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

P-手性膦配体是不对称氢化等不对称反应的有效配体，但它们具有包括光学拆分在内的合成困难，并且在较高温度下遭受外消旋化。对称的N-P-N配体如果将其中一个N-单元选择性地连接到金属上，则有望形成P-手性，从而为不对称反应构建一个有效的手性场。N-P-N配体骨架中手性中心的存在将在非对映体金属络合物之间提供大的偏差。以手性苯乙胺和手性2-苯基恶唑啉为原料，通过邻位锂化和二氯膦的膦化反应，合成了含苯乙胺单元的膦二胺配体1和双恶唑啉膦配体2。在[Rh（nbd）_2]BF_4、PdCl_2（PhCN）_2和K_2PtCl_4等金属配合物中，通过这些配体，可以选择性地将其中一个N-单元与金属连接，并选择性地形成两种非对映体配合物中的一种，从而得到P-手性配合物。PN 2-Ph（1a）和PN 2-iPr（1b）配体的非对映异构体混合物中，磷原子上的取代基影响了非对映异构体混合物的偏差，推测它们形成了相反的P-手性。在Pd-PN_2-R（1）催化剂上的不对称烯丙基烷基化反应中，（S，S）-1a和（S，S）-1b配体诱导了产物的相反构型。

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.