Katalytisch vermittelte C-H-Silylierung von aromatischen Verbindungen mit neuartigen (PSiP)-Pincer-Komplexen
Final Report Abstract
Derived from studies towards catalytic C-H borylation reactions, bis(donor)silyl ligand systems and their corresponding metal complexes of group 9 (Ir, Rh) were thought to be active motifs for C-H functionalisation catalysts. A series of bis(pyridyl)silane derivatives and complexes via Si-H oxidative addition could be synthesized. The spectroscopic and structural characterization of the isolated complexes with the metal center in the formal oxidation state +3 showed a facial coordination of the ligand. Attempts to reduce the metal center to the oxidation state +1, and thereby forcing the ligand in a meridonal coordination mode, were not successful. As anticipated, the complexes showed activity in the catalytic, intermolecular C-H borylation of benzene and the intramolecular C-H silylation of O-silyl-benzylalcohol derivatives. However, the activity and selectivity was lower compared to simple, commercially available state-of-the-art catalysts. In addition, the complexes showed activity in the reduction of CO 2 using silanes as reducing agents. Related bis(silylene) and bis(germylene) pincer ligand systems were investigated in collaboration with the group of Matthias Driess at the TU Berlin. Synthesis and characteristion of [ECE]MHCl(coe) (M = Ir, Rh; E = Si, Ge, P) complexes revealed the strinkingly strong σ-donor proporties of silylene and germylene ligands compared to P(III)-based systems. These complexes could be applied in the C-H borylation of benzene using pinacolborane. Surprisingly, the novel metallylene ligands did not only show a preference for C-H borylation compared to the usually preferred hydroboration reaction, but the presence of cyclooctene led to an rate accelerating effect by acting as a H2-acceptor.
Publications
- Pushing the σ-Donor Strength in Iridium Pincer Complexes: Bis(silylene) and Bis(germylene) Ligands Are Stronger Donors than Bis(phosphorus(III)) Ligands; Angew. Chem Int. Ed.. 2012, 51, 11478; Angew. Chem. 2012, 46, 11645
A. Brück, D. Gallego, W. Wang, E. Irran, M. Driess, J. F. Hartwig
(See online at https://doi.org/10.1002/anie.201205570)
