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.