Indium-Mediated Asymmetric Barbier-Type Propargylations: Additions to Aldehydes and Ketones and Mechanistic Investigation of the Organoindium Reagents

We report a simple, efficient, and general method for the indium-mediated enantioselective propargylation of aromatic and aliphatic aldehydes under Barbier-type conditions in a one-pot synthesis affording the corresponding chiral alcohol products in very good yield (up to 90%) and enantiomeric excess (up to 95%). The extension of this methodology to ketones demonstrated the need for electrophilic ketones more reactive than acetophenone as the reaction would not proceed with just acetophenone. Using the Lewis acid indium triflate [In­(OTf)₃] induced regioselective formation of the corresponding homoallenic alcohol product from acetophenone. However, this methodology demonstrated excellent chemoselectivity in formation of only the corresponding secondary homopropargylic alcohol product in the presence of a ketone functionality. Investigation of the organoindium intermediates under our reaction conditions shows the formation of allenylindium species, and we suggest that these species contain an indium­(III) center. In addition, we have observed the presence of a shiny, indium(0) nugget throughout the reaction, irrespective of the stoichiometry, indicating disproportionation of indium halide byproduct formed during the reaction

Dissolution of Sn, SnO, and SnS in a Thiol–Amine Solvent Mixture: Insights into the Identity of the Molecular Solutes for Solution-Processed SnS

Binary solvent mixtures of alkanethiols and 1,2-ethylenediamine have the ability to readily dissolve metals, metal chalcogenides, and metal oxides under ambient conditions to enable the facile solution processing of semiconductor inks; however, there is little information regarding the chemical identity of the resulting solutes. Herein, we examine the molecular solute formed after dissolution of Sn, SnO, and SnS in a binary solvent mixture comprised of 1,2-ethanedithiol (EDT) and 1,2-ethylenediamine (en). Using a combination of solution ¹¹⁹Sn NMR and Raman spectroscopies, bis­(1,2-ethanedithiolate)­tin­(II) was identified as the likely molecular solute present after the dissolution of Sn, SnO, and SnS in EDT–en, despite the different bulk material compositions and oxidation states (Sn⁰ and Sn²⁺). All three semiconductor inks can be converted to phase-pure, orthorhombic SnS after a mild annealing step (∼350 °C). This highlights the ability of the EDT–en solvent mixture to dissolve and convert a variety of low-cost precursors to SnS semiconductor material

Chalcogenol Ligand Toolbox for CdSe Nanocrystals and Their Influence on Exciton Relaxation Pathways

We have employed a simple modular approach to install small chalcogenol ligands on the surface of CdSe nanocrystals. This versatile modification strategy provides access to thiol, selenol, and tellurol ligand sets <i>via</i> the <i>in situ</i> reduction of R₂E₂ (R = ^<i>t</i>Bu, Bn, Ph; E = S, Se, Te) by diphenylphosphine (Ph₂PH). The ligand exchange chemistry was analyzed by solution NMR spectroscopy, which reveals that reduction of the R₂E₂ precursors by Ph₂PH directly yields active chalcogenol ligands that subsequently bind to the surface of the CdSe nanocrystals. Thermogravimetric analysis, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy provide further evidence for chalcogenol addition to the CdSe surface with a concomitant reduction in overall organic content from the displacement of native ligands. Time-resolved and low temperature photoluminescence measurements showed that all of the phenylchalcogenol ligands rapidly quench the photoluminescence by hole localization onto the ligand. Selenol and tellurol ligands exhibit a larger driving force for hole transfer than thiol ligands and therefore quench the photoluminescence more efficiently. The hole transfer process could lead to engineering long-lived, partially separated excited states