Homoleptic ruthenium(iii) chalcogenolates: A single precursor to metal chalcogenide nanoparticles catalyst

Article abstract of DOI:10.1039/c1cc12422f

Eight homoleptic metal(iii) arylchalcogenolate polymers [M(EPh-p-X) ₃]_n (M = Ru, Cr, and Mo) were characterized by PXRD. Structural solution of [Ru(SPh-p-tBu)₃]_n1 was achieved by Rietveld refinement of the PXRD data. Pyrolysis of [Ru(SePh)₃] _n4 produced nanostructured RuSe₂, which selectively catalyzed the reduction of nitro compounds in the presence of other functionalities.

Full text of DOI:10.1039/c1cc12422f

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2011, 47, 8808–8810
www.rsc.org/chemcomm
COMMUNICATION
Homoleptic ruthenium(III) chalcogenolates: a single precursor to metal
chalcogenide nanoparticles catalystw
Sharon Lai-Fung Chan, Kam-Hung Low, Gary Kwok-Ming So, Stephen Sin-Yin Chui and
Chi-Ming Che*
Received 26th April 2011, Accepted 21st June 2011
DOI: 10.1039/c1cc12422f
Eight homoleptic metal(III) arylchalcogenolate polymers
[M(EPh-p-X)3]n (M = Ru, Cr, and Mo) were characterized
by PXRD. Structural solution of [Ru(SPh-p-tBu)3]n 1 was
achieved by Rietveld refinement of the PXRD data. Pyrolysis
of [Ru(SePh)3]n 4 produced nanostructured RuSe2, which selectively
catalyzed the reduction of nitro compounds in the presence of
other functionalities.
para-substituted thiophenols at 195 1C under Ar for 12 h.10
Alternatively, 1 can be prepared by heating a mixture of
Ru(acac)3 and 4-tert-butylthiophenol at 195 1C under Ar for
12 h. The latter method was preferred as the product was
free from polymeric metal carbonyl [Ru(SR)2(CO)2]n
contamination.11 We conceive that [Ru(SR)2(CO)2]n was
formed at a lower temperature and subsequently dissolved in
the reaction mixture to undergo further reaction with excess
para-substituted thiophenol to form the homoleptic polymer
[Ru(SR)3]n. Attempts to synthesize homoleptic polymers with
other substituted arylthiophenols were not successful,z and
only the reactions of 4-tert-butylthiophenol, 4-isopropyl-
thiophenol and 4-methoxythiophenol with Ru3(CO)12 afforded
polycrystalline solids 1–3. Presumably, the arylthiols bearing
tert-butyl, isopropyl or methoxy substituent can enhance
the solubility of [Ru(SR)2(CO)2]n in the reaction mixture,
subsequent reactions of which with para-substituted thiophenols
gave the polymers 1–3. Polymers 4 and 5 were prepared by
refluxing Ru(acac)3 with PhSeH or p-tBu-PhSeH in an aqueous
alcoholic medium under Ar for 12 h.z The solids obtained are
air-stable and powder X-ray diffraction (PXRD) experiments
revealed that 1–8 are isostructural to each other (Fig. S2 in ESI).
Structural solution of 1 (CCDC 823139) was obtained by
Rietveld refinement from the PXRD data.12 1 crystallized in
hexagonal P63/m with a = b = 17.403(1) A, c = 5.417(8) A.
Fig. 1 shows the perspective view of 1 along the b-axis. 1
consists of a 1-D chain of ruthenium atoms with each adopting
a face-sharing octahedral geometry with a Ru–Ru and a Ru–S
distance of 2.709 A and 2.209 A respectively and a Ru–S–Ru
angle of 75.631. The Ru–Ru distance in 1 is comparable to the
Ru–Ru distance of 2.87 A in [Ru(SPh)3]n reported by
Functional self-assembled coordination polymers (SACPs)
have potential diverse applications such as new materials for
gas storage,1 advanced electronics,2 and as new catalysts for
organic synthesis.3 Homoleptic metal chalcogenolates are
a class of functional SACPs with attractive optoelectronic
properties and intriguing structures arising from the metal
ions and chalcogenide atoms organized in one-dimensional
and two-dimensional structures.4 The utilization of pre-organized
networks of metal ions and chalcogenide atoms for the
metamorphosis from organometallic polymers into metal
chalcogenide nanoparticles has been demonstrated.5 Semi-
conducting transition metal chalcogenide nanoparticles have
continued to receive considerable interest because of their
potential applications in photovoltaic devices,6 field-effect
transistors,7 fuel cells,8 and catalysis.9 In this work,
five homoleptic ruthenium arylchalcogenolate polymers
[Ru(EPh-p-X)3]n (E = S, X = tBu 1, iPr 2, OMe 3;
E = Se, X = H 4, tBu 5), two homoleptic chromium
arylthiolate polymers [Cr(SPh-p-X)3]n (X = H 6, tBu 7), and
[Mo(SPh-p-tBu)3]n
8 were prepared and characterized
by powder X-ray diffraction (PXRD). Pyrolysis of 4 gave
nanocrystalline ruthenium diselenide (nano-RuSe2) as revealed
from the transmission electron microscopy (TEM) image as
well as PXRD data. The nano-RuSe2 was demonstrated to be
an efficient catalyst for chemoselective reduction of organic
nitro compounds in the presence of other functionalities.
