Unprecedented Reaction Pathway of Sterically Crowded Calcium Complexes: Sequential C−N Bond Cleavage Reactions Induced by C−H Bond Activations

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• 作者：Dr. Yang Yang ; Dr. Haobing Wang and Prof. Dr. Haiyan Ma
• 刊名：Chemistry – An Asian Journal
• 出版年：2017
• 出版时间：January 17, 2017
• 年：2017
• 卷：12
• 期：2
• 页码：239-247
• 全文大小：873K
• ISSN：1861-471X

文摘

Five bis(quinolylmethyl)-(1H-indolylmethyl)amine (BQIA) compounds, that is, {(quinol-8-yl-CH₂)₂NCH₂(3-Br-1H-indol-2-yl)} (L¹H) and {[(8-R³-quinol-2-yl)CH₂]₂NCH(R²)[3-R¹-1H-indol-2-yl]} (L^2–5H) (L²H: R¹=Br, R²=H, R³=H; L³H: R¹=Br, R²=H, R³=iPr; L⁴H: R¹=H, R²=CH₃, R³=iPr; L⁵H: R¹=H, R²=nBu, R³=iPr) were synthesized and used to prepare calcium complexes. The reactions of L^1–5H with silylamido calcium precursors (Ca[N(SiMe₂R)₂]₂(THF)₂, R=Me or H) at room temperature gave heteroleptic products (L^1, 2)CaN(SiMe₃)₂ (1, 2), (L^3, 4)CaN(SiHMe₂)₂ (3 a, 4 a) and homoleptic complexes (L^3, 5)₂Ca (D3, D5). NMR and X-ray analyses proved that these calcium complexes were stabilized through Ca⋅⋅⋅C−Si, Ca⋅⋅⋅H−Si or Ca⋅⋅⋅H−C agostic interactions. Unexpectedly, calcium complexes ((L^3–5)CaN(SiMe₃)₂) bearing more sterically encumbered ligands of the same type were extremely unstable and underwent C−N bond cleavage processes as a consequence of intramolecular C−H bond activation, leading to the exclusive formation of (E)-1,2-bis(8-isopropylquinol-2-yl)ethane.