Research in our group focuses on catalysis, chirality and materials chemistry. In particular, we are interested in developing new reactions to prepare compounds of interest to the pharmaceutical industry, specifically reactions that are enantioselective or enantiospecific. We also have a significant program investigating the use of carbon–based molecules as ligands for self-assembled monolayers on gold and other metals. Our materials program also includes the synthesis and analysis of novel nanoporous materials, particularly the study of chirality transfer in the solid state. In addition, we are interested in developing novel main group (non-metal) catalysts for important organic reactions. Although fundamental research is always the most important driver, our projects have significant applications in synthesis, pharmaceuticals, bio-sensing, automotive materials, petrochemical and agrochemical industries such that students are highly employable upon graduation.
Self-Assembled Monolayers on Gold
A new project in our group revolves around the study of the use of N-heterocyclic carbenes (NHCs) as ligands for gold surfaces. In 2014, we described the first example of well-formed NHC monolayers on gold surfaces. Despite their widespread use in catalysis, NHCs have seen remarkably few applications in materials chemistry.
In molecular complexes, these species are known to provide considerably greater stability to the metal centres than traditional ligands, due in part to the strong metal–carbon bond. These molecular complexes are more resistant to heat and oxidation than related phosphine complexes. Assuming that these properties would translate to materials, we examined the ability of NHCs to form bonds to gold surfaces.
Indeed it turned out that self–assembled monolayers of NHCs on gold formed easily and were significantly more stable than the state-of-the-art thiol-based films. These monolayers can be imaged by STM and other techniques. The NHC films are stable to high temperature, refluxing organic solvent, high temperature acid, base and oxidation with dilute hydrogen peroxide.
Applications of this work are currently being extensively explored, and include automotive, bio-sensing, cancer detection and chemotherapy and clean energy. Stay tuned for more exciting stuff from this project!
C.M. Crudden, J.H. Horton, I.I. Ebralidze, O.V. Zenkina, A.B. McLean, B. Drevniok, Z. She, H.-B. Kraatz, N.J. Mosey, T. Seki, E.C. Keske, J.D. Leake, A. Rousina-Webb, G. Wu, “Ultra Stable Self-Assembled Monolayers of N-Heterocyclic Carbenes on Gold” Nature Chemistry, 2014, 6,409-414.
This work was highlighted in Chemistry and Physics news magazines around the world including Physics Today, Chemistry World (RSC), Chemical and Engineering News, Canadian Chemistry News, Science Media Centre Canada, and others, and called “Game changing”, “the new gold standard”, and “elegant”.
Asymmetric Catalysis & Organoboron Chemistry
A key project in our group revolves around our key report of the first ever example of a Suzuki-Miyaura cross coupling reaction using chiral secondary boronic esters. This reaction generates enantiomerically enriched 1,1-diaryl ethanes, which are extremely difficult to prepare by other methods. The reaction proceeds with >90% retention of configuration in all cases except one. Remarkably, the linear boronate ester does not react under these conditions.
Current work in this area includes understanding the differences in reactivity of the linear and branched positions, expanding this to the synthesis of pharmaceutically relevant compounds, and further investigating the enantiospecific Suzuki-Miyaura reaction mechanistically and synthetically.
D. Imao, B.W. Glasspoole, V.S. Laberge, C.M. Crudden*, “Cross coupling reactions of chiral secondary organoboronates with retention of chirality”. Journal of the American Chemical Society, 2009, 131, 5024-5025.
Borenium ions are a unique class of molecules that are highly Lewis acidic by virtue of the positive charge on the already electron deficient boron atom. In our first paper in the area “Taking the F out of FLP”, we described how these unique main group materials as catalysts for the pinacol borane-mediated reduction of imines. Rather than an FLP mechanism as might be expected, we demosntrated that the reducing agent was most likely a pinacol borane•DABCO adduct.
Using the extremely versatile “click” reaction, we also reported the development of mesoionic carbene boranes, which, after hydride abstraction, can be used to generate borenium ions.
Current work is directed at expanding the scope of reactivity and structure in borenium ions and developing enantioselective metal-free catalysts from this class of compounds.
P. Eisenberger, A.M. Bailey, C.M. Crudden, “Taking the F out of FLP. Simple Lewis acid-base pairs for mild reductions with neutral boranes via borenium ion catalysis.”Journal of the American Chemical Society, 2012, 134, 17384-17387.  L. Baptista de Oliveira Freitas, P. Eisenberger and C.M. Crudden, “Mesoionic carbene boranes”, Organometallics, 2013, 32, 6635-6638.