Synthesis of a stable organopalladium (IV) complex through the aerobic oxidation of a dimethylpalladium (II) complex

A number of organometallic complexes of Pd(II) and Pd(IV), [PdMe2(COD)], K[PdMe2(Tp*)], and [PdMe3(Tp*)] were prepared and characterized. At first, the [PdMe2(COD)] complex was synthesized through the methylation of [Pd(COD)Cl2] using the solution of Me2CuLi. Then, the K[PdMe2(Tp*)] complex was obtained through the reaction of [PdMe2(COD)] with KTp*. Moreover, the oxidation of K[PdMe2(Tp*)] complex was investigated through the aerobic method. The facile aerobic oxidation of K[PdMe2(Tp*)] complex led to the formation of a stable organopalladium(IV) complex, [PdIVMe3(Tp*)]. The high reactivity of the K[PdMe2(Tp*)] complex toward the aerobic oxidation is likely due to the ability of the Tp* ligand to stabilize the octahedral geometry of a Pd(IV) complex. The X-ray crystallography study of [PdIVMe3(Tp*)] complex shows that it has an octahedral structure and a symmetric pseudo-C3v geometry. The [PdIVMe3(Tp*)] complex is very stable in both solid and solution states at room temperature and does not undergo ethane elimination. The reactivity of [PdIVMe3(Tp*)] complex toward the C–C bond formation and the reductive elimination of ethane was investigated by 1H NMR through the thermolysis in C6D6 at 70 ˚C. The low reductive elimination and C–C bond formation reactivity for the [PdMe3(Tp*)] complex is due to the high stability of this complex which has a symmetric pseudo-C3v geometry.