Synthesis and Characterization of Group 3 and 13 Metal Complexes Supported by Phosphasalen Ligands

Why This Project: Through a research program that I participated in called the High School Youth Researcher Summer (HYRS), I was able to further pursue my interest in chemistry. Being in the HYRS program allowed me to do chemistry research in a university environment, which is how I created the project you’re seeing right now.

Background: Each year, 8-11 million tonnes of non-degradable plastic

waste is released into the ocean. Polylactide (PLA) is a polymer that shares similar properties

with traditional plastics such as polyethylene, but is biodegradable. PLA can be used for functions such as food packaging, disposable utensils, and garbage bags. PLA also has medical uses such as for slow release medication and absorbable bone screws. Well-defined chemical compounds called metal complexes can trigger the process of ring-opening polymerization, which creates PLA, leading to high-quality, well-defined products. A major issue with producing PLA on an industrial scale, is that it lacks selectivity, meaning that it’s inefficient to produce and often yields unnecessary byproducts. Organic frameworks called ligands can be designed to make highly active and selective catalysts for PLA, making it more efficient to produce.

Previous Work: The Hayes Lab (the lab which I was working under for my research) synthesized the ligands and complexes which I used for my experiments. The part of the project which I conducted was the complexation of the auxiliary ligand. I would use complexes containing different metals (Yttrium, Scandium, Lutetium, Aluminum, Indium, and Gallium) and attempt to react them with another compound called an auxiliary ligand, in order to create a catalyst for PLA.

Materials and Methods: I would typically weigh about 10 mg of a metal complex in a container called a glovebox. A glovebox is a container used to create a stable environment for pyrophoric chemicals, which are chemicals that ignite when exposed to air. I would use calculations to figure out how much of the auxiliary ligand I need compared to the complex, and weigh the auxiliary ligand in the glovebox as well. I would dissolve the auxiliary ligand and complex using a solvent (typically benzene) then put them both in an NMR (Nuclear Magnetic Resonance) tube so I can test the reaction. I would seal the tube and bring it to a machine called an NMR spectrometer to get data on the chemical structure of the sample and figure out if the reaction was successful in creating a new product. The spectrometer can also give me information such as how pure the product is and whether a reaction is incomplete.

Results: I used two different auxiliary ligands for my experiments, alkoxide (OtBu) and HMDS (N[Si(Me3)3]2). The Yttrium complex yielded a mixture of products for both alkoxide and HMDS. The scandium complex yielded the most successful reaction, reacting completely with both alkoxide and HMDS. The lutetium complex had no reaction with alkoxide but a mixture of products with HMDS. The aluminum complex yielded an incomplete reaction for both alkoxide and HMDS. The Indium complex yielded a mixture of products with alkoxide but an incomplete reaction with HMDS. The Gallium complex had no reaction with either alkoxide or HMDS.

Data: I used a graph called an NMR spectrum to represent my data. When I initially get information from an NMR spectrometer, I wouldn’t simply be shown what exactly the chemical structure of what I’m looking at is. Instead, the spectrometer would display a chart called an NMR spectrum with peaks where a certain element is detected. The differing positions of these peaks are called chemical shifts, and every compound would have its own typical chemical shifts. I would compare the peaks on the NMR spectrum of my experiment with the chemical shifts of peaks on an NMR spectrum typical to the product I’m trying to make. If the peaks on the two charts match, then I was successful in creating a new product. The stars on the chart represent where the peaks on the NMR spectrum corresponded to the chemical structure of the Scandium complex bonded to the auxiliary ligand.

Using my results, I was able to conclude that the Scandium metal complex was a successful potential catalyst for making PLA production more efficient. This is highly important to my research since it indicates that bonding certain metal complexes to auxiliary ligands does have potential to absolve a major barrier to producing PLA, and therefore make PLA a more viable option for plastic products.

In future, the Hayes lab would synthesize more complexes that are similar to the ones I tested and attempt to react them with auxiliary ligands, so there would be a larger family of possible catalysts for PLA. Putting results into action, we would react the complexes that were successful in forming a new product with lactide to create a PLA-like compound through ring-opening polymerization.

I would like to thank Dr. Paul G. Hayes for welcoming me into his lab and giving me guidance in developing and presenting my project. I would also like to thank my fellow Hayes Lab Members Thamara Salazar-Barrientos and Emily Trew for teaching me the skills I needed to know for my experimentation and guiding me throughout my project. I would like to thank the University of Lethbridge Research Fund (ULRF) for funding the equipment and facilities which I used for my research. I would like to thank the High School Youth Researcher Summer program (HYRS) for providing me the opportunity to pursue a project like this in a university environment.

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(2) Robert, J. L.; Aubrecht, K. B. Ring-Opening Polymerization of Lactide to form a Biodegradable Polymer. J. Chem. Educ. 2008, 85 (2), 258.

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(4) Dickie, T. K. K.; MacNeil, C. S.; Hayes, P. G. Consecutive N2

loss from a uranium diphosphazide complex. Dalton Trans. 2020, 49, 578-582.

(5) Perez, F. [A sea turtle entangled in a ghost net] [Photograph]

https://oceanchampions.ca/great-pacific-garbage-patch-may-16-times-massive-previously-thought/great-pacific-garbage-patch-16-times-larger-a-sea-turtle-entangled-in-a-ghost-net-photo-by-francis-perez/