Mild Chemical Synthesis of Indium(0) Nanoparticles. Characterization and Application in Allylations of Carbonyl Compounds

In recent years, the synthesis of metal nanoparticles has attracted significant attention because of their unique properties. These nanoparticles are useful for diverse fields including catalysis, electronics, clinical diagnosis, etc. Although many strategies for the preparation of noble- and transition-metal nanoparticles have been published, the synthesis of indium nanoparticles (InNPs) has been scarcely reported. Some top-down methods involve the use of specific equipments and/or high temperatures, and most of the bottom-up methods require the use of indium salts and strong reducing agents such as sodium metal, zinc power, alkalides/electrides, or decomposition of organometallic complexes.¹ Regrettably, some of them provide little control over particle size and size distribution, and generally it is mandatory the presence of stabilizing agents. On the other hand, the reducing systems based on the use of alkali-metals in combination with arenes in aprotic media, with the arene acting as electron carrier have received much attention. Some of us have been working on the preparation of transition metal nanoparticles by fast reduction of the corresponding metal chlorides with lithium and a catalytic amount of an arene [naphthalene, 4,4´-di-tert-butylbiphenyl (DTBB)].² Herein, we report, a simple, mild, and efficient synthesis of very reactive, monodisperse (4.0 ± 1.5 nm) spherical InNPs, using indium(III) chloride in the presence of lithium powder and a catalytic amount of DTBB in THF at room temperature, and in the absence of any anti-agglomeration additive or ligand. Focusing on one of the most studied indium-mediated synthetic transformation, we decided to explore the above-mentioned InNPs-based system for the allylation of a variety of aldehydes and ketones in a one-pot procedure, by adding allyl bromide over a suspension of InNPs followed by the addition of the corresponding carbonyl compound. For most of the tested compounds, the homoallylic alcohol product was obtained in good yields. The InNPs were characterized by transmission electron microscopy (TEM) and UV-Visible spectroscopy. ¹ Estager J., Nockemann P., Seddon K. R., Srinivasan G., y Swadźba-Kwaśny M. ChemSusChem 2012, 5, 117–124 and references therein. ² F. Nador; L. Fortunato; Y. Moglie; C. Vitale and G. Radivoy Synthesis, 2009, 4027-4031 and references therein.