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 [TeIIIPtICl­(o-dppp)2]+ ([1]+, o-dppp = o-(Ph2P)­C6H4) by reaction of the new bis­(phosphino) telluroether (o-(Ph2P)­C6H4)2Te with (Et2S)2PtCl2. Complex [1]+ is chemically robust and undergoes a clean two-electron oxidation reaction in the presence of PhICl2 to afford ClTeIIIPtIIICl3(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 Cl2 equivalent when 2 is irradiated at 350 nm in the presence of a radical trap such as 2,3-dimethyl-1,3-butadiene. This photoreductive 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)2TeVPtICl­(o-dppp)2 (4), the first metalated hexavalent tellurium compound, which is formed by reaction of 2 with KF in the presence of MeOH.