Synlett 2016; 27(06): 831-847
DOI: 10.1055/s-0035-1560405
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© Georg Thieme Verlag Stuttgart · New York

Iron Chemistry Made Easy: Chiral N2P2 Ligands for Asymmetric Catalysis

Raphael Bigler
Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland   Email: mezzetti@inorg.chem.ethz.ch
,
Raffael Huber
Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland   Email: mezzetti@inorg.chem.ethz.ch
,
Antonio Mezzetti*
Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland   Email: mezzetti@inorg.chem.ethz.ch
› Author Affiliations
Further Information

Publication History

Received: 09 November 2015

Accepted after revision:10.12.2015

Publication Date:
27 January 2016 (online)


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