Wang Xiaoming, Han Zhaobin, Wang Zheng, Ding Kuiling
State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China.
Frontiers Science Center for Transformative Molecules, School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.
Acc Chem Res. 2021 Feb 2;54(3):668-684. doi: 10.1021/acs.accounts.0c00697. Epub 2021 Jan 14.
ConspectusWhile spectacular successes have been achieved in homogeneous catalysis with the use of achiral diphosphine ligands featuring a wide natural bite angle, such as XantPhos, chiral diphosphines that can induce a large P-M-P bite angle in their transition metal complexes are conspicuously less explored in asymmetric catalysis, probably due to the challenges in the identification and efficient construction of a suitable chiral backbone. In the past decade, a highly efficient synthesis of chiral aromatic spiroketals and the corresponding diphosphine ligands (SKPs) has been developed in this group.Based on a one-pot catalytic tandem double asymmetric hydrogenation-spiroketalization ring-closure reaction sequence, these SKP ligands featuring an extraordinarily long P···P distance and a flexible backbone have been readily prepared in large scale. Remarkably versatile coordination modes have been found in the complexes of SKP with some catalysis-relevant transition metals, for example, Pd, Cu, Au, and Rh. Whereas SKP enforces an unusually large bite angle in [Pd(SKP)Cl] and [Cu(SKP)Cl] complexes (160.1° and 132.8°, respectively), it also allows for a bimetallic Au-Au interaction (3.254 Å) in the complex of [Au(SKP)Cl] or a square-planar coordination geometry for the [Rh(SKP)(cod)]SbF complex. Such an adaptable nature of SKP ligands for transition metal coordination has profound consequences in homogeneous asymmetric catalysis, as demonstrated by their unique performance in several types of catalytic asymmetric reactions. One of the most exciting examples is SKP/Pd-catalyzed asymmetric allylic amination of Morita-Baylis-Hillman (MBH) adducts, in which SKP/Pd complexes demonstrated excellent control of regio- and enantioselectivities and exhibited exceptionally high efficiency (with a TON up to 4750) in the catalysis. SKP ligands have also found a diversity of successful applications in Cu-, Au-, or Rh-catalyzed asymmetric reactions, further attesting their wide utilities in asymmetric catalysis. Overall, this class of readily accessible SKP ligands featuring a chiral aromatic spiroketal skeleton have demonstrated unique adaptable structures in a variety of transition metal complexes and provided outstanding performance in some difficult asymmetric transformations. The works delineated herein would be expected to stimulate further research efforts on the application of this type of chiral ligand and to provide useful clues in the design of new chiral diphosphine ligands with adaptable bite angles for transition metal catalyzed asymmetric reactions.
概述
虽然在使用具有宽自然咬合角的非手性二膦配体（如XantPhos）进行均相催化方面取得了显著成功，但在不对称催化中，能在其过渡金属配合物中诱导较大P-M-P咬合角的手性二膦却明显较少被探索，这可能是由于在识别和高效构建合适的手性骨架方面存在挑战。在过去十年中，该研究小组开发了一种高效合成手性芳族螺环缩酮及相应二膦配体（SKP）的方法。
基于一锅法催化串联双不对称氢化 - 螺环缩酮化闭环反应序列，这些具有极长P···P距离和柔性骨架的SKP配体已能很容易地大规模制备。在SKP与一些与催化相关的过渡金属（如Pd、Cu、Au和Rh）的配合物中发现了非常多样的配位模式。例如，在[Pd(SKP)Cl]和[Cu(SKP)Cl]配合物中，SKP强制形成异常大的咬合角（分别为160.1°和132.8°），而在[Au(SKP)Cl]配合物中它还允许双金属Au - Au相互作用（3.254 Å），对于[Rh(SKP)(cod)]SbF配合物则形成平面正方形配位几何结构。SKP配体对过渡金属配位的这种适应性在均相不对称催化中具有深远影响，这在几种类型的催化不对称反应中其独特性能得到了证明。最令人兴奋的例子之一是SKP/Pd催化的森田 - 贝利斯 - 希尔曼（MBH）加合物的不对称烯丙基胺化反应，其中SKP/Pd配合物在区域和对映选择性控制方面表现出色，并且在催化中表现出极高的效率（TON高达4750）。SKP配体在Cu、Au或Rh催化的不对称反应中也有多种成功应用，进一步证明了它们在不对称催化中的广泛用途。总体而言，这类具有手性芳族螺环缩酮骨架的易于获得的SKP配体在各种过渡金属配合物中表现出独特的适应性结构，并在一些困难的不对称转化中提供了出色的性能。本文所述的工作有望激发对这类手性配体应用的进一步研究，并为设计用于过渡金属催化不对称反应的具有适应性咬合角的新手性二膦配体提供有用线索。
