Chiral Titanium Bis(aminopyridinates) Based on a Biaryl Backbone

The new chiral biaryl-bridged aminopyridine proligand H2L is synthesized readily via palladium-catalyzed amination. This ligand system provides a very robust environment for reaction chemistry in comparison to known nonchelate aminopyridinate ligands. Reaction with Ti(NMe2)4 gives the C2-symmetric amide [LTi(NMe2)2] (91% isolated), which on reaction with SiMe3Cl gives the chloride [LTiCl2] (95%). Metalation of H2L with KH followed by reaction with TiCl3 and oxidation also gives [LTiCl2] (87%). This latter complex has been crystallographically characterized and has the expected cis structure, in which the chirality arising in the biaryl backbone is very well expressed in the reactive coordination sphere of the metal. Reaction of [LTiCl2] with MeMgBr gives the dimethyl compound [LTiMe2] (72%). The dibenzyl complex [LTi(CH2Ph)2] is prepared directly from the reaction of H2L with [Ti(CH2Ph)4] (90%).