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オレフィンメタテシス触媒におけるNMR化学的シフトと電子構造の関連解明

Stéphanie Halbert¹, Christophe Copéret², Christophe Raynaud¹

¹Institut Charles Gerhardt, UMR 5253 CNRS, cc 1501, Université de Montpellier , Place. E. Bataillon, F-34095 Montpellier, France.

Journal of the American Chemical Society

|January 21, 2016

まとめ

シュロックアルキリデンの転移触媒は,支配的なパラマグネティック貢献により,低炭素の化学的シフトを示します. このパラマグネティック効果は,軌道エネルギーギャップと金属同一性によって影響を受け,これらの重要な触媒の観測傾向を説明します.

科学分野:

有機金属化学
カタリシス
コンピュータ化学

背景:

d(0) シュロックアルキリデン転移触媒は,予想外の低いダウンフィールド化学シフト (δ(iso)) と大きな化学シフトアニソトロピーを持つ核性炭素を特徴としています.
これらの触媒の電子構造を理解することは,オレフィン転化におけるその反応性を予測し,最適化するために極めて重要です.

研究の目的:

シュロックアルキリデン転移触媒における化学シフトテンソーの分子レベルの理解を図る.
観測された低いダウンフィールドの化学的シフトと大きなアニソトロピーの起源を解明する.
電子構造と触媒性能と金属のアイデンティティを相関させる.

主な方法:

最先端の4コンポーネント相対論計算を用いて化学シフトテンソールを決定した.
化学的シフトへの貢献を解剖するために,局所的軌道を用いた2つの構成要素の分析が行われました.
軌道分析は,パラマグネティック貢献と分子幾何学との関係を理解するために使用されました.

主要な成果:

分析により,アルキリデンの炭素が圧倒的に多いことが明らかになった.
最大のパラマグネティック貢献は,エチレンのσ(CC) -π*(CC) 結合に類似したアルキリデン σ(MC) とπ*(MC) 軌道との結合から生じる.
観測された δ ((iso) 値の傾向 (Mo > W,Re > Ta) は,これらの軌道間の異なるエネルギーギャップによって説明される.

結論:

電子構造,特に軌道エネルギーギャップによって支配されるパラマグネティック貢献は,d ((0) シュロックアルキリデン触媒における化学シフトテンソールと δ (((iso) を決定する.
アゴスティック相互作用は,化学シフトテンソールの主要構成要素の方向性に影響を与える.
この研究は,これらの触媒のNMRパラメータの基本的な理解を提供し,触媒設計とメカニズム研究に役立ちます.

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