Electrochemical generation of hydridopentamminerhodium(III) and its reaction with molecular oxygen

Abstract

The electrochemistry of Rh(NH3),0HZ+ has been studied in a buffered ammoniacal solution. The polarographic reduction wave at the dropping mercury electrode had equal to -1.10 V (vs. saturated calomel electrode) in a 0.10 M N H , -0.10 MNH,C10, electrolyte, and gross Hg cathode electrolysis at -1.19 V produced a stable Rh(NH3),Hz+ hydride species. Both reductions were found to take place through a Rh(I) intermediate.The reaction of the Rh(NH3),HZ+ with molecular OZ in the ammoniacal electrolyte was also studied. The product was demonstrated to be a stable Rh(NH3)4(0H)(OZH)+ hydroperoxo species.

Cyclic Voltammetry and Chronocoulometry with trans-Rh(en)[sub 2]Cl[sub 2]+] at Mercury Electrodes

“…These voltammograms, Fig. 7 during an initially positive potential scan with alkaline solutions of Rh(en)2H(OH2) 2+ to be ascribed to reactions [5] and [6] occurring at potentials too close together to yield separate waves. Thus the reduction wave near --500 mV in Fig.…”

“…) unless CC License in place (see abstract The fact that electrons are liberated in reaction [5] is the main reason that chronocoulometric plots having slopes well below the level corresponding to a twoelectron reduction of trans-Rh(en) 2C12 + are obtained at --700 mV (Fig. 6A) despite the fact that all of the Rh(III) is reduced to Rh(I).…”

“…6A) despite the fact that all of the Rh(III) is reduced to Rh(I). And the increasing deviations of these slopes from the two-electron value at larger initial concentrations of trans-Rh(en)2C12 + reflects the increasing importance of reaction [5] as the concentration of Rh(en)2 + generated at the electrode surface in reaction [1] increases. The reason that the mercurated product is not observed at low pH is that the concentration of Rh(en)2 + generated in acid solutions is much lower because the equilibrium involved in reaction [2] lies far to the right.…”

“…The reason that the mercurated product is not observed at low pH is that the concentration of Rh(en)2 + generated in acid solutions is much lower because the equilibrium involved in reaction [2] lies far to the right. At high pH, the trans-Rh(en)2C12 + initially present is converted to trans-Rh(en)2Cl(OH) + very early in the electrolysis (vida supra) and the latter complex can be reduced only at more negative potentials where reaction [5] proceeds at an insignificant rate (8).…”

“…The adsorption of Rh(en)~ + which is maximal at these potentials (Fig. During the initial stages of such an electrolysis when the concentration of Rh (on)2 + is largest, its adsorption on the electrode could be responsible for the temporary inhibition of reaction [5] while reaction [1] proceeds. Such an effect would also help to account for the previous observation (8) that [(en)2Rh]2Hg ~+ is slowly reduced at --700 mV although this is also the potential where the same complex can be generated during the reduction of trans-Rh(en)2C12 + via reactions [1] and [5].…”