[Os(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)<sub>2</sub>]: A carbon-free analog of ferrocene.

Mohapatra, Stutee; Saha, Suvam; Joshi, Gaurav; Gupta, Urvashi; Patel, Deepak Kumar; Jemmis, Eluvathingal D; Ghosh, Sundargopal · Science · 2026

basic_science · Level V

Where this comes from

Abstract

The synthesis of a carbon-free analog of ferrocene has been a long-standing goal in inorganic chemistry. We report here the preparation and crystallographic characterization of the carbon-free sandwich complex [Os(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)<sub>2</sub>], which is qualitatively similar to ferrocene in structure and bonding. The metal-ring bonding is much stronger in [Os(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)<sub>2</sub>], owing to rehybridization of the π molecular orbitals brought in by the bridging B-H-B hydrogens and the bent B-H<sub>t</sub> bonds of the larger B<sub>5</sub>H<sub>10</sub> ring (where B-H<sub>t</sub> is the terminal B-H bond). This also leads to an unusually short ring-ring separation of 3.071 angstroms and a staggered conformation. The isomeric [Os(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)(η<sup>3</sup>-B<sub>5</sub>H<sub>10</sub>)], which features a coordination mode unknown for ferrocene, has also been isolated. A similar attempt for [Ru(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)<sub>2</sub>] resulted only in [Ru(η<sup>5</sup>-B<sub>5</sub>H<sub>10</sub>)(η<sup>3</sup>-B<sub>5</sub>H<sub>10</sub>)].