ph-o, J = 8.4 Hz), 7.50 (t, 4H, Ph-m, J = 7.6 Hz), 7.46 (t,
2H, Ph-p, J = 8.0 Hz). 13C{1H} NMR (100 MHz, CDCl3): δ 188.1,
149.9, 138.7, 138.3, 129.2, 127.7, 127.2, 123.2. Anal. Calcd for
C19H15N3S2: C, 65.30; H, 4.33; N, 12.02; S, 18.35. Found: C, 65.13; H,
4.36; N, 12.03; S, 18.40.
1
2H)]Cl (294 mg, 97%). H NMR (400 MHz, CDCl3): δ 12.85 (br,
2H, NH), 9.34 (br, 2H, pyridine-H3, 5), 8.10 (br, 1H, pyridine-H4)
7.54 (d, 4H, Ph-o, J = 6.0 Hz), 7.35−7.30 (m, 6H, Ph-m and Ph-p),
5.09 (s, 4H, CH2). IR (KBr): νCO 2068 and 2006 cm−1. Anal. Calcd for
C23H19Cl2N3O2RuS2: C, 45.62; H, 3.16; N, 6.94. Found: C, 45.88; H,
3.38; N, 7.03.
Synthesis of 2,6-Bis(benzylaminothiocarbonyl)pyridine (BnSNS·
2H). A mixture of 2,6-pyridinedicarboxyaldehyde (274 mg, 2.0 mmol),
benzylamine (656 μL, 6.0 mmol), and sulfur (160 mg, 5.0 mmol as
elemental sulfur) was stirred in anhydrous DMF (3 mL) for 5 h at 115
°C under a nitrogen atmosphere. After cooling to room temperature,
the resulting mixture was extracted with CHCl3 and washed with water
and brine. After drying over Na2SO4, the solution was filtered and
evaporated in vacuo. The product was isolated by column
chromatography on silica gel using CHCl3 as an eluent (641 mg,
84%). 1H NMR (400 MHz, CDCl3): 9.51 (br, 2H, NH), 8.84 (d, 2H,
pyridine-H3, 5, J = 7.6 Hz), 7.98 (t, 1H, pyridine-H4, J = 8.0 Hz),
7.36−7.26 (m, 10H, Ph), 5.00 (d, 4H, J = 5.2 Hz, CH2). 13C{1H}
NMR (150 MHz, CDCl3): 190.5, 149.4, 138.5, 136.1, 129.1, 128.2,
128.1, 127.7, 50.2. MALDI-TOF MS (m/z) calcd for C21H19N3S2
377.1 [M]+, found 377.1 [M]+. Anal. Calcd for C21H19N3S2: C, 66.81;
H, 5.07; N, 11.13. Found: C, 66.92; H, 5.24; N, 11.08.
Synthesis of anti-[Ru(BnSNS)(CO)2]2. [RuCl(BnSNS·2H)(CO)2]Cl
(249 mg, 0.41 mmol) was treated with column chromatography on
Al2O3 (pH = 3.5−4.5) using a mixture of CHCl3 and ethanol (50:1) as
an eluent. The yellow band was collected to give a mixture of syn- and
anti-[Ru(BnSNS)(CO)2]2 (159 mg, 73%). Recrystallization of the
mixture from CHCl3/hexane = 1:2 gave only one isomer of anti-
[Ru(BnSNS)(CO)2]2 (45.6 mg, 21%). 1H NMR (400 MHz, CDCl3): δ
8.67 (dd, 1H, pyridine-H3 or H5, J = 8.2 Hz, J = 1.2 Hz), 8.59 (dd,
1H, pyridine-H3 or H5, J = 7.6 Hz, J = 1.2 Hz), 8.14 (t, 1H, pyridine-
H4, J = 8.0 Hz), 7.52 (d, 2H, Ph-o, J = 6.8 Hz), 7.41−7.34 (m, 6H,
Ph), 7.31−7.22 (m, 2H, Ph), 5.38 (d, 1H, CH2, J = 17 Hz), 5.16 (d,
1H, CH2, J = 17 Hz), 5.02 (d, 1H, CH2, J = 18 Hz), 4.90 (d, 1H, CH2,
J = 17 Hz). IR (KBr): νCO 2042 and 1998 cm−1. Anal. Calcd for
C46H34N6O4Ru2S4: C, 51.87; H, 3.22; N, 7.89. Found: C, 52.02; H,
3.15; N, 8.12.
