Reactivity Studies of Iridium(III) Porphyrins with Methanol in Alkaline Media

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• 作者：Chi Wai Cheung ; Hong Sang Fung ; Siu Yin Lee ; Ying Ying Qian ; Yun Wai Chan ; Kin Shing Chan
• 刊名：Organometallics
• 出版年：2010
• 出版时间：March 22, 2010
• 年：2010
• 卷：29
• 期：6
• 页码：1343-1354
• 全文大小：901K
• 年卷期：v.29,no.6(March 22, 2010)
• ISSN：1520-6041

文摘

Ir(ttp)Cl(CO) (1a; ttp = 5,10,15,20-tetrakis(p-tolyl)porphyrinato dianion) was found to cleave the C−O bond of CH₃OH at 200 °C to give Ir(ttp)CH₃ (3a). Addition of KOH promoted the reaction rate and gave a higher yield of Ir(ttp)CH₃ in 70% yield in 1 day. Mechanistic studies suggest that, in the absence of KOH, Ir(ttp)Cl(CO) reacts with CH₃OH initially to give Ir(ttp)OCH₃, which then undergoes β-hydride elimination to produce Ir(ttp)H (4a). Ir(ttp)H further reacts slowly to cleave the C−O bond of CH₃OH, likely via σ-bond metathesis, to give Ir(ttp)CH₃. In the presence of KOH, Ir(ttp)Cl(CO) initially reacts with KOH more rapidly to give Ir(ttp)OH, which then cleaves the O−H bond of CH₃OH by metathesis to give Ir(ttp)OCH₃. Ir(ttp)OCH₃ further isomerizes via β-hydride elimination/reinsertion to give Ir(ttp)CH₂OH and concurrently undergoes base-assisted β-proton elimination to give Ir(ttp)⁻K⁺ (5a). Ir(ttp)CH₂OH subsequently condenses with CH₃OH to form Ir(ttp)CH₂OCH₃ (2). Finally, Ir(ttp)⁻K⁺ cleaves the C−O bond in CH₃OH, most probably via nucleophilic substitution, to give Ir(ttp)CH₃. Ir(ttp)CH₂OCH₃ also serves as the precursor of Ir(ttp)⁻K⁺ as it undergoes nucleophilic substitution by KOH to give Ir(ttp)⁻K⁺.