Versatile Syntheses of Optically Pure PCE Pincer Ligands: Facile Modifications of the Pendant Arms and Ligand Backbones

A series of chiral C-stereogenic
PCP and PCN ligand precursors
were prepared in situ from inexpensive achiral starting materials
via a simple catalytic asymmetric P–H addition reaction in
good overall yields. This facile catalytic method of preparing the
ligand backbones renders easy and economical modifications of the
electronically crucial para-substituent, chiral functionalities,
and donor atoms for different transition metal ions. A one-pot synthetic
procedure was used efficiently to prepare the corresponding optically
pure pincer complexes. All the new complexes were characterized by
NMR and mass spectroscopy. The molecular structures of several selected
complexes have also been elucidated by X-ray crystallography. Preliminary
studies indicated that minor structural changes on these novel pincer
complexes affect their chemical properties significantly when they
were applied as catalysts for the reaction between diphenylphosphine
and chalcone.

一系列具有手性碳立体中心的PCP与PCN型配体前体，可由廉价易得的非手性起始原料，通过简便的催化不对称P-H加成反应原位制备得到，且总收率良好。该制备配体骨架的简便催化方法，可实现电子效应关键的对位取代基、手性官能团以及适配不同过渡金属离子的配位原子的便捷且经济的修饰。研究采用一锅法合成策略，高效制备得到了对应的光学纯钳形配合物。所有新型配合物均通过核磁共振波谱与质谱进行了表征。部分代表性配合物的分子结构亦通过X射线晶体衍射法得以解析。初步研究表明，当这类新型钳形配合物用作二苯膦与查尔酮之间反应的催化剂时，其结构上的细微变化会对其催化性能产生显著影响。