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Formation of C-N bonds is a quintessential transformation in organic synthesis. Among the various methods to access them, hydrogen borrowing catalysis offers a green, atom economical, and cost-effective approach with water as the sole by-product. In this reaction, amines are alkylated with alcohol coupling partners in the presence of a transition metal catalyst. Several catalytic systems have been developed and employed in the synthesis of pharmaceutical intermediates and complex natural products, replacing conventional amination reactions with hydrogen borrowing reactions that deliver improved selectivity and yield. In this short review, we compare hydrogen borrowing N-alkylation with other classical and modern C-N bond forming reactions and discuss applications in pharmaceutical synthesis. 

We report a rapid route to reclaim carbon fiber (CF) fabric and monomeric chemicals from amine-epoxy CF-reinforced polymer (CFRP) composites. We use a reaction that occurs in molten NaOH- KOH eutectic to selectively cleave aryl ether and amine linkages, which involves two temperature-dependant mechanisms. Bisphenol-A is isolated in up to quantitative yields, and recovered CF fabric is remanufactured into 2nd-generation CFRPs. 

Carbon fiber reinforced polymers (CFRPs, or composites) are increasingly replacing traditional manufacturing materials used in the automobile, aerospace, and energy sectors. With this shift, it is vital to develop end-of-life processes for CFRPs that retain the value of both the carbon fibers and the polymer matrix. Here we demonstrate a strategy to upcycle pre- and post-con- sumer polystyrene-containing CFRPs, crosslinked with unsaturated polyesters or vinyl esters, to benzoic acid. The thermoset matrix is upgraded via biocatalysis utilizing an engineered strain of the filamentous fungus Aspergillus nidulans, which gives access to valuable secondary metabolites in high yields, exemplified here by (2Z,4Z,6E)-octa-2,4,6-trienoic acid. Reactions are engineered to preserve the carbon fibers, with much of their sizing, so that the isolated carbon fiber plies are manufactured into new composite coupons that exhibit mechanical properties comparable to virgin manufacturing substrates. In sum, this represents the first system to reclaim high value from both the fiber fabric and polymer matrix of a CFRP. 

The oxygen evolution reaction (OER) of water splitting is essential to electrochemical energy storage applications. While nickel electrodes are widely available heterogeneous OER catalysts, homogeneous nickel catalysts for OER are underexplored. Here we report two carbene-ligated nickel(II) complexes that are exceptionally robust and efficient homogeneous water oxidation catalysts. Remarkably, these novel nickel complexes can assemble a stable thin film onto a metal electrode through poly-imidazole bridges, making them supported heterogeneous electrochemical catalysts that are resilient to leaching and stripping. Unlike molecular catalysts and nanoparticle catalysts, such electrode-supported metal-complex catalysts for OER are rare and have the potential to inspire new designs. The electrochemical OER with our nickel-carbene catalysts exhibits excellent current densities with high efficiency, low Tafel slope, and useful longevity for a base metal catalyst. Our data show that imidazole carbene ligands stay bonded to the nickel(II) centers throughout the catalysis, which allows the facile oxygen evolution. 

We introduce an electrochemical approach to recycle carbon fiber (CF) fabrics from amine-epoxy carbon fiber-reinforced polymers (CFRPs). Our novel method utilizes a Kolbe-like mechanism to generate methyl radicals from CH 3 COOH to cleave C–N bonds within epoxy matrices via hydrogen atom abstraction. Recovered CFs are then remanufactured into CFRPs without resizing. 

Most students enter college without any exposure to polymer science, which leads to the poor understanding and slow implementation of plastics recycling programs in the United States. To address the knowledge gap in chemical recycling, we introduce a 2-part laboratory experiment that was conducted in multiple high schools and public outreach events to demonstrate the depolymerization of PET via aminolysis and the remanufacturing of cleaved PET fragments into a new aramid polymer. Student experiences were evaluated with two post-lab assignments. 

We report two bifunctional (pyridyl)carbene-iridium( i ) complexes that catalyze ketone and aldehyde hydrogenation at ambient pressure. Aryl, heteroaryl, and alkyl groups are demonstrated, and mechanistic studies reveal an unusual polarization effect in which the rate is dependant of proton, rather than hydride, transfer. This method introduces a convenient, waste-free alternative to traditional borohydride and aluminum hydride reagents. 

Polystyrene (PS) is one of the most used, yet infrequently recycled plastics. Although manufactured on the scale of 300 million tons per year globally, current approaches toward PS degradation are energy- and carbon-inefficient, slow, and/or lim- ited in the value that they reclaim. We recently reported a scalable process to degrade post-consumer polyethylene-containing waste streams into carboxylic diacids. Engineered fungal strains then upgrade these diacids biosynthetically to synthesize pharmacologi- cally active secondary metabolites. Herein, we apply a similar reaction to rapidly convert PS to benzoic acid in high yield. Engi- neered strains of the filamentous fungus Aspergillus nidulans then biosynthetically upgrade PS-derived crude benzoic acid to the structurally diverse secondary metabolites ergothioneine, pleuromutilin, and mutilin. Further, we expand the catalog of plastic- derived products to include spores of the industrially relevant biocontrol agent Aspergillus flavus Af36 from crude PS-derived ben- zoic acid.