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Microwave synthesis and thermal analysis of ruthenium-DMSO complexes

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Microwave Synthesis and Thermal Analysis of Ru-DMSO Complexes
Shengkuei Chiu
A Thesis presented to the faculty of Arkansas State University
In partial fulfillment of the requirements for the Degree of
Arkansas State University
April 2009
Aproved by
Dr. Mark Draganjac, Thesis Advisor
Dr. Scott Reeve, Committee Member
Dr. Ellis Benjamin, Committee Member
Dr. John M. Pratte, Department Chair
UMI Number: 1462447
Copyright 2009 by
Chiu, Shengkuei
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Shengkuei Chiu
In order to remove sulfur from fossil fuels during the HDS process, RuS2 has been
applied for decades. However, the real mechanism for removing sulfur by using RuS2 is
vague. The RuS2 model compound studies are in demand to understand the interaction
between substrates and catalysts during the HDS process. The model compounds such are
thiophene compounds, η1,S-thiophene complexes, π-complexes of benzo- and
dibenzothiophenes and Ru-S compounds.
Ru-DMSO is a versatile starting reagent for preparing Ru compounds. Compare
literature preparation of Ru-DMSO complexes with microwave synthesis, microwave
technique improve the preparation of Ru-DMSO compounds. The reaction time was
reduced from approximately three hours to a few minutes depending on the Ru-DMSO
compound’s components and structure.
Studying the thermal properties of Ru(dmso)xCly compounds may help understand the
HDS process. Trans-[H(dmso)2]Ru(dmso)2Cl4 showed four stages DMSOs loss in TGA
mass loss curve. The onset reaction temperature was different between cis- and transisomers of Ru-DMSO complexes in TGA plots due to the trans influence and the bond
lengths between Ru and ligands.
My foremost thanks goes to my thesis adviser Dr. Draganjac, for all these two years
he has helped me and given me the incentive to do research and self confidence to
persevere. I thank him for his patience and encouragement that helped me to go through
difficult time, for his intuitions and suggestions that helped me to shape my research
I wish to thank my thesis committee members: Dr. Scott Reeve and Dr. Ellis
Benjamin. I am grateful to them for their valuable feedback and appreciate Dr. Ellis
Benjamin for helping me on Microwave synthesis.
I thank Dr. Benjamin Rougeau for his assistance on research. I also thank all staffs and
our laboratory group and the chemistry and physics department for their assistance during
this two years study.
I wish to thank my mother and family, especially my wife, for all their support
throughout the long process of accomplishing this goal.
List of Tables……………………………………………………………………………viii
List of Figures……………………………………………………………………………ix
Hydrodesulfurization Reaction………………………………….....2
Thiophene Compounds………………………………………….....7
S-Bound Thiophene Complexes…………………………………...8
η1,S-Thiophene Complexes………………………………………...8
η1,S-Benzo- and Dibenzothiophene Complexes…………………...9
Thiaporphyrin Complexes………………………………………...10
η5-Thiophene Complexes and Derivatives……………………......10
π-Complexes of Benzo- and Dibenzothiophenes…………………12
η2- and η4-Thiophene complexes……………………………….....12
η4-Thiophene complexes……………………………………….....12
η 1, η4-Thiophene complexes……………………………………..13
Thiophene from Metal Sulfides…………………………………..13
Ru-S Compounds………………………………………………....14
Thiols ...…………………………………………………………..14
v Thiolates…….……………………………………………..........15
Thioamide compounds …………………………………………17
Ru-DMSO Complexes…..……………………………………...17
Microwave Synthesis…………………………………………...22
MICROWAVE SYNTHESIS…………..……………………….23
Experimental Section…………………………………………23
Materials and methods………………………………………..23
Microwave synthesis of cis-Ru(dmso)4Cl2 ………...………...24
Microwave synthesis of trans-[H(dmso)2][Ru(dmso)2Cl4]…..25
Microwave synthesis of trans-(Ph4P)[Ru(dmso)2Cl4]………..26
Synthesis of mer-Ru(dmso)3Cl3 ….………….……………….26
Synthesis of trans-Ru(dmso)4Cl2 ……………….…….……...26
Microwave synthesis of Ru(PPh3)3Cl2 …………….….……...27
Results and Discussion ...…………………………….……….27
vi Introduction…………………………………………………….40
Experimental Section.....………………………………………..41
Results and Discussion ...……..………………………………...42
Table 1. Ru(PPh3)Cl2 compound’s yields with different reaction,
solvent, and amount of Triphenylphosphine……………………………...35
Table 2. [RuCl2(dmso)[9]aneS3-k3S] microwave reaction at different
temperature and reaction time…………………………………………….37
Table 3. Yield and melting point comparison of Ruthenium compounds…………39
Figure 1. Structure of the thiopheneylide C4H4SC(CO2Me)2 …………………..… 8
Figure 2. Structure of [(ThiopheneCH2Cp)Ru(PPh3)2]+
(phenyl groups omitted), after Draganjac et al ..………………………...9
Figure 3. The structure of CpFe(CO)2(η1, S-DBT)+ …………………………….....9
Figure 4. The structure of Cr(Me3Si)nH4-nC4S)(CO)3 …………………………….11
Figure 5. Isomers of Fe(η5-5-MeC7H4S)2 …...……………………………………11
Figure 6. Structure of (CpRu)2(DBT) after Wang and Angelici ..………………...12
Figure 7. The decomposition of e2S2(S2C2Ph2)2 ….………………………………13
Figure 8. Reaction of RuCl2(dmso)4, L1=1,10-phenanthroline or 2,2’-bipyridyl;
L2=pyridine or 3-methylpyridine; L3=2-aminopyridine;
Figure 9. Half-sandwich ruthenium(II) complexes with six-electron lgands……..20
Figure 10. Structure of Ru(MeCN)3([9]aneS3-k3S)][CF3SO3]2 …………………..21
Figure 11. Structure of [RuCl2(dmso) [9]aneS3-k3S)]…………………………….21
Figure 12. Overlaid visible spectrum of three methods of trans[H(dmso)2][Ru(dmso)2Cl4]
microwave reaction…………………….30
Figure 13. TGA curves for RuCl3 on Cu pans under Argon gas ..………………..43
Figure 14. TGA curves for RuCl3 on Cu pans under Nitrogen gas ..……………..45
Figure 15. TGA curves for RuCl3 on Cu pans under Air gas ……..……………...46
Figure 16. TGA curves for RuCl3 on Alumina pans under Argon gas…..……….47
ix Figure 17. TGA curves for RuCl3 on Alumina pans under Nitrogen gas………….48
Figure 18. TGA curves for AgCl on Cu pans under Argon gas…………………...50
Figure 19. TGA curves for cis-Ru(dmso)4Cl2 on Cu pans under Argon gas….......51
Figure 20. TGA curves for cis-Ru(dmso)4Cl2 on Cu pans under Nitrogen gas.......52
Figure 21. TGA curves for trans-Ru(dmso)4Cl2 on Cu pans under Argon gas.......55
Figure 22. TGA curves for trans-[H(dmso)2][Ru(dmso)2Cl4] on Cu pans
under Argon gas……………………………………………………………………56
Figure 23. TGA curves for trans-(Ph4P)[Ru(dmso)2Cl4] on Cu pans
under Argon gas……………………………………………………………………57
Figure 24. Bond distances in cis-Ru(dmso)4Cl2 …………………………………..60
Figure 25. Bond distances in trans–Ru(dmso)4Cl2 ………………………………..61
Figure 26. Bond distances in trans-Ru(dmso)2Cl4- …..……………………………61
The problem of air pollution due to diesel engine fumes has become more and
more serious in the world. The quantity of sulfur released in the atmosphere is
mentioned as being an important issue of pollution. The environmental regulations
concerning the sulfur content in the diesel engine fuels are becoming more and more
severe. The maximum sulfur quantity had to be decreased to 15 ppm in the US by
2006 [1], and to 10 ppm in EU by 2009 [2]. Hence, a number of approaches focusing
at improving the deep hydrodesulfurization of light gas oil have been investigated
through the development of new HDS (hydrodesulfurization) catalysts together with
completed studies of the relevant reaction mechanism[3, 4, 5].
Combustion of sulfur laden fuels leads to SO2 emissions. Long-term exposures
to high concentrations of SO2 and it results in respiratory illness, alterations of the
lungs’ defenses and cardiovascular disease. The odor threshold of SO2 in humans is
0.3-2.5 ppm. Irritation of the respiratory tract occurs at 5-10 ppm. The higher
concentrations cause irritative coughing and 400-500 ppm results in death, even upon 1 short-term exposure. Long-term exposure causes loss of appetite, constipation, loss of
taste, red tongue, convulsions, eye inflammation, and bronchopneumonia. Frostbite on
skin and mucous membranes are results of contact with liquid SO2 [6, 7].Not only does
exposure to SO2 result in health problems, but the environment is also harmed. Sulfur
dioxide reacts with O2 in the atmosphere to produce SO3. Sulfur trioxide, subsequently,
reacts with water vapor to form sulfuric acid, which falls as acid rain.
