# Can ferrocene type sandwich compounds be made with fluorene?

Ferrocene will be well known to made members of this site. It consists of two cyclopentadienyl anions sandwiching an iron-II ion.

During my first year organic chemistry course (about 40 years ago) I remember a friend suggesting that the fluorene anion had a similar stability and it might be possible to make ferrocene type compounds with an iron-II ion sandwiched between two fluorene anions.

A group of us persuaded a sympathetic professor to let us have a go, and as I recall we prepared the anion by adding lithium aluminium hydride to solution of fluorene in ether cooled with dry ice then adding iron-II chloride. The iron chloride immediately went into solution, so some form of complex was formed, but we couldn't get much further as on warming to room temperature we got a hideous mess of many different products and we didn't have time to analyse it thoroughly.

So my question is whether these types of fluorene compound are known, or alternatively whether it is known that they cannot be prepared? I have attempted to Google this, but there is such a vast literature on ferrocene type compounds that I have not been able to find anything relevant.

• You mean sandwich compounds in general? They sure are. – Mithoron Apr 7 at 15:45
• I rather doubt you added LiAlH4 to a solution of flourene in acetone. The reaction between LiAlH4 and acetone is immediate and violent. Have you misremembered? – Waylander Apr 8 at 7:00
• @Waylander It was 40 years ago so I have quite possibly misremembered. Maybe the solvent was ether? – John Rennie Apr 8 at 7:57
• Ether is much more likely, or THF – Waylander Apr 8 at 9:12
• @Waylander the guy who set it up for us kept an eye on us to make sure we didn't harm ourselves or anyone else :-) – John Rennie Apr 8 at 9:14

• @JohnRennie What the image depicts is only a selection of the structure model, the ($\eta^5$-Cyclo­penta­dienyl)($\eta^6$-9H-fluorene)­iron(II) cation. There equally is a hexaphosphate anion, $\ce{PF6^-}$ in the model, too. If you access the publication as .html (journals.iucr.org/e/issues/2004/12/00/hg6105/index.html), the fourth button in the left hand column, just below «cif» opens an interactive 3D view (direct: publcif.iucr.org/cifmoldb/gui/cifjmol.php?cifid=hg6105) -- and this tetragonal bipyramide easily is seen. – Buttonwood Apr 7 at 19:22