My PhD research in Ken Kustin's lab centered around reactions of aquamanganese(III) and has fostered an ongoing interest in transition metals in uncommon oxidation states. Uncomplexed Ag2+ is highly oxidizing and exists only in strong acid and in the presence of high concentrations of Ag+. Silver(III) on the other hand is stable in strong base (t1/2  ? hr in 1.2 M NaOH) and exists as the tetrahydroxo ion, [Ag(OH)4]?.[Ag(OH)4]? is rather unique in that it is a strong oxidizing agent with a low-spin (d8) square-planar structure. Hence, silver(III) redox reactions are inner-sphere and can occur either within a five-coordinate intermediate or after substitution of one or more of the hydroxyl groups by the reducing/complexing agent. Reduction to Ag(I) can occur ?via? a two-electron step or in a sequence involving an Ag(II) intermediate.We have studied the kinetics and mechanisms of [Ag(OH)4]? reactions with a variety of substrates. Only with periodate and tellurate as complexing ligands have we seen stable silver(III) products and, indeed, these complexes are well-known. Metastable complexes and their oxidation products have been characterized after reaction with vic-dioximes and some tri- and tetrapeptides. Spectral evidence for an intermediate of expanded coordination is found in reduction by nicotinamide while kinetic rate laws point to similar intermediates in a number of other cases. Reduction of [Ag(OH)4]? by simple inorganic anions occurs either by a single two-electron step (including oxygen atom transfer) or by successive one-electron redox. All reactions of [Ag(OH)4]? are rapid and have activation parameters consistent with inner-sphere/associative reactivity.

Reactions of higher-valent silver

248th National Meeting (2014)

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