Ruthenium(III) chloride

Ruthenium(III) chloride
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.139
RTECS number VM2650000
UNII
Properties
RuCl3·xH2O
Molar mass 207.43 g/mol
Melting point > 500 °C (932 °F; 773 K) (decomposes)
Soluble
+1998.0·10−6 cm3/mol
Structure
trigonal (RuCl3), hP8
P3c1, No. 158
octahedral
Hazards
Flash point Non-flammable
Related compounds
Other anions
 Ruthenium(III) bromide
Other cations
 Rhodium(III) chloride
Iron(III) chloride
Related compounds
 Ruthenium tetroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Ruthenium(III) chloride is the chemical compound with the formula RuCl3. "Ruthenium(III) chloride" more commonly refers to the hydrate RuCl3·xH2O. Both the anhydrous and hydrated species are dark brown or black solids. The hydrate, with a varying proportion of water of crystallization, often approximating to a trihydrate, is a commonly used starting material in ruthenium chemistry.

Preparation and properties

Anhydrous ruthenium(III) chloride is usually prepared by heating powdered ruthenium metal with chlorine. In the original synthesis, the chlorination was conducted in the presence of carbon monoxide, the product being carried by the gas stream and crystallising upon cooling.[1] Two allotropes of RuCl3 are known. The black α-form adopts the CrCl3-type structure with long Ru-Ru contacts of 346 pm. The dark brown metastable β-form crystallizes in a hexagonal cell; this form consists of infinite chains of face-sharing octahedra with Ru-Ru contacts of 283 pm, similar to the structure of zirconium trichloride. The β-form is irreversibly converted to the α-form at 450–600 °C. The β-form is diamagnetic, whereas α-RuCl3 is paramagnetic.[2]

RuCl3 vapour decomposes into the elements at high temperatures ; the enthalpy change at 750 °C (1020 K), ΔdissH1020 has been estimated as +240 kJ/mol.

Coordination chemistry of hydrated ruthenium trichloride

As the most commonly available ruthenium compound, RuCl3·xH2O is the precursor to many hundreds of chemical compounds. The noteworthy property of ruthenium complexes, chlorides and otherwise, is the existence of more than one oxidation state, several of which are kinetically inert. All second and third-row transition metals form exclusively low spin complexes, whereas ruthenium is special in the stability of adjacent oxidation states, especially Ru(II), Ru(III) (as in the parent RuCl3·xH2O) and Ru(IV).

Illustrative complexes derived from "ruthenium trichloride"

  • RuCl2(PPh3)3, a chocolate-colored, benzene-soluble species, which in turn is also a versatile starting material. It arises approximately as follows:[3]
2RuCl3·xH2O + 7 PPh3 → 2 RuCl2(PPh3)3 + OPPh3 + 5 H2O + 2 HCl
2 RuCl3·xH2O + 2 C6H8 → [RuCl2(C6H6)]2 + 6 H2O + 2 HCl + H2

The benzene ligand can be exchanged with other arenes such as hexamethylbenzene.[5]

  • Ru(bipy)3Cl2, an intensely luminescent salt with a long-lived excited state, arising as follows:[6]
RuCl3·xH2O + 3 bipy + 0.5 CH3CH2OH → [Ru(bipy)3]Cl2 + 3 H2O + 0.5 CH3CHO + HCl

This reaction proceeds via the intermediate cis-Ru(bipy)2Cl2.[6]

  • [RuCl2(C5Me5)]2, arising as follows:
2 RuCl3·xH2O + 2 C5Me5H → [RuCl2(C5Me5)]2 + 6 H2O + 2 HCl

[RuCl2(C5Me5)]2 can be further reduced to [RuCl(C5Me5)]4.

  • Ru(C5H7O2)3, a red, benzene-soluble coordination complex arising as follows:[7] RuCl3·xH2O + 3 C5H8O2 → Ru(C5H7O2)3 + 3 H2O + 3 HCl
  • RuO4, an orange CCl4-soluble oxidant with a tetrahedral structure, which is of some interest in organic synthesis.

Some of these compounds were utilized in the research related to two recent Nobel Prizes. Noyori was awarded the Nobel Prize in Chemistry in 2001 for the development of practical asymmetric hydrogenation catalysts based on ruthenium. Robert H. Grubbs was awarded the Nobel Prize in Chemistry in 2005 for the development of practical alkene metathesis catalysts based on ruthenium alkylidene derivatives.