Acid rain, which damages forests and growth, changes the makeup of soil and
makes streams or rivers unsuitable for fish. Using HDS catalysts for the removal of sulfur
from fossil fuel feed stocks is the key to preventing poisoning of referring catalysts and
for lowering fuel combustion contributions to the acid rain problem. When fuel is passed
over a catalyst under high hydrogen pressure and elevated temperatures, this process not
only removes the unwanted hetero atoms but also hydrogenates unsaturated carboncarbon bonds simultaneously.
The primary forms of sulfur found in coal are classified as pyritic (FeS2), sulfatic
(FeSO4), and organic. The pyritic and organic forms are generally dominant. Pyritic and
sulfatic forms of sulfur are easily removed by mechanical means or with an acid or base
wash. There are several sulfur containing organic compounds found in coal, which
include thiols, organic sulfides and disulfides, and thiophene and its derivatives [8].
Since the 1970s, important progress has been made by the worldwide community
in studying HDS catalysts and their reactions. However, a topic of enormous interest in
petroleum and automotive industries is still ‘‘ultra clean transportation fuels’’ since
stricter fuel specifications demand redrawing of refinery flow sheets with the inclusion of
desulfurization units at many stages of petroleum refining. Research efforts in these areas
are important, especially the search for efficient catalysts for the HDS process [9, 10].
Hydrodesulfurization reaction
In the hydrodesulfurization (HDS) process, two methods are used to remove sulfur
from fossil fuel stocks: pre-ignition methods or post-ignition methods [15]. In the preignition process, binary molybdenum sulfides are used to catalyze the removal of sulfur
from petroleum fractions and coal. During the HDS process and after crudes are desalted
and distilled into low and high boiling fractions, sulfur vapors are forced over an HDS
catalyst where they are converted to hydrogen sulfide and hydrocarbons. In this process,
sulfur is cleaved from the carbon atoms of thiols, sulfides, disulfides, thiophenes,
benzothiophenes, and dibenzothiophenes found in the high boiling fractions of crude [11].
Organic sulfur in the form of thiols (RSH), sulfides (RSR), and disulfides (RSSR) are
readily desulfurized by the HDS process whereas thiophene, benzothiophene, and
dibenzothiophene are more difficult to desulfurize.
Hydrogen sulfide recovered from the HDS process is usually deposited in a sulfur
plant where it is reacted with SO2 to form S8, the most stable sulfur allotrope, and water.
The organic sulfur is the main focus of the HDS process because it is more difficult to
remove [11, 12].
There are three factors that influence the catalytic activity: electronic, geometric and
chemical. Electronic effects include the degree of covalency of the metal-sulfur bond, the
orbital occupation of the HOMO, as well as the metal-sulfur bond strength [13] and
change with location of the metal on the periodic table [14]. When ruthenium disulfide is
used as the catalyst, the greatest HDS activity for the desulfurization of dibenzothiophene
occurs. The maximum activity of RuS2 suggests the metal-sulfur bond at the catalyst
surface is neither too strong nor too weak [15].
The metal d electronic configuration plays an important role here. The greater
availability of d electron density on the metal leads to higher activity. As the number of
electrons in the 2t2g level increases, the activity increases. The maximum catalytic
activity occurs for the transition metal sulfides when the maximum numbers of d
electrons are in the HOMO. Harris and Chianelli suggest that not only do the more active
catalysts have more electrons in the HOMO, but also the HOMO in this active catalysis is
the 2t2g level [13].
The catalytic activity of second and third row TMS (transition metals) is a product of
their metal sulfur bond strengths and their 4d or 5d electrons (Pauling percentage d
character) [13]. The second and third row transition metals have intermediate values of
heat of formation [16]. Intermediate heats of formation are important to HDS, if it is too
high, the substrate remains attached to the catalyst surface and the catalyst is poisoned; if
it is too low, the catalyst-sulfur interactions are weak and the substrate can be lost before
catalysis occurs [11].
Catalyst/support, catalyst/substrate, and catalyst/promoter ion interactions are three
approaches that can be taken in studying the HDS process. Among the large number of
new catalytic formulations reported in the literature, the non-supported ruthenium
sulfides were found to exhibit particularly remarkable properties for removing S from
dibenzothiophene during the HDS reaction [17–20]. Researchers have studied the HDS
reaction over ruthenium sulfide supported on various carriers such as alumina [21–24],
carbon [25–27], zeolites [28–32], MgF2 [33] and amorphous silica-alumina [34]. All of
these efforts improved the HDS ability of the ruthenium sulfide catalysts.
Due to their important industrial applications as catalysts for hydrodesulfurization
(HDS), hydrodenitrogenation (HDN) and aromatic hydrogenation (HN) in the presence
of sulfur impurities, transition metal sulfides have been widely studied. The screening of
the HDS and HN properties of various transition metal sulfides (TMS) has demonstrated
the prominent catalytic activity of RuS2. The pioneering paper of Pecoraro and Chianelli
describing the ‘‘volcano’’ curve activities of the transition metal sulfides (TMS) was the
starting point in the quest of new active phases [35]. Several TMS appeared as good new
candidates for active phases presenting either very high activities or specific selectivities.
The geometric factors that control the catalytic activity include surface area, crystallite
size, and pores size. By employing RuS2 at elevated temperatures in the presence of H2 at
high pressures, HDS process can achieve successful removal of sulfur. The mechanism
for this desulfurization is unknown. There is a slight correlation between surface area and
HDS activity, but other studies have shown correlations between catalytic activity and
parameters such as the type of support used, mode of preparation, calcinations and
pretreatment. Ruthenium disulfide shows the greatest HDS activity but is not used
commercially due to its extremely high cost [14, 36 - 38].
To better understand the interactions between substrates and catalyst during the HDS
process, model studies for the substrate/ catalyst interactions have been conducted [15,
36]. The hydrogenation properties of the conventional catalysts were enhanced by
addition of ruthenium sulfide supported on zeolite [35]. Thus ruthenium sulfide catalysts
provide a means to increase the formation of the hydrogenated intermediates which are
then easily transformed by conventional industrial catalysts. It was shown that the general
term ‘‘support effect’’ includes many different aspects, for example, modification of the
electronic properties or the morphology of the active phase or bifunctional reaction with
acid sites. All these effect, as well as developments in the synthesis of new supports have
been summarized [10, 39].
In the models developed to explain these large differences in activity, it has been
assumed that the hydrocarbon adsorption takes place on coordinatively unsaturated
cations. These vacancies would be formed by removal of superficial sulfur atoms in the
highly reducing conditions used for hydrotreatment reactions [40–42].
Harvey and Matheson [43] were the first to report that ruthenium sulfide in zeolites
was very active for the hydrogenation reactions. Zotin has extensively studied the
properties of ruthenium sulfide clusters encaged in various zeolites [44–46] and showed
the outstanding catalytic properties of this active phase when supported on dealuminated
acidic zeolites. These properties have been pointed to the beneficial influence of the
zeolite acidic framework on the properties of the active phase. The interest in using
zeolites is to stabilize nanoparticles of ruthenium sulfide. A high number of active sites
are obtained, the average particle size being roughly three to four times smaller than three
observed with conventional supports such as silica or alumina. Similarly to unsupported
ruthenium sulfide, a fully sulfur saturated catalyst was not active for hydrogen activation
and a reduction of the surface was required to achieve high catalytic activity.
The periodic trend in the hydrodesulfurization activity was proposed to be related
to the metal sulfur bond strength and the optimum HDS activity for RuS2 was assigned to
an optimum active site with sulfur containing reactant interaction for ruthenium [47]. One
other particularity of ruthenium is its ability to form metallic domains which is evidenced
by previous EXAFS studies, either during sulfidation, when H2 is present in the
sulfidation feed or during catalytic test [48, 49].
Due to the high temperature and pressure that are necessary for this process, direct
observation of the catalyst/substrate interaction is prohibited. Therefore, model
compounds have been created to represent these interactions [50].
Thiophene Compounds
Because thiophenes are the most difficult to desulfurize, their coordination
chemistry has been studied extensively. Also due to the ability of Ru+2 to bind weak
sulfur donor ligands, the coordination of thiophene to ruthenium metal centers has been
investigated. The higher HDS activity of Ru may facilitate the C-S bond cleavage in the
coordinated thiophene of these model compounds.
Understanding of the interactions of thiophene with transition metals requires
knowledge of the electronic structure of the heterocycle. There are six valence orbitals,
all of which primarily have p-orbital character. The symmetries of the π levels of
thiophene resemble those for cyclopentadienyl. The significantly higher basicity of the
latter is the major difference in the coordinating properties of thiophene and
cyclopentadienyl anion. For this reason benzene represents a superior model for
thiophene coordination, at least as it applies to η2, η4, and η5 thiophene complexes.
S-bound Thiophene Complexes
S-alkylation of thiophenes can only be effected with the most potent alkylating
agents such as the trialkyoxonium salts and methyl trifluoromethanesulfonate [51].
Qualitatively, it appears that the ease of S-alkylation follows the order thiophenes <
benzothiophenes < dibenzothiophenes. Gillespie presents the structure of the
thiopheneylide C4H4SC(CO2Me)2 in the paper as an example for S-alkylthiophenes.
