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.

本研究以廉价的非手性起始原料为底物，通过简便的催化不对称P-H加成反应原位制备了一系列具有碳手性中心的PCP与PCN型配体前体，产物总收率良好。该制备配体骨架的简便催化方法，可对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进行便捷且经济的修饰。我们采用一锅法合成策略，高效制备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（Nuclear Magnetic Resonance, NMR）和质谱（Mass Spectrometry, MS）完成了结构表征。部分代表性配合物的分子结构还通过X射线晶体学（X-ray Crystallography）得到解析。初步催化性能研究结果表明，当将这些新型钳形配合物用作二苯基膦与查尔酮反应的催化剂时，其结构上的细微改动会对其化学性质产生显著影响。