Titanium(IV)-Mediated Conversion of Carboxamides to Amidines and Implications for Catalytic Transamidation

Cp*-ligated imidotitanium(IV) complexes, Cp*TiCl(NR)(py)Cl (R = tBu (5a), PhCH₂ (5b), n-C₅H₁₁ (5c), p-MeC₆H₄ (5d), p-MeOC₆H₄ (5e)), react with tertiary and secondary carboxamides to yield amidines, a result that is in contrast with previously reported titanium-catalyzed transamidation reactions. The tertiary amide dimethylacetamide reacts directly with the imidotitanium(IV) fragment, whereas the secondary amide phenylacetamide forms an amidate adduct, {(η⁵-C₅Me₅)TiCl[OC(Me)NPh]₂} (10), which undergoes subsequent reaction with exogenous amine.