Iron complexes generated in situ catalyze homogeneously the transfer hydrogenation of aliphatic and aromatic ketones by utilizing 2-propanol as a hydrogen donor in the presence of base. The influence of different reaction parameters on the catalytic activity is investigated in detail by applying a three-component catalyst system composed of an iron salt, 2,2':6',2''-terpyridine, and PPh3. The scope and limitations of the described catalyst is shown in the reduction of 11 different ketones. In most cases, high conversion and excellent chemoselectivity are obtained. Mechanistic studies indicate a monohydride reaction pathway for the homogeneous iron catalyst.

Tridentate N,N,N-pyridinebisimidazolines have been studied as new ligands for the enantioselective transfer hydrogenation of prochiral ketones. High yields and excellent enantioselectivity up to > 99 % ee have been achieved with an in situ generated catalytic system containing dichlorotris(triphenylphosphine)ruthenium and 2,6-bis-([4R,5R]-4,5-diphenyl-4,5-dihydro-1H-imidazol-2-yl)-pyridine (3a) in the presence of sodium isopropoxide.Keywords: asymmetric transfer hydrogenation; ketones; phosphines; ruthenium; tridentate nitrogen ligands Enantiomerically pure alcohols have a wide range of applications, for example, building blocks and synthons for pharmaceuticals, agrochemicals, polymers, syntheses of natural compounds, auxiliaries, ligands and key intermediates in organic syntheses.[1] Within the different molecular transformations to chiral alcohols, transition metal-catalyzed reactions offer efficient and versatile strategies, such as addition of organometallic compounds to aldehydes, hydrosilylation, and hydrogenation of prochiral ketones.[2] From an economic and environmental point of view the asymmetric hydrogenation, in particular the transfer hydrogenation, represents a powerful tool for their synthesis because of its high atom economy and safety advantages.[3] Here, Noyoris ruthenium-based catalysts comprising chiral tosylated diamines constitute state-of-the-art transfer hydrogenation systems.[3d,4] Based on this seminal work an increasing number of ruthenium catalysts with chiral bidentate N,N-ligands were developed in the last decade.[3] Significantly fewer systems are known in which transfer of chiral information is promoted by tridentate ligands. [5,6] Up to now only a limited number of auspicious tridentate nitrogen-containing N,N,N ligands were established in the field of transfer hydrogenation. For example (R)-phenyl-ambox (1) [5] and different pyridinebisoxazoline (pybox) ligands (2) [6] have been applied for the reduction of acetophenone (Scheme 1).Recently, we reported the synthesis of a new class of chiral tridentate amines.[7] The preparation and tunability of these pyridinebisimidazolines (3) (socalled pybim ligands, Scheme 1) are easier and more flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. To date there is no report on the performance of these ligands in hydrogenation reactions. The resemblance between pybim (3) and pybox (2) stimulated our research to study the potential of this class of ligands in the transfer hydrogenation of aromatic and aliphatic ketones.In exploratory experiments, isopropyl alcohol-based transfer hydrogenation of acetophenone was examined using a simple in situ catalyst system composed of [RuCl 2

The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic N-acyl enamides to give N-acyl-protected optically active amines has been examined for the first time in detail in the presence of chiral monodentate 4,5-dihydro-3H-dinaphthophosphepines 5a-i. The enantioselectivity is largely dependent on the nature of the substituent at the

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