SYNTHESIS
Coupling nitrogen-containing aromatics Metal-free reaction uses phosphorus to knit ligands together
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ligands. Acidic alcohol triggers C–C bond To forge carbon-carbon bonds between formation between the two ligands (Science two aryl groups, chemists typically turn to metal-catalyzed cross-couplings—powerful 2018, DOI: 10.1126/science.aas8961). “These ligand-coupling processes had transformations that garnered their inventors the 2010 Nobel Prize in Chemistry. But been observed before, but no one had used them practically,” notes Andrew McNally, these reactions can be problematic when who led the research effort with colleague applied to nitrogen-containing aromatic Robert S. Paton. The key, compounds. The reactants can be tough to McNally says, was designprepare and can H3C ing a good phosphorus also poison the N reagent. metal catalysts. N N N The reaction takes Chemists at Colorado place in stages, Paton notes, State University have develHN N unlike metal-catalyzed couoped an alternative coupling N pling reactions, in which the for nitrogen-containing steps take place all at once. aryl groups—specifically, O N This, he says, “allows you to pyridines and diazines— H think about how you might that eschews metal for Chemists used phosphorus. phosphorus to assemble control this reaction and also, more excitingly, how it can be The reaction works this complex molecule explored to make other types by assembling two nitrofrom the cancer drug of C–C bonds.” gen-containing aryl groups Gleevec (blue) and McNally says the reaction onto a phosphorus atom as 4-methylquinoline (red).
will help medicinal chemists construct complicated drug candidates quickly. “You can take small, relatively complex fragments that would be in a pharmaceutical company’s collection and very rapidly couple those together.” He acknowledges that the phosphorus by-products aren’t environmentally friendly but says they are less problematic on the small scale of drug discovery. David Rees, chief scientific officer at Astex Pharmaceuticals, says the reaction is attractive to the pharmaceutical industry. “Although it has not been used to make a known drug, the authors show the methodology works for druglike substrates containing polar functional groups, and they’ve applied it to make new heterobiaryl derivatives of drugs that would be difficult to access with existing methods,” he says. Alexander Radosevich, an organic chemist at Massachusetts Institute of Technology, adds that the research “reshapes an esoteric transformation in main-group chemistry into a powerful synthetic sequence.”—BETHANY HALFORD
3-D PRINTING
Combo method prints batteries in any shape
C R E D I T: ACS N A NO
Customizable batteries could power hearing aids and personal electronics Using three-dimensional printing, designers can make customized products, including shoe soles, engine parts, and hearing aids. But when designers want to make new personal electronics, their imaginations are limited by the shapes of existing batteries, such as coin shapes, rectangles, cylinders, and pouches. Harvard University materials scientist Jennifer Lewis, who specializes in materials and methods for 3-D printing, wants to make it possible for batteries to be designed around the electronics they will power, not vice versa. She and her colleagues have now combined 3-D printing and other techniques to make batteries in any shape, including rings, letters, circles, and more (ACS Nano 2018, DOI: 10.1021/acsnano.8b02744).
cathode that could be cut to In 2013, Lewis’s lab was the 3-D-printed any desired shape and laser first to make 3-D-printed batbatteries in a micromachining to make teries using lithium-ion chemvariety of shapes. other parts. Finally, they used istry (Adv. Mater. 2013, DOI: stereolithography to print packages for 10.1002/adma.201301036). Because the materials in these batteries are water sen- the batteries and applied methods Lewis developed previously to 3-D print electrisitive and flammable, she says, they had cal connections. to do all their work in a glovebox filled They made fast-charging zinc-ion with inert gas, which made it difficult to batteries, graphene supercapacitors, and move beyond the initial demonstration. zinc-manganese dioxide batteries. Lewis collaborated with KAIST nanoIt’s hard to predict just what designers materials scientist Il-Doo Kim to work on other battery chemistries, chiefly zinc ion, will make when freed from the constraints which uses water-based electrolytes and is of conventional batteries, Lewis says, easier to toy around with in open air. They though she imagines niche applications such as personalized, wearable, and imdecided to “go with a chemistry we don’t plantable medical devices. It’s “meant to have to worry about,” Lewis says. be provocative,” she says.—KATHERINE The team integrated several methods, using electrospinning to make a BOURZAC NOVEMBER 19, 2018 | CEN.ACS.ORG | C&EN
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