Direct Access to Palladium(II) Complexes Based on Anionic ,,-Phosphonium Ylide Core Pincer Ligand.

The reaction of readily available imidazolium-phosphonium salt MesIm(CH)PPh with PdCl in the presence of an excess of CsCO afforded selectively in one step the cationic Pd(II) complex (,,)Pd(NCMe) exhibiting an LX-type NHC-ylide-aryl ,,-pincer ligand via formal triple C-H bond activation. The replacement of labile MeCN in the latter by CNBu and CO fragments allowed to estimate the overall electronic properties of this phosphonium ylide core pincer scaffold incorporating three different carbon-based donor ends by IR spectroscopy, cyclic voltammetry, and molecular orbital analysis, revealing its significantly higher electron-rich character compared to the structurally close NHC core pincer system with two phosphonium ylide extremities. The pincer complex (,,)Pd(CO) represents a rare example of Pd(II) carbonyl species stable at room temperature and characterized by X-ray diffraction analysis. The treatment of isostructural cationic complexes (,,)Pd(NCMe) and (,,)Pd(CO) with (allyl)MgBr and BuLi led to the formation of zwitterionic phosphonium organopalladates [(,,)PdBr] and [(,,)Pd(COBu)], respectively.