Current research is focusing on utilizing bimetallic catalysts for the
functionalization of aromatic heterocycles. A catal...
of 1

Nassar S USciences

Published on: Mar 3, 2016

Transcripts - Nassar S USciences

  • 1. Current research is focusing on utilizing bimetallic catalysts for the functionalization of aromatic heterocycles. A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. These catalysts will contain two different metals which can work together to facilitate C-H activation. C-H activation is a reaction that cleaves a C-H bond and can lead to the formation of C-X bonds. Past studies have suggested that C-H activation could lead to the conversion of cheap and plentiful alkanes in valuable organic compounds. The noble metals are particularly good at catalyzing this type of reaction. Scheme 1 shows that by utilizing a transition metal as a catalyst, it will turn the CH bond into a C-X bond, where X is a halogen, which would then be used for other transformations. Direct C-H activation is the most efficient. Scheme 2 shows nitrogen forming a bond with the Pd atom and allowing the C-H bond of the benzene ring to be broken, this in turn will allow a new heteroatom, which is any atom that is not carbon or hydrogen, to replace the hydrogen atom on the benzene ring. We hope to accomplish a similar type of directing group assisted bond activation where the directing group is on the catalyst rather than the substrate. We want the secondary metal to bind the substrate, limiting us to things with a heteroatom capable of bidning to the secondary metal. Primarily, for now, the main focus is on aromatic substrates, such as pyridine. Scheme 3 (target ligand) is used to facilitate catalytic compounds, it has the ability to coordinate to two metals simultaneously. Scheme 4 shows the possibility of bonding zinc and platinum to the ligand and activating the C-H bond of pyridine. Synthesis of Noble Metal Catalysts for the Functionalization of Heterocyclic Compounds Sherin Nassar, Steven Rossi, Megan Mohadjer Beromi, Kaitlin Earley and Nathan West* Department of Chemistry & Biochemistry, University of the Sciences, Cherry Hill High School East The functionalization of aromatic heterocycles is a vital aspect in both the industrial and academic setting. Various methods for the synthesis of these compounds exist, however, no atom efficient catalytic formation has been reported. Experimentation is currently being conducted on the synthesis of bimetallic catalysts to help facilitate the functionalization of these compounds. Thus far, Rhodium and Platinum have been the primary metal explored. Using these noble metals, additional synthesis of bidentate ligands has been conducted increase the stability of the potential catalysts. To try and increase the reactivity, a second metal to synthesize bimetallic, species. The second metal allows for the functionalization of the C-H bond, by coordination to the heteroatom in the ring and holding it in proximity to the noble metal. Preliminary studies on the reaction chemistry of these complexes have been done and the results are reported here. In conclusion, although we were able to synthesize our desired ligand and bind it to both Pt and Rh, we still need to create a type of directing group assisted bond activation with the directing on the catalyst rather than the substrate. Though we were successful in reacting the rhodium complex with the Zn(Cl)2 (pyridine), no C- H activation occurred because we were unable to displace the COD. We need to figure out a way to hydrogenate the COD off of rhodium, since when this does occur, it will make an open site on the rhodium where C-H activation of pyridine to occur. The NBD complex of Rh has also been synthesized because it is generally easier to displace than COD, but its reactivity has not yet been explored. Hull, K.L. ; Lanni, E. L. ; Sanford, M.S. J. Am. Chem. Soc. 2006, 128, 14042 Chen, X.; Engle, K. M., Wang, D-H. ; Yu, J-Q. Ange W. Chem. , Int. Ed. 2009, 48, 5094 Bodes A. J. ; Bol, J. E; Driessens, W. L; Hulsbergen, F.B. ; Reedi; K, J. ; Spek, A.L. Inors. Chem, 1999, 38, 1239Our primary focus currently is on chelating ligands, since it is vital that some clean cut ligands are created for future catalytic research. Reaction with sodium hydride, in excess, yielded a deprotonated version of the ligand, which we were able to react with rhodium to give the desired complex and NaCl, which was easily filtered out. With the isolated rhodium complex was reacted with the Zn(Cl)2 (pyridine), however the COD has not been displaced. Currently, attempts to hydrogenate the COD off of rhodium have not been successful. However, when the hydrogenation is successful with the rhodium, hopefully it will open a vacant site on rhodium for C-H activation of pyridine to occur, which will yield the product that is ultimately desired. As of right now, the experiments have only been successful in yielding a rhodium complex with zinc bound to the ligand nitrogen, but shows no reactivity between the two metals. In the future, we need to find a more reactive rhodium starting material that does not have difficult to displace COD on it and may be more reactive towards C-H bonds. I would really like to thank Steve, Megan and Kaitlyn for all of their help during this experience, as well as Dr. West for allowing me to use his lab. I also would like to thank the Chem Department for allowing me to be a part of this program and my mom for driving me. Scheme 5: Synthesis of a ligand (part 1) Scheme 6: Synthesis of a Rhodium Complex Scheme 1 Scheme 2 Scheme 3 Scheme 4 Scheme 7: Synthesis of a Platinum Complex Figure 1: NMR Spectra Scheme 7: Synthesis of a Rhodium Complex and Zinc Chloride

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