Nicolas J. Treat

Metal-free atom transfer radical polymerization

Overcoming the challenge of metal contamination in traditional ATRP systems, a metal-free ATRP process, mediated by light and catalyzed by an organic-based photoredox catalyst, is reported. Polymerization of vinyl monomers are efficiently activated and deactivated with light leading to excellent control over the molecular weight, polydispersity, and chain ends of the resulting polymers. Significantly, block copolymer formation was facile and could be combined with other controlled radical processes leading to structural and synthetic versatility. We believe that these new organic-based photoredox catalysts will enable new applications for controlled radical polymerizations and also be of further value in both small molecule and polymer chemistry.

Chemoselective Radical Dehalogenation and C–C Bond Formation on Aryl Halide Substrates Using Organic Photoredox Catalysts

Despite the number of methods available for dehalogenation and carbon-carbon bond formation using aryl halides, strategies that provide chemoselectivity for systems bearing multiple carbon-halogen bonds are still needed. Herein, we report the ability to tune the reduction potential of metal-free phenothiazine-based photoredox catalysts and demonstrate the application of these catalysts for chemoselective carbon-halogen bond activation to achieve C-C cross-coupling reactions as well as reductive dehalogenations. This procedure works both for conjugated polyhalides as well as unconjugated substrates. We further illustrate the usefulness of this protocol by intramolecular cyclization of a pyrrole substrate, an advanced building block for a family of natural products known to exhibit biological activity.

Low-temperature ketene formation in materials chemistry through molecular engineering

The thermolysis of Meldrums acid derivatives has emerged as a powerful methodology to generate ketenes in polymeric structures, but the required high temperatures for ketene formation may reduce its broad applicability. We take a molecular approach toward addressing this limitation by engineering Meldrums acid derivatives to undergo thermolysis at significantly lower temperatures. Two distinct strategies are presented and a thorough understanding of the molecular interactions governing their reactivity is provided through model compound design and synthesis, crystal structure analysis, and computation of transition structures. The generality of these molecular design principles allows for the generation of ketenes under mild thermal conditions, providing significant opportunities as a comprehensive and wide-ranging tool for controlling reactivity in both chemical and materials science applications.

A Versatile and Highly Selective Colorimetric Sensor for the Detection of Amines

The utility of Meldrums activated furan (MAF) for the colorimetric detection of sub ppm levels of amines in solution, on solid supports, and as vapors is reported. MAF is synthesized in one step from inexpensive and commercially available starting materials and exhibits high selectivity for primary and secondary amines in the presence of competing nucleophiles. The reaction between activated furans and amines results in a distinct color change, discernable by the naked eye. UV/Vis absorption spectroscopy was utilized to monitor reactions in solution and determine detection limits. Additionally, solutions of MAF were useful as stains for thin layer chromatography and for monitoring solid-phase synthesis of peptides and peptidomimetics. Finally, MAF was used to detect volatile amines released from fish samples, demonstrating potential for food spoilage applications.

Triazine-mediated controlled radical polymerization: New unimolecular initiators

Triazine-based unimolecular initiators are shown to mediate the controlled radical polymerization of several monomer classes, yielding polymers with low dispersities, targeted molecular weights, and active chain ends. We report the modular synthesis of structurally and electronically diverse triazine-based unimolecular initiators and demonstrate their ability to efficiently control the radical polymerization of modified styrene monomers. Copolymerizations of styrene with butyl acrylate or methyl methacrylate were conducted to highlight the monomer family tolerance of this system. Notably, in the case of methyl methacrylate and styrene, up to 90 mol% methyl methacrylate comonomer loadings could be achieved while maintaining a controlled polymerization, allowing the synthesis of a range of block copolymers. This class of triazine-based mediators has the potential to complement current methods of controlled radical polymerization and marks an important milestone in ongoing efforts to develop initiators and mediators with high monomer tolerance that are both metal and sulfur-free.

Simultaneous Preparation of Multiple Polymer Brushes under Ambient Conditions using Microliter Volumes

The fabrication of well-defined, multifunctional polymer brushes under ambient conditions is described. This facile method uses light-mediated, metal-free atom-transfer radical polymerization (ATRP) to grow polymer brushes with only microliter volumes required. Key to the success of this strategy is the dual action of N-phenylphenothiazine (PTH) as both an oxygen scavenger and polymerization catalyst. Use of simple glass cover slips results in a high degree of spatial and temporal control and allows for multiple polymer brushes to be grown simultaneously. The preparation of arbitrary 3D patterns and functional/emissive polymer brushes demonstrates the practicality and versatility of this novel strategy.