IR spectroelectrochemical investigation of the disproportionation of bis(benzenemethanethiolato)octacarbonylditungstate(2-)

Abstract

The UV-vis and IR spectroelectrochemistry of W2(SBz)2(CO)8* 12 3" (1) in 0.1 (TBA)PF6/CH2CI2 is reported (where SBz~= benzyl mercaptide). The reversible 2e~oxidation of W2(SBz)2(CC))82~i s analyzed in terms of the individual le~redox potentials, E e'_/2-and E by measuring the homogeneous disproportionation constant, Adisp. of the electrochemically generated W2(SBz)2(CO)8~r adical. At 25 ®C, we find KnSf equal to 7500 ± 4000. This value places E 0,-/2-at a potential nearly 0.23 V positive of E ®'0/-(E °'-ß---0.46 V; E ®'0/-= -0.69 V vs aqueous AgCl/Ag). The reversal in positions of the leredox potentials drives the disproportionation reaction and is rationalized to be a consequence of the electronic destabilization of W2(SBz)2(CO)8" relative to W2(SBz)2(CO)82' and W2(SBz)2(CO)8.

Manipulating the Electrolyte Medium to Favor Either One-Electron or Two-Electron Oxidation Pathways for (Fulvalendiyl)dirhodium Complexes

“…The IR results are qualitatively consistent with the voltammetry data in that the disproportionation reaction of eq 4 is shown to be weighted in favor of 2 + under these conditions (Δ E 1/2 ≈ 90 mV). , More importantly, information is obtained about the molecular and electronic structures of 2 + . The fact that the neutral complex 2 has a single ν CO absorbance and the dication 2 2+ has two carbonyl absorptions is well understood based on known structures .…”

“…It is informative that the energetically less-shifted of the bands (at 1992 cm -1 ) for 2 + is still some 50 cm -1 higher in energy than the 1942 cm -1 band of 2 . On the basis of arguments made earlier on IR shifts in formally mixed-valence complexes, the magnitude of this shift is indicative of strong electronic coupling between the two metals, strengthening support for metal−metal bond formation in 2 + . It is also worth noting that shifts in ν CO with the oxidation state of 2 n + track the overall change in molecular charge between n = 0 and either n = 1+ (larger shift, 81 cm -1 ; average 65 cm -1 ) or n = 2+ (larger shift, 140 cm -1 , average 125 cm -1 ).…”

Influence of Pyridine on the Multielectron Redox Cycle of Nickel Diethyldithiocarbamate

“…Electron-transfer reactions with first-row transition metals typically follow one-electron (1e – ) pathways. Therefore, many synthetic first-row metal complexes that have shown multielectron reactivity incorporate multiple metal centers, where each is oxidized/reduced by 1e – . − For complexes that achieve multielectron redox chemistry at monometallic centers, however, structural changes around the metal center and/or noninnocent ligands have been utilized to force a multielectron pathway over single electron transfer. − In these examples, the 1e – redox potentials associated with the metal center are shifted from their normal ordering to a condition known as potential inversion …”

Energetics of Concerted Two-Electron Transfer and Metal−Metal Bond Cleavage in Phosphido-Bridged Molybdenum and Tungsten Carbonyl Complexes

“…Concerted multielectron transfer reactions occur widely in chemistry and biology. − Although seemingly paradoxical, the electrostatic restrictions on such processes are lifted when an accompanying structural or compositional change (proton transfer, ligand binding, or ion-pair formation) makes transfer of a second unit of charge more favorable than the first. Some years ago, we encountered a family of ligand-bridged binuclear complexes that undergo one-step, two-electron transfer by a mechanism wherein the stoichiometry of the redox center does not change. − Experimental − and computational − studies have been conducted on many such systems, from which it is evident that metal−metal bond cleavage accompanied by structural reorganization provides the necessary driving force for a multielectron event.…”