TiIV-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.