Serial Ligand Catalysis

Christina White of the University of Illinois’ Department of Chemistry, along with some of her colleagues, have recently published research on a serial ligand catalyst. A ligand is a group bonded to a metal, which donates electron density to (or sometimes withdraws it from) the metal.¹ Organopalladium is an example of a ligand. An organopalladium is a compound that contains a carbon-palladium bond.¹ One of the most common organopalladium ligands is palladium acetate, abbreviated Pd(OAc)₂, which is also part of both catalysts utilized in this experiment.

In the experiment an alkene was reacted with a carboxylic acid in the presence of one of two ligand catalysts. The reaction which involved the ligand catalyst also containing DMSO, produced a linear product, however, the reaction involving the polydentate sulfoxide ligand resulted in a branched allylic C-H oxidation. The team found this to be interesting and by further studying the mechanism of the branched product, they developed the concept of a serial ligand catalyst. This is 2+ different ligands binding reversibly to one metal (Pd in this case) to promote different steps for product formation in a particular catalytic cycle.²

The following is an image of the reaction and shows both catalysts:

¹ Smith, J. Organic Chemistry. 2^nd ed.; McGraw-Hill, 2008, pp 1005-1006   

²"Serial Ligand Catalysis: A Highly Selective Allylic C-H Oxidation".
M.S. Chen; N. Prabagaran; N.A. Labenz; and M.C. White.
JACS 2005, 127, 6970-6971.