Pentamethylcyclopentadienyl ruthenium dichloride dimer explained

Pentamethylcyclopentadienyl ruthenium dichloride is an organoruthenium chemistry with the formula [(C₅(CH₃)₅)RuCl₂]₂, commonly abbreviated [Cp*RuCl₂]₂. This brown paramagnetic solid is a reagent in organometallic chemistry. It is an unusual example of a compound that exists as isomers that differ in the intermetallic separation, a difference that is manifested in a number of physical properties.

Preparation, structure, reactions

The compound has C_2h symmetry, with each metal atom having pseudo-octahedral geometry. In the crystal structure, two isomers are observed in the unit cell, one with a 2.93 Å ruthenium–ruthenium bond and the other with a long internuclear distance of 3.75 Å. The former isomer is diamagnetic, and the latter is magnetic.^{[1] [2]}

It is prepared by the reaction of hydrated ruthenium trichloride with pentamethylcyclopentadiene.^[3]

2 Cp*H + 2 RuCl₃·3H₂O → [Cp*RuCl₂]₂ + 2 HCl + 6 H₂OThe reaction is accompanied by formation of decamethylruthenocene.

Pentamethylcyclopentadienyl ruthenium dichloride can reduced to the diamagnetic tetramer of Ru(II):

2 [Cp*RuCl₂]₂ + 2 Zn → [Cp*RuCl]₄ + 2 ZnCl₂

Methoxide also can be used to produce a related diruthenium(II) derivative, which is also diamagnetic:

[Cp*RuCl₂]₂ + 3 NaOCH₃ + HOCH₃ → [Cp*RuOCH₃]₂] + 3 NaCl + CH₂O + HClTreating the tetramer with 1,5-cyclooctadiene in etheral solvent gives the mononuclear complex chloro(1,5-cyclooctadiene)(pentamethylcyclopentadienyl)ruthenium(II).^{[4] [5]}

0.25 [Cp*RuCl]₄ + 1,5-cyclooctadiene → Cp*RuCl(1,5-cyclooctadiene)Compounds like Cp*RuCl(1,5-cyclooctadiene), the tetramer [Cp*RuCl]₄, and related diamagnetic Cp*Ru(III) complexes have been investigated as hydrogenation catalysts.^[6]

See also

• (Cymene)ruthenium dichloride dimer - [(cymene)RuCl₂]₂
• Pentamethylcyclopentadienyl iridium dichloride dimer - [Cp*IrCl₂]₂

References

1. McGrady . John E.. [(Cp*RuCl)₂(μ-Cl)₂]

   bond-stretch or spin-state isomerism?

   . Angewandte Chemie International Edition. 2000. 39. 17. 3077–3079. 10.1002/1521-3773(20000901)39:17<3077::AID-ANIE3077>3.0.CO;2-B. 11028037.
2. Dichloro(pentamethylcyclopentadienyl)ruthenium—Novel Dichotomy in a Molecular Structure . Urich . Kölle . Janusz . Kossakowski . Norbert . Klaff . Lars . Wesemann . Ulli . Englert . Gerhard E. . Herberich . Angew. Chem. Int. Ed. Engl. . 30 . 6 . 1991 . 690–691 . 10.1002/anie.199106901 .
3. Book: Di-μ-Chloro-Bis[(η5-Pentamethylcyclopentadienyl) Chlororuthenium(III)], [Cp*RuCl₂]₂ and Di-μ-methoxo-Bis(η5-Pentamethylcyclopentadienyl)diruthenium(II), [Cp*RuOMe]₂. Urich. Kölle. Janusz. Kossakowski. Di-μ-Chloro-Bis[(η5 -Pentamethylcyclopentadienyl) Chlororuthenium(III)], [Cp* RuCl2 ]2 and Di-μ-methoxo-Bis(η5 -Pentamethylcyclopentadienyl)diruthenium(II), [Cp* RuOMe]2 . Inorganic Syntheses. 1992. 29. 225–228. 10.1002/9780470132609.ch52. 9780470132609 .
4. Koelle . Ulrigh . Kossakowski . Janusz . May 1989 . Pentamethylcyclopentadienylruthenium complexes . Journal of Organometallic Chemistry . 362 . 3 . 383–398 . 10.1016/0022-328x(89)87260-2 . 0022-328X.
5. Fagan . Paul J. . Mahoney . Wayne S. . Calabrese . Joseph C. . Williams . Ian D. . June 1990 . Structure and chemistry of the complex tetrakis(.eta.5-pentamethylcyclopentadienyl)tetrakis(.mu.3-chloro)tetraruthenium(II): a useful precursor to (pentamethylcyclopentadienyl)ruthenium(0), -(II), and -(IV) complexes . Organometallics . en . 9 . 6 . 1843–1852 . 10.1021/om00156a025 . 0276-7333.
6. Fürstner . Alois . 2019-01-09 . trans -Hydrogenation, gem -Hydrogenation, and trans -Hydrometalation of Alkynes: An Interim Report on an Unorthodox Reactivity Paradigm . Journal of the American Chemical Society . en . 141 . 1 . 11–24 . 10.1021/jacs.8b09782 . 30422659 . 53303730 . 0002-7863.