Max-Planck-Institut für Kohlenforschung, Kaiser Wilhelm Platz 1, 45470-Mülheim an der Ruhr (Germany), Fax: (+49) 208-306-2994.
Chemistry. 2014 Feb 17;20(8):2208-14. doi: 10.1002/chem.201303686. Epub 2014 Jan 23.
A straightforward synthesis of cyclopropenylidene-stabilized phosphenium cations 1 a-g through the reaction of [(iPr2N)2C3(+)Cl]BF4 with secondary phosphines is described. Their donor ability was evaluated by analysis of the CO stretching frequency in Rh complexes RhCl(CO)L22 and electrochemical methods. The cyclopropenium ring induces a phosphite-type behavior that can be tuned by the other two substituents attached to the phosphorus atom. Despite of the positive charge that they bear, phosphenium cations 1 a-g still act as two-electron donor ligands, forming adducts with Pd(II) and Pt(II) precursors. Conversely, in the presence of Pd(0) species, an oxidative insertion of the Pd atom into the Ccarbene-phosphorus bond takes place, providing dimeric structures in which each Pd atom is bonded to a cyclopropenyl carbene while two dialkyl/diaryl phosphide ligands serve as bridges between the two Pd centers. The catalytic performance of the resulting library of Pt(II) complexes was tested; all of the cationic phosphines accelerated the prototype 6-endo-dig cyclization of 2-ethynyl-1,1'-biphenyl to afford pentahelicene. The best ligand 1 g was used in the synthesis of two natural products, chrysotoxene and epimedoicarisoside A.
通过[(iPr2N)2C3(+)Cl]BF4 与仲膦反应，我们描述了环丙烯叉稳定的磷翁阳离子 1a-g 的直接合成。通过 Rh 配合物RhCl(CO)L22 中 CO 伸缩频率的分析和电化学方法评估了它们的供电子能力。环丙烯基团诱导出一种亚磷酸酯类型的行为，这种行为可以通过连接在磷原子上的另外两个取代基来调节。尽管它们带有正电荷，但磷翁阳离子 1a-g 仍然作为两电子供体配体，与 Pd(II)和 Pt(II)前体形成加合物。相反，在 Pd(0)物种存在下，Pd 原子插入 Ccarbene-磷键中发生氧化插入，提供了二聚体结构，其中每个 Pd 原子与环丙烯碳键合，而两个二烷基/二芳基膦配体作为两个 Pd 中心之间的桥梁。测试了所得 Pt(II)配合物库的催化性能；所有的阳离子膦都加速了 2-乙炔基-1,1'-联苯的原型 6-endo-dig 环化反应，得到五轮烯。最佳配体 1g 用于两种天然产物 Chrysotoxene 和 Epimedoicarisoside A 的合成。
