Design of Novel Octahedral Stereogenic-at-Metal Complexes for Applications in Asymmetric Catalysis

This thesis details the synthesis of three classes of chiral octahedral metal complexes and their applications in asymmetric catalysis. In the first section, two new octahedral chiral-at-metal iridium(III) and rhodium(III) Lewis acid complexes with modified ligands were synthesized to expand the fa...

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Bibliographic Details
Main Author: Zheng, Yu
Contributors: Meggers, Eric (Prof. Dr.) (Thesis advisor)
Format: Dissertation
Language:English
Published: Philipps-Universität Marburg 2018
Chemie
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Summary:This thesis details the synthesis of three classes of chiral octahedral metal complexes and their applications in asymmetric catalysis. In the first section, two new octahedral chiral-at-metal iridium(III) and rhodium(III) Lewis acid complexes with modified ligands were synthesized to expand the family of previous complexes in our group. While the newly synthesized complexes Λ/Δ-Ir/Rh(Se) did not demonstrate higher catalytic activities than the existing ones, we believe that these Lewis acid catalysts might be applied to other enantioselective reactions such as visible-light driven photocatalysis in the future. In the second section, four new bis-cyclometalated rhodium(III) and iridium(III) complexes were synthesized in a diastereomerically and enantiomerically pure fashion by employing chiral cyclometalating ligands. One of these complexes was identified to catalyze the enantioselective alkynylation of 2-trifluoroacetyl imidazoles with different substituted alkynes to provide the propargyl alcohols in good to excellent yields with excellent enantioselectivities (up to >99% ee). We found that the asymmetric induction in the course of creating a new stereogenic center is controlled by the metal-centered chirality not the chirality of the coordinating ligands. Moreover, the rhodium complexes display higher catalytic reactivity than our previous catalysts and thus our chiral catalyst library is further expanded. Importantly, the synthetic methodology provides a new strategy for the straightforward synthesis of enantiomerically pure octahedral complexes with metal-centered chirality. Lastly, the first example of an octahedral chiral-at-ruthenium complex bearing two N-(2-pyridyl)-subsituted N-heterocyclic carbene (PyNHC) ligands was successfully developed. It was demonstrated that the helically chiral catalyst catalyzes the enantioselective alkynylation of simple trifluoromethyl ketones to provide the corresponding propargylic alcohols with high efficiency at catalyst loading down to 0.2% and with excellent enantioselectivities of up to > 99% ee. A significant application of our new catalyst is the enantioselective catalytic synthesis of two key chiral intermediates of the anti-AIDS drug efavirenz.
Physical Description:260 Pages
DOI:https://doi.org/10.17192/z2018.0084