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.

五甲基环戊二烯基（Cp*）配位的亚胺基钛(IV)配合物Cp*TiCl(NR)(py)Cl（其中R分别为叔丁基(tBu，5a)、苄基(PhCH₂，5b)、正戊基(n-C₅H₁₁，5c)、对甲苯基(p-MeC₆H₄，5d)、对甲氧基苯基(p-MeOC₆H₄，5e)）可与叔、仲羧酰胺反应生成脒，该结果与此前报道的钛催化转酰胺化反应存在显著差异。叔酰胺二甲基乙酰胺可直接与亚胺基钛(IV)片段发生反应，而仲酰胺苯乙酰胺则首先形成酰胺基加合物{(η⁵-C₅Me₅)TiCl[OC(Me)NPh]₂} (10)，该加合物可进一步与外源胺进行后续反应。