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

The titanocene dinitrogen complex [(η 5 -C 5 H 2 -1,2,4-Me 3 ) 2 Ti] 2 (μ 2,η 2,η 2 -N 2 ) ( 1-N 2 ) 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-N 2 contains a side-on bound N 2 ligand with an N−N bond length of 1.216(3) Å, consistent with a significant contribution from a two-electron-reduced diazenido ([N 2 ] 2- ) fragment. Attempts to maintain side-on coordination of the N 2 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 -[Me 2 Si(η 5 -C 5 H 2 -2-SiMe 3 -4- t Bu) 2 Ti] 2 (μ 2,η 1,η 1 -N 2 ) ( 4-N 2 ) and [Me 2 Si(η 5 -C 5 Me 4 )(η 5 -C 5 H 3 -3- t Bu)Ti] 2 (μ 2,η 1,η 1 -N 2 ) ( 5-N 2 ) 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 N 2 upon cooling under a dinitrogen atmosphere in pentane solution.