Our research explores the electronic structure, reactivity, and connectivity modes of main group elements with the goal of developing greener materials. We do this by generating cleaner catalysts for biomass polymerization and by developing alternative "inorganic plastics" that are compatible with a NetZero future.
Our methodology focuses on systematic geometric perturbation of molecules using multidentate ligands. Besides sterics and electronics, geometric tuning represents an attractive (but understudied) means of controlling chemistry at main group centres. We synthesize compounds whose shape — rather than their electron richness/poorness or steric bulk — imbue them with functional properties. We then evolve applications of these compounds as catalysts or materials.
This program spans the molecular and macromolecular length scales, training colleagues in a wide range of experimental and computational techniques while fostering a quantitative and mechanistic mindset. Through this approach, we are able to reveal the chemical consequences of the molecules we find to be aesthetically pleasing and also contribute to addressing the important global challenge of moving away from fossil fuels for our energy and materials needs.
We are developing phosphorus-nitrogen cages into new 3-dimensional "scaffolding molecules" from which additional functional groups can be extended with well-defined bond angles and lengths. Traditionally, certain organic molecules such as adamantanes and tetraarylmethanes have been used as scaffolds due to their ability to covalently link functional groups in rigidly defined arrangements, leading to applications in optoelectronic materials, thermally-stable energetic compounds, catalysts with enhanced robustness or multi-catalytic sites, bioactive frameworks, and pharmaceuticals. In reticular chemistry, such scaffolds also have many applications due to their symmetry and ability to space out nodes. The inorganic cages we have developed in this context are much easier to synthesize and derivatize, offer a phosphorus NMR handle, and fill a geometric gap between the scaffold sizes currently available. We are interested in applying these cages in materials chemistry. Polymers are generally comprised of linear or ring based monomers. We are curious about the possibility of making cage-dense polymers - materials that feature a large number of 3-dimensional cages in their backbone. Such materials are not well-represented because it is difficult to make polymerizable organic cages. On the other hand, reactive inorganic cages are relatively straightforward to make and we believe they represent an excellent means of exploring the uncharted territory that is cage-dense polymers and materials. Specifically, we are seeking to develop these cages into robust nitrogen-rich and carbon-negative monomers for making green inorganic polymers that can be recycled back into natural systems by conversion to P- and N-rich fertilizer components.
Lead References:
Chem. Commun., 2024, In Press.
J. Am. Chem. Soc., 2023, 145 7569-7579
Angew. Chem. Int. Ed., 2022, e202204851. (Highlighted in ChemistryViews magazine)
The use of multidentate ligands is ubiquitous in transition metal chemistry, but less developed for main group centres. Such ligands can engender novel electronic structure at main group centres by enforcing nonclassical geometries. We are interested in developing this concept with the aim of eliciting new reactivity modes because understanding the design rules governing changes in frontier orbital energies as a function of geometry and ligand environment will reveal new stoichiometric and catalytic applications. For example, we showed that planar bismuth compounds, accessible using a triamido pincer ligand, exhibit very interesting redox confusion and also behave as potent catalysts for polymerization of bio-mass derived green monomers to give biodegradable materials (polylactide and polycaprolactone). We are also interested similarly in making new types of bonds that have never been made before. For example, we reported the first Sb-Bi single bond in 2020 and analyzed the role of dispersion in enabling its synthesis.
Lead References:
Chem. Sci., 2023, 14, 4549.
Chem. Commun., 2020, 56, 8015. (Invited submission to the 2020 Emerging Investigators Issue)
Angew. Chem. Int. Ed., 2019, 58, 7850.
We have unlocked the antimony version of hydroboration - named 'hydrostibination'. This was achieved by using a strategically deformed amido ligand at a reactive Sb-H centre. The geometric distortion lowers the metal-centered LUMO and enables substrate binding and activation. A variety of unsaturated organic compounds undergo hydrostibination with our distorted antimony hydrides at ambient temperature. We are also interested in detailed mechanistic studies of the reactions we discover, and use quantitative physical methods and high level DFT calculations to elucidate the elementary steps involved.
Lead References:
Chem. Eur. J., 2020, 26, 17134. (Selected by editors as a 'Hot Paper')
Angew. Chem. Int. Ed., 2019, 58, 18096.
