Synthesis and Characterization of Zr and Hf Triazenido Complexes with Rare Kappa 1N-Coordination Built Directly in the Coordination Sphere of the Metal

The synthesis and characterization of triazenido complexes of the group IV metals zirconium and hafnium is reported. The reaction of the group IV pentafulvene complexes Cp*(pi-15:o--11-pentafulvene)-zirconium(IV) and -hafnium(IV)chlorides with the sterically demanding 2,6-dimesitylphenyl azide results in the insertion of the gamma-nitrogen atom of the ligand precursor into the polarized M-Cexo (Cexo: exocyclic carbon atom) bond of the pentafulvene ligand, forming a formal Cp,N,N tridentate ligand system. The molecular structures of the furnished complexes reveal the rare kappa 1N coordination of the gamma-nitrogen atom to the zirconium or hafnium center along with a localized N alpha-N beta double bond. Unusually, in one case, the ligand system shows additional coordination of the alpha-nitrogen atom to the central metal atom and well-balanced N-N distances, thus, forming the chelating kappa 2N,N coordination mode of the triazenido ligand. The potential use of the formed complexes as precursors for cationic group IV cationic complexes was investigated by reaction with methyl lithium.