One-Electron Oxidation of Heterodinuclear Organometallic Compounds Having Polyphosphido Bridges

The electrochemical behavior of several heterometallic compounds having polyphosphido bridges has been investigated. Reversible one-electron oxidations were observed for Cp*Fe(P5)TaCp‘ ‘ (2), Cp*Fe(P5)[Ir2(CO)2Cp*2] (3), and Cp‘ ‘‘2Co2(P2)2 (4) (Cp* = C5M5, Cp‘ ‘ = C5H3tBu2, Cp‘ ‘‘ = C5H2tBu3). In contrast to the pseudo-sandwich polyphosphido complex Cp*FeP5 (1), compounds 2−4 undergo very facile oxidations and the corresponding monocations may be generated by bulk electrolysis or by reaction with ferrocenium ion. E1/2 values (vs Cp2Fe0/+) for the oxidations are −0.24 V for 2, −0.58 V for 3, and −0.33 V for 4 in CH2Cl2/0.1 M [NBu4][PF6], in contrast to 0.57 V for 1. Although ESR spectra of 2+ display hyperfine coupling to 181Ta, the SOMO appears to have only minor Ta character. IR spectroelectrochemistry of the 3/3+ couple reveals an increase of νCO of only 11 cm-1, indicating that the oxidation of 3 also occurs predominantly at the iron center. The fact that the Fe-based oxidations of 2 and 3 are more ne...