The nicotinamide coenzyme NADH, consumed in enantioselective reduction of ketones catalysed by alcohol dehydrogenases, needs to be regenerated in order to maintain enzymatic activity. We therefore studied the catalytic potential of the cationic complexes [(η5-C5Me5)Rh(N∩N)Cl]+ (1: N∩N = 1,10-phenanthroline; 2: N∩N = 5-nitro-1,10-phenanthroline; 3: N∩N = 5-amino-1,10-phenanthroline), [(η5-C5Me5)Ir(N∩N)Cl]+ (4: N∩N = 5-nitro-1,10-phenanthroline) and [(η6-C6Me6)Ru(N∩N)Cl]+ (5: N∩N = 5-nitro-1,10-phenanthroline), isolated as the water-soluble chloride salts, for transfer hydrogenation of NAD+ to give NADH in aqueous solution. The best results were obtained with rhodium complex 1, which gave catalytic turnover frequencies up to 2000 h–1 in aqueous solution at pH 7 and 60 °C with sodium formate as the hydrogen source. When this NADH-regenerating catalytic system is combined with NADH-dependent enzymes, it is possible to chemoenzymatically reduce prochiral ketones such as acetophenone or 4-phenylbutan-2-one with high enantioselectivity. Combination of horse liver alcohol dehydrogenase (HLADH) or alcohol dehydrogenase from Rhodococcus sp. (S-ADH) with 1/formate as the NADH-regenerating system resulted in ee values up to 98 %, depending on the nature of the substrate and the enzyme. In order to explain the different catalytic activities, the electrochemical behaviour of complexes 1–5 has been studied.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Water-Soluble Phenanthroline Complexes of Rhodium, Iridium and Ruthenium for the Regeneration of NADH in the Enzymatic Reduction of Ketones

Schiff base complexes of rare earth metal ions: Synthesis, characterization and catalytic activity for the oxidation of aniline and substituted anilines

Synthesis, spectroscopic characterization and antibacterial studies of lanthanide(III) Schiff base complexes containing N, O donor atoms

Energy transfer processes affecting the luminescence properties and methods of controlling them by a change in the compositions and structures of luminescent compounds are analyzed in the review on example of lanthanide aromatic carboxylates. The analysis demonstrates clearly how the understanding of the physical regularities of the processes leading to luminescence makes it possible to perform the purposeful design of organic ligands and their brightly luminescing complexes with lanthanides.

Photoluminescence of lanthanide aromatic carboxylates

Asymmetric transfer hydrogenation (ATH) is frequently carried out in the azeotropic mixture of formic acid (F) and triethylamine (T), where the F/T molar ratio is 2.5. This study shows that the F/T ratio affects both the reduction rate and enantioselectivity, with the optimum ratio being 0.2 in the ATH of ketones with the Ru-TsDPEN catalyst. Under such conditions, a range of substrates have been reduced, affording high yields and good to excellent enantioselectivities. In comparison with the common azeotropic F-T system, the reduction is faster. This protocol improves both the classic azeotropic and the aqueous-formate system when using water-insoluble ketones.

Varying the ratio of formic acid to triethylamine impacts on asymmetric transfer hydrogenation of ketones

Six new lanthanide Schiff-base complexes were synthesized by reactions of hydrated lanthanide nitrates with H2L (H2L = N,N′-bis(salicylidene)-1,2-cyclohexanediamine) and characterized by elemental analysis, DTA–TG, IR, UV and luminescence spectra. The microanalyses and spectroscopic analyses indicate a 1D polymeric structure with the formula of [Ln(H2L)(NO3)3(MeOH)2] n [Ln = La (1), Ce (2), Pr (3), Sm (4), Gd (5) & Dy (6)]. The fluorescence spectrum of complex 4 exhibited Sm3+ centered, Schiff-base sensitized orange fluorescence, indicating that energy levels of the triplet state of H2L match closely to the lowest excited state (4G5/2) of Sm3+ ion.

Synthesis, characterization and fluorescence of lanthanide Schiff-base complexes

Heterometallic [(THF)2Na]3[Ln(R-Binolate)3(H2O)] [Ln = Sm (1) and Gd (2)] has been synthesized by the reactions of either LnCl3 or LnBr3 with 3 equiv. Na(R-HBinolate) and characterized by X-ray crystallographic analysis. Structural analyses proposed that 1 and 2 are isomorphous complexes, crystallizing in the hexagonal space group P63 with C3 symmetry. The coordination geometry of the lanthanide ions in 1 and 2 can be best approximated as a mono-capped triangle antiprism. When complexes 1 and 2 were employed as catalysts in the Meerwein–Ponndorf–Verley (MPV) reactions of acetophenone, the S-phenylethanol was separated in 94 and 85% enantiomeric excess (e.e.) for 1 and 2, respectively. Copyright © 2005 John Wiley & Sons, Ltd.

Chunhong Nie

Papers

Synthesis, characterization and fluorescence of lanthanide Schiff-base complexes

Crystal structure of chiral binaphthol lanthanide complexes and their catalysis in asymmetric transfer hydrogenation of acetophenone