Design of Y-P-Y type Chiral Ligands Affording An Effective Chiral Field and Their Application to Asymmetric Reactions

对手性膦配体是不对称氢化反应的有效配体，但其合成存在光学分辨率和高温下易外消旋等困难。对称的N-P-N配体如果选择性地将其中一个n -单元与金属结合，从而为不对称反应建立有效的手性场，则可以形成p -手性。N-P-N配体骨架中手性中心的存在会使非对映体金属配合物之间产生较大的偏差。以相应的手性苯乙胺和手性2-苯氧苄唑啉为原料，经二氯膦的正锂化和磷化制备了具有苯乙胺单元的膦二胺配体1和双（恶唑啉）膦配体2作为手性N-P-N配体。利用这些配体，金属配合物(如[Rh（nbd)_2]BF_4, PdCl_2(PhCN)_2和K_2PtCl_4）可以选择性地将其中一个n -单元与金属结合，并选择性地形成两个非对映异构体中的一个以提供p -手性配合物。磷原子上的取代基影响了非对映体混合物的偏差，推测PN2-Ph （1a）和PN2-iPr（lb）配体的p -手性形成是相反的。PN2-Metal配合物应用于不对称反应；在丙烯酸衍生物的不对称加氢反应中，Rh-1b配合物对2-甲基肉桂酸的还原能提供高达90%以上的ee。在Pd-PN2-R(1)催化剂的不对称烯丙基烷基化反应中，（S， S）-1a和（S， S）-lb配体诱导了相反构型的产物。

P-Chiral phosphine ligands are effective ligands for asymmetric reactions such asymmetric hydrogenation, but they have synthetic difficulties including optical resolution and suffer racemization at higher temperatures. Symmetrical N-P-N ligands would be expected to form a P-chirality if selective ligation of one of N-units to metals occurs ant to construct an effective chiral filed for asymmetric reactions. The presence of chiral centers in the N-P-N ligand skeleton would afford a large deviation between diastereomeric metal complexes. As chiral N-P-N ligands, phosphinediamine ligands 1 having phenethylamine units and bis(oxazolinyl)phosphine ligands 2 were prepared from corresponding chiral phenethylamine and chiral 2- phenyloxazoline by ortho-lithiation and phosphination with dichiorophosphine. Using these ligands, selective ligation of one of N-units to metal occurred for metal complexes, such as [Rh(nbd)_2]BF_4, PdCl_2(PhCN)_2 and K_2PtCl_4, and one of two diastereomeric complexes was formed selectively to afford P-chiral complexes. Substituent on phosphorus atom affects the deviation in the diastereomeric mixture and reversed P-chirality formation was supposed for PN2-Ph (1a) and PN2-iPr(lb) ligands.PN2-Metal complexes were applied to the asymmetric reactions ; In the asymmetric hydrogenation of acrylic acid derivatives, Rh-1b complex could afford high %ees more than 90 %ee for the reduction of 2-methylcinnamic acid. In the asymmetric allylic alkylation by Pd-PN2-R(1) catalyst opposite configurations of the product were induced by using (S, S)-1a and (S, S)-lb ligands.