Polymers 1–3, 6–8 were prepared in 70–90% yields by heating
Ru3(CO)12, Cr(CO)6 or Mo(CO)6 with the corresponding
Strahle.10 A TEM image revealed that a solid sample of 1
¨
contained phase-pure irregular nanoparticles. Subsequent
selected area electron diffraction (SAED) study on individual
nanocrystals of 1 revealed a d spacing of 15.26 A, which is
consistent with the PXRD data. Indexing of the PXRD
patterns of polymers 2, 3, 6, 7, and 8 revealed a hexagonal
space group with a = 16.18 A, 14.22 A, 12.96 A, 17.04 A, and
17.57 A respectively. The lengths of a-axis for 1, 7, and 8 are
similar (17.04–17.57 A) as the cell dimension is predominantly
determined by the size of ligand (–SPh-p-tBu). The order of the
lengths of a-axis (1 4 2 4 3 4 6) is consistent with the size of the
para substituent on the phenyl ring (tBu 4 iPr 4 OMe 4 H).
Department of Chemistry, State Key Laboratory of Synthetic
Chemistry, and Institute of Molecular Functional Materials,
The University of Hong Kong, Pokfulam Road, Hong Kong SAR,
China. E-mail: cmche@hku.hk; Fax: 852 2857 1586; Tel: 852 2859 2154
w Electronic supplementary information (ESI) available: PXRD data,
TGA, TEM images and detailed experimental procedure. See DOI:
10.1039/c1cc12422f
c
8808 Chem. Commun., 2011, 47, 8808–8810
This journal is The Royal Society of Chemistry 2011

View Article Online
(M = Ru, Cr) were observed up to 440 1C, indicating that the
as-formed MS2 were amorphous.
The PXRD patterns of the pyrolysis product of 4 at
different temperatures under vacuum (0.02 mmHg) for 4 h
are depicted in Fig. 3. No distinctive peaks were observed
when 4 was pyrolyzed at 200 1C, indicating the polymer
skeleton was destroyed. When the temperature of pyrolysis
was increased to 450 1C, new diffraction peaks could be
observed. The as-formed solid residue was identified by
matching its diffraction pattern with authentic crystal data
of RuSe213 and by using energy dispersive X-ray spectroscopy
(EDS). TEM images and SAED of the solid residue revealed
that they were crystalline nanoparticles with diameters in the
range of 3–15 nm. We envisaged that the resultant nano-RuSe2
could be a useful catalyst14 if it is supported on an inert matrix
such as graphite. A composite of nano-RuSe2 deposited on
graphite was achieved by pyrolyzing a physical mixture of
polymer 4 and graphite under vacuum. PXRD confirmed that
the nano-RuSe2 was formed on the surface of graphite without
disturbing the crystallinity.
The catalytic property of nano-RuSe2 was demonstrated by
the reduction of nitro-containing aromatic compounds using
aqueous hydrazine as reductant (Scheme 1). Reduction
of 9a with hydrazine monohydrate in the presence of 1 mol%
Fig. 1 (a) Perspective drawing of the chains structure of 1 viewed
along the b direction. Hydrogen atoms have been omitted for clarity.
(b) TEM and (c) SAED image of polycrystalline 1. The scale bars
represent 200 nm and 0.5 nmꢀ1 respectively.
