The synthesis of the first carbon-free inorganic sandwich compound [Os(η5-B5H10)2] (an osmium ion sandwiched between two boron rings), is a fundamental advancement in chemistry. This was sought by chemists for seven decades since discovery of ferrocene Fe(C5H5)2.
Ferrocene Fe(C5H5)2 is an iconic organometallic compound. It was discovered in 1951. It has a symmetrical sandwich structure where a central iron atom (Fe2+) is bound between two planar cyclopentadienyl (C5H5–) rings through delocalised π electrons resulting in a stable 18-electron configuration.
Unravelling of this molecular structure based on a new way of chemical bonding between metals and flat organic rings through delocalised π-electrons above and below the rings yielding stable sandwich compounds was a milestone in chemistry. It contributed to the understanding of chemical interaction of metals with organic molecules and led to the beginning of a new field of organometallic chemistry. Many such sandwich compounds have been developed since the discovery of ferrocene that have found wide ranging industrial applications as catalysts and in the electrochemical sector.
Chemists had wondered whether inorganic non-carbon rings would give rise to a stable sandwich compound like ferrocene. They sought to synthesise a stable ferrocene analog with inorganic rings for the last seven decades. Finally, successful synthesis of a stable carbon-free sandwich compound has been reported on 23 April 2026.
The new carbon-free sandwich compound is [Os(η5-B5H10)2] which is an osmium ion sandwiched between two boron rings. It is qualitatively similar to ferrocene Fe(C5H5)2 in structure and bonding however, the metal-ring bonding is much stronger in the new sandwich compound.
This synthesis of the first carbon-free inorganic sandwich compound is a fundamental advancement in chemistry because it expands the concept beyond organometallic to inorganometallic. A new field of inorganometallic chemistry thus begins.
***
References:
- Heinze K. and Lang H. , 2013. Ferrocene—Beauty and Function. Organometallics. Vol 32/Issue 20 DOI: https://doi.org/10.1021/om400962w
- Mohapatra et al. 2026. [Os(η5-B5H10)2]: A carbon-free analog of ferrocene. Science. 23 April 2026. Vol 392, Issue 6796 pp. 411-414. DOI: https://doi.org/10.1126/science.aed9192
***
2] (an osmium ion sandwiched between two boron rings) is a fundamental advancement in chemistry. This was sought by chemists for seven decades since discovery of Ferrocene Fe(C5H5)2.){kind=link}