Carbon monoxide derivatives

RuCl3(H2O)x reacts with carbon monoxide under mild conditions.[8] In contrast, iron chlorides do not react with CO. CO reduces the red-brown trichloride to yellowish Ru(II) species. Specifically, exposure of an ethanol solution of RuCl3(H2O)x to 1 atm of CO gives, depending on the specific conditions, [Ru2Cl4(CO)4], [Ru2Cl4(CO)4]2−, and [RuCl3(CO)3]−. Addition of ligands (L) to such solutions gives Ru-Cl-CO-L compounds (L = PR3). Reduction of these carbonylated solutions with Zn affords the orange triangular cluster [Ru3(CO)12].

3 RuCl3·xH2O + 4.5 Zn + 12 CO (high pressure) → Ru3(CO)12 + 3x H2O + 4.5 ZnCl2

Sources

  • Gmelins Handbuch der Anorganischen Chemie

References

  1. ↑ Remy, H.; Kühn, M. (1924). "Beiträge zur Chemie der Platinmetalle. V. Thermischer Abbau des Ruthentrichlorids und des Ruthendioxyds". Z. Anorg. Allg. Chem. 137 (1): 365–388. doi:10.1002/zaac.19241370127.
  2. ↑ Fletcher, J. M.; Gardner, W. E.; Fox, A. C.; Topping, G. (1967). "X-Ray, infrared, and magnetic studies of α- and β-ruthenium trichloride". Journal of the Chemical Society A: Inorganic, Physical, Theoretical: 1038. doi:10.1039/J19670001038.
  3. ↑ P. S. Hallman, T. A. Stephenson, G. Wilkinson "Tetrakis(Triphenylphosphine)Dichloro-Ruthenium(II) and Tris(Triphenylphosphine)-Dichlororuthenium(II)" Inorganic Syntheses, 1970 Volume 12, . doi:10.1002/9780470132432.ch40
  4. ↑ Bennett, Martin A.; Smith, Anthony K. (1974-01-01). "Arene ruthenium(II) complexes formed by dehydrogenation of cyclohexadienes with ruthenium(III) trichloride". Journal of the Chemical Society, Dalton Transactions (2). doi:10.1039/dt9740000233. ISSN 1364-5447.
  5. ↑ Bennett, M. A.; Huang, T. N.; Matheson, T. W. & Smith, A. K. (1982). "(η6-Hexamethylbenzene)ruthenium Complexes". Inorg. Synth. Inorganic Syntheses. 21: 74–8. doi:10.1002/9780470132524.ch16. ISBN 978-0-470-13252-4.
  6. 1 2 Broomhead, J. A.; Young, C. G. (1990). "Tris(2,2'-bipyridine)Ruthenium(II) Dichloride Hexahydrate". Inorganic Syntheses. Inorganic Syntheses. 28: 338–340. doi:10.1002/9780470132593.ch86. ISBN 9780470132593.
  7. ↑ Gupta, A. (2000). "Improved synthesis and reactivity of tris(acetylacetonato)ruthenium(III)". Indian Journal of Chemistry, Section A. 39A (4): 457. ISSN 0376-4710.
  8. ↑ Hill, A. F. (2000). ""Simple" Ruthenium Carbonyls of Ruthenium: New Avenues from the Hieber Base Reaction". Angew. Chem. Int. Ed. 39 (1): 130–134. doi:10.1002/(SICI)1521-3773(20000103)39:1<130::AID-ANIE130>3.0.CO;2-6. PMID 10649352.

Further reading

  • Carlsen, P. H. J.; Martin, Victor S.; et al. (1981). "A greatly improved procedure for ruthenium tetroxide catalyzed oxidations of organic compounds". J. Org. Chem. 46 (19): 3936. doi:10.1021/jo00332a045.
  • Gore, E. S. (1983). Platinum Met. Rev. 27: 111. Missing or empty |title= (help)
  • Cotton, S. A. "Chemistry of Precious Metals," Chapman and Hall (London): 1997. ISBN 0-7514-0413-6
  • Ikariya, T.; Murata, K.; Noyori, R. "Bifunctional Transition Metal-Based Molecular Catalysts for Asymmetric Syntheses" Organic Biomolecular Chemistry, 2006, volume 4, 393–406.
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