Electrochemical Evidence of the Reorientation of Alkynes on Trimetallic Clusters during a Two-Electron Reduction

The electrochemical two-electron reduction of isoelectronic and isostructural alkyne clusters of iron and osmium has been investigated by fast-scan cyclic voltammetry. Both Fe₃(CO)₉(EtCCEt) and Os₃(CO)₇(Ph₂PCH₂PPh₂) (PhCCPh) undergo a two-electron reduction. While Fe₃(CO)₉(EtCCEt) is reduced in two separate one-electron waves, Os₃(CO)₇(Ph₂PCH₂PPh₂)(PhCCPh) displays a single two-electron wave. Fast-scan voltammetry detects one additional adsorption post-peak for the iron cluster which, under certain experimental conditions, gives rise to apparent anomalous shapes of voltammograms. Differences in electrochemical pattern of iron and osmium title compounds are interpreted on the basis of follow-up and concomitant isomerization reactions with respect to the first electron transfer, respectively.