Rigid and Flexible Linker Systems for Superior Immobilized Catalysts
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abstract
The NSF Chemical Catalysis Program supports the efforts of Professor Janet Bluemel of Texas A&M University to investigate homogeneous and immobilized molecular nickel catalysts in order to clarify the processes by which metal complexes decompose to form nanoparticles. Nickel(0) catalysts are immobilized on surfaces via phosphine linkers chosen from a broad range of mono-, di-, and tridentate ligands that incorporate flexible alkyl chains or rigid tetraphenylelement cores. Strategic ligand selection helps discriminate between dimerization on the surface and agglomeration as the crucial step in the eventual nanoparticle formation. The cyclotrimerization of phenylacetylene is used as a model reaction to study the selectivity and activity of the immobilized catalysts and to monitor potential nanoparticle formation. The dynamics of metal complex migration from one uncoordinated phosphine linker to the next on the surface is quantified using 31P T1 relaxation times and HRMAS NMR data. Metal complexes other than Ni(0) and different catalytic reactions are also investigated to probe the general applicability of the insights gained with the model catalytic system. Immobilized catalysts have the potential to improve industrial scale chemical processes and thus, this project may improve the environmental sustainability of large scale chemical synthesis by providing general methodologies for the preparation and use of non-precious metal catalysts with superior activities, selectivities, and lifetimes. Graduate and undergraduate students involved in the project receive interdisciplinary training and gain experience in advanced techniques for the characterization of amorphous materials. The Chemical Catalysis Program supports the efforts of Professor Janet Bluemel of the Texas A&M University to compare differences in homogeneous and immobilized catalysts. During homogeneous catalysis, nanoparticles can form from the metal catalyst resulting in a suspension of heterogeneous catalysts in solution. Starting from immobilized catalysts, the same process leads to nanoparticle formation on the surface. This uncontrollable scenario is undesirable because it is not predictable, not generally preventable, and may change the selectivity of the catalyst or shorten its lifetime, diminishing the recyclability of the catalyst. This research project investigates homogeneous and immobilized molecular nickel catalysts in order to clarify the processes associated with metal catalyst decomposition (e.g. decomposition on the surface or agglomeration in solution) to form nanoparticles. This project has the potential to improve the environmental sustainability of large scale chemical synthesis by providing general methodologies for the preparation and use of non-precious metal catalysts with superior activities, selectivities, and lifetimes. Graduate and undergraduate students involved in the project receive interdisciplinary training, collaborate internationally, and gain experience in advanced analytical techniques.
