Bis(cyclopentadienyl) Titanium Dinitrogen Chemistry: Synthesis and Characterization of a Side-on Bound Haptomer

The titanocene dinitrogen complex [(η5-C5H2-1,2,4-Me3)2Ti]2(μ2,η2,η2-N2) (1-N2) has been prepared both by dihydrogen reductive elimination from the in situ generated monohydride derivative and by alkali metal reduction of the corresponding monoiodide. In the solid state, 1-N2 contains a side-on bound N2 ligand with an N−N bond length of 1.216(3) Å, consistent with a significant contribution from a two-electron-reduced diazenido ([N2]2-) fragment. Attempts to maintain side-on coordination of the N2 ligand but increase the wedge dihedral by introducing isopropyl or tert-butyl substituents induced a change in hapticity to end-on and a less activated bridging dinitrogen ligand. The ansa-titanocene dinitrogen complexes rac-[Me2Si(η5-C5H2-2-SiMe3-4-tBu)2Ti]2(μ2,η1,η1-N2) (4-N2) and [Me2Si(η5-C5Me4)(η5-C5H3-3-tBu)Ti]2(μ2,η1,η1-N2) (5-N2) have also been prepared and crystallographically characterized and shown to have weakly activated, end-on dinitrogen ligands. The latter example coordinates two additional equivalents of N2 upon cooling under a dinitrogen atmosphere in pentane solution.