Lack of Evidence Supporting Widespread Use of 1,2-Dibromoethane as an Activator for Zinc: Alternative Stirring or TMSCl Activation

Decades of protocols use 1,2-dibromoethane as an activating agent for zinc metal powder to promote direct insertion into organohalides, but kinetics experiments examining its effect on reaction rates are absent. Here condition- and concentration-controlled 1H NMR spectroscopy kinetics experiments measure rates, induction periods, and yields─and surprisingly showed that typically reported synthetic conditions and quantities of 1,2-dibromoethane (4 mol %) had no effect on the rate of direct insertion of alkyl iodides. Instead, an acceleration was caused by the physical stirring processes alone that accompanied the published synthetic procedures for the “chemical” activation protocol. This finding was adapted to aryl iodides as an example substrate with longer induction periods, leading to the discovery that relatively short prestir times (1 h) with a magnetic stir bar produced activation of zinc that approached similar degrees (∼85%) in the absence of 1,2-dibromoethane. An origin of the previously observed activation is therefore reassigned, in part, to mechanical activation of the surface during these processes. When 1,2-dibromoethane and trimethylsilyl chloride (TMSCl) were both present, as in many reported synthetic protocols, TMSCl caused full activation, and 1,2-dibromoethane caused no additional effect. The broad replacement of 1,2-dibromoethane activation is thus supported.

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Polymer Size–Catalytic Activity Relationships in Solution by Fluorescence Correlation Spectroscopy

Fluorescence correlation spectroscopy coupled with chemoselective fluorescent monomers enables catalytic activity characterization of catalysts associated with polymers in solution and determines cat...

chemistry-europe.onlinelibrary.wiley.com

Tetramethylethylenediamine Stabilizes Organozinc Surface Intermediates against Chemical Etching but Not against Protodemetalation

N,N,N’,N’-Tetramethylethylenediamine (TMEDA) is known to increase yields in Negishi-type cross-coupling reactions in aqueous–surfactant mixtures, presumably by increasing the persistence of the organo...

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Three-Phase Emulsions during Cross-Coupling Reactions in Water

Fluorescence lifetime imaging microscopy (FLIM) enabled identification of three-phase emulsions during a cross-coupling reaction in water, offering insight into their features and factors driving thei...

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Self‐Assembly Methods Induce Different Individual‐Polymer‐Block Solvation Responses

Different processing methods of the otherwise same block copolymer produce materials that respond distinctly to solvent stimuli. FLIM, which reveals changes in the tightness or looseness of individua...

chemistry-europe.onlinelibrary.wiley.com

Canceled meetings and confusion: NIH grant funding in limbo despite court injunction

Science researchers awaiting National Institutes of Health funding say their grant meetings are being canceled, despite a court order blocking the Trump administration from freezing federal funds.

wbur.org