Abstract
In this account, we summarize our recent work on the preparation of C
2-symmetric macrocyclic N2P2 and open-chain NPPN iron(II) complexes. The investigation of these new ligand classes
is enabled by the development of a synthetic route to the key enantiopure, P-stereogenic dialdehyde. Macrocyclization with a diamine affords N2P2 ligands, the iron(II) complexes of which are highly active and selective precatalysts
for the asymmetric transfer hydrogenation of ketones. Condensation with monoamines
affords open-chain NPPN ligands, of which the highly azaphilic iron(II) complexes
are tested in the asymmetric Strecker reaction.
1 Introduction
1.1 Iron Complexes: The Issue of Stability
1.2 Open-Chain PNNP Ligands
1.3 Goals and Motivation
2 N2P2 Macrocycles
2.1 The Key C
2-Symmetric Synthon
2.2 C
2-Symmetric N2P2 Macrocycles
3 Macrocyclic Iron(II) Complexes
3.1 Bis(acetonitrile) N2P2 Complexes
3.2 Bis(acetonitrile) (NH)2P2 Complexes
3.3 Enlarging the Toolbox: Isonitrile (CNR) Ligands
3.4 Asymmetric Transfer Hydrogenation Fe/N2P2
4 Chiral Open-Chain NPPN Ligands
4.1 Synthesis of Bis(acetonitrile) Complexes
4.2 Complex Derivatization
4.3 Asymmetric Transfer Hydrogenation Fe/NPPN
4.4 Strecker Reaction of Azomethine Imines
5 Conclusion and Outlook
Key words
macrocycles - iron - asymmetric catalysis - hydrogen transfer - alcohols