Science & Technology (Commonwealth Union) – The discovery of ferrocene was what contributed to Otto Fischer and Geoffrey Wilkinson receiving the Nobel prize in 1973, moving a significant step forward in the field of chemistry.
When an iron (Fe) atom is “sandwiched” between two rings made of carbon and hydrogen – (C5H5)Fe(C5H5). This discovery transformed the field of transition metal chemistry and made ferrocene a key tool in catalysis, materials science, biology, and medicine. For decades, researchers have wondered if a similar sandwich structure could exist without carbon, using boron instead. Proving this would show that these intricate molecular shapes aren’t limited to carbon-based chemistry.
A new study published in Science reports that researchers at the Indian Institute of Technology Madras (IITM) and Indian Institute of Science (IISc) have successfully made a carbon-free boron version of ferrocene for the first time. The team connected rings of boron and hydrogen with osmium (Os), a metal related to iron. The resulting molecule, ((B5H10)Os(B5H10)), mimics the classic ferrocene sandwich. Interestingly, the bond that holds the boron rings to the osmium is even stronger than the original iron-carbon bond. This is because the hydrogen atoms of the boron rings (B-H and BHB) are positioned in a way that allows them to bind to the metals more strongly than the carbon rings can.
This finding demonstrates that boron can mimic carbon’s capacity to form stable rings and complex molecular structures. “Knowing these bonding patterns could open up avenues to new materials in the future.”
Scientists, including Eluvathingal D Jemmis, National Science Chair at IISc, have for years been exploring if carbon rings in ferrocene can be replaced by B–1, a boron-based ion that has the same number of electrons as carbon.
Jemmis has collaborated with Sundargopal Ghosh, a professor at IITM, for over 15 years, studying ways to stabilize boron clusters with metals. Using insights from orbital engineering, their teams identified ((B5H10)Os(B5H10)) as a promising target, and Ghosh’s students were able to successfully create it in the laboratory.
To create the compound, the researchers employed a chemical method known as thermolysis, heating an osmium precursor together with a boron-hydrogen source at 100°C. After this process, they were able to isolate the new substance as a colourless solid. Through X-ray crystallography and NMR spectroscopy, the team confirmed that they had successfully constructed the “sandwich” structure.
Ghosh of IIT Madras, one of the corresponding authors pointed out that just as ferrocene launched a new chapter in organometallic chemistry, these findings mark the beginning of a new era in inorganometallic chemistry and are likely to appear in future inorganic chemistry textbook, they are now investigating the reactions of these novel compounds.
In this new arrangement, the osmium atom is positioned between the two planar boron rings. These rings are closer together than in the carbon-based counterpart, and the bonding is stronger. During the synthesis, the researchers also identified an alternative version of the molecule (an isomer) where one of the rings is attached in a previously unseen configuration. This discovery demonstrates that boron atoms can form connections with metals in ways that carbon cannot.
“With the renaissance in the 2D chemistry of boron during the last decade – with borophenes, bilayer borophenes, and multilayer borophenes on the horizon – the possibility of metal sandwiched/intercalated bilayers and multilayers will be a reality soon,” explained Jemmis, who is a corresponding author. Researchers of the study pointed out that the materials could possibly rival graphene in a lot of applications.
The findings mark a significant stepping stone for the field of inorganic chemistry, as this knowledge gives researchers greater insights.
