The hydride complex CpRu(CO)(PMe3)H (1) undergoes a chemically irreversible oxidation at 0.34 V vs the ferrocene/ferrocenium couple. By the judicious choice of reaction conditions, the oxidation of 1 in acetonitrile may be directed toward a 2/3-, 1-, or 2-electron process. The room temperature oxidation of 1 with Cp2Fe+PF6- in acetonitrile-d3 leads to the virtually quantitative (by H-1 NMR) generation of [CpRu(CO)(PMe3)]2(mu-H)+ (5), HRu(CO)(PMe3)(NCCD3)3+ (4-d9), and cyclopentadiene in a 1:1:1 molar ratio, in accord with an overall 2/3-electron oxidation of 1. A trace of CpRu(CO)(PMe3)(NCCD3)+ (2-d3) was also observed. Dihydrogen complex CpRu(CO)(PMe3)(eta-2-H-2)+ (3) was observed as an intermediate in the reaction, and it reacted to form 4-d9 and cyclopentadiene. Ferrocenium oxidation of 1 in the presence of 2,6-lutidine proceeded as a 1-electron process, yielding 5 and H+. In the presence of pyrrolidine, a 2-electron process ensued and resulted in the formation of 2-d3 and H+. Coulometry and preparative-scale experiments performed in acetonitrile proceeded somewhat differently. The electrochemical oxidation was a 1-electron process in the absence of base, yielding mostly 2 and 4, whereas a 2-electron process took place in the presence of 2,6-lutidine or pyrrolidine, yielding 2. The key to explaining all of the results is that an initial proton-transfer reaction from 1.+ to a base occurs. This transfer may take place rapidly from 1.+ to pyrrolidine, but only slowly to 2,6-lutidine. Proton transfer from 1.+ to the base yields the radical CpRu(CO)(PMe3).. The latter results in the formation of 5 via combination with 1.+ when 1.+ concentrations are relatively high. This is the case when 1 or 2,6-lutidine functions as a base. Otherwise, a second oxidation of CpRu(CO)(PMe3). produces 2. Pyrrolidine effects the rapid deprotonation of the cation radical, effectively depleting the solution of 1.+ and closing the pathway leading to 5.
