Ruthenocene Explained

Ruthenocene is an organoruthenium compound with the formula (C₅H₅)₂Ru. This pale yellow, volatile solid is classified as a sandwich compound and more specifically, as a metallocene.

Structure and bonding

Ruthenocene consists of a ruthenium ion sandwiched in between two cyclopentadienyl rings. It features ruthenium centre bound symmetrically to the planes of two cyclopentadienyl rings. It is closely related to the isoelectronic ferrocene.

In contrast to ferrocene, wherein the cyclopentadienyl rings are in a staggered conformation, those of ruthenocene crystallise with an eclipsed conformation. This difference is due to the larger ionic radius of ruthenium, which increases the distance between the cyclopentadienyl rings, decreasing steric interactions and allowing an eclipsed conformation to prevail. In solution, these rings rotate with a very low barrier.

Preparation

Ruthenocene was first synthesized in 1952 by Geoffrey Wilkinson, a Nobel laureate who had collaborated in assigning the structure of ferrocene only a year earlier.^[1] Originally, ruthenocene was prepared by the reaction of ruthenium trisacetylacetonate with excess of cyclopentadienylmagnesium bromide.^[1]

Ru(acac)₃ + C₅H₅MgBr → Ru(C₅H₅)₂ + 3 "acacMgBr" + "C₅H₅"

Ruthenocene may also be prepared by the reaction of sodium cyclopentadienide with "ruthenium dichloride" prepared in situ by reduction of ruthenium trichloride.^{[2] [3]}

Chemical properties

Ruthenocene typically oxidises via two electron change, instead of one.^[4] With weakly coordinating anions as electrolyte, the oxidation proceeds via a 1e step.^[5]

Ruthenocene has been investigated as a photoinitiator for polymerization reactions.^[6]

Notes and References

1. Wilkinson, G. . 1952 . The Preparation and Some Properties of Ruthenocene and Ruthenicinium Salts . . 74 . 6146–6147 . 10.1021/ja01143a538 . 23.
2. Bublitz, D. E; McEwen, W. E.; Kleinberg, J. . 1961 . Ruthenocene . 41 . 96 . Organic Syntheses. 10.15227/orgsyn.041.0096.
3. 10.1021/acs.jchemed.2c01258. The Synthesis of Ruthenocene─A Methodology Appropriate for the Inorganic Undergraduate Curriculum . 2023 . Harrypersad . Shane . Canal . John P. . Journal of Chemical Education . 100 . 3 . 1320–1325 . 2023JChEd.100.1320H . 257322557.
4. Smith, T. P . Taube, H. . Bino, A. . Cohen, S. . 1984 . Reactivity of Haloruthenocene(IV) complexes . . 23 . 1943 . 10.1021/ic00181a030 . 13.
5. Geiger, W. E. and Barrière, F., "Organometallic Electrochemistry Based on Electrolytes Containing Coordinating Fluoroarylborate Anions", Accounts of Chemical Research, 2010. .
6. Cynthia T. Sanderson, Bentley J. Palmer, Alan Morgan, Michael Murphy, Richard A. Dluhy, Todd Mize, I. Jonathan Amster, and Charles Kutal "Classical Metallocenes as Photoinitiators for the Anionic Polymerization of an Alkyl 2-Cyanoacrylate" Macromolecules 2002, volume 35, pp. 9648-9652.