Aromaticity in Octahedral Cyclopentadienylberyllium Transition Metal Clusters

High‐spin overall spherical (CpBe) 6 M structures having octahedral coordination of the central metal atom are predicted for the five metals (M = Mn, Fe, Co, Ni, Cu). Among these five complexes, the singlet spin state (CpBe) 6 Ni has a closed‐shell 52‐electron 1S 2 1P 6 1D 10 2S 2 1F 14 1G 18 configuration, suggesting aromaticity based on the jellium model. The remarkably high +6 apparent formal oxidation states of the central metal atom in these structures are stabilized by electron donation from filled π‐orbitals of the σ + 2π Cp≡Be metal‐ring triple bond into empty transition metal d orbitals. This process can be viewed as the reverse of the stabilization of low transition metal oxidation states in metal carbonyls such as Cr(CO) 6 by back‐donation of electrons from filled metal d orbitals into CO antibonding orbitals. The predicted low‐energy (CpBe) 6 M structures for Cr and V have the six CpBe units joined to form two uninegative trihapto Cp 3 Be 3 ligands, leading to high‐spin formal +2 central metal oxidation states.