Nowadays, CÀCb ond formation is one of the reaction types that most interests organic chemists. Thus, it has become an essential tool in organic synthesis that provides access to compounds of great value for different areas;s uch as materials, pharmaceuticals or fine chemicals. This kind of reactions can be performed under catalytic conditions employing transitionmetals,a sf or Suzuki-Miyaura, [1] Heck, [2] Negishi, [3] Stille, [4] Kumada, [5] Hiyama, [6] and Sonogashira reactions. [7] All thesea pproaches are typicallyp erformedi nv olatile organic solvents (VOC), whichn owadays are would preferably be replaced by "greener"m edia. Am ediumc an be considered green when its components satisfy different criteria,s uch as non-toxicity,r ecyclability,l ow price, availability,b iodegradability,a nd renewability,a mong others. Some deep eutectic solvents (DESs) could be considered as an alternative to hazardousV OC solvents. DESs are systemsf ormed by simple mixing Lewis or Brønsted acids and bases. [8] As ar esult of the strongh ydrogen bond interactions, the melting or phase transition point becamem uch lower than that of each individual component. [9] Nevertheless, the use of DES as reactionm edia in organic synthesis is in its childhood, [10 ] with very few reports of related metal-catalyzed process. [11] Only,v ery recently,p alladiumc hemistry has startedt ob e tested in DESm edia. More specifically, Suzukir eaction has been performed using Pd(OAc) 2 (10 mol %) in at ernary mixture of mannitol, dimethyl urea and ammonium chloride as DES combination. [12] Regarding Sonogashira coupling, the synthesis of only two products have been published in DES medium (dmannose/DMU), whereas the Heck cross-couplingr eaction has been performed in d-mannose-dimethyl urea (DMU) as reaction media. [13] Other publishedp alladium-catalyzed reactions performed in DES media include Ts uji-Trost allylation of amines in methylated b-cyclodextrine-DMU, [14 ] synthesis of thiophenes in ChCl-glycerol, [15] as well as the Stille reaction in lactose-DMU-NH 4 Cl. [16] This latest example is especially interesting, because is one of the few examples in which al igand was added to theD ES media:t riphenylarsine, in combination with palladium, permitted the coupling of 4-bromoanisole and tetraphenylstannanei n8 7% yield. However,w hen the reaction was performed using CyJohnPhos (a Hartwig-Buchwald-type ligand), only am odest6 1% yield was obtained. These facts clearlyd emonstrate the importance of appropriate design of the ligand in order to get good results in this new media.With all these precedents, we aimed to develop DES compatible phosphine ligands, since the best traditional palladium ligandsf or cross-coupling reactions seemed not to be so effective in this kind of solvents. We thoughi nc ationic pyridiniophosphine structures [17] as general strategy for ligandsi nt he palladium-catalyzed cross-couplingr eactions.We started by the synthesis of ac ationic pyridiniophosphine ligand with ac hloride as counter ion (Scheme 1). In order ...
