Versatile bridging ability of secondary thioamide group for constructing metal cluster based on pincer complex

Article abstract of DOI:10.1016/j.jorganchem.2010.11.028

The crystallization of the SCS pincer platinum complex with secondary thioamide groups, [4-methyl-2,6-bis(anilinothiocarbonyl)-κ²S, S'-phenyl-κC¹]chloroplatinum(II), spontaneously forms a trinuclear cluster complex accompanied by lib

Full text of DOI:10.1016/j.jorganchem.2010.11.028

Journal of Organometallic Chemistry 696 (2011) 1305e1309
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Versatile bridging ability of secondary thioamide group for constructing metal
cluster based on pincer complex
,
,b,
Ken Okamoto a, Junpei Kuwabara a b, Takaki Kanbara a
*
a Tsukuba Research Center for Interdisciplinary Materials Science (TIMS), University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan
b Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The crystallization of the SCS pincer platinum complex with secondary thioamide groups, [4-methyl-2,6-
bis(anilinothiocarbonyl)-
complex accompanied by liberating HCl in DMSO/EtOH mixture. The crystal structure of the SNS pincer
copper complex with secondary thioamide groups, [2,5-bis(benzylaminothiocarbonyl)-
2S,S’-pyrrolyl-
N1]chlorocopper(II), exhibits a dimer structure bearing the bridging thioamide group. The thioamide
k k
2S,S’-phenyl- C1]chloroplatinum(II), spontaneously forms a trinuclear cluster
Received 30 September 2010
Received in revised form
17 November 2010
k
Accepted 17 November 2010
k
group acts as the bridging ligand of the multimetallic complexes in different anionic and neutral
manners.
Keywords:
Secondary thioamide
Pincer ligand
Ó 2010 Elsevier B.V. All rights reserved.
Bridging ligand
Platinum complex
Copper complex
1. Introduction
secondary thioamide group has potential for bridging the metal
centers, the pincer complexes would assemble to form metal
Metal chalcogenido clusters are of great interest because of their
unique electrical, magnetical, chemical, and catalytical properties
[1]. Sulfur containing ligands such as thiols [2], thiosemicarbazone
[3], and mercaptonicotinic acid [4] are often used as bridging
ligands for constructing metal clusters due to their strong coordi-
nation property. However, the number of examples of thioamide-
based metal clusters is limited. A thioamide group is one of the
sulfur-based donating groups for constructing organometallic
compounds [5,6]. Upon deprotonation, a secondary thioamide
group forms thioamidate and iminothiolate as resonance structures
(Scheme 1). The deprotonation gives a dramatically change in terms
of bridging ability of a thioamide group. Therefore, the secondary
thioamide group serves as a bridging ligand in three manners such
as neutral thioamide, thioamidate and iminothiolate. The versa-
tility of the thioamide group as bridging ligand is expected to afford
a new metal clusters.
cluster based on pincer complexes. Herein, we report a formation of
two kinds of cluster complexes from the monometallic pincer Pt
and Cu complexes having the secondary thioamide moiety. The
secondary thioamide group in each complex acts as a bridging
ligand in different manners.
2. Results and discussion
2.1. Synthesis and X-ray diffraction study of the trinuclear
complex 2
The Pt pincer complex 1 was prepared in accordance with the
method in the previous report [5d]. The crystallization of 1 from
DMSO gives single crystals having monometallic structure [5d]. In
contrast, crystallization of 1 in a mixture of DMSO and EtOH gives
different crystals having monoclinic lattice in 4% yield. The single
X-ray diffractional analysis revealed the trimetallic structure as
shown in Fig. 1. The chloride ligand on the Pt center and one of
the proton in the NeH groups disappear in the trimetallic
structure compared with the structure of the parent complex 1
(Scheme 2). These results indicate that HCl was liberated during
the crystallization process. The deprotonation of the secondary
thioamide group provides iminothiolate moieties bridging Pt
centers.
Pincer complexes generally have a tridentate ligand (ECE ligand)
composed of a cyclometalating carbon and donating groups such as
PR2, NR2 and SR [7]. The pincer complexes bearing thioamide
groups as a donating group were also investigated [5]. Since the
* Corresponding author. Tsukuba Research Center for Interdisciplinary Materials
Science (TIMS), University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8573, Japan.
Tel.: þ81 29 853 5066; fax: þ81 29 853 4490.
E-mail address: kanbara@ims.tsukuba.ac.jp (T. Kanbara).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.11.028

