Synthesis, characterization and catalytic activity of polymer anchored transition metal complexes toward oxidation reactions
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Keywords:
Polystyrene
Organometallic Chemistry
Alcohol Oxidation
Alcohol Oxidation
Reusability
Molecular oxygen
Filtration (mathematics)
Allylic alcohol
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Organometallic Chemistry
Homogeneous Catalysis
Rational design
Characterization
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Abstract We describe a simple and general method for the preparation and molecular engineering of supported trifunctional catalysts and their application in the representative Cu/TEMPO/NMI‐catalyzed aerobic oxidation of benzyl alcohol. The methodology allows in one single step to immobilize, with precise control of surface composition, both pyta, Cu I , TEMPO, and NMI sites on azide‐functionalized silica particles. To optimize the performance of the heterogeneous trifunctional catalysts, synergistic interactions are finely engineered through modulating the degree of freedom of the imidazole site as well as tuning the relative surface composition, leading to catalysts with an activity significantly superior to the corresponding homogeneous catalytic system.
Alcohol Oxidation
Imidazole
Benzyl alcohol
Homogeneous Catalysis
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Organometallic Chemistry
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Organometallic Chemistry
Coordination geometry
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Organometallic Chemistry
Heteropoly acid
Solid acid
Keggin structure
Acid catalysis
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Organometallic Chemistry
MCM-41
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Cordierite
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Addressed herein is the 20+ year-old question of whether the true benzene and cyclohexene hydrogenation catalysts derived from the organometallic precursor [Rh(η5-C5Me5)Cl2]2, 1, are homogeneous or heterogeneous. The methodology employed is that developed earlier (Lin, Y.; Finke, R. G. Inorg Chem. 1994, 33, 4891, "A More General Approach to Distinguishing Homogeneous from Heterogeneous Catalysis..."). The kinetic evidence especially, but also the metal product (nanoclusters plus bulk metal), Hg(0) poisoning and other experiments, provide compelling evidence that Rh(0) nanoclusters are the true benzene hydrogenation heterogeneous catalyst derived from [Rh(η5-C5Me5)Cl2]2, 1, at the required more vigorous conditions of 50−100 °C and 50 atm H2. However, the same methods reveal that the cyclohexene hydrogenation catalyst derived from 1 at the milder conditions of 22 °C and 3.7 atm H2 is a nonnanocluster, homogeneous catalyst, most likely the previously identified complex, [Rh(η5-C5Me5)(H)2(solvent)] (Gill, D. S.; White, C.; Maitlis, P. M J. C. S. Dalton Trans. 1978, 617). In short, the present results solve the two-decade-old problem of identifying the true benzene and cyclohexene hydrogenation catalysts derived from [Rh(η5-C5Me5)Cl2]2. Perhaps most significant is the demonstration that the methodology employed has the ability to identify both heterogeneous and homogeneous catalysts from the same catalyst precursor.
Homogeneous Catalysis
Nanoclusters
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