(251f) C-H Activation and C-C Coupling of 4-Methylpyridine Using Palladium Supported on Nanoparticle Alumina

Nano technology has opened an exciting dimension in modern catalysis research, both in the study of the nanostructures of traditional heterogeneous catalyst and their application. Not only have this opened up possibilities for improved performance of traditional catalysts and the development of new types of catalysts, they also allow study of reaction systems that have not yet been optimized to a viable industrial process. An example of such a system is the palladium-catalyzed coupling of bypyridyls. One product of this reaction, 4,4' dimethyl 2,2' bypyridine, is a useful chelating agent with wide potential uses in processes ranging from catalyst formation to artificial photosynthesis. Unfortunately, current production techniques make it prohibitively expensive for industrial scale application. Some techniques rely upon multi-step synthesis involving the use of halogenated precursors that in addition to adding serious environmental considerations can act as poisons in end use applications if not fully removed. Oxidative coupling of 4-methylpyridine over palladium is a simple one step reaction. However it is slow and produces poor yields. Most research in literature for the palladium catalyst system has focused on carbon supports. This appears to be for the good reason that other supports such as alumina have not shown significant activity. With the new availability of nano-particle supports we have revisited the palladium on alumina catalyst for this reaction. It is our hypothesis that nano-particle alumina supported palladium catalysts could potentially have unique properties that can result in significantly higher activity for this reaction. In our research we deposited palladium on a nano-alumina support by precipitation and wet impregnation and compared these catalysts to commercial carbon- and alumina-supported catalyst, as well catalysts prepared using a traditional alumina support. While the commercial carbon catalyst showed results consistent with literature, the precipitated nano-alumina catalyst not only gave significant yields, but also surpassed the commercial Pd/C catalyst in activity. The other alumina catalysts exhibited little activity. Additional experiments have shown that the activity of the catalyst supported on nanoparticle alumina was largely insensitive to loading, and verified that this reaction system is heterogeneous. This catalyst system offers an exciting opportunity for continuing research to both optimize the new catalyst and study the mechanisms behind the high activities of nano-particle supported catalyst.