New Sandwich and Half-Sandwich Titanium Hydrazido Compounds

Abstract

New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2−) compounds were prepared by tert-butyl imide/N,N-disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(NtBu)Cl(py) (1) with Ph2NNH2 gave the terminal hydrazide Cp*Ti(NNPh2)Cl(py) (4), whereas the corresponding reaction of CpTi(NtBu)Cl(py) gave the dimer Cp2Ti2(μ-η1:η1-NNPh2)(μ-η2:η1-NNPh2)Cl2. Reaction of 1 with Me2NNH2 (1 equiv) also gave a dimer, Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8), while the reaction with 2 equiv of Me2NNH2 gave Cp*Ti(η2-NHNMe2)2Cl (7) containing two η2-bound hydrazide(1−) ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NHtBu)(η2-NHNMe2)Cl, observed by NMR spectroscopy. Reaction of 4 with LiNHNPh2 gave the mixed hydrazide(2−)/hydrazide(1−) derivative Cp*Ti(NNPh2)(NHNPh2)(py) (10). The corresponding reaction of 1 formed Cp*Ti(NtBu)(NHNPh2)(py), which rearranged to Cp*Ti(NHtBu)(NNPh2)(py). The titanocene derivative Cp2Ti(NNPh2)(py) (14) was prepared by reaction of Cp2Ti(NtBu)(py) (13) with Ph2NNH2, whereas the corresponding reaction with Me2NNH2 gave mixtures including CpTi(NHtBu)(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the Cp rings and on the imido N, in 14 this is the HOMO−1 and one of the Ti═Nα π-bonding MOs is the HOMO, destabilized by an Nα−Nβ antibonding interaction.