(N-salicylidene)aniline derived Schiff base complexes of methyltrioxorhenium(VII): ligand influence and catalytic performance.
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.
Zhou
Ming-Dong
MD
Molecular Catalysis, Catalysis Research Center, Technische Universität München, Lichtenbergstrasse 4,D-85747 Garching bei München, Germany.
Yu
Yang
Y
Capapé
Alejandro
A
Jain
Kavita R
KR
Herdtweck
Eberhardt
E
Li
Xiao-Rong
XR
Li
Jun
J
Zang
Shu-Liang
SL
Kühn
Fritz E
FE