Selective Catalysts with an Inward Facing N-Heterocyclic Carbene
Steven Diver Principal Investigator
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The Chemical Catalysis Program supports research led by Professor Steven T. Diver at the State University of New York (SUNY) at Buffalo on the synthesis of a new macrocyclic N-heterocyclic carbene. This unique macrocycle design features a versatile ligand pointing inward toward the inside of the molecular cavity. N-Heterocyclic carbenes are powerful nucleophiles useful both for catalytic carbon-carbon bond formation and as ligands for transition metals such as ruthenium. The macrocyclic ligand is designed to hold transition metals firmly in its interior where selective alkene metathesis reactions take place. Current ruthenium carbene catalysts display high chemoselectivity (preference for alkenes), but some of their key shortcomings are addressed by this research, including decomposition, lifetime of a key catalytic intermediate, and selectivity. The restrictive nature of the macrocycle is expected to limit decomposition pathways and will display size selectivity for its chemical reactants, an unknown type of selectivity in the alkene metathesis reaction. Alkene metathesis is an important reaction for the synthesis of small molecules, materials, and for energy applications and is used in large-scale industrial applications, the synthesis of pharmaceuticals, and in medicinal chemistry for drug discovery.<br/><br/>With the support of the Chemical Catalysis Program in the Chemistry Division at the National Science Foundation, Professor Steven T. Diver and his research team access new chemical catalysts with a wide range of applications based on the metal occupying the interior of the cavity. Fundamental properties of the strong nucleophilic ligand are investigated in this controlled environment. The investigation of new ruthenium carbene catalysts is expected to produce more durable catalysts for applications in sustainable energy. For example, higher lifetime ruthenium carbene catalysts are critical in producing biodiesel fuel that are economically-viable. The outreach component seeks to increase awareness of chemistry as an experimental science to youth through a catalysis project for high school students and for K-12 students through a chemistry merit badge day, relying on high school students and graduate students to lead activities. Kinetics experiments are ideal to illustrate how natural phenomenon can be controlled through experiment and how data can be presented. Catalysts that display increased activities, longer lifetimes, and higher selectivities are in demand and alkane metathesis, the reaction under scrutiny in this research project, is used as a tool to make probes and dyes for chemical biology. Encapsulation of ruthenium carbenes represents a new approach to controlling selectivity and improving stability of a catalyst by limiting bimolecular decomposition. This concept may prove broadly useful to other metal-catalyzed applications.