Two-electron redox chemistry at the dinuclear core of a TePt platform: chlorine photoreductive elimination and isolation of a Te(V)Pt(I) 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 [Te(III)Pt(I)Cl(o-dppp)(2)](+) ([1](+), o-dppp = o-(Ph(2)P)C(6)H(4)) by reaction of the new bis(phosphino) telluroether (o-(Ph(2)P)C(6)H(4))(2)Te with (Et(2)S)(2)PtCl(2). Complex [1](+) is chemically robust and undergoes a clean two-electron oxidation reaction in the presence of PhICl(2) to afford ClTe(III)Pt(III)Cl(3)(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 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)(2)Te(V)Pt(I)Cl(o-dppp)(2) (4), the first metalated hexavalent tellurium compound, which is formed by reaction of 2 with KF in the presence of MeOH.