Synthesis and properties of dimethyl-and monomethylbis(phosphite) palladium(II) complexes

Article abstract of DOI:10.1246/bcsj.70.1141

New dimethylpalladium complexes having alkyl and aryl phosphites as the supporting ligands, cis-[PdMe₂{P-(OR)₃}₂] (R = Me, 1a; Ph, 1b), have been prepared by two routes, (1) by the reaction of [Pd(acac)₂] with [AlMe₂(OEt)] in the presence of the phosphite ligands, and (2) by the ligand exchange reaction of [PdMe ₂(cod)] (COD= 1,5-cyclooctadiene) with two molar amounts of the phosphites. Monomethylpalladium chloride complexes, [PdMe(Cl){P(OR) ₃}₂] (R = Me, 2a; Ph, 2b; Prⁱ, 2c) have been prepared by ligand exchange reaction of [PdMe(Cl)(cod)] with two molar amounts of the phosphites, whereas [PdMe(OAc){P(OR)₃}₂] (R = Me, 3a; Ph, 3b) has been synthesized by treatment of 1 with acetic acid. Strong influence of the coordinated phosphite ligand on the cis or trans configuration of the monomethylpalladium complexes was observed, the results being in contrast with those of complexes having the trimethylphosphine ligands that give preferentially trans complexes. Removal of the chloride ligand in 2 with an equimolar amount of AgBF₄ or treatment of the dimethylpalladium complex 1 with HBF₄ in the expectation of obtaining a bis(phosphite)-coordinated complex led to formation of a mixture of the tris(phosphite) complex, [PdMe{P(OR)₃}₃] ⁺BF₄^- and the mono-phosphite complex [PdMe{P(OR)₃}(s)₂]⁺BF₄^- (s = solvent), presumably through the rapid disproportionation of an unstable intermediate [PdMe{P(OR)₃}₂(s)]⁺BF ₄^-.