Selectivity studies in the reaction between iodobenzene and phenylacetylene: Sonogashira coupling vs hydroarylation

Abstract

The selectivity of the coupling reaction between iodobenzene and phenylacetylene was evaluated. Several palladium catalysts, ligands and reaction conditions were tested, showing that supported catalysts, room temperature or ionic liquids (NHC precursors) favor Sonogashira coupling, while the non-supported ones, higher temperature and PPh 3 as ligand, favor hydroarylation. Neither excess of iodobenzene nor phenylboronic acids are required; and it is possible to avoid the use of PPh 3 , although this lowers selectivity.

Exploratory Studies on the Reaction Between Iodoarenes and Acetylenes: One-pot, Pd-[Bmim][BF4] Catalyzed Preparation of Trianisylethylene

“…This corroborates our previous results of the role of ligands (PPh 3 vs NHC) in directing the selectivity to a Sonogashira reaction or an hydroarylation [31].…”

“…A mechanistic pathway for this kind of reaction was proposed by Wu [42] and by us [31] and comprised a Sonogashira coupling to furnish aryl-trimethylsilyl acetylene, a sila-Sonogashira coupling to furnish diarylacetylene, and finally an hydroarylation of the diarylacetylene with iodoarene to furnish triarylethylene. In this case EtOH serves as a source of hydrogen, and acetaldehyde is released.…”

“…Our group has been involved in the reaction between haloarenes and acetylenes involving either Sonogashira coupling [29,30] or tandem Sonogashira coupling-hydroarylation [31] to furnish trisubstituted olefins, and in that case, it was possible to direct the selectivity based on catalyst nature, ligand and solvent properties, also the phosphine-free and ionic liquid promoted reaction were tested (Scheme 1).…”

“…For this we have subjected alkynes and halides to our optimized conditions [31] for a tandem reaction involving a Sonogashira coupling followed by hydroarylation using Pd(OAc) 2 , PPh 3 , K 2 CO 3 and EtOH as a suitable solvent and hydrogen transfer promoter [32].…”

Pdo.o2Ceo.98O2: a copper- and ligand-free quasi-heterogeneous catalyst for aquacatalytic Sonogashira cross-coupling reaction

“…In this direction, researchers have immobilised Pd on solid supports such as activated carbon (charcoal) (Rossy et al, 2014) (Djakovitch and Rollet, 2004), metal oxides (Cwik, Hell and Figueras, 2006;Hosseini-Sarvar, Razmi and Doroodmand, 2014;Roy, Senapati and Phukan, 2015;Kotadia et al, 2014) (MgO, ZnO, TiO 2 , ZrO 2 , Fe 2 O 3 , CeO 2 , . ), clays (Borah and Dutta, (2013), alkaline earth salts (CaCO 3 , BaSO 4 , BaCO 3 , SrCO 3 ) (Barros et al, 2008) and organic polymers (Ye and Yi, 2008;Kim et al, 2007). However, the leaching of palladium from the catalyst is still the main problem, even though most researchers have reported that their catalysts can be recycled by the redeposition of Pd onto the support (Redon, Peña and Crescencio, 2014).…”