Hydrogenation and hydrogenolysis of furfural and furfuryl alcohol catalyzed by ruthenium(II) bis(diimine) complexes

The catalytic activity of ruthenium(II) bis(diimine) complexes cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](Z)₂ ( 1 , Z = CF₃SO₃; 2 , Z = (3,5‐(CF₃)₂C₆H₃)₄B, i.e. BArF) and cis‐[Ru(4,4′‐Cl₂bpy)₂(OH₂)₂](Z)₂ ( 3 , Z = CF₃SO₃; 4 , Z = BArF) for the hydrogenation and/or the hydrogenolysis of furfural (FFR) and furfuryl alcohol (FFA) was investigated. The molecular structures of cis‐[Ru(4,4′‐Cl₂bpy)₂(CH₃CN)₂](CF₃SO₃)₂ ( 3 ′) and dimeric cis‐[(Ru(4,4′‐Cl₂bpy)₂Cl)₂](BArF)₂ ( 5 ) were characterized by X‐ray crystallography. The structures are consistent with the anticipated reduction in steric hindrance about the ruthenium centers in comparison with corresponding complexes containing 6,6′‐Cl₂bpy ligands. While compounds 1 , 2 , 3 , 4 are all active and highly selective catalysts for the hydrogenation of FFR to FFA under modest reaction conditions, 3 and 4 showed decreased activity. This is best explained in terms of reduced Lewis acidity of the Ru²⁺ centers and reduced steric hindrance about the metal centers of catalysts 3 and 4 . cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](BArF)₂ ( 2 ) also displayed high catalytic efficiency for the hydrogenation of FFA to tetrahydrofurfuryl alcohol. Presumably, this is because coordination of C═C bonds of FFA to the ruthenium center is poorly inhibited by non‐coordinating BArF counterions. Interestingly, cis‐[Ru(6,6′‐Cl₂bpy)₂(OH₂)₂](CF₃SO₃)₂ ( 1 ) showed some catalytic activity in ethanol for the hydrogenolysis of FFA to 2‐methylfuran, albeit with fairly modest selectivity. Nonetheless, these results indicate that ruthenium(II) bis(diimine) complexes need to be further explored as catalysts for the hydrogenolysis of C―O bonds of FFR, FFA, and related compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

Making Spiroketal‐based Diphosphine (SKP) Ligands via a Catalytic Asymmetric Approach

The spiro concept for chiral ligand design represents an important contribution to the area of asymmetric catalysis. Due to the considerable difficulties in the construction of enantiopure all‐carbon spiro backbones, the development of catalytic asymmetric synthesis of chiral spiro structures via short steps is highly valuable. Herein we present our studies on the catalytic asymmetric synthesis of aromatic spiroketals and the corresponding diphosphine (SKP) ligands.     

Transfer hydrogenation of aryl ketones with homogeneous ruthenium catalysts containing diazafluorene ligands

Novel cationic ruthenium(II) complexes bearing a 4,5‐diazafluorene unit and p‐cymene as ligands have been synthesised. The complexes were characterised based on elemental analysis and Fourier transform infrared and nuclear magnetic resonance spectroscopies. The synthesised Ru(II) complexes were employed as pre‐catalysts for the transfer hydrogenation of aromatic ketones using 2‐propanol as both hydrogen source and solvent in the presence of NaOH. All complexes showed high catalytic activity as catalysts in the reduction of substituted acetophenones to corresponding secondary alcohols. The products of catalysis were obtained with conversion rates of between 80 and 99%. Among the seven new complexes investigated, the most efficient catalyst showed turnover frequencies in the range 255–291 h^?1 corresponding to 85 to 97% conversion, respectively. Copyright © 2016 John Wiley & Sons, Ltd.     

Ruthenium(II) complexes derived from 2‐phenylthiazoline‐4‐carboxylic acid: structure and catalytic activity for transfer hydrogenation reaction

Piano‐stool ([(p‐cymene)Ru(thz)Cl], 2 ) and six‐coordinated ([Ru(thz)₂(PPh₃)₂], 3 ) ruthenium complexes derived from 2‐phenylthiazoline‐4‐carboxylic acid (Hthz, 1 ) were synthesized for the first time, and fully characterized using conventional methods. Also, the molecular structure of complex 3 was determined using X‐ray analysis. These complexes were evaluated as catalysts for transfer hydrogenation of carbonyl compounds in the presence of isopropyl alcohol and KO^tBu. Complex 2 was found to be more active than 3 in transfer hydrogenation. Copyright © 2016 John Wiley & Sons, Ltd.     

Birefringence control by hydrogen bonding on compatible polymer pair composed of hydrogenated ring‐opening polymer and modified polystyrene

A new polymer blend composed of a hydrogenated ring‐opening polymer (HROP) with an ester group and hydroxyl functionalized polystyrene (HFP) produced the excellent transparent materials which enabled a precise birefringence control in keeping with the other physical properties for optical film use. The blend with a composition from 0.28 to 0.35 for the HFP weight fraction showed an extraordinary wavelength dispersion, transmitting through a zero birefringence point at the critical fraction of 0.45, while each polymer showed an ordinary wavelength dispersion. The observed excellent transparency even above those of the glass transition temperature was attributed to a depressed phase separation that resulted from strong hydrogen bond between the ester and hydroxyl groups. An IR analysis of the film demonstrated a remarkable red‐shift in the carbonyl peak with an increase of the hydroxylated polystyrene content, indicating a strong hydrogen bond between those groups. This new polymer blend provides a useful design to achieve practical demands for film use, both optical and mechanical under the fabrication conditions using the melt extrusion technique. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3132–3143