The Negishi cross‐coupling is a powerful CC bond forming reaction. The method is less commonly used relative to other cross‐coupling methods in part due to lack of availability of organozinc species. While organozinc species can be prepared, problems with reproducibility and handling of these sensitive species can complicate these reactions. Herein, we describe the continuous formation, using an activated packed‐bed of metallic zinc, and subsequent use of organozinc halides. We demonstrate that a single column of zinc can provide excellent yields of organozinc halides and that they can be used downstream in subsequent Negishi cross‐couplings. The preparation of the zinc column and the scope of the reaction are discussed.
Soluble polyphosphide anions were successfully generated in a number of organic solvents by the reaction between shelf-stable red phosphorus and potassium ethoxide. The species were identified by (31)P NMR spectroscopy in solution and by X-ray crystal-structure determination of (Bu4N)2P16 in the solid state. The reaction was scaled up to gram quantities by using a flow-chemistry process.
Photooxygenations of naphthols under continuous flow conditions using porphyrinoids as photocatalysts are described. Reaction conditions, long-term experiments and scope were performed, thus allowing the production of substituted naphthoquinones.
Reactions between red phosphorus (P red ) and potassium ethoxide in various organic solvents under reflux convert this rather inert form of the element to soluble polyphosphides. The activation is hypothesized to proceed via a nucleophilic attack by ethoxide on the polymeric structure of P red , leading to disproportionation of the latter, as judged from observation of P(OEt) 3 in the reaction products. A range of solvents has been probed, revealing that different polyphosphide anions (P 7 3− , P 16 2− , P 213− , and P 5 − ) can be stabilized depending on the combination of the boiling point and dielectric constant (polarity) of the solvent. The effectiveness of activation also depends on the nature of nucleophile, with the rate of reaction between P red and KOR increasing in the order t-Bu < n-Hex < Et < Me, which is in agreement with the increasing order of nucleophilic strength. Thiolates and amides were also examined as potential activators, but the reaction with these nucleophiles were substantially slower; nonetheless, all reactions between P red and NaSR yielded exclusively P 16 2− as a soluble polyphosphide product.
Monodisperse silica microcapsules are typically fabricated using hard templating methods. Though soft templating methods are known, none yet provides a fast and easy method to produce monodisperse capsules. Herein, we describe a mesofluidic strategy whereby monodisperse droplets of reactive silica precursors are formed using a snap-off mechanism via a T junction. Both the mesofluidic system and the composition of the reactive silica formulation are critical features. Using solid-and solution-state 29 Si nuclear magnetic resonance, scanning electron microscopy, and optical microscopy, we have developed models for why some formulations form exploding capsules, why some capsules contain crystalline materials, and why some capsules have thin or thick walls.
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