Formation of a Cationic Vinylimido Group upon C–H Activation of Nitriles by Trialkylamines in the Presence of TaCl5

We report a new CH3CN activation mode where an imido group is directly formed by deprotonation of the nitrile coordinated to the highly Lewis acidic TaV center. The unexpected deprotonation of TaCl5(CH3CN) by NEt3 resulted in isolation of the triethylammonium vinylimido complex [HNEt3]­[Ta­(NC­(CH2)­NEt3)­Cl5]. The reaction is proposed to proceed through rearrangement of the initial nucleophilic carbanion to the electrophilic azaallene/carbocation intermediate. The use of more sterically hindered (i-Pr)­CN and weakly nucleophilic N­(i-Pr)2Et resulted in the isolation of a vinylimido group formed upon dimerization of deprotonated nitriles, suggesting deprotonation as the first step of the transformation.