Structures of dimetallocenes M2(C5H5)2 (M = Zn, Cu, Ni, Co, Fe) and their perfluorinated derivatives

Abstract

The unexpected 2004 discovery of decamethyldizincocene suggested some new possibilities for organometallic compounds in which an M₂ unit is sandwiched between two planar carbocyclic rings. Density functional theory shows that the low-energy structures for the dizincocenes Zn₂(C₅X₅)₂ (X = H, F) are singlet coaxial structures having two (η⁵-C₅X₅)Zn units linked by a Zn–Zn single bond of length ∼2.3 Å. However, the low-energy M₂(C₅H₅)₂ (M = Cu, Ni, Co, Fe) structures have perpendicular configurations with bridging C₅H₅ ligands. They exhibit increasingly higher spin states from singlet (Cu, Ni) to triplet (Ni,Co), quintet (Co,Fe), and septet (Fe). The low-energy structures of the perfluorinated systems M₂(C₅F₅)₂ (M = Co, Fe) have irregular geometries with one bent bridging C₅F₅ ring and one planar terminal pentahapto η⁵-C₅F₅ ring, with the metal atom bearing the terminal η⁵-C₅F₅ ligand has the favored 18-electron configuration while the other metal atom has only a lower electron configuration and vacant coordination sites.