Zwitterionic Iridium Complexes with P,N-Ligands as Catalysts for the Asymmetric Hydrogenation of Alkenes
Zwitterionic Iridium Complexes with P,N-Ligands as Catalysts for the Asymmetric Hydrogenation of Alkenes
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DOI：
10.1002/chem.201003314
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发表时间：
2011-04-01
影响因子：
4.3
通讯作者：
Pfaltz, Andreas
中科院分区：
文献类型：
--
作者：
Franzke, Axel;Pfaltz, Andreas
合成了几种以咪唑啉或恶唑啉为手性磷、氮配体，四芳基硼酸或芳基三氟硼酸为阴离子取代基的两性铱配合物。还制备了相应的阳离子类似物，以评价阴离子和阳离子金属络合物之间的共价键在催化反应中的作用。已比较了各自对结构类似的预催化剂在非官能化烯烃的不对称氢化中的功效。在大多数情况下，阴离子衍生化对铱络合物的不对称诱导几乎没有影响。这与X射线结构研究一致，X射线结构研究表明阳离子金属中心的手性环境不受阴离子取代基的影响。取决于所采用的阳离子的性质，两性离子催化剂被证明是显着更具反应性比它们的阳离子对应物在非极性溶剂中。
Several zwitterionic iridium complexes based on chiral P,N-ligands with imidazoline or oxazoline donors and anionic tetraarylborate or aryltrifluoroborate substituents have been synthesized. The corresponding cationic analogues have also been prepared, to evaluate the effect of the covalent linkage between the anion and the cationic metal complex in catalytic reactions. The respective pairs of structurally analogous precatalysts have been compared for their efficacies in the asymmetric hydrogenation of unfunctionalized olefins. In most cases, the anionic derivatization has virtually no influence on the asymmetric induction of the iridium complex. This is in accordance with X-ray structural studies, which have shown that the chiral environment of the cationic metal center is not affected by the anionic substituent. Depending on the nature of the counterion employed, the zwitterionic catalysts proved to be significantly more reactive than their cationic counterparts in nonpolar solvents.