Periodic Reporting for period 2 - EARTHCAM (Earth-Abundant Metals with Exclusively Achiral Ligands for Sustainable Chiral-at-Metal Catalysis)
Okres sprawozdawczy: 2022-07-01 do 2023-12-31
The implementation of chiral-at-metal catalysts from earth-abundant metals relies on taming the high lability of coordinative bonds of 3d metals to warrant a satisfactory configuration stability. This is addressed by exploiting the chelate effect of tailored multidentate ligands in combination with strong-field ligands and attractive weak interactions between coordinated ligands.
Employing meridional tridentate ligands:
We developed a stereogenic-at-iron(II) catalyst scaffold which contains one coordinated meridional tridentate imidazolidin-2-ylidene-functionalized 2,2'-bipyridine, one bidentate pyrazolylpyridine, and one monodentate acetonitrile ligand (D. Baran, L. Hinterlang, S. I. Ivlev, E. Meggers, Eur. J. Inorg. Chem. 2023, doi.org/10.1002/ejic.202300148). This (3+2+1)-coordination sphere implements a stereogenic iron center. A carbon stereocenter in the N-heterocyclic carbene moiety controls the absolute metal-centered configuration. The obtained enantiopure complexes were applied as chiral catalysts in the ring contraction of an isoxazole to a chiral 2H-azirine.
Employing linear tetradentate ligands:
We investigated stereogenic-at-iron(II) complexes containing linear tetradentate ligands. For example, non-C2-symmetric stereogenic-at-iron complexes were synthesized, analyzed and investigated for asymmetric catalysis (P. S. Steinlandt, M. Hemming, X. Xie, S. I. Ivlev, E. Meggers, Chem. Eur. J. 2023, e202300267). Related C2-symmetric stereogenic-at-iron complexes with linear tetradentate ligands were successfully applied to nitrene-mediated C-H insertion chemistry. This led to the discovery of a novel 1,3-migratory nitrene C-H insertion (C.-X. Ye, X. Shen, S. Chen, E. Meggers, Nat. Chem. 2022, 14, 566; B. Zhou, C.-X. Ye, E. Meggers, Eur. J. Org. Chem. 2023, e202300296), a directed nitrene-mediated C-H amination (C.-X. Ye, D. R. Dansby, S. Chen, E. Meggers, Nat. Synth. 2023, doi.org/10.1038/s44160-023-00267-w) and an iron-catalyzed enantioselective ring-closing C-H amination to chiral 2-imidazolidinones (T. Cui, C.-X. Ye, J. Thelemann, D. Jenisch, E. Meggers, Chin. J. Chem. 2023, doi.org/10.1002/cjoc.202300162).
Employing tripodal ligands:
We investigated stereogenic-at-iron(II) complexes containing tripodal pentadentate ligands. The properties of such complexes were investigated and the complexes applied to asymmetric catalysis (P. S. Steinlandt, X. Xie, S. Ivlev, E. Meggers, ACS Catal. 2021, 11, 7467).
Furthermore, we spent significant efforts to understand the factors that provide sufficient configurational stability for stereogenic metal centers of 3d metals. This allowed us to succeed in improving the configurational stabilty of chiral-at-iron catalysts containing two N-(2-pyridyl)-substituted N-heterocyclic carbene ligands by carefully tuning the sigma-donor and pi-acceptor properties of the bidentate ligands (N. Demirel, J. Haber, S. I. Ivlev, E. Meggers, Organometallics 2022, 41, 3852). Remarkably, the developed chiral-at-iron complex is completely configurational stable, even in the presence of water and air. The complex was demonstrated to be an excellent catalyst for an asymmetric hetero-Diels-Alder reaction.