Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
J Am Chem Soc. 2009 Nov 25;131(46):16678-80. doi: 10.1021/ja9079308.
Two new ligands 1a,b are reported. Upon treatment with 1 equiv of NiCl(2) x (MeOCH(2))(2), 1a,b give the corresponding Ni complexes. X-ray analysis of 1a x NiCl(2) established that the NiCl(2) is selectively coordinated to the phenanthroline nitrogens. Ni/Cr heterobimetallic catalysts 1a,b x CrCl(2)/NiCl(2), prepared from 1a,b x NiCl(2), have been shown to behave exceptionally well in catalytic asymmetric Ni/Cr-mediated couplings, with highlights including the following: (1) 1-2 mol % catalyst is sufficient to complete the coupling; (2) only negligible amounts of the dimers, byproducts formed through the alkenyl Ni species, are observed; (3) the coupling goes to completion even with a 1:1 molar ratio of the coupling partners; and (4) the asymmetric induction is practically identical with that obtained from the coupling with the Cr catalysts prepared from (S)-sulfonamides 2a,b. The scope of the new Ni/Cr heterobimetallic catalysts was briefly studied using four additional aldehydes. The applicability of the new catalysts to polyfunctional substrates was demonstrated by two C-C bond formations chosen from the halichondrin/E7389 synthesis as examples.
报道了两种新的配体 1a,b。用 1 当量的 NiCl(2) x (MeOCH(2))(2)处理时，1a,b 生成相应的 Ni 配合物。1a x NiCl(2) 的 X 射线分析表明，NiCl(2) 选择性地与菲咯啉氮配位。由 1a,b x NiCl(2) 制备的 Ni/Cr 杂双金属催化剂 1a,b x CrCl(2)/NiCl(2) 在催化不对称 Ni/Cr 介导的偶联中表现出色，具有以下特点：(1) 1-2 mol%的催化剂即可完成偶联；(2) 通过烯基 Ni 物种形成的二聚体副产物仅观察到痕量；(3) 即使偶联物的摩尔比为 1:1，偶联也能完全进行；(4) 不对称诱导与从(S)-磺酰胺 2a,b 制备的 Cr 催化剂得到的偶联结果几乎相同。使用另外四种醛对新的 Ni/Cr 杂双金属催化剂的范围进行了简要研究。通过 halichondrin/E7389 合成中的两个 C-C 键形成作为实例，证明了新催化剂在多功能底物中的适用性。
