Synthesis and characterization of binuclear Pt(IV) complexes and tetranuclear mixed valence complexes of Platinum(II)-Platinum(IV)

Abstract

The binuclear platinum(IV) complexes [NBu4]2[PtIV2(μ-Cl)2(C6F5)4Cl4] (2) and [PtIV2(μ-C8H6N4)2(C6F5)4Cl4] (4) have been synthesized by oxidative addition of chlorine to the binuclear platinum(II) species, but [NBu4]2[PtIV2(μ-OH)2(C6F5)4Cl4] (3) has been synthesized by substitution of the chloride bridges of the platinum(IV) complex. The square planar platinum environments of the Pt(II) starting materials change, as expected, to Pt(IV) octahedral environments with the chloride ligands in trans-position. Only minor changes in the Pt-X (X = Clbridge, OH) interatomic distances are produced because of the oxidation.Depending on the size of the bridging ligands and also probably the anionic character of the diplatinum(IV) complexes, the apical chloride ligands can still act as bridges toward other Pt centers. Thus, the organometallic tetra-nuclear mixed-valence platinum(IV)-platinum(II) complexes with formulas [NBu4]2[{PtIV(μ-X)(C6F5)2}2(μ-Cl)4{PtII(C6F5)2}2] [X = Cl (5), OH (6)] were obtained by reaction of 2 and 3 with cis-[PtII(C6F5)2(thf)2]. The structures of complexes 2, 4 and 6 have been determined by single-crystal X-ray diffraction studies. These crystal structures confirm that the oxidative addition of the chlorine molecule to the platinum(II) complexes 2 and 3 takes place on the axial positions of the platinum centers suggesting a SN2 mechanism. On the other hand, the central core of the anion of 6 has a chair like conformation and the long Pt⋯Pt distances (>3.2 Å) clearly exclude any Pt.···Pt interaction.On the other hand, cis-[(C6F5)2Pt(μ-C8H6N4)Pt(C6F5)2] (1) can be reduced either electrochemically or by reacting with [CoCp2] to the anion [Pt2(μ-C8H6N4)(C6F5)4]- which in the last case, can be isolated as complex 7. According to the EPR studies the anion is not a mixed Pt(II)/Pt(I) compound but a binuclear Pt(II) derivative with the anion [C8H6N4]- as bridging ligand.