DOI: 10.1002/adsc.201300641 Hydrosilylation of Internal Alkynes Catalyzed by Tris- Imidazolium Salt-Stabilized Palladium Nanoparticles Marc Planellas, a Wusheng Guo, a Francisco Alonso, b Miguel Yus, b Alexandr Shafir, a, * Roser Pleixats, a, * and Teodor Parella a,c a Departament de Química, Universitat Autònoma de Barcelona, Cerdanyola del Valls, 08193 Barcelona, Spain Fax: (+ 34)-93-581-2477; phone: (+ 34)-93-581-2067; e-mail: Alexandr.Shafir@uab.cat or Roser.Pleixats@uab.cat b Departamento de Química Orgµnica, Facultad de Ciencias and Instituto de Síntesis Orgµnica (ISO), Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain c Servei de Ressonància Magntica Nuclear, Universitat Autònoma de Barcelona, Cerdanyola del Valls, 08193-Barcelona, Spain Received: July 22, 2013; Revised: October 4, 2013; Published online: January 13, 2014 Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300641. Abstract: Palladium nanoparticles stabilized with tris-imidazolium tetrafluoroborates catalyze the ste- reoselective hydrosilylation of internal alkynes in a dry inert atmosphere to give (E)-vinylsilanes in ex- cellent yields. In the presence of controlled amounts of water a transfer hydrogenation reaction takes place with the formation of (Z)-alkenes or the corre- sponding alkanes. Keywords: alkynes; hydrosilylation; imidazolium salts; nanoparticles; palladium; transfer hydrogena- tion Introduction The transition metal-catalyzed hydrosilylation of al- kynes represents the most straightforward and con- venient route for the preparation of vinylsilanes. This transformation proceeds with 100% atom efficiency, [1] and the resulting organosilicon reagents are versatile building blocks in a number of synthetic processes. Some examples of reactions involving vinylsilanes in- clude protodesilylation [2] to produce the correspond- ing alkene, the Hiyama cross-coupling [3] with vinyl and aryl halides, as well as the Tamao–Fleming oxida- tion [4] to generate the carbonyl derivatives. In general, vinylsilanes exhibit reactivity similar to that of certain organometallic vinyl derivatives, but may offer advan- tages in terms of cost, low molecular weight, low tox- icity, functionality tolerance and high chemical stabili- ty. Platinum-based catalysis is the most usual choice for the addition of silanes to unsaturated C À C bonds, [5] most famously chloroplatinic acid (Speiers catalyst), [5a,b] and olefin-stabilized Karstedts cata- lyst. [5c,d] More recently, ruthenium complexes, despite being generally less reactive, have also become popu- lar in alkyne hydrosilylation due to their high levels of stereoselectivity. [6] Thus, the regio- and stereochem- istry of the metal-catalyzed alkyne hydrosilylation is known to be controlled by the nature of the catalyst. Terminal acetylenes tend to be far more reactive in this process, although certain systems, including Trosts ruthenium catalyst, [6g] do perform well with the more challenging internal alkynes. Our own work on C À C bond formation catalyzed by Pd nanoparticles led us to explore the preparation of vinylsilanes using the same class of catalyst. We found only few reports dealing with the addition of si- lanes to acetylenic compounds catalyzed by metal nanoparticles. In one instance, the regioselective hy- drosilylation of terminal alkynes was recently ach- ieved [7] with supported rhodium, [7a] rhodium-platinu- m [7a] and gold nanoparticles; [7b] in addition, the hydro- silylation of internal alkynes and diynes has been de- scribed with platinum deposited on titania [8a,b] and on magnetite. [8c] Although palladium nanoparticles (Pd np ) have found widespread applications as catalysts, mainly in hydrogenation, oxidation and cross-coupling reactions, [9] little attention has been paid to their use in the hydrosilylation reactions of unsaturated hydro- carbons. Thus, while there are few examples describ- ing their use in the hydrosilylation of enals, enones, [10] and styrene, [11] to the best of our knowledge they have never been reported as catalysts in the hydrosi- lylation of alkynes. In fact, even discrete Pd com- plexes are quite uncommon in this process, with some examples appearing in the past years. [12] Adv. Synth. Catal. 2014, 356, 179 – 188  2014 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 179 FULL PAPERS