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銅 (II) とニトロキシルラジカルによって媒介されるアルコール酸化のメカニズム

Bradford L Ryland¹, Scott D McCann, Thomas C Brunold

¹Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.

Journal of the American Chemical Society

|August 5, 2014

まとめ

TEMPO (2,2,6,6-テトラメチルピペリジン-N-オキシル) を含む銅触媒は,アルコールを効率的に酸化する. この研究は,反応機構を明確にし,重要な水素転送ステップとアルコールの酸化のためのオッペナウアーのような経路を明らかにします.

科学分野:

カタリシスカタリシスカタリシス
有機化学オーガニック・ケミストリー
コンピューティング・ケミストリー

背景:

2,2'-ビピリジンとTEMPO (2,2,6,6-テトラメチルピピリジン-N-オキシル) を含んだ銅複合体は,エロビックアルコール酸化触媒として有効です.
Cu (II) /TEMPO媒介によるアルコールの酸化の正確なメカニズムについては,様々な経路が提案されているが,議論が続いている.

研究の目的:

TEMPOを用いて銅触媒によるエアロビックアルコール酸化のメカニズムを解明する.
実験的および計算的方法を用いて提案されたメカニズム的経路を区別する.
この触媒システムに関する文献の矛盾するデータを調和させる.

主な方法:

ラジカルプローブ基板を用いた実験研究.
密度関数理論 (DFT) による計算.
運動的および機械的分析.

主要な成果:

実験的証拠は,長寿命のラジカルは酸化反応の中間物質ではないことを示しています.
DFTの計算では,Cu (II) -アルコキシドから調整されたニトロキシル種への水素原子の移転が,自由ニトロキシル基への移転よりもエネルギー的に優れていることが明らかになっています.
提案されたオッペナウアー様経路は,アルコール反応性 (ベンジル対アリファティック,プライマリ対二次) の観察された傾向と,TEMPOとABNO (9-azabicyclo[3.3.1]nonane N-oxyl) のようなバイサイクルニトロキシルとの違いを説明する.

結論:

この研究は,TEMPO.で銅触媒によるエアロビックアルコール酸化のメカニズムを明らかにしています.
協調されたニトロキシル種を含む特定の水素転送経路は,キーとして特定されています.
発見は,以前の実験データと計算データを調和させ,オッペナウアーのようなメカニズムを確立します.

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