The first successful demonstration of the amination of an olefin by a transition-metal-catalyzed N-H activation mechanism was accomplished in a stepwise manner with an Ir(I) catalyst and the substrates aniline and norbornylene. The initial N-H oxidative addition step envisioned in such a mechanism was demonstrated for the complexes Ir(PMe3)4PF6, Ir(PMe3)3(C8H14)Cl, and Ir(PEt3)3Cl, all of which gave rise to stable cis anilido hydride complexes when reacted with aniline. The second step, olefin insertion, was accomplished from the reaction of Ir(PEt3)2(C2H4)2Cl (1) with aniline and norbornylene. The resulting insertion product, Ir(PEt3)2(NHPhC7H10)(H)Cl (6), was characterized by NMR spectroscopy and single-crystal X-ray diffraction and was found to have an azoiridacyclobutane type structure. The relevant crystal data for 6 are a = 10.702 (3) Å,b= 13.176 (21) Å, c = 19.498 (5) Å, β= 98.61 (2); P21/c. T = -70 °C, dc = 1.591 g/cm3, μ = 51.21 cm−1; 3029 reflections, R = 0.039 and Rw= 0.036. Decomposition studies of 6 established two competing reaction pathways. C-N and Ir-C bond breaking, the microscopic reverse of the formation of 6, gave norbornylene and a reactive Ir intermediate. The competing pathway of C-H reductive elimination occurs by prior ligand dissociation and yields the amination product, exo-2-(phenylamino)norbornane (7). Labeling studies indicated an overall cis addition of the N-H group across the exo face of norbornylene. The individual steps for this reaction were elaborated into a catalytic cycle for the addition of aniline to norbornylene and a mechanism based on these individual steps proposed.
ASJC Scopus subject areas
- Colloid and Surface Chemistry