Polymers 1–8 were subjected to thermogravimetric analysis
(TGA) and all of them showed similar decomposition temperature
at around 300–350 1C. The residual products were found to be
RuS2 (1, 2 and 3), RuSe2 (4 and 5), CrS2 (6 and 7), and MoS2
(8) based on the calculations from weight percentage. The low
decomposition temperature of these metal chalcogenolate
polymers indicates that they are apposite to be single-source
precursors for metal chalcogenides. The structural integrity of
both 1 and 7 was evaluated by variable-temperature (VT)
PXRD and the patterns of 1 measured at temperatures from
30–440 1C are depicted in Fig. 2 (Fig. S3 in ESI for VT-PXRD
of 7). At 300 1C, the characteristic peaks of 1 and 7 disappeared
completely but no diffraction peaks from the resultant MS2
Fig. 3 (a) PXRD patterns of pyrolysis residue from 4 at 200–450 1C
under vacuum (0.02 mmHg) for 4 h. Simulated PXRD pattern from
RuSe2 coordination data from ref. 13 is presented at the topmost.
Dotted lines show the two theta positions which match with the
simulated pattern. Diffraction originating from graphite is indicated
by *. (b) TEM and (c) SAED of the nano-RuSe2-deposited graphite.
The scale bars represent 5 nm and 5 nmꢀ1 respectively.
Fig. 2 VT-PXRD patterns of 1 at 30 1C to 440 1C.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 8808–8810 8809

View Article Online
of the nano-RuSe2 towards reduction of nitro-containing
aromatics was found to be efficient (quantitative isolated yield
for 10a and 10f) and chemoselective.
This work was supported by The University of Hong Kong
and the University Grants Council of HKSAR (the Area of
Excellence Scheme: AoE/P-03/08). KHL is partially supported
by a grant from The Committee on Research and Conference
Grants, HKU (small project funding 2010).
Notes and references
z Reactions of Ru3(CO)12 with 2-methylthiophenol, 3-methylthio-
phenol, 4-methylthiophenol, 4-ethylthiophenol, 3,4-dimethylthiophenol,
2,4,6-trimethylthiophenol, and dodecahexanethiol did not produce
polycrystalline homoleptic polymeric solid. Representative experimental:
[Ru(SePh)3]n 4. Diphenyl diselenide (0.156 g, 0.5 mmol) was added to a
solution of NaOH (0.03 g, 0.75 mmol) in water (10 mL), and a solution
of NaBH4 (0.0285 g, 0.75 mmol) in methanol (10 mL) was added. The
yellow suspension was heated until a clear solution was obtained.
After cooling to room temperature, the solution was adjusted to pH E
5–6 by dropwise addition of concentrated hydrochloric acid (12 M).
Ru(acac)3 (0.133 g, 0.33 mmol) was added and the reaction mixture
was refluxed for 12 h. The insoluble dark green precipitate was filtered
and washed with methanol (3 ꢁ 10 mL) and diethyl ether (10 mL). The
resultant dark green solid was placed in a vacuum oven (5 mmHg,
40 1C) for 12 h. Yields: 85% (0.16 g). Elemental analysis calcd (%):
C 37.96, H 2.64; found: C 37.22, H 2.65.
Scheme 1 (i) 10 equiv. NH2NH2ꢂH2O, 1 mol% nano-RuSe2, ethanol
reflux. Reaction time is indicated for each substrate. Conversion yields
are reported based on 1H-NMR determination. Isolated yields in
parentheses were obtained by column chromatography.
