Zhou Ming-Dong, Yu Yang, Capapé Alejandro, Jain Kavita R, Herdtweck Eberhardt, Li Xiao-Rong, Li Jun, Zang Shu-Liang, Kühn Fritz E
Molecular Catalysis, Catalysis Research Center, Technische Universität München, Lichtenbergstrasse 4,D-85747 Garching bei München, Germany.
Chem Asian J. 2009 Mar 2;4(3):411-8. doi: 10.1002/asia.200800358.
Methyltrioxorhenium(VII) (MTO) readily forms 1:1 adducts with several N-(salicylidene)aniline derived Schiff bases. If the aromatic rings of the N-(salicylidene)aniline ligands display non-donating or electron withdrawing substituent groups, the resulting MTO adducts show good activities in olefin epoxidations. However, steric effects seem to play a major role, leading often to instable o- and m-Schiff base-MTO adducts, while p-substituted Schiff bases usually lead to more stable adducts. In catalysis, electron-withdrawing substituents on the aniline moiety lead to better catalysts than electron donating ones. The gap between good catalysts and instable or non-existing compounds, however, is small. The general tendency, however, that good donors on the Schiff base ligands lead to shorter Re-O(Schiff base) bridges and lower catalytic activity, while the opposite is true with acceptor ligands on the Schiff bases, seems to be quite clear.
七氧化三甲基铼(VII)（MTO）很容易与几种N-（水杨醛）苯胺衍生的席夫碱形成1:1加合物。如果N-（水杨醛）苯胺配体的芳环带有非供电子或吸电子取代基，则生成的MTO加合物在烯烃环氧化反应中表现出良好的活性。然而，空间效应似乎起主要作用，常常导致邻位和间位席夫碱-MTO加合物不稳定，而对位取代的席夫碱通常会生成更稳定的加合物。在催化反应中，苯胺部分的吸电子取代基比供电子取代基能产生更好的催化剂。然而，优良催化剂与不稳定或不存在的化合物之间的差距很小。不过，席夫碱配体上的优良供体导致铼-氧（席夫碱）桥键较短且催化活性较低，而席夫碱上的受体配体情况则相反，这一总体趋势似乎相当明显。
