The Lipke group employs supramolecular and macromolecular chemistry in service of transition-metal catalysis, with interests that include C–H functionalization, cross-coupling reactions, and the conversion of C1 feedstocks (e.g. CH4, CO2) into liquid fuels. Our approach to catalysis combines mechanistic insight with the development of new synthetic methods to create catalysts that exhibit cooperativity between multiple metal centers, or between a metal center and its surrounding chemical environment.
Supramolecular Synthetic Methods for Bimetallic Complexes.
Metal-metal cooperativity is important to the activity of many metalloenzymes and artificial homogeneous catalysts, but synthetic limitations make it difficult to freely tune bimetallic catalysts that contain more than one type of metal. We aim to overcome the present challenges by designing pairs of ligands that include complementary noncovalent recognition sites for selectively bringing together two different metal complexes. This approach will facilitate the synthesis of libraries of heterobimetallic catalysts that are not easily synthesized by other means.
Radical Stabilization in Nanoconfined Environments.
Many important catalytic processes involve organic radicals as intermediates. Examples include C–H oxidations mediated by Mn-, Fe-, and Cu-oxo complexes (pictured above), as well as Ni-catalyzed Kumada couplings. We are searching for ways to increase the efficiency or modify the outcome of radical-based transformations by examining these reactions within specially tailored chemical environments. We surround the catalyst with functional groups – persistent organic p-radicals and metalloradicals – that might stabilize reactive radical intermediates and/or transition states that exhibit radical character.
Mechanochemically Stimulated Transition Metal Reactivity.
Catalysts make reactions more efficient and/or selective by reducing the activation energy that is needed for a desired transformation. We are exploring an innovative method to accomplish this goal by coupling the reactivity of transition metal catalysts with the dynamics of polymers in solution. Elongation of polymers can lower the barrier to bond-rupture and/or other reactivity near the center of the polymer chain. By incorporating metal complexes into polymers, we hypothesize that this phenomenon can be used to “pull” catalytic reactions over extremely high energy barriers (≥50 kcal/mol).
Lipke, M. C.; Wu, Y.; Roy, I.; Wang, Y.; Wasielewski, M. R.; Stoddart, J. F. (in preparation)
“Shuttling Rates and Electronic States of a Ring-In-Ring Rotaxane”
Lipke, M. C.; Cheng, T.; Wu, Y.; Arslan, H.; Xiao, H.; Wasielewski, M. R.; Goddard III, W. A.; Stoddart, J. F. J. Am. Chem. Soc. 2017, 139, 3986 – 3998.
“Size-Matched Radical Multivalency”
Lipke, M. C.; Liberman-Martin, A. L.; Tilley, T. D. Angew. Chem. Int. Ed. 2017, 56, 2260 – 2294.
“Electrophilic Activation of Silicon-Hydrogen Bonds in Catalytic Hydrosilations”
Lipke, M. C.; Liberman-Martin, A. L.; Tilley, T. D. J. Am. Chem. Soc. 2016, 138, 9704 – 9713.
“Significant Cooperativity Between Ruthenium and Silicon in Catalytic Transformations of an Isocyanide”
Lipke, M. C.; Tilley, T. D. J. Am. Chem. Soc. 2014, 136, 16387 – 16398.
“Hypercoordinate Ketone Adducts of Electrophilic h3-H2SiRRꞌ Ligands on Ruthenium as Key Intermediates for the Efficient and Robust Hydrosilation of Ketones”
“Interconversion of h3-H2SiRRꞌ complexes and 16-Electron Silylene Complexes via Reversible H—H or C—H Elimination”
Fasulo, M.; Lipke, M. C.; Tilley, T. D. Chem. Sci. 2013, 4, 3882 – 3887.
“Structural and Mechanistic Investigation of a Cationic Hydrogen-Substituted Ruthenium Silylene Catalyst for Olefin Hydrosilation”
Lipke, M. C.; Tilley, T. D. J. Am. Chem. Soc. 2013, 135, 10298 – 10301.
“Silane-Isocyanide Coupling Involving 1,1-Insertion of XylNC into the Si—H Bond of a s-Silane Ligand”
Lipke, M. C.; Tilley, T. D. Angew. Chem., Int. Ed. 2012, 51, 11115 – 11121.
“Stabilization of ArSiH4- and SiH62- Anions in Diruthenium Si—H s-Complexes”
Lipke, M. C.; Tilley, T. D. J. Am. Chem. Soc. 2011, 133, 16374 – 16377.
“High Electrophilicity at Silicon in h3-Silane s-Complexes: Lewis Base Adducts of a Silane Ligand, Featuring Octahedral Silicon and Three Ru—H—Si Interactions”
Lipke, M. C.; Woloszynek, R. A.; Ma, L.; Protasiewicz, J. D. Organometallics 2009, 28, 188 – 196.
“m-Terphenyl Anchored Palladium Diphosphinite PCP Pincer Complexes that Promote the Suzuki-Miyaura Reaction Under Mild Conditions”