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K. Okamoto et al. / Journal of Organometallic Chemistry 696 (2011) 1305e1309
Ph
Ph
M
R
M
R
M'
S
Ph
N
S
S
S
HN
M
M
M
M'
M'
M'
R'
S
R'
R'
R
N
H
N
H
N
H
H
N
H
N
-3HCl
Pt
S
NH
Ph
Pt
S
Ph
Ph
thioamide
S
N
EtOH/DMSO
S
Pt
Cl
S
Ph
deprotonation
N
Pt
1
S
M
R
M
R
M'
N
S
S
S
S
S
Ph NH
R'
R'
R'
R'
R'
2
N
R
N
iminothiolate
Scheme 2.
six-membered ring, the PteS bonds in each SCS pincer structure is
2.304 Å on average, which is shorter than the PteS bonds con-
necting each pincer complex (2.415 Å on average) (Table 1). The
bond angles involving bridging sulfur atoms are as follows: Pt1-S2-
Pt2, 88.79(10)ꢀ; Pt2eS3ePt3, 98.92(9)ꢀ; Pt1-S1-Pt3, 100.45(10)ꢀ.
The average bond distances between the carbon atom and the
bridging S atom such as S1eC2 in cluster 2 is 1.823 Å, which is
longer than the average of CeS bonds in parent complex 1 (1.707 Å).
These changes of bond lengths are consistent with formations of
SeC single bonds of iminothiolate moieties in the cluster structure.
In addition, the CeN distances of the iminothiolate moiety (1.261 Å
on average) are shorter than those of the thioamide groups in
complex 1 (1.318 Å) and 2 (1.34 Å) owing to a double bond character
of the iminothiolate structure. The distances between the Pt centers
(Pt1ePt2 3.3135(6) Å; Pt2ePt3 3.5741(7) Å; Pt1ePt3 3.6207(7) Å)
indicate that there is no direct bond between the Pt atoms. Lei et al.
reported SNS pincer Pd complexes having a centered 2,6-pyridine
unit bearing secondary thioamide groups [8]; deprotonation of the
secondary thioamide groups by strong base affords tetrametallic or
trimetallic cluster depending on the substituent on thioamide
group. The structure of the trimetallic cluster is similar to that of 2.
In the case of these clusters, both of thioamide groups are depro-
tonated during the formation of the cluster because the SNS pincer
ligand is neutral.
M'
S
R'
R
N
M
R
N
R
N
M
thioamidate
Scheme 1. The neutral and anionic forms of
presumable coordination mode as a building block of metal clusters.
a
secondary thioamide group and
Since the total of the bond angles around the Pt centers are close
to 360ꢀ, the each Pt center retains a distorted square planar
structure in the trimetallic structure. The core of trimetallic
cluster 2 consists of a six-membered ring of alternating Pt and S
atoms (Fig. 1b). In terms of the lengths of six PteS bond in the
Table 1
Selected bond length (Å) and angles (deg) for complexes 1 and 2
1a
2
Pt1eC2
1.957(7) Pt1eC1
Pt2eC22
1.992(11) Pt1eS1
1.985(10) Pt1eS2
1.968(13) Pt1eS4
1.815(12) Pt2eS2
1.821(11) Pt2eS3
1.833(13) Pt2eS5
1.724(12) Pt3eS1
1.712(12) Pt3eS3
1.690(14) Pt3eS6
1.256(15)
2.310(2)
2.440(2)
2.292(2)
2.293(2)
2.401(2)
2.292(3)
2.401(2)
2.301(3)
2.289(3)
Pt3eC43
S1eC8b
1.700(7) S1eC2c
1.714(7) S2eC23c
S3eC44c
S2eC15b
S4eC3b
S5eC24b
S6eC45b
N1eC8b
1.328(8) N1eC2c
1.307(8) N2eC3b
N3eC23c
N2eC15b
1.348(13)
1.274(16)
1.328(17)
1.252(15)
N4eC24b
N5eC44c
N6eC45b
1.35(2)
S1ePt1eS2 170.77(6) S1ePt1eS4
S2ePt2eS5
169.06(10) S1ePt1eS2 93.36(9)
169.60(9) S2ePt1eS4 97.24(10)
169.99(11) S2ePt2eS3 92.23(10)
S3ePt3eS6
S1ePt1eC1
S4ePt1eC1
S2ePt2eC22
S5ePt2eC22
S3ePt3eC43
S6ePt3eC43
85.6(3)
83.9(3)
85.2(3)
85.2(3)
85.4(4)
84.6(4)
S3ePt2eS5 97.47(10)
S1ePt3eS3 93.28(10)
S1ePt3eS6 96.71(11)
a
Fig. 1. (a) ORTEP drawing of 2 with thermal ellipsoids shown in 50% probability level
and (b) ball and stick model viewed along the Pt3S3 core. Solvating molecules are
omitted for clarity.
From Ref. [5d].
Thioamide moiety.
Imino-thiolate moiety.
b
c