Figure 1. Structure of the thiopheneylide C4H4SC(CO2Me)2 [52].
η1, S-Thiophene Complexes
A 1H NMR study of the reaction of CpRu(PPh3)2Cl and thiophene in the presence
of AgBF4 revealed a two step process. The first product was the S-bound thiophene
complex [CpRu(PPh3)2(η1-Thiophene)]+, a metastable species that converts on standing
to [CpRu(η5-Thiophene)]+. The η1 to η5 conversion is analogous to the corresponding
CpFe(CO)2C5H5Æ ferrocene. (ThiopheneCH2Cp)Ru(PPh3)2Cl is a nonelectrolyte with a
pendant, uncoordinated thienyl group. A yellow salt of [(ThiopheneCH2Cp)Ru(PPh3)2]+
is given from the treatment of this compound, (ThiopheneCH2Cp)Ru(PPh3)2Cl, with
AgBF4 which was the first structurally characterized complex containing S-bonded
thiophene. The Ru-S bond is robust in part because the methylene tether prevents the
formation of the η5 –thiophene complex.
Figure 2. Structure of [(ThiopheneCH2Cp)Ru(PPh3)2]+ (phenyl groups omitted), after
Draganjac et al. [53].
η1, S-Benzo- and Dibenzothiophene Complexes
Dichloromethane solutions of [CpFe(CO)2(isobutene)]BF4 react with benzothiophene and
dibenzothiophene to give thermally stable, crystalline adducts in high yield. An example
of η1, S-benzo- and dibenzothiophene complexes has been reported by Goodrich et al.
Figure 3. The structure of CpFe(CO)2(η1, S-DBT)+ [54].
Thiaporphyrin Complexes
Thiaporphyrins form an unusal series of complexes containing S-bound thiophene
ligands. One, two, and four of the nitrogen atoms in porphyrins can be replaced with
sulfur atoms, but only the coordination chemistry of the monothiaporphyrins has been
examined. The monoprotic N3S macrocycles are prepared by the condensation of 2,5di(carbinol)thiophenes with pyrrole and
benzaldehyde in propionic acid [55]. The
metallothiaporphyrinate twists from the planar structure characteristic of the free ligand,
being puckered at the metal-thiophene bond.
η5-Thiophene complexes and related derivatives
The discovery of stable π-arene complexes, dibenzenechromium, evolved naturally
into the study of related π complexes of thiophenes. In all cases π-thiophenes are more
kinetically labile than π-arene ligands although TMT (2,3,4,5-tetramethylthiophene) often
forms quite stable complexes. The first transition metal thiophene complex,
Cr(thiophene)(CO)3 is below,
Cr(CO)6 + C4H4S Æ Cr(η5-C4H4S)(CO)3 + 3CO
After the thermal reaction of thiophene and Cr(CO)6, Cr(T)(CO)3 was obtained in low
yield as red-orange, volatile crystals [56]. The dipole moments of Cr(T)(CO)3 and related
complexes have been described. It is a fact that its dipole moment is higher than that for
the corresponding benzene complex [57].
Setkina and coworkers found that Cr(T)(CO)3 readily deprotonates at the 2 and 5
positions of thiophene with butyl lithium. These workers mentioned that what they
propose to be Cr(2,5-Li2H2C4S)(CO)3 precipitates from ether at -50oC. These
intermediates were treated with Me3SiCl to give, depending on conditions, Cr(Me3Si)nH4nC4S)(CO)3,
where n = 1 or 2.
Figure 4. The structure of Cr(Me3Si)nH4-nC4S)(CO)3 [58].
A number of thiophene complexes are cationic replicas of ferrocene. This area of
research was opened by Braitsch and Kumarappan, who discovered the Friedel-Craftslike reaction of TMT, ferrous chloride, and AlCl3. The reaction formula is below,
FeCl2 + 2AlCl3 + 2C4Me4S Æ [Fe(η5-C4Me4S)2](AlCl4)2
The thiophene analogue of indenyl is thieno[b]cyclopentadienl. Volz et al. [59].
showed that two stereoisomers of Fe(η5-5-MeC7H4S)2 were given from the reaction of
the 5-methyl derivative of this anion with ferrous chloride. The cyclopentadienyl rings
are coordinated in these isomers.
Figure 5. Isomers of Fe(η5-5-MeC7H4S)2 [60].
π -Complexes of Benzo- and Dibenzothiophenes
Reduction of trans-[(CpRu)2(η6, η6-DBT)](PF6)2 with BHEt3- afforded a mixture of
trans-(CpRu)2(DBT) and trans-(CpRu)2(DBTH2). Both compounds give (CpRu)2(η6, η6DBT)2+ upon treatment with Ph3C+. The structure of (CpRu)2(DBTH2) shows that the Ruaren distances are elongated by 0.059 Å relative to [CpRu(BT)]BF4 but the Ru-Cp
distances are the same. The compound is diamagnetic and the DBT ligand is planar.
Figure 6. Structure of (CpRu)2(DBT) after Wang and Angelici [61].
η2- and η4-Thiophene complexes
Normally, η2-arene ligands are observed only for 16e- metal centers that are
exceptional π donors and which have only one coordination site available for ligand
binding. There are three ways that coordination to a 16e- metal fragment can occur in the
case of thiophene: η1-s-coordination, η2 coordination of any pair of adjacent carbon
atoms, and oxidative addition of the C-S bond [62].
η4-Thiophene complexes
The electrochemical reduction of [Cp*M(η5-C4R4S)]2+ occurs in two well-defined
steps for the cases of Ir(T) and Rh(TMT). While reduction of the iridium complex is
electrochemically irreversible, a cyclic voltametry study shows that [Cp*Rh(TMT)]2+ is
reversibly reduced at -250 and -350mV versus Ag/AgCl [63]. It is interesting that the
reductant does not lead to hydride addition to the thiophene ligand n contrast to the cases
for [Mn(C4R4S)(CO)3]+ and [CpRu(C4R4S)]+. Depending on the substituent on thiophene,
the products of this reaction are Cp*Ir(η4-C4R4S), Cp*Ir(η4-C4R4S·BH3), or the
metallacyclic species Cp*IrSC4R4 [62].
η 1, η4-Thiophene complexes
S-oxidation and S-alkylation lead to more diene-like reactivity for the heterocycle.
S-coordination should have a similar effect, an expectation met in the case of
Cp*Re(CO)2(η1, S-T). Under comparable conditions, Fe2(CO)9 does not react with
thiophenes. This finding points out that S-coordination diminishes the aromaticity of the
thiophene ligand. Complexation of the Fe(CO)3 to the diene strongly impacts on the
rhenium, lowering the frequencies of the νCO bands. This effect can be attributed to the
buckling of the heterocycle, which accompanies the addition of the iron group. The sulfur
center in the ligand (η4-T)Fe(CO)3 is a better σ donor than thiophene itself.
Thiophene from Metal Sulfides
The exclusive organic product, 2-phenylbenzothiophene (2-PhBT), is given from
pyrolysis of the Ni(S2C2Ph2)2 at 290oC. By heating a toluene solution of [Fe(S2C2Ph2)2]2
at 190oC in a sealed tube, 2-PhBT was also obtained. The reaction being balanced by the
formation of Fe2S2(S2C2Ph2)2. Schrauzer and Kish suggest that the 2PhBT arises via the
intermediacy of Ph2C2S2, a diphenylthiocarbene.
~300 C
Figure 7. The decomposition of Fe2S2(S2C2Ph2)2 [64, 65].
Ru-S Compounds
It is necessary to understand the coordination chemistry of organic thiols to a
CpRu(PPh3)2+ (Cp=η5-C5H5) fragment for better understanding of the interactions
between the organosulfur substrates and the catalyst in the HDS process. The proposed
binding modes of the thiophene to the metals utilize either sulfur bound (η1), π-bound
(η5), or bound through a thiophene double bond (η1). This binding possibly starts the
participation of the thiophene in reactions that lead to desulfurization [66].
Ruthenium-sulfur compounds have been prepared with a variety of sulfur ligands,
The effect of coordination on the S-H stretching frequencies in Ru-mercaptan
complexes is studied to determine possible shifts in the electron density about the sulfur
atom. This may be important step to the understanding of the cleavage of the C-S bond in
the HDS process.
The first reported Ru-mercaptan complex, [CpRu(PPh3)2(n-C3H7SH)]BF4, was
structurally characterized by X-ray diffraction techniques [67]. The complexes
[CpRu(PPh3)(ButNC)-(ButSH)]PF6 and [CpRu(dppm)( ButSH)]PF6 were reported. By
NH4PF6,yellow crystals of [CpRu(PPh3) (ButNC)(ButSH)]PF6 were obtained and were
also prepared by the reaction of dihydrogen cation complex [CpRu(PPh3) (ButNC)(η2H2)]PF6 with the thiol in dichloromethane. The synthesis of [CpRu(PPh3)(dtc)]
(dtc=dimethyldithiocarbamato) by the reaction of [CpRu(PPh3) (HSC3H7)]+ with sodium
dimethyldithiocarbamate in CH2Cl2 and its structure was reported by Cordes et al [68].
