Hydrocarbyl Ligand “Tuning” of the Pt^II/IV Redox Potential

The potentially tridentate macrocycle [2.1.1]-(2,6)-pyridinophane (L) enables the transient LPt^II(CH₃)⁺ to cleave the C−H bond of two molecules of C₆F₅H. The resulting product has two aryl groups on Pt but, in contrast to nonfluorinated analogue, varies in its location of the cleaved H, as is evident from the two products (HL⁺)Pt^IIR₂ and (η³-L)Pt^IVH(R)₂⁺. At equilibrium, the related example where R = CH₃ is purely the Pt^IV redox isomer, which with R = C₆H₅ shows detectable populations of both isomers, and with R = C₆F₅ is purely the pyridine-protonated (HL⁺)Pt^II redox isomer. All species show a hydrogen bond from the pyridinium proton to Pt^II. Consistent with the idea that electron-withdrawing R makes platinum(II) more resistant to oxidation (i.e., a proton on Pt), and thus less Brønsted basic, the ¹J_PtH coupling constant falls in the series R = Me (90 Hz), R = C₆H₅ (86 Hz), and R = C₆F₅ (63 Hz).