The Golden Age of Transfer Hydrogenation

Iron Catalysis in Organic Synthesis

The use of 3d metals in de/hydrogenation catalysis has emerged as a competitive field with respect to “traditional” precious metal catalyzed transformations. The introduction of functional pincer ligands that can store protons and/or electrons as expressed by metal–ligand cooperativity and ligand redox-activity strongly stimulated this development as a conceptual starting point for rational catalyst design. This review aims at providing a comprehensive picture of the utilization of functional pincer ligands in first-row transition metal hydrogenation and dehydrogenation catalysis and related synthetic concepts relying on these such as the hydrogen borrowing methodology. Particular emphasis is put on the implementation and relevance of cooperating and redox-active pincer ligands within the mechanistic scenarios.

First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands.

http://pubs.acs.org/doi/pdf/10.1021/acs.organomet.7b00605

Toxicity of Metal Compounds: Knowledge and Myths

Hydrogenations constitute fundamental processes in organic chemistry and allow for atom-efficient and clean functional group transformations. In fact, the selective reduction of nitriles, ketones, and aldehydes with molecular hydrogen permits access to a green synthesis of valuable amines and alcohols. Despite more than a century of developments in homogeneous and heterogeneous catalysis, efforts toward the creation of new useful and broadly applicable catalyst systems are ongoing. Recently, Earth-abundant metals have attracted significant interest in this area. In the present study, we describe for the first time specific molecular-defined manganese complexes that allow for the hydrogenation of various polar functional groups. Under optimal conditions, we achieve good functional group tolerance, and industrially important substrates, e.g., for the flavor and fragrance industry, are selectively reduced.

Selective Catalytic Hydrogenations of Nitriles, Ketones, and Aldehydes by Well-Defined Manganese Pincer Complexes

ConspectusChiral alcohols are important building blocks in the pharmaceutical and fine chemical industries. The enantioselective reduction of prochiral ketones catalyzed by transition metal complexes, especially asymmetric transfer hydrogenation (ATH) and asymmetric hydrogenation (AH), is one of the most efficient and practical methods for producing chiral alcohols. In both academic laboratories and industrial operations, catalysts based on noble metals such as ruthenium, rhodium, and iridium dominated the asymmetric reduction of ketones. However, the limited availability, high price, and toxicity of these critical metals demand their replacement with abundant, nonprecious, and biocommon metals. In this respect, the reactions catalyzed by first-row transition metals, which are more abundant and benign, have attracted more and more attention.As one of the most abundant metals on earth, iron is inexpensive, environmentally benign, and of low toxicity, and as such it is a fascinating alternative to the preci...

Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer Hydrogenation and Asymmetric Hydrogenation of Ketones

Chiral molecules, such as alcohols, are vital for the manufacturing of fine chemicals, pharmaceuticals, agrochemicals, fragrances, and novel materials. These molecules need to be produced in high yield and high optical purity and preferentially catalytically. Among all the asymmetric catalytic reactions, asymmetric hydrogenation with H2 (AH) is the most widely used in the industry. With few exceptions, these AH processes use catalysts based on the three critical metals, rhodium, ruthenium, and iridium. Herein we describe a simple, industrially viable iron catalyst that allows for the AH of ketones, a process currently dominated by ruthenium and rhodium catalysts. By combining a chiral, 22-membered macrocyclic ligand with the cheap, readily available Fe3(CO)12, a wide variety of ketones have been hydrogenated under 50 bar H2 at 45–65 °C, affording highly valuable chiral alcohols with enantioselectivities approaching or surpassing those obtained with the noble metal catalysts. In contrast to AH by most nobl...

Iron catalyzed asymmetric hydrogenation of ketones

A new protocol for the enantioselective hydrogenation of ketones bearing aryl or heteroaryl substituents and β-keto esters is presented.

Iron Catalyzed Asymmetric Hydrogenation of Ketones.

Novel chiral tetraaza ligands, N1,N2-bis(2-(piperidin-1-yl)benzylidene)cyclohexane-1,2-diamine 1 and N1,N2-bis(2-(piperidin-1-yl)benzyl)cyclohexane-1,2-diamine 2, have been synthesized and fully characterized by analytical and spectroscopic methods. The structure of (R,R)-1 has been established by X-ray crystallography. Asymmetric transfer hydrogenation of aromatic ketones with the catalysts prepared in situ from [IrHCl2(COD)]2 and the chiral tetraaza ligands in 2-propanol gave the corresponding optically active secondary alcohols in high conversions and good ees (up to 91%) under mild reaction conditions.

Novel chiral tetraaza ligands: synthesis and application in asymmetric transfer hydrogenation of ketones

National Natural Science Foundation of China [20423002, 20703034]; Natural Science Foundation of Fujian Province of China [2008J0235]; State Key Laboratory of Physical Chemistry of Solid Surfaces in Xiamen University

Asymmetric transfer hydrogenation of aromatic ketones with chiral diamino-thiophene/iridium catalyst systems

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