The electron-rich compound CpRu(PPh3)2SH has been reported and its chemistry was
studied [67]. Treatment of CpRu(PPh3)2Cl with excess NaSH in hot methanol solution
gives a good yield of CpRu(PPh3)2SH. Carbonylation of this compound yields
CpRu(PPh3)(CO)SH; protonation of this compound yields [CpRu(PPh3)2(SH2)+;
alkylation of the this compound gives [CpRu(PPh3)2(RSH)]+. The reaction of
CpRu(PPh3)2SH with sulfur forms the ruthenium polysulfides [CpRu(PPh3)]2Sx (X=4, 6)
Treatment of CpRu(PPh3)2Cl with NaSR (R=1-C3H7, or CHMe2) gives trimers, with
the formula [CpRuSR]3. All of the PPh3 ligands were lost in this reaction. The moderately
air-sensitive compound CpRu(PPh3)2SR easily loses PPh3 and shows a high degree of
nucleophilicity for the coordination sulfur atom. The compound CpRu(PPh3)(L)SR (R=1C3H7, CHMe2, 4-C6H4Me; L=PPh3, CO) is very easy to insert CS2 into the Ru-SR bond
of CpRu(PPh3)(L)SR to give the thioxanthate complex CpRu(PPh3)S2CSR [69].
Hidai reported the preparation and reaction and reactivites of a series of paramagnetic
diruthenium complexes [Cp*Ru(µ-SR)3RuCp*] (R=i-Pr, Et, cyclohexyl, Benzyl, Ph).
Koelle showed the dinuclear rutherium complexes Cp*Ru(µ-SR)3RuCp* (R= Et, Pr, Bu)
and the telated complex Cp*Ru(η1-C6F5)( µ-S)( µ-S C6F5) RuCp* react with polar alkynes
at room temperatures to give a vinyl thioether compound [70].
Activation of the C-S bond by the electrophilic ruthenium fragment Ru(η-C5Me5)+
was based on reactions of Ru(η-C5Me5)+ with saturated, sulfur-containing hydrocarbons,
such as cyclohexene sulfide, 1,3 or 1,4-dithiane. The C-S bond activation occurs easier
with 1,3-dithiane as compared to 1,4-dithiane. The reaction of Ru(η-C5Me5)+ with
cyclohexene sulfide, is the first report of H2S evolution upon desulfurization, was found
to form hydrogen sulfide and Ru(η-C5Me5)(η-C5Me5)+ [71]. The sulfur-donor ligand
tetrahydrothiophene reacts with the ruthenium (III) original complex [(Cp*RuCl2)n] by
electron transfer to give a diamagnetic complex [Cp*RuCl2(SC4H8)2]PF6, which is air and
[CpRu(PPh3)2(SC3H6)]CF3SO3, and determined the molecular and crystal structure of this
compound by X-ray analysis [72].
The first monodentate thiometallate complex [CpRu(PPh3)2]2MS4, was prepared from
the reaction of CpRu(PPh3)2otf and MS42- at 0oC (M= W, Mo). If heated to 40oC,
[CpRu(PPh3)]2MS4 will form by losing two PPh3 ligands from the compound
[CpRu(PPh3)2]2MS4 [73]. The tetrathiometallates have been used as ligands for transition
metals for a long time, because certain thiometallate complexes are structurally related to
catalytic sites in both nitrogen-fixing enzymes and industrial hydrotreating catalysts.
When the compound, (RCp)2Ru2(PPh3)2WS4, was treated with PMe3, both PPh3 were
substituted by PMe3 to give (RCp)2Ru2(PMe3)2WS4. Treatment of dichloromethane
solutions of these compounds with MeNC, tBuNC, or benzylisocyanide all resulted in
substitution at both ruthenium centers. If treated with an excess of CO, only one of the
PPh3 is substituted to give (RCp)2Ru2(PPh3)(CO)WS4. Complexes of (RCp)2Ru2L2MS4
(RCp)2Ru2(PPh3)(CO)WS4 is more difficult to oxidize than bis(triphenylphosphine)
compound (RCp)2Ru2(PPh3)2WS4 [74].
Thioamide compounds
The {[CpRu(PPh3)2]2(µ-dtoxa)}(BF4)2 and [CpRu(PPh3)(dtoxa-H2O)]BF4 complexe
are formed when [CpRu(PPh3)2]2(n-C3H7SH)BF4 reacts with a ten-fold excess of
dithioxamide(dtoxa) in CH2Cl2. The complex {[CpRu(PPh3)2]2(µ-dtoxa)}(BF4)2 was
prepared by the reaction of CpRu(PPh3)2Cl and dtoxa in a 1:2 = Ru:dtoxa ratio in the
presence of AgBF4 [75].
Ru-DMSO Complexes
The chemistry of halogen-dimethyl sulfoxide-ruthenium(II) complexes has been
extensively studied in recent years, and several derivatives have been structurally
characterized. In particular, cis-RuCl2(dmso)4 is a well-known and versatile starting
material for the synthesis of Ru-S derivatives [76].
Recently a nitroimidazole derivative of this complex has been reported to act as a
radiosensitizer. The promising results obtained with cis-RuCl2(dmso)4 prompted us to
undertake a systematic study of halogen-dimethyl sulfoxide-Ru(II) complexes.
Regardless the remarkable number of publications on this subject, it is not well
understood the chemistry of these complexes, and many synthetic as well as structural
aspects need further investigation. A comparative study of the chemical behavior of cis17
and trans-RuCl2(dmso)4 in aqueous solution and some foundation results on the
antitumor properties of cis and trans isomers are reported [77].
For cis-Ru(dmso)4Cl2, Cl is not expected to exert a greater trans influence than oxygen,
the observed lengthening is essentially due to steric effects that prevent a closer approach
of equatorial dimethyl sulfoxide molecules. Further indication of intramolecular steric
interactions is derived from the significant distortion of the S atoms from the tetrahedral
geometry, with an increase of the Ru-S-O (117o) and Ru-S-C (114o) angles and
consequent narrowing of the C-S-O (106o) and C-S-C (98o) bond angles.
Alessio found that trans-RuCl2(dmso)4 can be obtained from cis-RuCl2(dmso)4
through a photochemical isomerization in dimethyl sulfoxide solution at room
temperature. Trans-RuCl2(dmso)4 is thermodynamically unstable with respect to cisRuCl2(dmso)4. It slowly isomerizes in dimethyl sulfoxide solution with first-order
kinetics, as indicated spectrophotometrically. Therefore the following reaction can be
drawn for the two isomers:
cis-RuCl2(dmso)4 is currently used as a versatile starting material in the synthesis of
ruthenium(II) derivatives, and both cis-RuCl2(dmso)4 and trans-RuCl2(dmso)4 were
found to be good catalyst for the selective oxidation of alkyl sulfides to sulfoxides with
molecular oxygen [77].
Podmore reported that the complex RuCl2(dmso)4 usually in either toluene or ethanol,
commonly reacts with other ligands, L, according to the reaction:
RuCl2(dmso)4 + xL
RuCl2(dmso)yLx + 4-y DMSO
Figure 8. Reaction of RuCl2(dmso)4, L1=1,10-phenanthroline or 2,2’-bipyridyl;
L2=pyridine or 3-methylpyridine; L3=2-aminopyridine; L4=2-mercaptobenzthiazole [78].
With a ligand dissolved in an inert solvent only two of the DMSO molecules are
generally displaced. With chelating ligands, displacement of the more weakly held Obonded DMSO presumably occurs first, followed by displacement of a DMSO molecule
cis to it. Using triphenylphosphine, two DMSO molecules are lost, but the complex
RuCl2(PPh3)(dmso)2 is obtained. This has a normal molecular weight in chloroform at
room temperature and is hence pseudo six-co ordinate, with a ring hydrogen of one of the
phosphine groups presumably blocking the vacant octahedral position as in RuCl2(PPh3)3.
Sodium diethyldithiocarbamate yields the complex Ru(Et2NCS2)2(dmso)2 and 2mercaptobenzthiazole(mbth) yields the complex RuCl2(mbth)2(dmso)2. The IR of the
former complex indicates bidentate Et2NCS2- only. Both complexes exhibit only one
resonance in the NMR for the methyl protons of the co-ordinated DMSO. Bonding is
occurring through the sulfur, and it is showed from the positions of the resonances
downfield from free DMSO unambiguously. The one sharp resonance strongly implies
that the DMSO ligands are trans [78].
Landgrafe reported the preparation of the complex [Ru(MeCN)3([9]aneS3k3S)][CF3SO3]2
k3S)][CF3SO3]2 has been employed as a starting material for the synthesis of the mixedligand
trithiacyclononane,[9]aneS3, is to coordinate with transition metals in a facial manner as a
six-electron donor.
Figure 9. Half-sandwich ruthenium(II) complexes with six-electron ligands [79].
Figure 10. Structure of [Ru(MeCN)3([9]aneS3-k3S)][CF3SO3]2 [79].
Figure 11. Structure of [RuCl2(dmso) ([9]aneS3-k3S)] [79].
