Removal of a palladium-bound tertiary phosphine ligand with silver(I) salts to generate cationic monoorganopalladium(II) complexes having one trimethylphosphine ligand

Treatment of neutral monoorganobis(trimethylphosphine)palladium(II) halide complexes, trans-[PdR(X)(L)₂] 1 (R = Me, Et, or Ph group, X = halide ligand, L = trimethylphosphine), with an equimolar amount of a silver salt such as AgBF₄ usually gives cationic monoorganobis(trimethylphosphine) palladium(II) complexes, trans-[PdR(s)L₂]BF₄ (s = solvent) 2. But employment of an excess amount of the silver salt in the reaction with 1 or treatment of 2 with an additional amount of the silver salt yields a cationic monoorganopalladium(II) complex coordinated with one PMe₃ ligand, cis-[PdR(L)(s)₂]⁺ 3 by removing one of the PMe₃ ligands in 2. The cationic mono-phosphine complex 3 can be also prepared by addition of an equimolar amount of a silver salt to the neutral dinuclear Cl-bridged, monophosphine complex [PdMe(μ-Cl)(PMe ₃)]₂ 5. The cis configuration of 3 was supported by comparison of the NMR spectra with those of cationic, cyclooctadiene (COD)-coordinated monomethylmono(trimethylphosphine)palladium complex, cis-[PdMe(PMe₃)(cod)]BF₄, 6. Complex 6 was prepared by two routes, by treatment of 3 with COD and by reaction of [PdMe(Cl)(cod)] 7 with an equimolar amount of AgBF₄ followed by addition of an equimolar amount of PMe₃. The cationic mono-phosphine complex 3 having one PMe₃ ligand shows greater reactivity for the CO insertion than the bis-phosphine complex 2.