Catalytic applications of polysiloxane stabilized transition metal nanoclusters.
Item
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Title
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Catalytic applications of polysiloxane stabilized transition metal nanoclusters.
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Identifier
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AAI3334677
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identifier
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3334677
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Creator
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Rathore, Jitendra Singh.
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Contributor
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Adviser: Bhanu P. S. Chauhan
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Date
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2008
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, Polymer
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Abstract
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We have demonstrated "in-situ" formation of polysiloxane stabilized Pd-nanoclusters during silaesterification reactions of PMHS. Controlled poisoning experiments (e.g. mercury and PPh3 poisoning tests), transmission electron microscopy (TEM), and UV-vis studies established Pd-nanoclusters to be real catalytic species during silaesterification reactions. Additionally, gram-scale synthesis of Pd-nanoclusters as stable and isolable powder was carried out using PMHS as reducing as well as stabilizing agent. Characterization of Pd-nanoclusters was carried out using a number of spectroscopic techniques, such as TEM, SEM, XPS, FT-IR, UV-vis, and multinuclear NMR spectroscopy (29Si and 13C nuclei). Catalytic use of isolated Pd-nanoclusters was demonstrated by using them as effective catalyst for alcoholysis of Si-H bonds of PMHS. Quantitative grafting of polyhydrosiloxanes backbone was achieved under mild reaction conditions with varied number of alcohols (primary, secondary, and tertiary alcohols).;Highly chemoselective hydrogenation of conjugated alkenes (alkenes, in which double bonds are conjugated with aromatic, enone, or ester functionalities) was achieved using polysiloxane-conjugated Pd-nanoclusters as catalyst and PMHS as "hydrogen-source". Polysiloxane-conjugated Pd-nanoclusters were generated during the catalysis by the reduction of Pd(OAc)2 to Pd(0) and subsequent stabilization of growing nanoclusters with PMHS. Electron microscopy analysis of the reaction mixture during the reaction in conjunction with controlled poisoning experiments (mercury and thiol poisoning) established Pd-nanoclusters to be active catalytic species. In addition, recyclability of the catalyst was also established.;Expanding the scope of our synthetic methodology, Pt-nanoclusters were synthesized by PMHS reduction of codPtMe2. The catalytic potential of isolated nanoclusters was explored for hydrosilylation reaction of alkenes. Using Pt-nanoclusters as catalyst, macromolecular grafting of polyhydrosiloxanes was carried out by substituting the alkenes on the polymeric backbone. In most of the cases, quantitative and selective (> 95% anti-Markovnikov ) attachment of the alkenes was achieved under mild reaction conditions without any noticeable side reactions. Thermal analysis of the hybrid polysiloxanes demonstrated enhanced thermal stability. Moreover, Well-defined hybrid nanostructures were generated by regioselective and quantitative catalytic substitution of olefins on octakis(dimethylsiloxy)-T8-silsesquioxane (Q8M 8H) and 1,3,5,7 Tetramethylcyclo-tetrasiloxane (D 4H). Additionally, Pt-nanoclusters exhibited excellent catalytic activity and selectivity for hydrogermylation reactions i.e. addition of Ge-H across the double bonds of alkenes. Excellent yields were achieved for the hydrogermylated products with tri-n-butylgermane and a number of structurally varied alkenes. The heterogeneous nature of the catalyst during the reaction was established with transmission electron microscopy (TEM), UV-vis spectroscopy, and controlled poisoning experiments.
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Type
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dissertation
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Source
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PQT Legacy Restricted.xlsx
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degree
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Ph.D.