nano-RuSe2 in refluxing ethanol gave 10a in quantitative yield
within 24 h. Replacing the hydroxymethyl group with an
electron-donating group such as n-propyl group (9b) or hydroxyl
group (9c) resulted in a drop of substrate conversion (38% and
20% respectively) as monitored by 1H-NMR. Bromoaryl
compounds are readily de-brominated in catalytic reduction
but in our catalytic system, 9d was reduced into 10d in 100%
conversion and was isolated in 64% yield together with
N-arylation product. In contrast, reduction of 9d using mild
reducing agent NaBH4 and using heterogeneous Pd(0)/C as
catalyst was reported to give aniline.15 O-Benzyl is a common
protecting group for alcohols and phenols. Avoiding the
removal of this protecting group is difficult if the nitro-
containing substrate is reduced by using heterogeneous Pd
catalyst such as 10% Pd(0)/C or Pd(0)EnCatt 30NP nano-
particulate.16 Reduction of 9e with nano-RuSe2 catalyst
showed 42% substrate conversion with the product 10e
obtained in 40% isolated yield. We also examined the reduction
of dinitro aromatics like 9f as controlling the reduction of one
nitro group in dinitro compounds was difficult.18 The mono
reduced compound 10f was achieved with a 100% substrate
conversion and a 70% isolated yield. Electron-deficient
substrate 9g with a nitrile group ortho to the nitro group
was reduced under high pressure (50 psi) with heterogeneous
Pd(0) catalyst.17 By using nano-RuSe2 catalyst, 10g was obtained
in 100% isolated yield within 25 h. Chemoselectivity was also
observed in the case of 9h as only the nitro group ortho to the
phenolic OH was reduced and the nitro group para to the OH
group remained intact. Noteworthily, 9h could be reduced into
1,3-diaminophenol without any selectivity by formic acid in
the presence of 10% Pd(0)/C.19
1 N. L. Rosi, J. Eckert, M. Eddaoudi, D. T. Vodak, J. Kim,
M. O’Keeffe and O. M. Yaghi, Science, 2003, 300, 1127.
2 G. J. Halder, C. J. Kepert, B. Moubaraki, K. S. Murray and
J. D. Cashion, Science, 2002, 298, 1762.
3 A. Corma, Chem. Rev., 1997, 97, 2373; B. Kesanli and W. Lin,
Coord. Chem. Rev., 2003, 246, 305.
4 C.-M. Che, C.-H. Li, S. S.-Y. Chui, V. A. L. Roy and K.-H. Low,
Chem.–Eur. J., 2008, 14, 2965; K.-H. Low, V. A. L. Roy,
S. S.-Y. Chui, S. L.-F. Chan and C.-M. Che, Chem. Commun.,
2010, 46, 7328.
5 K.-H. Low, C.-H. Li, V. A. L. Roy, S. S.-Y. Chui, S. L.-F. Chan
and C.-M. Che, Chem. Sci., 2010, 1, 515.
6 I. E. Anderson, A. J. Breeze, J. D. Olson, L. Yang, Y. Sahoo and
S. A. Carter, Appl. Phys. Lett., 2009, 94, 063101.
7 X. Dong, C. M. Lau, A. Lohani, S. G. Mhaisalkar, J. Kasim,
Z. Shen, X. Ho, J. A. Rogers and L.-J. Li, Adv. Mater., 2008,
20, 2389.
8 Y. Feng, A. Gago, L. Timperman and N. Alonso-Vante,
Electrochim. Acta, 2010, 56, 1009.
9 F. J. Vidal-Iglesias, J. Solla-Gullo
J. M. Feliu, Angew. Chem., Int. Ed., 2010, 49, 6998.
10 U. Berger and J. Strahle, Z. Anorg. Allg. Chem., 1984, 516, 19;
´
n, E. Herrero, A. Aldaz and
¨
U. Berger and J. Strahle, Mol. Cryst. Liq. Cryst., 1985, 120, 389.
¨
11 B. F. G. Johnson, R. D. Johnston, P. L. Josty, J. Lewis and
I. G. Williams, Nature, 1967, 213, 901.
12 H. M. Rietveld, J. Appl. Crystallogr., 1969, 2, 65.
13 W. N. Stassen and R. D. Heyding, Can. J. Chem., 1968, 46, 2159.
14 P. H. C. Camargo, Z. Peng, X. Lu, H. Yang and Y. Xia, J. Mater.
Chem., 2009, 19, 1024.
15 M. Petrini, R. Ballini and G. Rosini, Synthesis, 1987, 713.
16 M. Quai, C. Repetto, W. Barbaglia and E. Cereda, Tetrahedron
Lett., 2007, 48, 1241.
17 M. J. Luzzio, C. L. Autry, S. K. Bhattacharya, K. D. Freeman-
Cook, M. M. Hayward, C. A. Hulford, K. L. Nelson, J. Xiao and
X. Zhao, WO 2008129380.
SACPs 1–8 were prepared and characterized with PXRD,
TEM, SAED, and EDS. The polymers are isostructural
to each other. Nanocrystalline nano-RuSe2 was obtained
by heating polymer 4 under vacuum. Catalytic performance
18 Y. Zheng, K. Ma, H. Wang, X. Sun, J. Jiang, C. Wang, R. Li and
J. Ma, Catal. Lett., 2008, 124, 268.
19 D. C. Gowda and S. Gowda, Indian J. Chem., Sect. B: Org. Chem.,
2000, 39, 709.
c
8810 Chem. Commun., 2011, 47, 8808–8810
This journal is The Royal Society of Chemistry 2011