Designing the “Search Pathway” in the Development of a New Class of Highly Efficient Stereoselective Hydrosilylation Catalysts
作者:Vincent César、Stéphane Bellemin-Laponnaz、Hubert Wadepohl、Lutz H. Gade
DOI:10.1002/chem.200500132
日期:2005.4.22
coupling of oxazolines and N-heterocyclic carbenes leads to chelating C,N ancillary ligands for asymmetric catalysis that combine both an "anchor" unit and a stereodirecting element. Reacting various N-substituted imidazoles with 2-bromo-4(S)-tert-butyl- and 2-bromo-4(S)-isopropyloxazoline gave the imidazolium precursors of the stereodirecting ancillary ligands. A library of ten different ligand precursors
恶唑啉和N-杂环卡宾的直接偶联导致螯合C,N辅助配体用于不对称催化,该配体结合了“锚”单元和立体定向元件。使各种N-取代的咪唑与2-溴-4(S)-叔丁基-和2-溴-4(S)-异丙基恶唑啉反应,得到立体定向辅助配体的咪唑前体。通过使用该简单程序,可获得十种不同配体前体的文库(65-97%的收率)。通过与[Rh(mu-OtBu)(nbd)} 2](nbd =降冰片二烯)反应,在随后的步骤中将这些蛋白配体金属化,由KOtBu和[RhCl(nbd)} 2]原位生成相应的N -杂环卡宾配合物[RhBr(nbd)(恶唑啉基-卡宾)] 4 aj收率良好。两种铑配合物4 d和4 j的X射线衍射研究,建立了扭曲的方金字塔形配位几何结构,其中溴配体占据了顶端位置。发现铑-卡宾键的长度为2.070(4)A(4 d)和2.012(3)A(4 j)。用AgBF 4在二氯甲烷中处理配合物4 aj,得到用于酮的氢化