Synthesis of [RuCl(CO)2(PhSNS·2H)]Cl. A mixture of [Ru(CO)2Cl2]n
(68.4 mg, 0.30 mmol) and PhSNS·2H (105 mg, 0.30 mmol) was stirred
in anhydrous methanol (3 mL) for 3 days at room temperature under
a nitrogen atmosphere. The solution was evaporated in vacuo, and
anhydrous THF (3 mL) was added. The solution was refluxed for 24 h
under a nitrogen atmosphere. After cooling to room temperature, the
resulting precipitate was filtered off and washed with THF to remove
unreacted PhSNS·2H. A red-orange solid of [RuCl(CO)2(PhSNS·2H)]
Synthesis of [Ru(PhSNS)(CO)(PPh3)2]. A mixture of [Ru(PhSNS)-
(CO)2]2 (25.0 mg, 0.025 mmol) and triphenylphosphine (26.2 mg,
0.10 mmol) was stirred in anhydrous THF (5 mL) for 24 h at reflux
temperature under a nitrogen atmosphere. After cooling to room
temperature, the solution was evaporated in vacuo and the residue was
washed with hexane. Recrystallization of the product using CH2Cl2/
hexane = 1:5 gave a red solid of [Ru(PhSNS)(CO)(PPh3)2] (34.5 mg,
68%). 1H NMR (400 MHz, CDCl3): δ 7.65 (d, 2H, pyridine-H3, 5, J =
8.4 Hz), 7.37−7.28 (m, 19H, pyridine-H4 and PPh3), 7.21−7.14 (m,
16H, PPh3 and Ph-p), 6.97 (t, 2H, Ph-m, J = 7.2 Hz), 6.32 (dd, 4H,
Ph-o, J = 8.4 Hz, 1.2 Hz). 31P{1H} NMR (162 MHz, CDCl3): δ 35.4.
IR (KBr): νCO 1938 cm−1. Anal. Calcd for C56H43N3OP2RuS2·H2O: C,
66.00; H, 4.45; N, 4.13. Found: C, 65.77; H, 4.29; N, 3.89. The
presence of water was reproducibly observed.
1
Cl was obtained after drying in vacuo (109 mg, 63%). H NMR (400
MHz, CDCl3): δ 9.32 (d, 2H, pyridine-H3, 5, J = 7.6 Hz), 8.14 (t, 1H,
pyridine-H4, J = 8.0 Hz), 7.66 (d, 4H, Ph-o, J = 7.2 Hz), 7.43 (t, 4H,
Ph-m, J = 7.6 Hz), 7.40 (t, 2H, Ph-p, J = 7.2 Hz). IR (KBr): νCO 2069
and 2008 cm−1. Anal. Calcd for C21H15Cl2N3O2RuS2: C, 43.68; H,
2.62; N, 7.28. Found: C, 43.37; H, 2.79; N, 6.87.
Synthesis of [RuCl(PhSNS·1H)(CO)2]. A solution of [RuCl-
(CO)2(PhSNS·2H)]Cl (23.1 mg, 0.040 mmol) in CHCl3 was washed
with a saturated aqueous solution of NH4Cl using a separatory funnel.
The organic phase was separated, and the aqueous phase was extracted
with CHCl3. The combined organic phase was dried over Na2SO4.
After filtration, the solvent was evaporated in vacuo. The residue was
crystallized from CHCl3/hexane to give [RuCl(PhSNS·1H)(CO)2]
(18.2 mg, 84%). The analytically pure sample was obtained by
crystallization from CHCl3/Et2O/hexane. 1H NMR (400 MHz,
CDCl3): δ 8.72 (d, 2H, pyridine-H3, 5, J = 8.0 Hz), 7.95 (t, 1H,
pyridine-H4, J = 8.0 Hz), 7.50 (d, 4H, Ph-o, J = 7.6 Hz), 7.44 (t, 4H,
Ph-m, J = 7.8 Hz), 7.31 (t, 2H, Ph-p, J = 7.4 Hz). IR (KBr): νCO 2058
and 1993 cm−1. Anal. Calcd for C21H14ClN3O2RuS2·DMF: C, 46.94;
H, 3.45; N, 9.12. Found: C, 46.86; H, 3.38; N, 9.18.
