New Ruthenium Catalysts for Asymmetric Transfer Hydrogenation of Prochiral Ketones

Synthesis of Tridentate PNO Ligands with Planar Chirality and Application in Iridium-Catalyzed Asymmetric Hydrogenation of Simple Ketones

A series of [2,2]paracyclophane-based tridentate PNO ligands with planar chirality were designed and synthesized. The easily prepared chiral tridentate PNO ligands were successfully applied to the iridium-catalyzed asymmetric hydrogenation of simple ketones, giving chiral alcohols with high efficiency and excellent enantioselectivities (up to 99% yield and >99% ee). Control experiments revealed the indispensability of both N-H and O-H in the ligands.

Chiral Tridentate Ligands in Transition Metal-Catalyzed Asymmetric Hydrogenation

Asymmetric hydrogenation (AH) of double bonds has been one of the most effective methods for the preparation of chiral molecules and for the synthesis of important chiral building blocks. In the past 60 years, noble metals with bidentate ligands have shown marvelous reactivity and enantioselectivity in asymmetric hydrogenation of a series of prochiral substrates. In recent years, developing chiral tridentate ligands has played an increasingly important role in AH. With modular frameworks and a variety of functionalities on the side arms, chiral tridentate ligand complexes enable both reactivities and stereoselectivities. Although great achievements have been made for noble metal catalysts with chiral tridentate ligands since the 1990s, the design of chiral tridentate ligands for earth abundant metal catalysts has still been in high demand. This review summarizes the development of chiral tridentate ligands for homogeneous asymmetric hydrogenation. The philosophy of ligand design and the reaction mechanisms are highlighted and discussed as well.

Asymmetric Transfer Hydrogenation of Arylketones Catalyzed by Enantiopure Ruthenium(II)/Pybox Complexes Containing Achiral Phosphonite and Phosphinite Ligands

A family of complexes of the formula trans-[RuCl₂(L)(R-pybox)] (R-pybox = (S,S)-ⁱPr-pybox, (R,R)-Ph-pybox, L = monodentate phosphonite, PPh(OR)₂, and phosphinite, L = PPh₂(OR), ligands) were screened in the catalytic asymmetric transfer hydrogenation of acetophenone, observing a strong influence of the nature of both the R-pybox substituents and the L ligand in the process. The best results were obtained with complex trans-[RuCl₂{PPh₂(OEt)}{(R,R)-Ph-pybox}] (2c), which provided high conversion and enantioselectivity (up to 96% enantiomeric excess, e.e.) for the reduction of a variety of aromatic ketones, affording the (S)-benzylalcohols.

Monodisperse NiPd alloy nanoparticles decorated on mesoporous graphitic carbon nitride as a catalyst for the highly efficient chemoselective reduction of α,β-unsaturated ketone compounds

The study reported chemoselective reduction with selectivity (>99%) by the catalytic transfer hydrogenation of α,β-unsaturated ketones with a catalyst of NiPd alloy nanoparticles decorated on mesoporous graphitic carbon nitride (NiPd/mpg-C₃N₄).

Rapid Asymmetric Synthesis of Disubstituted Allenes by Coupling of Flow-Generated Diazo Compounds and Propargylated Amines

We report herein the asymmetric coupling of flow‐generated unstabilized diazo compounds and propargylated amine derivatives, using a new pyridinebis(imidazoline) ligand, a copper catalyst and base. The reaction proceeds rapidly, generating chiral allenes in 10–20 minutes with high enantioselectivity (89–98 % de/ee), moderate yields and a wide functional group tolerance.

Diruthenium(ii)–NNN pincer complex catalysts for transfer hydrogenation of ketones

A strategy to construct highly efficient diruthenium(ii)–NNN pincer complex catalysts was established for the transfer hydrogenation of ketones.

A simple and efficient in situ generated ruthenium catalyst for chemoselective transfer hydrogenation of nitroarenes: kinetic and mechanistic studies and comparison with iridium systems

A convenient and highly efficient in situ generated Ru(ii) system for synthesizing functionalized amines and mechanistic studies and comparison with iridium systems is presented.

Bifunctional Ru(ii) complex catalysed carbon–carbon bond formation: an eco-friendly hydrogen borrowing strategy

Bifunctional Ru(ii) complex (0.1 mol%) catalysed one-pot β-alkylation of secondary alcohols with primary alcohols and double alkylation of cyclopentanol were carried out successfully following the atom economical borrowing hydrogen methodology.

Asymmetric Transfer Hydrogenation of Imines in Water by Varying the Ratio of Formic Acid to Triethylamine

Asymmetric transfer hydrogenation (ATH) of imines has been performed with variation in formic acid (F) and triethylamine (T) molar ratios in water. The F/T ratio is shown to affect both the reduction rate and enantioselectivity, with the optimum ratio being 1.1 in the ATH of imines with the Rh-(1S,2S)-TsDPEN catalyst. Use of methanol as a cosolvent enhanced reduction activity. A variety of imine substrates have been reduced, affording high yields (94-98%) and good to excellent enantioselectivities (89-98%). In comparison with the common azeotropic F-T system, the reduction with 1.1/1 F/T is faster.

Lipophilic M(α,α′-OC5H11)8phthalocyanines (M = H2 and Ni(ii)): synthesis, electronic structure, and their utility for highly efficient carbonyl reductions

This paper describes the electronic structure of (α,α′-n-OC₅H₁₁)₈-H₂Pc and (α,α′-n-OC₅H₁₁)₈-Ni(ii)Pc and highly efficient carbonyl reductions catalyzed by Ni(ii)Pc.

Effect of the structure of the diamine backbone of P-N-N-P ligands in iron(II) complexes on catalytic activity in the transfer hydrogenation of acetophenone

The asymmetric transfer hydrogenation of aromatic ketones can be efficiently accomplished using catalysts that are based on platinum group metals which are more toxic and less abundant than iron. For that reason the discovery of iron based catalysts for the use in this transformation is important. To address this issue, we synthesized a new series of iron(II)-based precatalysts trans-[Fe(Br)(CO)(PPh(2)CH(2)CH═NCHRCHRN═CHCH(2)PPh(2))]BPh(4) (5a-5d) containing P-N-N-P ligands with the diamines (R,R)-1,2-diaminocyclohexane (a), (R,R)-1,2-diphenyl-1,2-diaminoethane (b), (R,R)-1,2-di(4-methoxyphenyl)-1,2-diaminoethane (c), and ethylenediamine (d) incorporated in the backbone using a convenient one-pot synthesis using readily available starting materials. All of the complexes, when activated with a base, show a very high activity in the transfer hydrogenation catalysis of acetophenone, using 2-propanol as a reducing agent under mild conditions. A comparison of the TOF of complexes 5a-5d show that the catalytic activity of complexes increase as the size of the substituents in the backbone of ligands increases (d < a < b = c).