In recent publications Schroder [80] and co-workers have described the preparation
and properties of low-valent cations of the type [M(alkene)2([9]aneS3-k3S)]+ (M=Rh or Ir)
and have presented the first examples of half-sandwich complexes of [9]aneS3 with
In recent years Landgrafe and co-workers have reported the synthesis and structural
characterization of diastereoisomeric η5-pentamethylcyclopentadienyl and η6-arene
complexes of Group 8 and 9 transition metals (η5-C5Me5, M=CoIII, RhIII, IrIII or RuII, η6arene, M= RuII or OsII), which bear amino acids or peptides as ligands. Conventional
starting materials for these and other organometallic half-sandwich complexes are
mononuclear tris(acetonitrile) complexes such as [Ru(η6-C6H6)(MeCN)3]2+ or chlorobridged dinuclear complexes such as [{RuCl2(η6-arene)}2] [88].
Microwave Synthesis
Microwave synthesis has been applied in organic and inorganic synthesis fields for
many years [81, 82]. High temperature and pressure readily obtained in the reaction
vessels has made great rate enhancements and savings in reaction time. Using microwave
synthesis, a reagent’s polar property is necessary, which is a dipole interaction between
polar molecules. The interaction of electric field component of the microwaves with the
sample results in an exothermic reaction [81]. In Richard’s paper, their study also
mentioned that the low-boiling solvent was affected most dramatically in microwave
synthesis reaction. The lower boiling point the solvent has, the greater enhancement rate
will be achieved [82]. In order to increase the reaction rate in synthesis, microwave
synthesis will be a good choice, compare to the classical synthesis reaction.
Because of the rate enhancements in reaction time, the use of microwave synthesis to
prepare a series RuClx(dmso)y compounds will be studied. Understanding the syntheris
and thermal stability of a series of RuClx(dmso)y complexes will be of significant and
fundamental research for understanding the HDS process.
The Ru(dmso)xCly compound is a versatile starting material for many kinds of
Ru complexes [78]. The original literature preparations for Ru(dmso)xCly complexes
need quite some time to synthesize the products [76,77]. In order to improve the
synthesis of the Ru-DMSO complexes, it is necessary to find a better method or
approach to achieve the desired products. Microwave synthesis techniques have been
mentioned in some papers [81]. The microwave radiation interacts with the molecules
at a very fast rate, for a short time, heat is generated and the reaction rate is greater
than the bulk reaction mixture. The main goal is to investigate the possibility of
microwave reaction for using the Ru complex synthesis.
Experimental Section
Materials and methods
The starting material, RuCl3(H2O)3, dimethyl sulfoxide and ethanol were
from Aldrich. All reagents were used as purchased without further
purification. Agilent 8453 UV-Visible Spectroscopy system and a Midac IR 23
spectrophotometers were used for the analysis of the compounds. The microwave
synthesis was performed by using a CEM Discover microwave reactor.
Microwave synthesis of cis-Ru(dmso)4Cl2
For the microwave reaction, 0.10g (0.38 mmol) RuCl3 was added to 2 mL
DMSO in a microwave reaction tube under N2 or Ar and heated to 135 OC for 5 min.
The visible and infrared spectra matched those reported in the literature [76,77]. Upon
standing, a yellow precipitate formed and was isolated by filtration. The product was
washed with acetone and air dried, yield = 49%, mp = 210oC-213oC.
Microwave reaction of trans-[H(dmso)2][Ru(dmso)2Cl4]
Method A:
For the microwave reaction, 0.15g (0.57 mmol) RuCl3 was dissolved in 0.7 mL
DMSO with 0.1 mL 37% aqueous HCl, and the mixture was placed in the microwave
reactor and
heated to 80 °C for 2 min. A red-orange color solution was obtained and
red orange crystals of the product formed after some hours at room temperature,
washed with addition of 5 mL acetone; yield = 95 %, melting point = 120oC-125oC.
Method B:
A 0.10g (0.38 mmol) sample of RuCl3 was placed in the reaction tube with 2
mL ethanol, and heated mixture to 75 °C for 15 min, then 0.2 mL DMSO and 0.1 mL
24 37% aqueous HCl was added and continued heating to 75 °C for 3 min. The resulting
solution was red-orange in color, red crystals of the product was formed after some
hours at room temperature and were filtered off, vacuum dried after washed with
acetone , yield = 79%, mp = 120oC-125oC.
Method C:
The reaction was done by putting the four reagents, 0.10g (0.38 mmol)
RuCl3(H2O)3, 0.2 mL DMSO, 0.1 mL 37% aqueous HCl, and 2 mL ethanol together
and the mixture was heated to 75 °C for 18 min. After only 18 min reaction time,
the red-orange color formed. Red crystals of the product was formed after some hours
at room temperature and were filtered off, vacuum dried after washed with acetone,
yield = 67%, mp = 120oC-125oC.
The visible spectrum of the products from all three methods matched the
literature spectrum for trans-[H(dmso)2][Ru(dmso)2Cl4] [76].
Microwave synthesis of trans-(Ph4P)[Ru(dmso)2Cl4]
A 0.15g (0.57 mmol) sample of RuCl3(H2O)3 was dissolved in 0.7 mL DMSO
and 2 mL ethanol, and 0.215 g (0.57mmol) Ph4PCl (tetraphenylphosphonium chloride)
was added. The mixture was placed in the microwave reactor and heated to 100oC for
2 min. An orange precipitate formed after the reaction. The yield was 53%, melting
25 point was 200oC-210oC and the visible spectrum matched the values reported in the
literature [76].
Synthesis of mer-Ru(dmso)3Cl3
A 0.05g (0.1 mmol) sample of trans-Ru(dmso)4Cl2 and 0.018g (0.11 mmol)
AgNO3 were dissolved in 1 mL DMSO, and stirred at room temperature for 24 hours.
A red orange color precipite formed, 0.1 mL diethyl ether was added and the reaction
was placed in a refrigerator for 24 hours. The solid was filtered and a visible spectrum
was obtained. The visible spectrum matched the literature values [76].
Synthesis of trans-Ru(dmso)4Cl2
The photolysis reaction to synthesize trans-Ru(dmso)4Cl2 was performed
following the literature preparation [77]. A 0.5g (1 mmol) sample of
cis-Ru(dmso)4Cl2 was dissolved in 25 mL DMSO, and transferred into a photo reactor
equipped with a 450 W UV lamp. The reaction was irradiated for 4 hours. During the
reaction, the hood was closed and blocked out by aluminum foil on the window of the
hood to prevent exposure to UV radiation. Ethylene glycol was used as the cooling
agent and passed through a copper cooling coil. The trans-Ru(dmso)4Cl2 gradually
separated from the solution as a yellow solid, filtered and washed with 1.5 mL DMSO
and 15 mL acetone. The complex was dried at room temperature, yield = 39%,
26 melting point = 210oC-220oC. The visible spectrum of the product matched the
literature value [77].
Microwave synthesis of Ru(PPh3)3Cl2
Under N2, 0.036g (0.1 mmol) sample of RuCl3(H2O)3 was dissolved in 2 mL of
methanol, and 0.6 g (2.3 mmol) of triphenylphosphine was added. The reaction
temperature and time were 50 oC for 5 min, respectively. A brown solid precipitated
after reaction, was filtered, and was washed several times with diethyl ether to
eliminate excess triphenylphosphine. The yield was 91% and melting point was
Results and Discussion
For the cis-Ru(dmso)4Cl2 microwave reaction, the initial microwave reaction
was done at 150oC for 5 min and the solution had a brown-yellow color. The reaction
temperature was increased to 165oC for 5 min, but the solution color was brown. The
literature preparation [69] was performed at DMSO reflux temperature (189oC),
therefore, microwave reaction temperature was increased to 180o C for 5 min, but the
solution didn’t show a yellow colored solution but was dark brown. Extending the
27 heating time at 150oC temperature may give a totally yellow color solution; therefore,
the reaction was tried at 150oC for 10 min. The reaction gave yellow color solution.
A lower temperature could be an appropriate temperature to do the microwave
reaction with a shorter reaction time. The microwave reaction was tried at 135oC for
10 min; the solution gave a better clear yellow color solution. The reaction was also
tried at 135oC for 5 min to see if the reaction could have the same result, and the
solution did reveal the same pure yellow colored solution. Using a bigger stir bar, the
reaction only took 3 min to be completed. Lowering the temperature to 120oC for the
reaction, it took 20 min to get yellow solution. The reaction was also tried at 110oC
temperature for 10 min, but the solution was red color solution. After trial and error
for cis-Ru(dmso)4Cl2 microwave reaction temperature, the reaction can be completed
at 135oC temperature for 5 min; by using a bigger stir bar, the reaction only took 3
min at 135oC.
Following the literature preparation by Evans et al. [69], RuCl3(H2O)3 is
refluxed in dmso for 5 minutes, reduced to half volume, cooled and precipitated with
20 mL of acetone. The yield from literature preparation is 72%; the total reaction time
is approximately 3 hours. Using microwave synthesis technique, the product can be
obtained in only 5 min.
28 For the yield, one microwave reaction tube could have around 50% yield; this
was lower than the literature preparation.
