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Hydrocarbyl Ligand “Tuning” of the PtII/IV Redox Potential

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journal contribution
posted on 2004-06-14, 00:00 authored by Andrei N. Vedernikov, Maren Pink, Kenneth G. Caulton
The potentially tridentate macrocycle [2.1.1]-(2,6)-pyridinophane (L) enables the transient LPtII(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+)PtIIR2 and (η3-L)PtIVH(R)2+. At equilibrium, the related example where R = CH3 is purely the PtIV redox isomer, which with R = C6H5 shows detectable populations of both isomers, and with R = C6F5 is purely the pyridine-protonated (HL+)PtII redox isomer. All species show a hydrogen bond from the pyridinium proton to PtII. 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 1JPtH coupling constant falls in the series R = Me (90 Hz), R = C6H5 (86 Hz), and R = C6F5 (63 Hz).