Nassar S USciences
Published on: Mar 3, 2016
Transcripts - Nassar S USciences
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
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 7: Synthesis of a Platinum Complex
Figure 1: NMR Spectra
Scheme 7: Synthesis of a Rhodium Complex and Zinc Chloride