To improve the yield, 9 reaction tube
solutions were put in a round bottom flask after completing the microwave reactions.
Without concentrating the mixed solutions, yellow crystals of the product were
formed and the yield was 88% and this yield was even higher than the literature
preparation yield. The higher concentration of cis-Ru(dmso)4Cl2 in the solution can
improve the yield and the precipitation could be formed faster as well.
Alessio et al. reported two ways to synthesize the trans-Ru(dmso)2Cl4- anion
[76]. The two methods are outlined below:
Method A, dissolved RuCl3 in 0.7 mL of DMSO and 0.1 mL 37% aqueous HCl.
The solution was heated to 80 °C and kept at this temperature for 20 min. Then the
solution was heated to 100 °C for 10 min. The trans-[H(dmso)2][Ru(dmso)2Cl4] is
precipitated with 3
mL of acetone. The yield was approximately 80%. The solution
color is red-orange color in the flask.
For method B, RuCl3 was refluxed in 10 mL ethanol for 3 hours, and then
reduced to 3 mL. After that, 0.1 mL 37% aqueous HCl and 0.2 mL DMSO were
added and heated to 80 °C. Acetone was added to flask to precipitate
29 trans-[H(dmso)2][Ru(dmso)2Cl4] complex. The literature preparation yield was about
80%. Using the same reagents, the reaction was done using the CEM microwave
reactor. The microwave reactions were faster.
trans-[H(dmso)2][Ru(dmso)2Cl4]. For the method A, the microwave reaction can have
the same red color solution with reaction temperature at 80oC for 2 min. For the
method B, the microwave reaction can have the same red color solution with reaction
temperature at 75oC for 18 min. For the method C, the microwave reaction can have
the same red color solution with reaction temperature at 75oC for 18 min as well.
Absorbance (AU)
Method A
Method B
Method C
Wavelength (nm)
Figure 12. Overlaid visible spectrum of three methods of
30 microwave reaction
In microwave synthesis of trans-(Ph4P)[Ru(dmso)2Cl4], the function of reagent,
tetraphenylphosphonium chloride (Ph4PCl) is two-fold. First, the Ph4PCl provides a
positive charge for the Ru-DMSO complex like the HCl in literature and second,
Ph4PCl acts as a Cl-
source. Two methods were used to synthesize
trans-(Ph4P)[Ru(dmso)2Cl4]. For the first method, tetraphenylphosphonium chloride
and RuCl3(H2O)3 were dissolved in DMSO. The reaction was heated at 80oC for 2
min, but there was no color change. Then the solution was heated to 90oC for 2 min,
but the solution’s color still had not changed to the red-orange color. Eventually, the
reaction temperature was increased to 100oC for 2 min, and the color of the solution
was red-orange with precipitation. After reaction time for 2 min at 100oC temperature,
an orange solid was formed and its spectrum in DMSO also matched the spectrum of
tetraphenylphosphonium chloride and RuCl3(H2O)3 were dissolved in a mixture of
DMSO and ethanol. After reaction time for 3 min at 75oC temperature, there were two
layers in the reaction tube. The top layer was red in color, the red solution was
separated and orange crystals formed after some hours at room temperature. The
orange crystals spectrum matched the spectrum of trans-[H(dmso)2][Ru(dmso)2Cl4].
31 The bottom layer was a brown colored precipitate. Comparing the two methods, the
first method’s yield was greater than second method because in the second method
only the top layer had the product. Therefore, the preferred synthesis for
trans-(Ph4P)[Ru(dmso)2Cl4] is the first method, which has less reaction time and gives
a greater yield.
In the literature preparation [77], the photolysis reaction was done using 150-W
UV lamp. In our synthesis process, the reaction was done using 450-W UV lamp
which generated a huge amount of heat during the reaction. The first attempt of the
reaction, the reaction did not use ethylene glycol cooling agent to cool the reaction.
After four hours of UV lamp illumination, the reaction mix was burned by the
UV-lamp. Therefore, the cooling system is necessary in order to avoid too much heat
to reaction. Ethylene glycol was passed through a copper coil tube which contained
the photo reactor. The cooling agent flowed through an ice bath. The reaction was not
successful because the reaction mixture was frozen by the cooling agent. The third
time, the reaction was done by adding dilute ethylene glycol in the cooling water.
32 Base
trans-[H(dmso)2][Ru(dmso)2Cl4] was reacted with AgBF3, forming Ru(dmso)3Cl3
plus AgCl. There was a problem isolating solid product from the reaction. The
trans-[H(dmso)2][Ru(dmso)2Cl4] into DMSO and adding AgNO3, the reaction was
stirred for two hours. After filtration, the filtrate was placed in the refrigerator for 24
hours. Before the filtrate was placed in the refrigerate, the visible spectrum still
showed mer-Ru(dmso)3Cl3. After the filtrate was removed from the refrigerator and
set at room temperature for a while, the visible spectrum was not mer-Ru(dmso)3Cl3
but the solution had converted back to trans-[H(dmso)2][Ru(dmso)2Cl4].
The reaction also was tried by microwave reaction. After the reaction was
heated at 50oC for 5 min, a pale gray solid was formed at the bottom of the reaction
tube. Filtration was performed to get the filtrate, which contained mer-Ru(dmso)3Cl3.
The problem was that the filtrate was quite a small amount. The yield was low and the
product was not completely dry. During the reaction, by adding AgNO3, the deep red
color solution was observed after trans-[H(dmso)2][Ru(dmso)2Cl4] and AgNO3 were
dissolved in DMSO. Perhaps the yield could be greater if the red solution was
separated from the mixture and concentrated dryness.
33 The
trans-[H(dmso)2][Ru(dmso)2Cl4], In the synthesis of mer-Ru(dmso)3Cl3 [67], the
reaction was tried as the same as trans-[H(dmso)2][Ru(dmso)2Cl4] synthesis reaction
temperature without adding acetone. In the RuCl3(H2O)3 was dissolved in DMSO and
the solution was placed in the round bottom flask on the heating pad to heat solution
at 80oC. The purpose of this experiment is to synthesize mer-Ru(dmso)3Cl3 by simply
heat mixture at 80oC for a period time. The solution was sampled every one hour and
did the visible spectrum test to see if there was any reaction occurred. After 12 hours,
the visible spectrum was different compared to first hour visible spectrum. The
reaction did occurred but the visible spectrum peaks didn’t match the literature peaks
for mer-Ru(dmso)3Cl3 complexes. Therefore, the microwave reaction was performed
for mer-Ru(dmso)3Cl3 synthesis. For the microwave reaction, the reagent, ethanol
was added in the test tube with RuCl3 and DMSO. The microwave reaction
temperature was set at 75oC and reaction times were raised: 5 min, 10 min, 15 min,
and 18 min respectively. The visible spectrum of the reaction using the 18 min
reaction time was almost the same as the visible spectrum of 12 hours reaction time
by heating at 80oC in the round flask. Using microwave synthesis technique, the
reaction time can be much faster from 12 hours to only 18 min.
34 Ru(PPh3)Cl2
A sample of RuCl3(H2O)3 was dissolved in of methanol, and triphenylphosphine was
added. The solution was heated under reflux for 4 hours. A brown solid was filtered
and washed several times with diethyl ether to eliminate the excess of
triphenylphosphine, the yield is 94% [83].
The microwave reaction was tried by using different amounts of PPh3 and
different reaction time to compare the yields. The three microwave reaction
conditions are shown in Table 1:
Time Solvent for wash
Triphenylphosphine (g)
Yield (%)
Table 1. Ru(PPh3)Cl2 compound’s yields with different reaction, solvent, and amount
of Triphenylphosphine.
35 From the table, the yield was less if the reaction time was short. The solution
was green, indicating Ru+3 in the solution. The amount of triphenylphosphine will
also influence the yield; the greater amount of triphenylphosphine will produce a
higher yield. The microwave reaction also was tried by changing the solvent for the
reaction. Methanol was replaced by benzene, and the reaction temperature increased
to 65oC because of the higher boiling point of benzene (80oC). This reaction was not
successful due to benzene’s non-polar property.
Microwave synthesis of [RuCl2(dmso)[9]aneS3-k3S] was tried in three ways.
All three ways had the same problem which was difficulty in concentrating the filtrate
down to dryness and the amount of filtrate was quite small. Those three solutions after
microwave reaction had the same color of the solution which was orange-yellow color.
The three reactions conditions are given in table 2.
36 Reaction
Temperature (co)
Time (min)
Color of solution
Table 2. [RuCl2(dmso)[9]aneS3-k3S] microwave reaction at different temperature and
reaction time.
The solutions had the same color compared to the product which has been done by
literature preparation [79] and it took 2 hours to reflux for the synthesis. According to
table 2, it only took 2 or 7 min to synthesize [RuCl2(dmso)[9]aneS3-k3S]. Microwave
synthesis technique can reduce the reaction significantly.
