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Aaron D. Sadow
Organometallic Chemistry and Asymmetric Catalysis
The Sadow Group investigates main group element, rare earth element, and transition-metal organometallic chemistry. Our work involves ligand design, organometallic synthesis, development of catalytic chemistry, and study of organometallic reaction mechanisms. These activities are applied in catalytic conversions for chemical synthesis, materials preparations, and energy-related transformations.
Oxazoline and Borate Ligands. The ancillary ligands studied in the Sadow Group contain multiple oxazoline donors linked by a monoanionic borate center. The borate center provides an anionic charge to the ligand and increases the electron donating power of the oxazoline groups. Oxazolines are chosen as donors because they are readily obtained in enantiopure form and they are resistant to oxidation and racemization. The tris(oxazolinyl)borate ligands prepared in the Sadow Group have been coordinated to transition-metal, main-group, and rare earth metal centers to make catalysts for a variety of transformations.
Alkyl ligands with beta Si–H Groups. Beta-hydrogen elimination is a common reaction pathway for transition-metal alkyl compounds that gives unsaturated organic molecules and a metal-hydrogen bond. This reaction often occurs under very mild conditions for transition-metals, whereas main group alkyls typically resist beta elimination. Our work has shown that beta-C–H and beta-Si–H bonds of main group alkyl and silyl ligands are reactive, even though elimination is not the favored pathway. We are creating new catalytic reactions based on the reaction pathways that become available in the absence of beta-elimination.
Catalytic Hydroamination. We are investigating early transition-metal and main group metal compounds as catalysts for C–N bond formations. Chiral amines are important in natural products, pharmaceuticals, materials, and agrichemicals. In this work, we've prepare new catalysts that provide chiral amines with exceptional enantioselectivity. Kinetics, isolated intermediates, and effects of isotopic substitution on enantioselectivity provide evidence for concerted N–C and C–H bond formation in the transition state. This mechanistic insight allows design of new catalysts for a range of carbon-element bond formations.
Silicon-element bond formations. Silicones -(SiR2–O)n-, silylethers (R3Si-OR), silazanes (R3Si–NR2), and silanes (R3Si–SiR3) are technologically important materials and are valuable in organic and inorganic chemistry. However, traditional syntheses generate significant wastes, use hydrolytically sensitive halosilanes as starting materials, and mixtures are often obtained. We are developing organometallic compounds to catalyze the formation of Si–O, Si–N, Si–C, and Si–Si bonds to address stereochemical issues, reduce waste production, and employ air-stable precursors. We are also investigating these bond forming reactions for selective transformations of small molecules.
C-H, C-C, and C-O Bond activation reactions. The oxidation/reduction chemistry of transition metals is central to catalytic conversions of organic molecules, from highly reduced hydrocarbons through oxygenated carbohydrates to carbon dioxide. We are studying transition-metal-mediated C-H oxidation and C-O reduction to develop catalytic transformations relevant to fuel and chemical production.