Ligand Electronic Effects in Asymmetric Catalysis: Enhanced Enantioselectivity in the Asymmetric Hydrocyanation of Vinylarenes
作者:Albert L. Casalnuovo、T. V. RajanBabu、Timothy A. Ayers、Timothy H. Warren
DOI:10.1021/ja00101a007
日期:1994.11
nickel-catalyzed, asymmetric hydrocyanation of vinylarenes using glucose- derived, chiral phosphinite ligands, L, increases dramatically when the ligands contain electron-withdrawing P-aryl substituents. The substrate and solvent also strongly influence the enantioselectivity, with the highest ee's (85-91% for 6-methoxy-2-vinylnaphthalene (MVN)) obtained for the hydrocyanation of electron-rich vinylarenes in a
当配体包含吸电子 P-芳基取代基时,使用葡萄糖衍生的手性次膦酸盐配体 L 对乙烯基芳烃进行镍催化的不对称氢氰化反应的对映选择性显着增加。底物和溶剂也强烈影响对映选择性,在非极性溶剂(如己烷)中对富含电子的乙烯基芳烃进行氢氰化可获得最高的 ee(6-甲氧基-2-乙烯基萘(MVN)为 85-91%)。机理研究表明,催化循环包括最初的 HCN 氧化加成或乙烯基芳烃配位到“NiL”,然后插入形成 (q3-benzy1) 氰化镍配合物,以及腈的不可逆还原消除。NiL.(COD) (L., P-芳基 = 3, 5-(CF3)2C6H3) 催化的 MVN 氢氰化表明,随着 HCN 浓度的增加,催化剂静止状态从 NiL,(COD) 转变为包含 MVN 和 HCN 的复合物,推测是 (q3-benzy1) 氰化镍中间体 NiL ,(q3-CH3CHClH60CH3)CN。中间体 NiL(MVN) 的 31P