Synthesis of [Ru(BnSNS)(CO)(PPh3)2]. A mixture of syn- and anti-
[Ru(BnSNS)(CO)2]2 (21.3 mg, 0.020 mmol) was reacted with
triphenylphosphine (21.0 mg, 0.080 mmol) in anhydrous DMSO (4
mL) for 24 h at 72 °C under nitrogen flow. After cooling to room
temperature, the solution was evaporated in vacuo and the residue was
washed with methanol and hexane. Drying the residue in vacuo gave a
red solid of [Ru(BnSNS)(CO)(PPh3)2] (36.9 mg, 90%). 1H NMR
(400 MHz, CDCl3): δ 7.53 (d, 2H, pyridine-H3, 5, J = 7.6 Hz), 7.38−
7.33 (m, 12H, Ph), 7.28−7.22 (m, 13H, pyridine-H4, Ph), 7.19−7.12
(m, 16H, Ph), 4.43 (s, 4H, CH2). 31P{1H} NMR (162 MHz, CDCl3):
δ 35.0. IR (KBr): νCO 1938 cm−1. Anal. Calcd for C58H47N3OP2RuS2:
C, 67.69; H, 4.60; N, 4.08. Found: C, 67.52; H, 4.77; N, 4.11.
Synthesis of [Ru(PhSNS)(CO)2]2. To a solution of [RuCl-
(CO)2(PhSNS·2H)]Cl (11.8 mg, 0.020 mmol) in methanol (3 mL)
was added H2O (10 mL). The formed brown precipitate was collected
by filtration and washed with H2O. The residue was extracted with
CHCl3. Crystallization from CHCl3/hexane gave [Ru(PhSNS)(CO)2]2
(10.0 mg, 97%). [Ru(PhSNS)(CO)2]2 was also obtained by treatment
of [RuCl(CO)2(PhSNS·2H)]Cl or [RuCl(PhSNS·1H)(CO)2] with
column chromatography on Al2O3 (pH = 3.5−4.5) using a mixture
of CHCl3 and ethanol (50:1) as an eluent. 1H NMR (400 MHz,
CDCl3): δ 8.65 (dd, 1H, pyridine-H3 or H5, J = 7.8 Hz, 1.2 Hz), 8.54
(dd, 1H, pyridine- H3 or H5, J = 8.0 Hz, 1.2 Hz), 8.18 (t, 1H,
pyridine-H4, J = 8.0 Hz), 7.47 (dd, 2H, Ph-m, J = 8.4 Hz, 7.6 Hz), 7.23
(t, 1H, Ph-p, J = 7.6), 7.19 (t, 2H, Ph-m, J = 7.8), 7.11 (dd, 2H, Ph-o, J
= 8.4 Hz, 1.2 Hz), 7.10 (t, 1H, Ph-p, J = 7.6), 7.01(dd, 2H, Ph-o, J =
8.4 Hz, 1.2 Hz). ESI-MS: calcd for C21H14N3O2RuS2 [M/2 + H]+
506.0, found 506.0. IR (KBr): νCO 2047 and 1991 cm−1. Anal. Calcd
ASSOCIATED CONTENT
■
S
* Supporting Information
Text, figures, and tables giving details of the synthesis and
characterization data for the compounds reported in this paper
and CIF files giving crystallographic data for the complexes.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: kuwabara@ims.tsukuba.ac.jp.
*E-mail: kanbara@ims.tsukuba.ac.jp.
F
dx.doi.org/10.1021/om400969p | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
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Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to the Chemical Analysis Center of
University of Tsukuba for X-ray diffractional studies, elemental
analyses, and NMR spectroscopy.
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dx.doi.org/10.1021/om400969p | Organometallics XXXX, XXX, XXX−XXX