Ti^IV-Mediated Reactions between Primary Amines and Secondary Carboxamides:  Amidine Formation Versus Transamidation

Titanium(IV)-mediated reactions between primary amines and secondary carboxamides exhibit different outcomes, amidine formation versus transamidation, depending on the identity of the Ti^IV complex used and the reaction conditions employed. The present study probes the origin of this divergent behavior. We find that stoichiometric Ti^IV, either Cp*Ti^IV complexes or Ti(NMe₂)₄, promotes formation of amidine and oxotitanium products. Under catalytic conditions, however, the outcome depends on the identity of the Ti^IV complex. Competitive amidine formation and transamidation are observed with Cp*Ti^IV complexes, generally favoring amidine formation. In contrast, the use of catalytic Ti(NMe₂)₄ (≤20 mol %) results in highly selective transamidation. The ability of Ti^IV to avoid irreversible formation of oxotitanium products under the latter conditions has important implications for the use of Ti^IV in catalytic reactions.