Theoretical Prediction on [5]Radialene Sandwich Complexes (CpM)2(C10H10) (Cp = η5-C5H5; M = Fe, Co, Ni): Geometry, Spin States, and Bonding

[5]Radialene, the missing link for synthesis of radialene family, has been finally obtained via the preparation and decomplexation of the [5]radialene–bis-Fe(CO)3 complex. The stability of [5]radialene complex benefits from the coordination with Fe(CO)3 by losing free 1,3-butadiene structures to avoid polymerization. In light of the similar coordination ability of half-sandwiches CpM(Cp = η5-C5H5; M = Fe, Co, Ni), there is a great possibility that the sandwiched complexes of [5]radialene with CpM are available. Herein, we present the first theoretical prediction on the geometry, spin states and bonding of (CpM)(C10H10) and (CpM)2(C10H10). For M = Fe, Co, Ni, the ground states of (CpM)(C10H10) and (CpM)2(C10H10) are doublet and triplet, singlet and singlet, and doublet and triplet states, where each Fe, Co, and Ni adopts 17, 18, and 19 electron-configuration, respectively. In particular, (CpFe)2(C10H10) and (CpNi)2(C10H10) have considerable open-shell singlet features. Generally the trans isomers of (CpM)2...