K. Okamoto et al. / Journal of Organometallic Chemistry 696 (2011) 1305e1309
1307
2.2. Detection of the intermediates for cluster 2 by MALDI-MS
To obtain the information of the mechanism for the formation of
cluster 2, the intermediates of the reaction were detected by
MALDI-MS. A portion of the solution for crystallization of 2 was
taken out and measured MALDI-MS using dithranol as a matrix.
Fig. 2 shows the spectrum of the molecular cations. The result
exhibits the existence of monomer (m/z ¼ 555), dimer (m/z ¼ 1111),
trimer (m/z ¼ 1665), tetramer (m/z ¼ 2221), and pentamer
(m/z ¼ 2276). This result indicates that the solution contains not
only trimetallic complex observed by X-ray diffractional analysis
but also the complexes with higher nuclearity. Since the ratio of the
signal intensities of these complexes depends on the laser intensity
for the acquisition of the spectrum, the laser partly breaks of the
multimetallic complexes. From the mass spectra, most of thioamide
groups in the complexes were deprotonated without an addition of
base, which indicates that the liberation of HCl spontaneous occurs
in a mixture of EtOH and DMSO. The unusual phenomenon is
presumably due to the thermodynamic stability of the multime-
tallic complexes. Since a solution of 1 in DMSO did not exhibit such
liberation of HCl, EtOH might induce a liberating HCl and the
formation of cluster 2.
2.3. Synthesis and crystal structure of the Cu complex 3
To inquire the versatility of the secondary thioamide group as
a bridging ligand, thioamide-based pincer ligand with a central
pyrrole (SNS) was investigated. Crystallization of Ni, Pd, and Pt
complexes bearing the SNS pincer ligand gave single crystals having
a monometallic structure [5c,5i]. In contrast, the copper complex
bearing the SNS pincer ligand spontaneously forms a dimer struc-
ture with another kind of a bridging manner. The copper complex 3
was obtained in good yield (98%) from the reaction of the SNS ligand
and an equimolar amount of CuCl2 at room temperature. Complex 3
is fairly stable to air and water and shows good solubility in polar
Fig. 3. ORTEP drawing of (a) dimer structure of 3 with thermal ellipsoids shown in 50%
probability level, (b) a view of the extended network of the intermolecular hydrogen
bonds in 3. The NeH/Cl hydrogen bonding distance is given.
organic solvents such as acetone, EtOH, DMF, and DMSO. In contrast
to the mass spectrometric analysis of the Pt complex, there is no
significant peaks of a cluster complex in the spectrum for the solu-
tion of Cu complex 3. However, crystal structure of the complex 3
exhibits dimer structure with the bridging neutral thioamide group
(Fig. 3). Each copper(II) center has a k
3SNS coordination of the pincer
ligand. The coordination geometry around each metal center is
a distorted square pyramidal, where the basal plane is defined by the
pyrrolic N atom and the two S atoms of the pincer ligand, and the
chloride ligand. Table 2 shows selected bond lengths and angles of
complex 3. The apical position of the square pyramid is occupied by
one of the sulfur atoms in the closest Cu complex. The basal planes of
the bridged two square pyramid are parallel to each other. The
Cu2(m-S)2 core is parallelogram, with a Cue(m-S)eCu angle of 93.45
(3)ꢀ. The two CueSbasal bond distances are 2.4137(11) Å and 2.3957
(9) Å, which are shorter than the CueSapical bond distance of 2.809
(2) Å. The unique structure is found only in a small number of Cu(II)
pincer complexes [9] and this is the first example of a dimer struc-
ture of a neutral copper pincer complex. Fig. 3b shows the existence
of an intermolecular NeH/Cl hydrogen bond of dimer 3 resulting in
the formation of a linear double chain network structure along the
a axis in the solid state.
Table 2
Selected bond lengths (Å) and angles (deg) for complex 3
Cu1eN1
Cu1eS1
Cu1eS2
Cu1eCl
N2eCu1eS1
N2eCu1eS2
N2eCueCl1
1.885(3)
2.4137(11)
2.3957(9)
2.2209(11)
82.36(8)
S1eC5
S2eC21
N1eC5
N3eC21
S1eCu1eCl1
S2eCu1eCl1
S1eCu1eS2
1.711(4)
1.716(4)
1.323(5)
1.315(4)
97.98(3)
94.88(3)
165.29(4)
83.24(8)
162.67(8)
Fig. 2. Possible chemical structures and MALDI-mass spectra from the solution of 1 in
DMSO/EtOH with different laser intensity (a) laser power 70 and (b) laser power 90.

