(455c) Using Active Site Confinement and Organic Ligand Approaches to Control Catalysis

The local environment of a catalyst’s active site plays a critical role in determining the catalyst’s activity and selectivity.  This effect is seen most profoundly in enzymatic systems where the environment of the active site is controlled through the chemical entities surrounding the active site and their precise geometric locations. 

Inspired by the GroEL/GroES system in E. coli, examples with a metal complex/cluster that is immobilized inside of mesoporous materials, particularly SBA-15, will be discussed.  These nano-confined active sites demonstrate an increased degree of activity and stability which provide valuable insight into structure-function relationships in catalysis. [1] [2]

Additionally, in different gold cluster systems, we explore approaches to controlling the environment that surround these sites as well as their ultimate effects on catalysis.  The use of organic ligands, such as calixarenes, is investigated to confine and to control catalytically active noble metal sites on metal oxide supports and in homogeneous solution, using an approach that is conceptually similar to that used by enzymes to control reactivity through organic side chains acting as ligands.  Gold catalysts have been synthesized with calixarene ligands bound to the metal nanoparticle, confining the gold cluster, yet these clusters still demonstrate reactant accessibility to the metal nanoparticle surface as measured by chemisorption probe experiments. [3] [4]  Catalytic activity has been demonstrated for these systems using different reaction systems such as reduction reactions on these gold catalysts.  Results provide a unique perspective into the structure-activity relationships present in gold cluster catalysis.

References:

[1]       F. Marras, J. Wang, M.-O. Coppens, J. N. H. Reek.  Chem. Comm.  2010, 46, 6587.

[2]       L.-C. Sang, A. Vinu, and M.-O. Coppens, Phys. Chem. Chem. Phys, 2011, 13, 6689.

[3]       N. de Silva, J.-M. Ha, A. Solovyov, M. M. Nigra, I. Ogino, S. W. Yeh, K. A. Durkin, A. Katz.  Nature Chem. 2010, 2, 1062.

[4]       M. M. Nigra, A. J. Yeh, A. Okrut, A. G. DiPasquale, S. W. Yeh, A. Solovyov, A. Katz.  Dalton Trans. 2013, 42, 12762.