Dynamic Ligands for Sustainable Molecular Catalysis

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The research program, 'Dynamic Ligands for Sustainable Molecular Catalysis', targets innovative catalysts for the synthesis of high-value organic compounds. Advances in catalyst development will be achieved by expanding the fundamental design parameters and principles of cooperative ligands. Transition-metal complexes of these ligands will be exploited in catalytic processes that are highly atom-economic and that use non-toxic and abundant feedstocks (i.e. water, oxygen and first-row metals). Specifically, we target allylic oxidation and hydration reactions. The new catalytic systems will be powerful in applications of organic synthesis in both the academic and industrial realms. Catalysts structures exploit cooperative characteristics, where reactivity at the metal centre is amplified or modulated by a secondary process or functionality. These synergistic relationships include ligands that demonstrate responsive hapticity (dynamic coordination) or second-coordination sphere processes. The latter includes functionalities that participate in hydrogen-bonding or intramolecular proton transfer. These cooperative relationships open new pathways for reactivity or selectivity that are inaccessible through traditional activation of substrates with transition metals. A main objective of this work is to gain a molecular-level understanding of these processes and how they are altered with changes in ligand design. This insight is crucial to the development of high-performance catalysts. The research program is divided between three main research branches. 1) Dynamic Mixed-Donor Ligands for Late-Metal Complexes. We are developing a new ligand family P-AzA that is comprised of a neutral phosphine and an anionic 1-azaallyl fragment. The ligand has the potential to bind to metals in a variety of modes and this coordination shift in response conditions of the system (i.e. introduction of other ancillary ligands or reagents). A thorough understanding of these systems is attained through detailed spectroscopic and reactivity studies, the results of which are necessary for the development of catalytic systems. Catalytic testing of this unique ligand framework is expected to uncover unprecedented activity and selectivity. 2) Selective Oxidation Mediated by Bifunctional Nickel Complexes. Dioxygen is an ideal oxidant and O-atom source as it is highly abundant and, if properly controlled, generates environmentally benign by-products. Control is a major challenge, which can be achieved with uniquely designed metal complexes. We target nickel-NHC complexes that contain hydrogen-bond donors adjacent, but not attached, to the metal centre (NHC = N-heterocyclic carbene). We postulate that these secondary interactions will alter reactivity, diverting away from deactivated or decomposed products. Reactivity studies will provide the groundwork for the development of aerobic oxidation catalysts. 3) High-Performance Catalysts for the Anti-Markovnikov Hydration of Alkynes. Conversion of alkynes to aldehydes with environmentally benign water is 100% atom-economic. Catalytic systems are needed that operate at lower catalyst loadings, lower temperatures and at faster rates. Proton transfer is a key step in the catalytic cycle and is dramatically assisted by ligands that promote intramolecular movement. An extremely promising, but underexploited system is the PR2NR'2 ligand family. Catalytic and stoichiometric studies of several variants (R/R' = Ph, Ar, Cy, Bn, tBu) will uncover the optimal phosphine donor strength and amine basicity for promoting rapid and selective product formation.