Faculty currently associated with this research theme.
Impact: Organic π-conjugated polymers are an increasingly important class of materials because of their widespread application in electronic devices (e.g., solar cells, light-emitting diodes, and transistors). Homopolymers are most often utilized, mainly due to their facile synthesis via traditional step-growth methods. An underexplored approach is to alter the sequence of two (or more) monomers along the polymer backbone. We have been targeting an entirely new sequence distribution called gradient copolymers, which we predict will exhibit tunable, sequence-dependent properties that are unique from other copolymer architectures, thereby providing access to a new set of design parameters.
Approach: To synthesize these new copolymers, a controlled chain-growth synthetic method is required. The first chain-growth method for synthesizing π-conjugated homopolymers was reported in 2004, however, the direct application of this newly discovered method towards generating copolymer structures has been limited by the narrow substrate scope, highly monomer-specific reaction conditions, and inefficient cross-propagation between two different monomers. To overcome these limitations, my research group is developing new Pd and Ni catalysts for chain-growth copolymerizations. Guided by mechanistic insight, we synthesize novel ligands and catalysts and determine their efficacy in promoting chain-growth behavior. Small molecule model systems are used to rapidly identify promising new scaffolds and optimize their properties. In situ spectroscopic techniques are used to monitor the polymerization rates, and as a result, elucidate the polymerization mechanism.
Impact: The assembly of carbon-carbon bonds is often achieved by addition reactions of metallated nucleophiles, which can present limitations in functional group compatibility and ease of handling as well as introduce undesirable waste and expense. Catalytic methods to provide the identical net bond constructions traditionally provided by metallated nucleophiles, but which utilize inexpensive and stable feedstock reagents, often introduce considerable advances in practicality and efficiency.
Approach: Our approach is to design classes of catalytic processes that enable the reductive coupling of two or more simple p-components, typically through the involvement of metallacyclic intermediates. Through careful design of catalysts and ligands, such processes can exert very high levels of control over regioselectivity and enantioselectivity, while providing rapid access to complex structures from simple, widely available substrates. The design of new methods is accompanied by detailed mechanistic analysis and the development of complex illustrations in total synthesis.
Impact: The development of methods for the site-selective oxidative transformation of inert C–H bonds into new functional groups (e.g., alcohols, esters, ethers, amines, halides, carbon-carbon bonds) remains a tremendous challenge in organic synthesis. Such procedures have the potential to fundamentally change the way chemists approach the assembly and late-stage modification of natural products, drug candidates, organic materials, and fine chemicals.
Approach: Our approach involves the design, synthesis and characterization of new organometallic catalysts, the conception and evaluation of fundamentally new transformations, and the investigation of individual steps of a given catalytic cycle. In all of these areas, advances in catalyst development are driven by careful assessment and study of reaction mechanisms. Novel transition metal-catalyzed methods for the site-, chemo-, regio-, and stereoselective functionalization of C–H bonds are targeted. Substrates of interest range from methane and benzene to complex biologically active natural products and pharmaceutical candidates.
Impact: The ability to generate well-defined metal-ligand complexes that promote the activation of small molecules is a coveted goal of synthetic catalysis. Mediating key bond breaking and bond making events by synergistic metal ligand cooperativity is a common strategy used by many enzymatic systems through highly specific, directed interactions. We are targeting the development of discrete transition metal complexes that feature appended functionality to cooperatively activate small molecule substrates and subsequently direct bond-forming reactions. Key organometallic transformations of interest are (transfer) hydrogenation, dehydrogenative coupling, hydrofunctionalization, and oxidations using low-cost reagents.
Approach: Our lab targets ligand architectures that, when metalated, feature well-positioned Lewis/Brönsted acids and bases within the secondary coordination sphere of a metal complex. These functional groups are selected to favorably interact with an appropriate metal-bound substrate. We use organic and inorganic syntheses to generate systems that allow us to probe the role that polar Lewis and Brönsted acid/base groups in the periphery of a metal’s coordination sphere might play to facilitate binding/activation of substrates. Particular emphasis is placed on synthetic approaches and design strategies to generate systems with appended functionality, as well as mechanistic aspects governing substrate binding/activation and importantly, reactivity.
Impact: Research in the Wolfe group is focused on the development of new transition-metal catalyzed reactions for the stereoselective synthesis of saturated heterocycles such as tetrahydrofurans and pyrrolidines. These moieties are displayed in a number of biologically active natural products, and are also of significant utility in the development of pharmaceuticals.
Approach: We are also involved in the total synthesis of natural products and studies of reaction mechanisms related to the transformations we develop. Our experiments have illustrated these transformations proceed through an unusual mechanistic pathway involving intramolecular insertion of an alkene into a Pd–N bond. Our current efforts are directed towards the development of catalytic enantioselective versions of these reactions and the use of these transformations in cascade processes that generate highly complex products from simple precursors.
- Analytical Chemistry
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