Two-Electron Redox Chemistry at the Dinuclear Core of a TePt Platform: Chlorine Photoreductive Elimination and Isolation of a TeVPtI Complex

As part of our interest in novel redox-active main group/transition metal platforms for energy applications, we have synthesized the chloride salt of [(TePtCl)-Pt-III-Cl-I(o-dppp)(2)](+) ([1](+), o-dppp = o-(Ph2P)C6H4) by reaction of the new bis(phosphino) telluroether (o-(Ph2P)C6H4)(2)Te with (Et2S)(2)PtCl2. Complex [1](+) is chemically robust and undergoes a clean two electron oxidation reaction in the presence of PhICl2 to afford (ClTePtCl3)-Pt-III-Cl-III(o-dppp)(2) (2), a complex combining a hypervalent four-coordinate tellurium atom and an octahedral platinum center. While the Te-Pt bond length is only slightly affected by the oxidation state of the TePt platform, DFT and NBO calculations show that this central linkage undergoes an umpolung from Te -> Pt in [1](+) to Te <- Pt in 2. This umpolung signals an increase in the electron releasing ability of the tellurium center upon switching from an eight electron configuration in [1](+) to a hypervalent configuration in 2. Remarkably, the two electron redox chemistry displayed by this new dinuclear platform is reversible as shown by the photoreductive elimination of a Cl-2 equivalent when 2 is irradiated at 350 nm in the presence of a radical trap such as 2,3-dimethyl-1,3-butadiene. This photo reductive elimination, which affords [1] [Cl] with a maximum quantum yield of 4.4%, shows that main group/late transition metal complexes can mimic the behavior of their transition metal only analogues and, in particular, undergo halogen photoelimination from the oxidized state. A last notable outcome of this study is the isolation and characterization of F(MeO)(2)(TePtCl)-Pt-V-Cl-I(o-dppp)(2) (4), the first metalated hexavalent tellurium compound, which is formed by reaction of 2 with KF in the presence of MeOH.