已开发出一种新的C 2 -对称P -chirogenic 双膦配体,在配体骨架上具有甲硅烷基取代基,( R , R )-5,8-TMS-QuinoxP*。该配体对环状烯丙基亲电试剂的直接对映会聚硼酸化显示出比其母体配体 ( R , R )-QuinoxP*更高的反应性和对映选择性(例如,对于哌啶类底物:95% ee 与 76% ee)。使用 ( R , R )-5,8-TMS-QuinoxP* (高达 90% ee, s= 46.4)。使用 X 射线晶体学和计算研究对配体骨架上甲硅烷基的作用进行了调查,结果显示 ( R , R )-5,8-TMS-QuinoxP*的膦和甲硅烷基部分之间存在互锁结构。DFT 计算结果表明,熵效应在热力学上破坏了催化循环中休眠的二聚体物种以提高反应性。此外,在直接对映收敛的情况下,详细的计算表明碳-碳双键具有明显的对映选择性识别,这实际上不受烯丙基位置手性的影
Optically active C 3 -symmetric triarylphosphines in asymmetric allylations
作者:Mark T. Powell、Alexander M. Porte、Joe Reibenspies、Kevin Burgess
DOI:10.1016/s0040-4020(01)00346-5
日期:2001.6
routes involving asymmetric reduction of aryl ketones ( , and ). Single crystal X-ray structures of trans-PdCl2(phosphine)2 complexes of ligands 1a, 2a and 3a showed that the ligands do not adopt perfect C3-symmetric conformations in the solidstate; in fact, all three have one aromatic ring lying ‘face-on’ to the metal. Circular dichroism studies of the same complexes provided some evidence for an