Instead of using the literature preparations for Ru-DMSO complexes,
microwave reaction can decrease reaction time and reaction temperatures compared
with classic preparation in the literature [79]. A look at table 3 (photolysis means
product was synthesized by photolysis) shows the yields of cis-Ru(dmso)4Cl2,
trans-[H(dmso)2]Ru(dmso)2Cl, and Ru(PPh3)3Cl2 comparable to yields reported in the
literature preparation. For cis-Ru(dmso)4Cl2, even a greater yield than the literature
preparation was observed when combining reactions. The melting points of products
37 were also close to literature values. Therefore, microwave synthesis is a better way to
synthesize Ru-DMSO complexes with lower energy require, less reaction time, and
lower reaction temperature.
38 Compounds
Microwave Reaction Literature Preparation
Melting Point
185oC decomp.
trans-[H(dmso)2][Ru(dmso)2Cl4] A
trans-[H(dmso)2][Ru(dmso)2Cl4] B
trans-[H(dmso)2][Ru(dmso)2Cl4] C
120oC decomp.
Not Applicable
165oC decomp.
trans-Ru(dmso)4Cl2 (photolysis)
Table 3. Yield and melting point comparison of Ruthenium compounds
39 145oC-152oC
RuCl3(H2O)3 is a suitable starting material for different inorganic chemistry
syntheses. Forti et al. used RuCl3(H2O)3 to synthesized the Ru0.3Ti0.3Sn0.4O2 complex
and looked at the decomposition process of the complex by using thermal gravimetric
analysis (TGA) [84]. SrRuO3 was also made from RuCl3(H2O)3 by Cao and
coworkers. Thermal gravimetric analysis revealed significant weight loss and
decomposition of organic compounds during the heating process [85]. Thermal
gravimetric analysis has been widely applied for the investigation of compounds
formation. In paper by Nunes, [Ru([14]aneS4)(4-FP)Cl]Cl has been examined by
thermal gravimetric analysis [86].
Studying the thermal properties of Ru(dmso)xCly compounds may help
understand the synthesis of Ru(dmso)xCly and improve Ru(dmso)xCly synthesis. Our
objective is to use TGA analysis to investigate the thermal properties and thermal
decomposition of Ru-DMSO complexes.
Experimental Section
A Seiko TG/DTA 320 instrument has been used for collecting data for thermal
gravimetric analysis. The heating process was controlled by the Exstar 6000 Thermal
Analysis & Rheology System computer program. The program was provided by RT
Instruments, Inc. distributor and made by Seiko Instruments, Inc. The reagent
RuCl3(H2O)3 was purchased from Aldrich Chemical Company, Inc, and the Ru-DMSO
complexes were synthesized as described in Chapter II. Each sample was heated from
room temperature to 800oC at the rate of 5oC/min and the heating process was under
either air, nitrogen or argon gas flow at 300 mL/min. Either alumina or copper pans were
used as sample and reference pans.
Results and Discussion
The mass loss curve differences were due to different structures of the Ru-DMSO
compounds. An exothermic or endothermic reaction could be observed in the Differential
Thermal Analysis (DTA). During the heating process, the compound gained energy or
released energy, which causes an exothermic or endothermic reaction. The complexes
that have been used for thermal analysis, most of their DTA plots showed endothermic
behavior when the mass loss was revealed. In order to compare the TGA analysis of
Ru(dmso)xCly compounds, RuCl3(H2O)3 was necessary to be examined and
analyzed by
TGA. During the RuCl3(H2O)3 TGA analysis, there was a very interesting discovery. A
sharp peak was revealed on the DTA analysis, and we also found some papers that have a
similar discovery [85]. The hydrated ruthenium trichloride showed a sharp peak on DTA
plot with copper pans but there was no sharp peak on DTA plot with alumina pans. This
41 revealed the hydrated ruthenium tri chloride reacted with the copper pans during the
heating process but not with alumina pans.
Figure 13 showed the mass loss curve of hydrated ruthenium trichloride with
copper pans under argon gas flow. There were three waters lost during the heating
process which correspond to 7.1%, 6.1% and 6.1% mass loss. The sharp peak on the
DTA curve was seen at 435oC and it also was close to the point that the whole ruthenium
trichloride decomposition started.
42 Figure 13. TGA curves for RuCl3 on Cu pans under Argon gas.
43 Therefore, a redox reaction had occurred, where Ru+3 was reduced to Ru and Cu was
oxidized to Cu+2 which reacted with chloride anion to form copper dichloride (CuCl2).
A look at the thermo chemical equation for the reaction of RuCl3 with copper at
standard state condition (25oC), 2RuCl3 + 3Cu Æ
3CuCl2 + 2Ru, a negative ΔH (-21.6
kcal/mol) was calculated. Though not at standard state conditions, the calculated
exothermic reaction matched the exothermic reaction on the DTA plot. Using
Kirchoff’s equation to calculate nonstandard state ΔH was not possible. No heat
capacity data is known for RuCl3. The black powder ash left in the copper pan should
be ruthenium which was formed from the reduction reaction.
In figure 14, the situation was similar when the hydrated ruthenium trichloride
was heated in an atmosphere of nitrogen gas; the water mass loss situation was similar
as well. The difference was the exothermic reaction temperature. The exothermic
reaction temperature in a nitrogen atmosphere occurred at a lower temperature
compared to the decomposition under argon gas.
The situation was more complicated when hydrated ruthenium trichloride was
heated in an atmosphere of air (figure 15). There were three exotherms revealed during
the heating process. TGA plots of hydrated ruthenium trichloride with alumina pans in
atmosphere of argon and nitrogen gas showed the similar result of water mass loss
during the heating process. Both figures 16 and 17 did not have a sharp peak around
425oC which was seen in the previous TGA plots. That indicated no reaction happened
during the process.
44 Figure 14. TGA curves for RuCl3 on Cu pans under Nitrogen gas.
45 Figure 15. TGA curves for RuCl3 on Cu pans under Air gas.
46 Figure 16. TGA curves for RuCl3 on Alumina pans under Argon gas.
47 Figure 17. TGA curves for RuCl3 on Alumina pans under Nitrogen gas.
48 In figure 18, silver chloride (AgCl) was examined for the reduction reaction
with copper pans. As shown in the DTA plot, there was an endothermic reaction during
the heating process. A look at thermal chemical equation for the reaction of AgCl with
copper at standard state condition (25oC), 2AgCl +
Cu Æ
CuCl2 + 2Ag, a positive
ΔH (11.52 kcal/mol) indicates an endothermic reaction. The ΔH of the silver chloride
thermal chemical equation at 430oC could be calculated by Kirchoff’s equation, ΔH (Tf)
= ΔH (Ti) + ΔCP (Tf-Ti). ΔCP values of AgCl, Cu, CuCl2 and Ag were calculated from
the tables in Rycerz et al. paper [90] by using the following equation, ΔCp = ΣCP(products)
- ΣCP(reactants). Therefore, ΔH at 430oC for 2AgCl + Cu Æ
CuCl2 + 2Ag is a positive
value (+42.23 kcal/mol) indicating an endothermic reaction which matched the
endothermic reaction, a sharp peak, in figure 18. Base on the calculation of ΔH at 430oC,
we can tell that there was an endothermic reaction and silver chloride reacted with
copper during the heating process. Examination of the sample pan showed Ag metal
deposited on the surface.
Figures 19 and 20 show the TGA curves of cis-Ru(dmso)4Cl2 on copper pans in
argon and nitrogen gas. In figure 19, the first onset temperature of cis-Ru(dmso)4Cl2
was 198oC which is closer to 210oC-213oC, which is melting point determined
experimentally than the melting point listed in literature paper (193oC) [78]. The first
mass loss, 7.96%, required energy from the heating process. This mass corresponds to
an acetone of solution. This could have been the result of washing the product with
acetone. The mass loss curve showed that two DMSOs came off next at 207oC with a
29.47% mass loss.
49 Figure 18. TGA curves for AgCl on Cu pans under Argon gas.
50 Figure 19. TGA curves for cis-Ru(dmso)4Cl2
51 on Cu pans under Argon gas.
Figure 20. TGA curves for cis-Ru(dmso)4Cl2
52 on Cu pans under Nitrogen gas.
At 207oC temperature, there was an endothermic peak occurring because
the two DMSOs required heat energy to break bonds and that was the reason to cause an
endothermic reaction. The other two DMSOs started to come off at 258oC and it also
had an endothermic reaction peak because of breaking bonds between DMSO and
ruthenium. The last two DMSOs mass loss were 31.41%. In figure 20, the mass loss
curve showed the similar situation like figure 19. Acetone came off first, then two
DMSOs second and the other two DMSOs came out at the end. The difference between
figure 19 and figure 20 was that endothermic reactions occurred at different
Figure 21 shows trans-Ru(dmso)4Cl2 TGA curves in an argon atmosphere.
first onset temperature is 149.9oC on the mass loss curve after 31.3 min into the heating
process. The melting temperature was lower than 165oC which was observed by eyes on
melting device. The trans-Ru(dmso)4Cl2 complex has lower melting temperature
compared to cis-Ru(dmso)4Cl2 compound because of the structure difference. The
cis-Ru(dmso)4Cl2 complex could provide a stronger structure and it takes more energy
to break bonds between DMSO and ruthenium. This trans structure, trans-Ru(dmso)4Cl2,
had only one DMSO came off after passed the first onset temperature and its mass loss
was 18.6%. The second DMSO came off at 195.7oC and its mass loss was 18.0%. After
two DMSOs came out, the other two DMSOs came out together at temperature around
276.5oC and a mass loss of 32.6%. The endothermic reactions were also revealed during
the mass loss stages, indicating energy is needed for breaking bonds between molecules.
