We are delighted to announce that the second Debye Lecture speaker for 2024 has been chosen: Dr. T. Don Tilley, from the UC Berkeley College of Chemistry. The Debye lecture series is one of the most prestigious seminars offered by the Cornell University Department of Chemistry and Chemical Biology, and is also one of the most important events sponsored by the Cornell local section of the ACS. The first lecture was offered by Dr. R.B. Woodward in 1963, and top chemists in all chemical disciplines have been offered the chance to lecture in the years since. Although the lecture series is historically offered only once a year, this second lecture is making up for lost time, as lectures were not held during the Covid 19 epidemic.
Dr. Tilley specializes in organometallic chemistry, with a particular focus on catalysis. He will give two lectures, as is standard for the Debye. The first, to be given on Thursday September 5 at 3:30 PM in Physical Sciences Building room 120, is titled “Oxo Metal Cubane Clusters in Water Splitting and Bond Activations”. The second, to be given on Friday September 6 at 4:00 PM in the same location, is titled “Metal-Mediated Ring Fusions for Scalable Syntheses of Conjugated Nanocarbons”.
“Oxo Metal Cubane Clusters in Water Splitting and Bond Activations”
September 5, 3:30 PM
The conversion of solar energy into a useful chemical fuel represents a major goal in the drive towards a society fully powered by renewable energy. Several potential fuels are of interest, including hydrogen from proton reduction, and various hydrocarbons from carbon dioxide reduction. To achieve meaningful rates of fuel production, the potential reduction reactions must be coupled to an oxidative reaction that generates electrons and protons. The most reasonable candidate to provide these electrons and protons is water, which can be chemically decomposed to 4 protons, 4 electrons, and oxygen (the oxygen evolution reaction, OER). For solar fuel applications, this water-splitting half reaction must be catalyzed to make it energetically efficient, as accomplished in nature’s photosynthesis by a tetra-manganese oxo cluster (the oxygen-evolving complex, OEC). Indeed, related transition-metal oxo cubane clusters represent intriguing model systems and catalyst design motifs for development of new water-splitting catalysts based on the most abundant metals. Molecularly derived catalysts of this type offer potential advantages, including the synthetic tunability of structure-activity relationships and chemical properties. Also, the study of model, high-valent molecular species can provide key insights into the mechanism of water oxidation, and thereby help bridge the gap between solid-state and molecular systems to allow for more rational design of catalysts. This presentation will describe high-valent tetracobalt oxo cubane clusters, and the experimental determination of a well-defined mechanism for cubane-catalyzed oxygen evolution via water oxidation. The systematic variation of electronic properties for these clusters, and strategies for their stabilization, will be described. The synthesis and study of clusters doped by another transition metal, and linked bis-cubane complexes, are further topics to be discussed.
“Metal-Mediated Ring Fusions for Scalable Syntheses of Conjugated Nanocarbon”
September 6, 4:00 PM
The discovery of graphene and its extraordinary properties have motivated research on large polycyclic aromatic hydrocarbons (PAHs), which are basic building blocks of graphene and other carbon-rich nanostructures. Various PAHs are of interest as molecular models, synthetic precursors, and components in electronic devices, due to unique properties that result from their extended conjugation and rigidity. Thus, a central goal in this area is the synthetic manipulation of electronic properties for nanocarbon materials, by generation of well-defined dimensionalities and functionalizations. This is particularly challenging since it requires high-yielding, efficient synthetic methods for multiple ring fusions within the same molecule. Importantly, near-quantitative yields are necessary for each ring-fusion event to avoid difficult separations and/or defects. Although the development of organometallic methods for difficult ring-fusion steps has received considerable attention, few are high-yielding enough for applications to very large PAHs.
The research group has employed selective metal-mediated cycloadditions for extension of π systems and introduction of multiple fused rings in the synthesis of π-conjugated oligomers, polymers, and macrocycles,
mainly via the reductive coupling of alkynes with a low-valent zirconocene reagent. In addition to the zirconocene coupling of alkynes, high-yielding and chemoselective [2+2+2] cycloadditions of alkynes (with an iridium catalyst) and/or [2+2+n] cycloadditions of nitriles (with titanocene) have been developed as complimentary synthetic tools for access to and elaboration of nanocarbon structures. Promising features of this approach are: 1) generation of a PAH directly from the precursor and 2) divergent introduction of functionality using metal-transfer reactions. This chemistry will be described, along with applications to scalable syntheses of large PAHs and carbon nanostructures such as expanded helicenes and carbon nanobelts. An additional aspect to zirconocene alkyne coupling chemistry involves reversible processes that allow “Dynamic Covalent Chemistry” assembly of large structures including macrocycles and cages. Application to multi-topic alkyne monomers leads to topologically complex, knotted structures.
- https://pubs.acs.org/doi/10.1021/jacs.1c04037
- https://onlinelibrary.wiley.com/doi/10.1002/anie.202012213
- https://pubs.acs.org/doi/full/10.1021/jacs.0c09941
- https://pubs.acs.org/doi/10.1021/jacs.2c02581
- https://pubs.acs.org/doi/pdf/10.1021/jacs.2c09555
We recognize that these lectures may be of interest to those unable to attend in person, and this year we began providing the lectures via Zoom link, as well as recording them. While our Zoom license is limited, and thus we can only distribute links to local section membership (check your email for the links, and reach out if you didn’t get them for some reason!), we will also upload the recordings to our Youtube channel, so that anyone can watch the lectures at a time of their choosing. The links will be posted to this website once the videos are available.