Acetate-Bridged Platinum(III) Complexes Derived from Cisplatin

摘要

Oxidation of the acetate-bridged half-lantern platinum(II) complex, cis-[Pt^II(NH3)2(µ-OAc)2Pt^II(NH3)2](NO3)2, [>1](NO3)2, with iodobenzene dichloride or bromine generates the halide-capped platinum(III) species, cis-[XPt^III(NH3)2(µ-OAc)2Pt^III(NH3)2X](NO3)2, where X is Cl in [>2](NO₃)₂, or Br in [>3](NO₃)₂, respectively. These three complexes, characterized structurally by X-ray crystallography, feature short (≈ 2.6 Å) Pt–Pt separations, consistent with formation of a formal metal-metal bond upon oxidation. Elongated axial Pt–X distances occur, reflecting the strong trans influence of the metal-metal bond. The three structures are compared to those of other known dinuclear platinum complexes. A combination of ¹H, ¹³C, ¹⁴N, and ¹⁹⁵Pt NMR spectroscopy was used to characterize [>1]²⁺–[>3]²⁺ in solution. All resonances shift downfield upon oxidation of [>1]²⁺ to [>2]²⁺ and [>3]²⁺. For the platinum(III) complexes, the ¹⁴N and ¹⁹⁵Pt resonances exhibit decreased linewidths by comparison to those of [>1]²⁺. Density functional theory (DFT) calculations suggest that the decrease in ¹⁴N linewidth arises from a diminished electric field gradient (EFG) at the ¹⁴N nuclei in the higher valent compounds. The oxidation of [>1](NO₃)₂ with the alternative oxidizing agent, bis(trifluoroacetoxy) iodobenzene, affords the novel tetranuclear complex, cis-[(O₂CCF₃)Pt^III(NH₃)₂(µ-OAc)₂Pt^III(NH₃)(µ-NH₂)]₂(NO₃)₄, [>4](NO₃)₄, also characterized structurally by X-ray crystallography. In solution, this complex exists as a mixture of species, the identities of which are proposed.