Iridium-mediated N-H and methyl C-H bond activations in N-(2鈥?6鈥?dimethylphenyl)pyrrole-2-aldimine. Synthesis, characterization and catalytic applications

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• 作者：Piyali Paul ; Michael G. Richmond ; Samaresh Bhattacharya
• 关键词：N-(aryl)pyrrole-2-aldimines ; Iridium ; N&ndash ; H and methyl C&ndash ; H bond activations ; Oppenauer oxidation
• 刊名：Journal of Organometallic Chemistry
• 出版年：1 February, 2014
• 年：2014
• 卷：751
• 期：Complete
• 页码：760-768
• 全文大小：2390 K

文摘

Reaction of N-(2鈥?6鈥?dimethylphenyl)pyrrole-2-aldimine (L-Me₂) with Ir(PPh₃)₃Cl in refluxing toluene affords two organometallic complexes (1 and 2), where the imine-ligand (L-Me₂) is coordinated to the metal center, via N-H and methyl C-H activations, as a di-anionic tridentate NNC-donor, along with two triphenylphosphines. In 1 the sixth coordination site is occupied by a hydride, while in 2 by a chloride. In both cases the hydride or chloride is trans to the coordinated imine-nitrogen, and the two triphenylphosphines are mutually trans. Similar reaction of N-(2鈥?methylphenyl)pyrrole-2-aldimine (L-Me) with Ir(PPh₃)₃Cl affords 3, where the imine-ligand is coordinated to the metal center as a mono-anionic bidentate NN-donor, along with two triphenylphosphines, a hydride and a chloride. Structures of 1, 2 and 3 have been determined by X-ray crystallography. DFT analyses have been carried out to understand the formation of the complexes. All the complexes show characteristic ¹H NMR signals and, intense transitions in the visible and ultraviolet regions. Cyclic voltammetry on all three complexes shows two irreversible oxidations within 0.89-1.34聽V vs. SCE and a reduction within聽鈭?.31 to聽鈭?.40聽V vs. SCE. Complexes 1, 2 and 3 have been found to efficiently catalyze the Oppenauer oxidation of alcohols.