Henry Rzepa's Blog

Sometimes, the properties of a molecule are predicted long before it is synthesised. One such is diberyllocene. I first encountered a related molecule, beryllocene itself, many moons ago.[1] This was unusual because unlike the original metallocenes, the metal atom was not symmetrically disposed between the two cyclopentadienyl faces. Now diberyllocene is finally reported in which replacing one Be by Be-Be induces (according to calculation, D₂) symmetry[2]. I will not repeat the excellent analysis of the wavefunction reported in this article, but confine myself to showing two molecular orbitals which examplify its bonding.

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References

1. M.J.S. Dewar, and H.S. Rzepa, "Ground states of molecules. 45. MNDO results for molecules containing beryllium", Journal of the American Chemical Society, vol. 100, pp. 777-784, 1978. http://dx.doi.org/10.1021/ja00471a020
2. J.T. Boronski, A.E. Crumpton, L.L. Wales, and S. Aldridge, "Diberyllocene, a stable compound of Be(I) with a Be–Be bond", Science, vol. 380, pp. 1147-1149, 2023. http://dx.doi.org/10.1126/science.adh4419

This is a venerable organic reaction, which curiously I have not previously covered here. First described in 1859, its nature was only properly elucidated in 1873. It is a member of a class of reaction I have previously named “solvolytically assisted pericyclic”, or “perisolvolytic“. Here I explore some of the subtle stereoelectronic effects observed for this apparently simple reaction.

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