- Microwave-Assisted Catalytic Acetylation of Alcohols by Gold-Nanoparticle-Supported Gadolinium Complex
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A gold nanoparticle (AuNP)-supported gadolinium complex (RS-Au-L-Gd) catalyst was prepared through simple chelation of GdCl3 to the surface-bound spacer, 1,4,7-tris(carboxymethyl)-10-(11-mercaptoundecyl)-1,4,7,10-tetraazacyclododecane (HSDO3A). This AuNP-supported Gd complex was found to be a highly effective catalyst for the acetylation of various alcohols and phenol in the presence of acetic anhydride. With a loading of 0.4 mol% of RS-Au-L-Gd, the almost complete transformation can be achieved in 60 s under microwave irradiation conditions. This hybrid catalyst was air stable, water soluble, dissolvable in many organic media, and precipitable. It can be readily recycled more than eight times without any significant loss of its catalytic activity. GRAPHICAL ABSTRACT.
- Chang, Tsao-Ching,Yu, Shuchun Joyce
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supporting information
p. 661 - 672
(2015/10/29)
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- Enantioselective recognition between chiral α-hydroxy-carboxylates and macrocyclic heptadentate lanthanide(III) chelates
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Three novel heptacoordinated Ln(III) complexes (Ln = Gd and Yb) have been synthesized and investigated by 1H NMR spectroscopy. These complexes contain two stereogenic centers, one associated with a δδδδ or λλλλ conformation of the ethylenediamine moieties in the tetraazamacrocycle and the latter arises from the orientation (Δ or Δ) of the coordinating arms. Evidence has been gained for the occurrence of a fast exchange between all the possible conformers. Upon addition of several (S)-α-hydroxy-carboxylate substrates, the formation of stable ternary adducts has been obtained. Their 1H NMR spectra are consistent with the presence of two diastereoisomers differing in the conformation adopted by the macrocyclic ligand wrapping the lanthanide(III) ion. The interaction leading to the formation of the ternary complexes is enantioselective depending on the hydrophilicity of the α-hydroxycarboxylate.
- Terreno, Enzo,Botta, Mauro,Fedeli, Franco,Mondino, Bruna,Milone, Luciano,Aime, Silvio
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p. 4891 - 4897
(2008/10/08)
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- Ligand basicity and rigidity control formation of macrocyclic polyamino carboxylate complexes of gadolinium(III)
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The formation reaction rates of some macrocyclic polyamino carboxylate complexes of gadolinium, GdL (where L is DO3A = 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid, H3L, HP-DO3A = 10-(hydroxypropyl)-1,4,7,-10-tetraazacyclododecane-1,4,7-triacetic acid, H3L, and DO3MA = (1R,4R,7R)-α,α′,α″-trimethyl-1,4,7,10- tetraazacyclododecane-1,4,7,10-triacetic acid, H3L), have been measured at 25.0 ± 0.1°C and at a constant ionic strength of 1.0 (NaCl) by an indicator method. The formation reactions are first order in the limiting reagent (ligand) and nearly independent of the excess reagent (gadolinium ion). A mechanism of the formation of the gadolinium complexes involves the formation of a precursor (intermediate) complex, Gd(*HL), in an equilibrium step followed by its deprotonation and reorganization to the final product in the rate-determining step. The stability constants (log KGd(*HL)) of the intermediate have been determined from the kinetic data and the values are 8.9 (DO3A), 9.0 (HP-DO3A), and 10.7 (DO3MA). The nature of the intermediate is proposed in which the metal is coordinated to oxygens and at least one nitrogen of the ligand. Deprotonation and reorganization of the intermediate are specific-base assisted. The second-order rate constants (kOH, M-1 s-1) for the reorganization of the intermediate, Gd(*HL) (L are given in the parentheses), are (2.1 ± 0.1) × 107 (DO3A), (1.23 ± 0.04) × 107 (HP-DO3A), and (7.2 ± 0.3) × 104 (DO3MA), compared to the literature data (7.1 ± 1) × 107 (NOTA) and (5.9 ± 0.2) × 106 (DOTA). The specific-base assisted rate of reorganization of the intermediate, Gd(*HL), is correlated with the ligand strain energy and its first protonation constant. These observations lead us to conclude that the rate of reorganization of the intermediate is governed by the basicity and rigidity of the ligand.
- Kumar, Krishan,Tweedle
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p. 4193 - 4199
(2008/10/08)
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