Synthesis, coordination behaviour, structural features and use in asymmetric hydrogenations of bifep-type biferrocenes
作者:Gustavo Espino、Li Xiao、Michael Puchberger、Kurt Mereiter、Felix Spindler、Blanca R. Manzano、Félix A. Jalón、Walter Weissensteiner
DOI:10.1039/b816544k
日期:——
A protocol for the synthesis of C2- and C1-symmetric 2,2″-diarylphosphino-substituted biferrocenes (bifep-type ligands) is presented and the preparation of four representatives is described [(Sp,Sp)-2-R12P-2″- R22P-1,1″-biferrocene; 1 (bifep): R1 = R2 = Ph; 2: R1 = Ph, R2 = Cy; 3: R1 = R2 = 3,5-Me2C6H3; 4: R1 = 3,5-Me2−4-OMe-C6H2, R2 = 3,5-(CF3)2C6H3]. In addition, the synthesis of three palladium(II) complexes ([PdX2(L)], 10: L = 1, X = Cl; 11: L = 4, X = Cl; 12: L = 1, X = C6F5 and of four bifep ruthenium complexes (13: [RuCl(p-cymene)(1)]PF6; 14: [RuI(p-cymene)(1)]PF6; 15: [RuCl(benzene)(1)]PF6; 16: [RuI(p-cymene)(1)]I) is reported. In the solid state the biferrocene unit of complexes 10, 11 and 15 adopt either a (P)-shaped (10) or an (M)-shaped (11, 15) conformation. In solution, palladium complexes 10 and 11 are present as equilibrium mixtures of rapidly interconverting (P)- and (M)-shaped conformers. Rhodium- and iridium-mediated asymmetric hydrogenations of a number of olefins and one imine give products with only low to moderate enantiomeric excess, while in the ruthenium-catalyzed hydrogenation of ketones a maximum e.e. of 82% is obtained. The low enantioselectivities are assumed to be related to the conformational flexibility of bifep-type ligands.
本文介绍了一种合成 C2- 和 C1-对称 2,2″-二芳基膦取代的双铁金属化合物(bifep型配体)的协议,并描述了四种代表性化合物的制备 [(Sp,Sp)-2-R12P-2″- R22P-1,1″-双铁金属化合物;1 (bifep): R1 = R2 = Ph; 2: R1 = Ph, R2 = Cy; 3: R1 = R2 = 3,5-Me2C6H3; 4: R1 = 3,5-Me2−4-OMe-C6H2, R2 = 3,5-(CF3)2C6H3]。此外,还报道了三种钯(II)配合物的合成([PdX2(L)], 10: L = 1, X = Cl; 11: L = 4, X = Cl; 12: L = 1, X = C6F5)以及四种 bifep 钌配合物的合成(13: [RuCl(p-cymene)(1)]PF6; 14: [RuI(p-cymene)(1)]PF6; 15: [RuCl(benzene)(1)]PF6; 16: [RuI(p-cymene)(1)]I)。在固态下,配合物 10、11 和 15 的双铁金属单元采取 (P)-形(10)或 (M)-形(11、15)构象。在溶液中,钯配合物 10 和 11 以快速相互转换的 (P)- 和 (M)-形构象的平衡混合物存在。铑和铱催化的不对称氢化反应对多种烯烃和一种亚胺的产物具有较低至中等的光学纯度,而在钌催化的酮氢化反应中,最高 e.e. 为 82%。低选择性被认为是由于 bifep 型配体的构象灵活性所致。