Steric control of coordination geometry in titanium-lmido complexes of n,n-bis(arylimino)acenaphthylene ligands


Titanium complexes of N,N-bis(arylimino)acenaphthylene (BIAN) α-diimine ligands with varied steric profiles have been prepared. Coordination of the BIAN ligand derivatives to TiCl4 afforded the adducts (dpp-BIAN)TiCl4 (1a), (tmp-BIAN)TiCl4 (1b), and (dmp-BIAN)TiCl4 (1c) (dpp = 2,6-diisopropylphenyl; tmp = 2,4,6-trimethylphenyl; dmp = 3,5-dimethylphenyi). While the least sterically crowded complex 1c is robust toward loss of the diimine ligand, the dpp-BIAN and tmp-BIAN ligands are readily displaced by pyridine from the more crowded derivatives 1 a and 1b, respectively. The crowded profiles engendered by the tmp-BIAN and dpp-BIAN ligands result in the formation of five-coordinate titanium-imide complexes, (dpp-BIAN)TiCl2(=NBu) (2a) and (tmp-BIAN)TiCl2(=NBu) (2b), upon addition of BuNH2 to solutions of 1 a or 1 b, respectively. Single-crystal X-ray diffraction studies reveal a square pyramidal coordination environment with an apical imide ligand and a short Ti-N distance, consistent with a Ti-N triple bond. Conversely, the less crowded dmp-BIAN ligand affords a six-coordinate titanium imido complex, (dmpBIAN)TiCl2(=NBu)(NH2Bu) (4), upon treatment of 1c with BuNH2. Surprisingly the imido ligand is coordinated trans to one arm of the diimine. This six coordinate species is fluxional in solution, and exchange and variable temperature 1H NMR experiments suggest dissociation of the coordinated BuNH2 ligand to generate a five-coordinate imido intermediate analogous to 2a and 2b. ©2010 American Chemical Society.

Publication Title

Inorganic Chemistry