不均衡のCPET反応性の限界をテストする: Co (III) -オクソ複合体によるH原子抽象における機械的クロスオーバー
Norman Zhao1, McKenna K Goetz1, Joseph E Schneider1
1Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States.
Journal of the American Chemical Society
|March 3, 2023
まとめ
この研究は,コバルト-オクソ複合体の基本性を増加させることで,C-H結合活性化メカニズムが変化することを明らかにしています. 非常に基本的な複合体は,協調された陽子電子伝送から段階的な経路へのシフトを示し,反応速度に影響を与えます.
科学分野:
- 有機金属化学
- カタリシス
- 反応メカニズム
背景:
- 移行金属-オクソ複合体は,酸化反応,特にC-H結合の活性化において重要な中間物質である.
- C-H活性化における反応速度は,協調型陽子電子移転 (CPET) による基板結合解離自由エネルギーとしばしば関連している.
- サブストラット/金属-オクソ酸性/塩基性またはリドックスポテンシャルを含む別の段階的な経路も反応のダイナミクスに影響を与える可能性があります.
研究 の 目的:
- 移行金属-オクソ複合体による基礎性によるC−H結合活性化の限界を調査する.
- より基本的なコバルト-オクソ複合体,PhB ((AdIm) 3CoIIIOを合成し,研究し,その反応性をより基本的なアナログと比較する.
- C-H と O-H 結合の活性化における協調した経路と段階的な経路のメカニズム的なクロスオーバーを探求する.
主な方法:
- 新しい,より基本的な末端コバルト-オクソ複合体,PhB ((AdIm) 3CoIIIOの合成.
- 水素原子ドナーとフェノール基板を用いた反応性研究
- 陽子転送 (PT) と電子転送 (ET) プロセスの熱力学分析.
主要な成果:
- より基本的なPhB ((AdIm) 3CoIIIO複合体は,PhB ((Im) 3CoIIIOと比較して,CPETの不均衡反応性を高めています.
- フェノール基質のO-H活性化により,CPETから段階的な陽子移転-電子移転 (PTET) への機械的シフトが示される.
- 協調反応と段階的な反応の間の熱力学的交差点を特定した.
結論:
- 塩基性は,コバルト-オクソ複合体によるC-H結合活性化のメカニズムを決定する上で重要な役割を果たします.
- 最も不均衡なシステムは,段階的な経路への機械的クロスオーバーが発生するまで,高速なCPET率を達成することができます.
- このクロスオーバーポイントは,より遅い製品形成につながり,協調と段階的な反応性の間の微妙なバランスを強調します.
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