1308
K. Okamoto et al. / Journal of Organometallic Chemistry 696 (2011) 1305e1309
3. Conclusions
b
¼ 99.976(2), V ¼ 5785.0(9) Å3, Z ¼ 4, Dcalc ¼ 2.003 gcmꢁ3. A total of
34085 reflections were measured, 12880 unique. The final cycle of
full-matrix least squares refinement on F was based on 8847
observed reflections (I > 2.00
Rw ¼ 0.1500, GOF ¼ 1.047.
In summary, we found versatility of a secondary thioamide
group as a bridging ligand. The thioamide group of the SCS pincer Pt
complex acts as the anionic bridging ligand in an iminothiolate
form for the formation of the trimetallic cluster. On the other hand,
copper complex with the SNS ligand forms dimer structure with
the neutral thioamide group as a bridging ligand. These new find-
ings provide a possibility of a thioamide group as a bridging block
for metal chalcogenide clusters.
s
(I)), with factors of R1 ¼ 0.0586,
3: C20H18ClCuN3S2, M ¼ 463.50, triclinic, space group P-1,
a ¼ 8.795(7), b ¼ 10.655(8), c ¼ 11.048(9) Å,
a
¼ 95.118(9), ¼ 111.780
b
(11),
g
¼ 95.122(9)ꢀ, V ¼ 949.1(12) Å3, Z ¼ 2, Dcalc ¼ 1.622 gcmꢁ3. A
total of 6604 reflections were measured, 3929 unique. The final cycle
of full-matrix least squares refinement on F was based on 3541
observed reflections (I > 2.00
Rw ¼ 0.0695, GOF ¼ 0.955.
s(I)), with factors of R1 ¼ 0.0513,
4. Experimental
4.1. General procedures
Acknowledgements
Commercially available solvents were used for recrystalliza-
tions. N,N0-dibenzyl-1H-pyrrole-2,5-dicarbothioamide and Pt
pincer complex 1 were prepared in accordance with the method in
the previous report [5c,5d]. NMR spectra were recorded on a JEOL
JNM-EX-400 NMR spectrometer. MALDI-TOF-MS analyses were
performed by an AXIMA-CFR plus MALDI-TOF mass spectrometer
(Shimadzu/Kratos) equipped with a pulse nitrogen laser operated
at 337 nm. MALDI-mass spectra were acquired in the linear mode
under following parameters: ion source; 20 kV, lens; 6.5 kV, pulsed
extraction; ꢁ2.5 kV, reflection; 25 kV [10]. For preparing the
The authors are grateful to the Chemical Analysis Center of
University of Tsukuba for elemental analyses and NMR spectros-
copy. The authors are grateful to Dr. Jun-Chul Choi and Dr. Yasu-
masa Takenaka for the measurement and refinement of the crystal
structure, and Dr. Katsuhiko Ariga and Dr. Jonathan P. Hill for the
measurements of mass spectrometry.
Appendix A. Supplementary material
CCDC 794887 and 798285 contains the supplementary crystal-
lographic data for complexes 2 and 3 respectively. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
samples, the solution of the complexes in DMSO and EtOH (1
mL)
was mixed with 3 L of matrix solution (using dithranol as
m
a matrix). The mixture was spotted onto the MALDI sample plate
and then evaporated under a gentle stream of air. For measure-
ments, a total of 100 profiles (5 shots per profile) were accumulated
by searching for 10e20 hot spots for the sample.
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K. Okamoto et al. / Journal of Organometallic Chemistry 696 (2011) 1305e1309
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