2-Aminopyridinate Titanium Complexes for the Catalytic Hydroamination of Primary Aminoalkenes

A series of mono(2-aminopyridinato)tris(dimethylamido) titanium complexes, ApTi(NMe2)(3) (where Ap = 2-aminopyridinato), have been prepared via protonolysis, and their reactivity for the hydroamination of primary aminoalkenes has been explored. The Ti complex incorporating N,6-dimesityl-2-aminopyridinate as the supporting ancillary ligand has been shown to yield a catalyst suitable for room-temperature intramolecular hydroamination reactions to give gem-disubstituted five- and six-membered-ring products. The comparison of ApTi(NMe2)(3) with other group 4 catalysts shows that controlling the steric environment at the metal center is the critical determining factor for hydroamination reactivity. The screening of known challenging primary aminoalkene substrates with the most reactive ApTi(NMe2)(3) shows good breadth of reactivity for the reaction. This complex is not able to cyclize secondary aminoalkene substrates, suggesting this reaction proceeds via an intermediate imido [2+2] cycloaddition pathway. An Ap-supported Ti imido complex, which also exhibits hydroamination activity, has been prepared and fully characterized from ApTi(NMe2)(3) and 2,6-dimethylaniline.