Bianca Wendt

Hydrogenation of Esters to Alcohols with a Well‐Defined Iron Complex

We present the first base-free Fe-catalyzed ester reduction applying molecular hydrogen. Without any additives, a variety of carboxylic acid esters and lactones were hydrogenated with high efficiency. Computations reveal an outer-sphere mechanism involving simultaneous hydrogen transfer from the iron center and the ligand. This assumption is supported by NMR experiments.

Mild and selective hydrogenation of aromatic and aliphatic (di)nitriles with a well-defined iron pincer complex

The catalytic hydrogenation of carboxylic acid derivatives represents an atom-efficient and clean reduction methodology in organic chemistry. More specifically, the selective hydrogenation of nitriles offers the possibility for a green synthesis of valuable primary amines. So far, this transformation lacks of useful, broadly applicable non-noble metal-based catalyst systems. In the present study, we describe a molecular-defined iron complex, which allows for the hydrogenation of aryl, alkyl, heterocyclic nitriles and dinitriles. By using an iron PNP pincer complex, we achieve very good functional group tolerance. Ester, ether, acetamido as well as amino substituents are not reduced in the presence of nitriles. Moreover, nitriles including an α,β-unsaturated double bond and halogenated derivatives are well tolerated in this reaction. Notably, our complex constitutes the first example of an homogeneous catalyst, which permits the selective hydrogenation of industrially important adipodinitrile to 1,6-hexamethylenediamine.

Phosphine–Imidazolyl Ligands for the Efficient Ruthenium‐Catalyzed Hydrogenation of Carboxylic Esters

The synthesis of phosphine-imidazolyl ligands 1 and 2 in good yields is presented. In combination with [{Ru(benzene)Cl(2)}(2)], ligands 1 c and 1 e formed efficient catalyst systems for the selective hydrogenation of various carboxylic esters into their corresponding primary alcohols. Furthermore, the structures of four ruthenium complexes with ligands 1 b, 1 c, 1 d, and 1 e were determined by X-ray crystallography, which showed the formation of different coordination modes depending on the ligand structure.

Iridium‐Catalyzed Hydrogenation of Carboxylic Acid Esters

The first selective iridium‐catalyzed hydrogenations of esters are presented. By using a commercially available iridium pincer complex more than 20 different aromatic, aliphatic, and (hetero)cyclic esters are reduced to the corresponding alcohols in moderate to very good yields. An outer‐sphere mechanism is proposed on the basis of our computational analysis.

Enantioselective zinc-catalyzed hydrosilylation of ketones using pybox or pybim ligands.

The combination of ZnEt(2) and chiral pyridinebisoxazoline (pybox) or pyridinebisimidazoline (pybim) ligands catalyzed the asymmetric hydrosilylation of aryl, alkyl, cyclic, heterocyclic, and aliphatic ketones. Under mild conditions, high yields and good enantioselectivities were achieved. ESI measurements allowed for the characterization of the active catalyst.

Ruthenium/Imidazolylphosphine Catalysis: Hydrogenation of Aliphatic and Aromatic Nitriles to Form Amines

A convenient and efficient catalyst system for the hydrogenation of aliphatic nitriles towards the corresponding primary amines in high to excellent yields is presented. In addition, aromatic nitriles are reduced smoothly, too. The use of low catalyst loadings and molecular hydrogen make this protocol an attractive methodology.

Ruthenium Catalysts for Hydrogenation of Aromatic and Aliphatic Esters: Make Use of Bidentate Carbene Ligands

Committed carbenes: The convenient application of bidentate carbene ligands is described for the hydrogenation of carboxylic acid esters. The ligand precursors are easily synthesized through the dimerization of N-substituted imidazoles with diiodomethane. The catalyst is generated in situ and exhibits good activity and functional group tolerance for the hydrogenation of aromatic and aliphatic carboxylic acid esters.

Cobalt Pincer Complexes for Catalytic Reduction of Carboxylic Acid Esters

A selection of cobalt(I) and cobalt(II) pincer type complexes with different substitution patterns was tested in the catalytic reduction of carboxylic acid esters to alcohols. The cobalt pincer type complex 4 is suitable for the hydrogenation of aromatic as well as aliphatic and cyclic esters. Mechanistic investigation indicated a metal ligand cooperated reaction pathway.