Synthesis of Ti Complexes Supported by an ortho-Terphenoxide Ligand and Their Applications in Alkyne Hydroamination Catalysis

The synthesis of a series of Ti complexes of an aryl-linked bis-phenoxide ligand, 3,3″-di-tert-butyl-5,5″-dimethyl-[1,1′:2′,1″-terphenyl]-2,2″-bis(olate), (TPO)H₂, is reported. This ortho-linked terphenyl ligand builds on previously reported meta- and para-linked terphenyl-based ligands, completing the isomeric series of terphenoxide ligands. The 4-coordinate (TPO)Ti(NMe₂)₂ is an active catalyst for alkyne hydroamination with a variety of arylamines, revealing good regioselectivity in reactions with unsymmetric alkynes. Terminal alkynes such as phenylacetylene undergo additional insertion reactions with the key azatitanacyclobutene intermediates, providing further evidence that Ti aryloxide complexes are susceptible to this further reactivity.