282912 New Opportunities in Metal Cluster Catalysis by Using Organic Ligands

Monday, October 29, 2012: 12:50 PM
317 (Convention Center )
Ron C. Runnebaum1, Alexander Okrut1 and Alexander Katz2, (1)Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, CA, (2)Department of Chemical and Biomolecular Engineering, University of California Berkeley, Berkeley, CA

Rate and selectivity of supported-metal clusters can be tuned by changing the cluster ligands. Much research has focused on investigating ligand-support interactions. This study, however, emphasizes the effects of organic ligands on catalysis by homogenous and by heterogeneous metal-cluster catalysts. A comparison of calixarene-bound Ir4-based carbonyl clusters consisting of Ir4(CO)9L3 and Ir4(CO)11L (L = t-butyl-calixarene[4](OPr)3(OCH2PPh2)) both in homogeneous solution and when immobilized on the surface of silica is performed.  Catalytic studies were performed by subjecting both materials to a reactive mixture of gases for ethylene hydrogenation.  Both clusters successfully catalyze the hydrogenation reaction at room temperature and appear to be stable after a brief approach to steady-state.  At 50 oC, the catalyst containing three calixarenes per active site, Ir4(CO)9L3, retains its stability features, showing a rapid approach to steady-state activity.  In contrast, however, catalyst Ir4(CO)11L consisting of only a single calixarene per active site shows a lack of stability.  We also describe a pretreatment of the calixarene-based clusters, which increases their catalytic activity for ethylene hydrogenation by nearly 50-fold.

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