The TGA plots of trans-[H(dmso)2][Ru(dmso)2Cl4] and trans-(Ph4P)[Ru(dmso)2Cl4]
are shown in Fig. 22 and 23, respectively. In figure 22, the sample showed mass loss
53 starting at the first onset temperature of 109.0oC. Calculation of the expected product
matched hydrogen chloride (HCl) coming off first and its mass loss was 8.02%.
In trans-[H(dmso)2][Ru(dmso)2Cl4]
complex, it has four DMSOs in itself,
therefore one DMSO came off first at 115.6oC just like trans-Ru(dmso)4Cl2. The first
DMSO mass loss was 14.20%. The second DMSO came off after first DMSO left and
its mass loss was 14.98%. The following DMSOs mass losses were 13.33% and 14.76%.
The first two DMSOs are located out of the coordination sphere of the octahedral
structure, so those two DMSOs came off at the lower first onset temperature compared
to trans-Ru(dmso)4Cl2.
There is a big temperature difference between where the first and last DMSOs
come off in the TGA plot of trans-[H(dmso)2][Ru(dmso)2Cl4]. The first DMSO came
off at 109.0oC and last DMSO came off at 245.7oC. It was 136.7oC difference and this
gap was larger than trans-Ru(dmso)4Cl2, which was 126.6oC and even greater than
cis-Ru(dmso)4Cl2 which was 87oC. The position of DMSO was inside of octahedral or
outside of octahedral structure influenced the onset temperature at certain levels. The
stronger structure like cis-Ru(dmso)4Cl2 provides a higher melting temperature.
Figure 23 showed trans-(Ph4P)[Ru(dmso)2Cl4] thermal decomposition, and it also
revealed the first onset temperature was 109.7oC which was almost the same onset
temperature as trans-[H(dmso)2][Ru(dmso)2Cl4] compound. Mass loss which was two
DMSOs coming out at 117.0oC; then the rest mass loss was triphenylphosphine (PPh3)
came from tetraphenylphosphonium group (Ph4P+). The first mass loss could be the
chlorobenzene (C6H5Cl) come off first. Following the initial mass loss was a 22.4%.
54 Figure 21. TGA curves for trans-Ru(dmso)4Cl2 on Cu pans under Argon gas.
55 Figure 22. TGA curves for trans-[H(dmso)2][Ru(dmso)2Cl4] on Cu pans under Argon gas.
56 Figure 23. TGA curves for trans-(Ph4P)[Ru(dmso)2Cl4] on Cu pans under Argon gas
57 At
trans-Ru(dmso)4Cl2 > trans-[H(dmso)2][Ru(dmso)2Cl4] = trans–(Ph4P)Ru(dmso)2Cl4.
No exothermic reaction was observed on the DTA plot for the trans-Ru(dmso)2Cl4anion.
Because ruthenium trichloride contains water molecules, water may be the
reason to cause the sharp peak. Therefore, trans-[H(dmso)2][Ru(dmso)2Cl4] was heated
to 300oC to remove all DMSOs, leaving only ruthenium trichloride on the copper pans.
After sample was cooled down to room temperature, a tiny drop of water was added to
the sample pan and the sample was heated to 800oC. On the DTA plot, there was no
sharp peak revealed. In this result, water was not the factor to cause the sharp peak for
the exothermic reaction when RuCl3(H2O)3 was heated on copper pans .
An exothermic reaction was revealed on RuCl3(H2O)3 DTA plots with copper
pans and no sharp peaks were found on RuCl3(H2O)3 DTA plots with alumina pans.
That result showed copper reacted with RuCl3(H2O)3 and it was an exothermic reaction
which also was a redox reaction. The reduction reaction of RuCl3(H2O) was more
complicated in atmosphere air situation. According to the table of standard reduction
potentials at 25oC, Ru would react with copper, and then silver would react with copper
as well. Therefore, AgCl was examined and the result showed an endothermic reaction.
For Ru-DMSO complexes, different structure provided different bond force
between metal and ligands. The cis-Ru(dmso)4Cl2 complex had stronger bond force
trans-[H(dmso)2][Ru(dmso)2Cl4] and trans-(Ph4P)[Ru(dmso)2Cl4]. In an atmosphere of
argon or nitrogen, the onset reaction temperature was slightly different for the same
58 cis-Ru(dmso)4Cl2. Mass loss curves showed the similar mass loss results of
cis-Ru(dmso)4Cl2 in argon and nitrogen gas flows. The mass loss situation was different
once Ru-DMSO complex structure changed from the cis- to trans-; trans-Ru(dmso)4Cl2
had the lower first onset reaction temperature and there were three stages of DMSO
mass loss. One DMSO was lost in first and second stages, respectively and two DMSOs
lost at the third stage.
Trans-[H(dmso)2][Ru(dmso)2Cl4] and trans-(Ph4P)[Ru(dmso)2Cl4] had the lowest
onset reaction temperature observed on DTA plots. Those complexes had H(dmso)+ and
Ph4P+ cation group outer sphere of the octahedral geometric structure, and the outer
sphere groups had a weaker bond force which caused lower onset reaction temperature.
trans-(Ph4P)[Ru(dmso)2Cl4]), four DMSOs came off gradually during the heating
process. Because the bond force was quite different between outer sphere of the
octahedral geometric structure and inner sphere of the octahedral geometric structure,
the onset reaction temperature difference between first and last DMSO came off from
trans-Ru(III) DMSO compounds was larger than Ru(II) DMSO compounds (cis- and
Trans influences could explain the interaction between ligand and metal between
onset reaction temperatures with cis- or trans- structures. Anderson et al. reported the
M-L bond has substantial M d- and relatively little M s- orbital character as in the d8, d6
and d0 cases, then the cis influence is small compared to the trans influence [88].
Therefore, trans influence could cause the trans–Ru(dmso)4Cl2 onset reaction
temperature was lower than cis-Ru(dmso)4Cl2. Trans influence is a thermodynamic
59 trend by which a strong ligand will arrange itself trans to a weaker ligand. Trans
influence is purely a thermodynamic phenomenon, ligands can influence the bond
distance of metal to ligand, the vibration frequency or force constant [89]. Bond lengths
are the most common measure of the trans influence; the longer bond lengths of Ru-Cl
could tell the trans influence of ligands (DMSO) is certainly stronger than other ligands
Figures 24, 25 and 26 showed the bond lengths with cis and trans structure,
DMSO ligand of trans–Ru(dmso)4Cl2 gave a longer distance of bond length of Ru-Cl
than trans-Ru(dmso)2Cl4-. The higher the trans influence the ligand is and the longer the
M-X bond is. Base on the bond lengths, DMSO was a stronger trans influence than Clligand. Because the trans influence, bond lengths were changed and onset reaction
temperature was influenced.
S 2.284
2.424 Cl
Figure 24. Bond distances in cis-Ru(dmso)4Cl2 [77].
60 H3C
Figure 25. Bond distances in trans–Ru(dmso)4Cl2 [77].
Figure 26. Bond distances in trans-Ru(dmso)2Cl4- [76]
The longer distance of bond length gave lower onset reaction temperature.
Therefore, cis-Ru(dmso)4Cl2 had the shortest bond length between Ru and DMSO
(2.134, 2.284, 2.274 and 2.245 Å in Figure 24) which had the highest onset reaction
temperature. The bond length (2.347 Å in Figure 25) of trans-[H(dmso)2][Ru(dmso)2Cl4]
was shorter than the bond length (2.352 Å in Figure 26) of trans–Ru(dmso)4Cl2, so the
61 onset
trans-[H(dmso)2][Ru(dmso)2Cl4] (which existed inner sphere of the octahedral) was
higher than the onset reaction temperature of the first DMSO of the length
In the conclusion, copper reacted with RuCl3(H2O)3 and the reaction was an
exothermic reaction which also was a redox reaction. AgCl was examined and the result
showed an endothermic reaction. For Ru-DMSO complexes, both cis- and transshowed DMSOs mass loss in TGA analysis plots. Trans-[H(dmso)2][Ru(dmso)2Cl4]
showed four clear stages for four DMSOs during the heating process. On the onset
reaction temperature comparison, cis-Ru(dmso)4Cl2 complex > trans-Ru(dmso)4Cl2 >
trans-[H(dmso)2][Ru(dmso)2Cl4] and trans-(Ph4P)[Ru(dmso)2Cl4], which was also
matched that shorter distance of bond length gave higher onset reaction temperature; the
distance of bond length between cis-Ru-DMSO complex is shorter than
trans-Ru-DMSO complex gave higher onset reaction temperature on cis-structure.
Trans influence could be the reason to cause the difference of distance of bond length
between cis-Ru-DMSO complex and trans-Ru-DMSO complex.
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