College of Chemistry and Chemical Engineering, Hunan University, Changsha, 410082, China.
Dalton Trans. 2011 Oct 7;40(37):9482-9. doi: 10.1039/c0dt01419b. Epub 2011 Aug 18.
In the direct Mannich reaction and synthesis of α,β-unsaturated ketones, the use of organobismuth complexes as catalysts leads to high diastereoselectivity and products of single trans conformation. In this paper, we illustrate the relationship between structure and catalytic activity as well as diastereoselectivity of organobismuth complexes having a 5,6,7,12-tetrahydrodibenz [c,f][1,5]thiobismocine framework as well as bearing a butterfly-shaped sulfur-bridged ligand and tunable anions. With the exposed bismuth center acting as a Lewis acid site and the uncoordinated lone pair electrons of sulfur as a Lewis base site, the cationic organobismuth complexes work as bifunctional Lewis acid/base catalysts. Due to the steric influence of the butterfly-shaped structure and synergistic effect of Lewis acid and Lewis base centers, the complexes can direct substrate attack in organic synthesis. By adjusting the electron-withdrawing ability of the counter anions, the S-Bi bond strength can be regulated, leading to a significant change in Lewis acidity and Lewis basicity as well as catalytic activity. Through synergistic modulation of the above effects, one can control the diastereoselectivity of the organobismuth complexes for the generation of a single diastereoisomer.
在直接曼尼希反应和α，β-不饱和酮的合成中，使用有机铋配合物作为催化剂可以得到高的非对映选择性和单一反式构象的产物。在本文中，我们展示了具有 5,6,7,12-四氢二苯并[c,f][1,5]硫杂双环[2.2.2]辛烷骨架和蝴蝶形硫桥联配体以及可调阴离子的有机铋配合物的结构与催化活性和非对映选择性之间的关系。暴露的铋中心作为路易斯酸位点，硫的未配位孤对电子作为路易斯碱位点，使阳离子有机铋配合物作为双功能路易斯酸碱催化剂发挥作用。由于蝴蝶形结构的空间位阻影响和路易斯酸和路易斯碱中心的协同效应，这些配合物可以在有机合成中引导底物进攻。通过调节抗衡阴离子的吸电子能力，可以调节 S-Bi 键的强度，从而导致路易斯酸度、路易斯碱度和催化活性的显著变化。通过对上述效应的协同调节，可以控制有机铋配合物的非对映选择性，从而生成单一的非对映异构体。
