One-Electron Oxidation of Heterodinuclear Organometallic Compounds Having

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′′ ) C5H3Bu2, Cp′′′ ) C5H2Bu3). 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 Cp2Fe) 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 negative than that of 1 by ca. 0.8 and 1.15 V, respectively, is ascribed to differences in the iron formal oxidation state which arise from the structural variations of the P5 bridging groups.