1165815-22-4Relevant academic research and scientific papers
Investigations of iridium-mediated reversible C-H bond cleavage: Characterization of a 16-electron iridium(III) methyl hydride complex
Bernskoetter, Wesley H.,Hanson, Susan Kloek,Buzak, Sara K.,Davis, Zoe,White, Peter S.,et al.
, p. 8603 - 8613 (2009/10/23)
New iridium complexes of a tridentate pincer ligand, 2,6-bis(di-tert- butylphosphinito)pyridine (PONOP), have been prepared and used in the study of hydrocarbon C-H bond activation. Intermolecular oxidative addition of a benzene C-H bond was directly observed with [(PONOP)IrI(cyclooctene)][PF 6] at ambient temperature, resulting in a cationic five-coordinate iridium(III) phenyl hydride product. Protonation of the (PONOP)IrI methyl complex yielded the corresponding iridium(III) methyl hydride cation, a rare five-coordinate, 16-valence electron transition metal alkyl hydride species which was characterized by X-ray diffraction. Kinetic studies of C-H bond coupling and reductive elimination reactions from the five-coordinate complexes have been carriedout. Exchange NMR spectroscopy measurements established a barrier of 17 .8(4) kcal/mol (22°C) for H-Caryl bond coupling in the iridium(III) phenyl hydride cation and of 9.3(4) kcal/mol (-105°C) for the analogous H-Calkyl coupling in the iridium(III) methyl hydride cation. The origin of the higher barrier of H-Caryl relative to H-Calkyl bond coupling is proposed to be influenced by a hindered rotation about the Ir-Caryl bond, a result of the sterically demanding PONOP ligand.
