Ruthenium(III) acetylacetonate explained

Ruthenium(III) acetylacetonate is a coordination complex with the formula Ru(O2C5H7)3. O2C5H7− is the ligand called acetylacetonate. This compound exists as a dark violet solid that is soluble in most organic solvents.[1] It is used as a precursor to other compounds of ruthenium.

Preparation

In 1914 tris(acetylacetonato)ruthenium(III) was first prepared by the reaction of ruthenium(III) chloride and acetylacetone in the presence of potassium bicarbonate.[2] Since then, alternative synthetic routes have been examined, but the original procedure remains useful with minor variations:[3]

RuCl3•3H2O + MeCOCH2COMe → Ru(acac)3 + 3 HCl + 3 H2O

Structure and properties

This compound has idealized D3 symmetry. Six oxygen atoms surround the central ruthenium atom in an octahedral arrangement. The average Ru-O bond length in Ru(acac)3 is 2.00 Å. Because Ru(acac)3 is low spin, there is one unpaired d electron, causing this compound to be paramagnetic. Ru(acac)3 has a magnetic susceptibility, χM, of 3.032×10−6 cm3/mol with an effective magnetic moment, μeff, of 1.66 μB.[4] As a solution in dimethylformamide, the compound oxidizes at 0.593 and reduces at -1.223 V vs the ferrocene/ferrocenium couple.[5]

Reduction of Ru(acac)3 in the presence of alkenes affords the related diolefin complexes. Typically, such reactions are conducted with zinc amalgam in moist tetrahydrofuran:[6]

2 Ru(acac)3 + 4 alkene + Zn → 2 Ru(acac)2(alkene)2 + Zn(acac)2The resulting compounds are rare examples of metal-alkene complexes that reversibly sustain oxidation:

Ru(acac)2(alkene)2 [Ru(acac)<sub>2</sub>(alkene)<sub>2</sub>]+ + e−

The complex has been resolved into individual enantiomers by separation of its adduct with dibenzoyltartaric acid.[7]

Notes and References

  1. [Ram Charan Mehrotra|R. C. Mehrotra]
  2. Systematic chemical investigations: ruthenium, rhodium, palladium . Barbieri, G. A.. Atti Accad, Lincei . 1914. 23. 1 . 334–40.
  3. Improved synthesis and reactivity of tris(acetylacetonato)ruthenium(III). Gupta, A.. Indian Journal of Chemistry, Section A . 2000. 39A. 4. 457. 0376-4710.
  4. The absorption spectra and magnetic properties of the chelated compounds of Ru(III) with β-diketones . Grobelny, R.. Journal of Inorganic and Nuclear Chemistry. 1966. 28 . 11 . 2715–2718. 10.1016/0022-1902(66)80398-6.
  5. Alkyl Substituent Effects in the Redox Thermochemistry of Coordination Compounds: Oxidation and Reduction Energetics for Ruthenium Tris(β-diketonate) Complexes in Solution and the Gas Phase. Paul Sharpe . N. George Alameddin . David E. Richardson . Journal of the American Chemical Society. 1994. 116. 24. 11098–11108. 10.1021/ja00103a027.
  6. The fragment bis(acetylacetonato)ruthenium: a meeting-point of coordination and organometallic chemistry. Bennett, M. A.. Journal of Organometallic Chemistry. 2004. 689. 24. 4463. 10.1016/j.jorganchem.2004.07.027. Byrnes. Matthew J.. Kováčik. Ivan.
  7. Drake, A. F. . Gould, J. M. . Mason, S. F. . Rosini, C. . Woodley, F. J. . The optical resolution of tris(pentane-2,4-dionato)metal(III) complexes. Polyhedron. 1983. 2. 6. 537–538. 10.1016/S0277-5387(00)87108-9.

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