Diverse <i>C</i>-Coordination Modes of NHC-Tricyclohexylphosphonium Ylide Ligands in Palladium(II) Complexes

Thanks to the +PCy3 substituents which are unlikely undergo intramolecular C–H activation, Pd(II) complex [(C,C,C)PdCl](OTf) having a neutral LX2-type NHC, diphosphonium bis(ylide) pincer ligand was selectively prepared by double deprotonation of [(NHC)PdCl2(Py)] precursor with tBuOK. The influence on overall electronic properties this scaffold evaluated IR spectroscopy data corresponding Pd–CO adduct, revealing its stronger electron-donating character in comparison structurally related NHC core bearing +PPh3 extremities. Treatment electron-rich AgOTf led C,C-chelating NHC-phosphonium ylide [(C,C)Pd(OTf)Cl](OTf) via oxidatively induced homolytic cleavage Pd–ylide bond. In presence base (KHMDS or LDA) cyclometalation +P–Cy substituent observed, affording constrained featuring unique anionic LX3-type C,C,C,C-NHC, tris(ylide) ligand.