Group-4 Dipyrrolylmethane Complexes in Intramolecular Olefin Hydroamination

Titanium and zirconium complexes bearing the 5,5-dimethyldipyrrolylmethane (dpm) ancillary ligand were tested for their activity in intramolecular hydroamination of olefins. The titanium precatalyst Ti(NMe2)2(dpm), despite being an excellent catalyst for intermolecular alkyne hydroamination, was a relatively poor catalyst for intramolecular olefin hydroamination. The zirconium derivative was significantly more active. With a secondary amine, [Zr(NMe2)2(dpm)]2 did catalyze the hydroamination reaction, albeit slowly. Consequently, the mechanism of the reaction with zirconium may use a 1,2-insertion into a Zr−N amido bond as the key mechanistic step, or the complex may be able to access both the [2 + 2]-cycloaddition and 1,2-insertion mechanisms. The zirconium precatalyst was structurally characterized by X-ray diffraction and is a dimer in the solid state, but solution molecular weight determination gave results closer to the monomer in benzene.