On the Coordination of Dinitrogen to Group 4 Metallocenes

A theoretical study on the basis of DFT calculations for complexes with the general formula [{MCp2}(2)N-2] (M = Ti, Zr, or Hf; Cp = cyclopentadienyl ligand) is presented. The relative stability of side-on and end-on isomers is determined for each metal atom. A survey of the electronic structure and molecular orbitals provides a simple interpretation of the chemical bonding within the M2N2 unit and reveals the factors that determine the choice of the coordination mode of dinitrogen to metallocenes. These results have been confirmed by vibrational calculations and topological analysis of the electron density together with a structural database study. The influence of the conformational changes on some molecular properties and their implications for the N-N bonding character will be discussed.