Distinct Thermodynamics for the Formation and Cleavage of N−H Bonds in Aniline and Ammonia. Directly-Observed Reductive Elimination of Ammonia from an Isolated Amido Hydride Complex

The reactions of aryl and alkylamines with the (PCP)Ir fragment (PCP = 1,3-di-tert-butylphosphinobenzene) were studied to determine the reactivities and stabilities of amine and amido hydride complexes relative to C−H activation products. Reaction of aniline with the (PCP)Ir unit generated from (PCP)IrH2 and norbornene resulted in the N−H oxidative addition product (PhNH)(H)Ir(PCP) (1a). In contrast, reaction of this fragment with ammonia gave the ammonia complex (NH3)Ir(PCP) (2). The amido hydride complex that would be formed by oxidative addition of ammonia, (PCP)Ir(NH2)(H) (1b), was generated independently by deprotonation of the ammonia complex (NH3)Ir(H)(Cl)(PCP) (3) with KN(SiMe3)2 at low temperature. This amido hydride complex underwent reductive elimination at room temperature to form the ammonia complex 2. Addition of CO to anilide complex 1a gave (PCP)Ir(PhNH)(H)(CO) (4a). Addition of CNtBu to terminal amido complex 1b formed (PCP)Ir(NH2)(H)(CNtBu) (4b), the first structurally characterized irid...