Fachbereich Chemie , Philipps-Universität Marburg , Hans-Meerwein-Strasse 4 , 35043 Marburg , Germany.
Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095-1569 , United States.
J Am Chem Soc. 2019 Dec 4;141(48):19048-19057. doi: 10.1021/jacs.9b09301. Epub 2019 Nov 21.
A new class of chiral ruthenium catalysts is introduced in which ruthenium is cyclometalated by two 7-methyl-1,7-phenanthrolinium heterocycles, resulting in chelating pyridylidene remote N-heterocyclic carbene ligands (rNHCs). The overall chirality results from a stereogenic metal center featuring either a Λ or Δ absolute configuration. This work features the importance of the relative metal-centered stereochemistry. Only the non--symmetric chiral-at-ruthenium complexes display unprecedented catalytic activity for the intramolecular C(sp)-H amidation of 1,4,2-dioxazol-5-ones to provide chiral γ-lactams with up to 99:1 er and catalyst loadings down to 0.005 mol % (up to 11 200 TON), while the -symmetric diastereomer favors an undesired Curtius-type rearrangement. DFT calculations elucidate the origins of the superior C-H amidation reactivity displayed by the non--symmetric catalysts compared to related -symmetric counterparts.
引入了一类新型手性钌催化剂，其中钌由两个 7-甲基-1,7-菲咯啉杂环螯合，形成螯合吡啶基远程 N-杂环卡宾配体（rNHCs）。整体手性源于具有 Λ 或 Δ 绝对构型的手性金属中心。这项工作强调了相对金属中心立体化学的重要性。只有非对称手性钌配合物才显示出对 1,4,2-恶唑-5-酮的分子内 C(sp)-H 酰胺化的前所未有的催化活性，以提供高达 99:1 的对映体过量和高达 0.005 mol%（高达 11200 吨）的催化剂负载量的手性 γ-内酰胺，而 -对称的非对映异构体有利于不期望的 Curtius 型重排。DFT 计算阐明了非对称催化剂与相关的 -对称对应物相比表现出优异的 C-H 酰胺化反应性的起源。
