Iron versus Ruthenium:  Dramatic Changes in Electronic Structure Result from Replacement of One Fe by Ru in [{Cp*(dppe)Fe}-CC-CC-{Fe(dppe)Cp*}]n+ (n = 0, 1, 2)

The reactions of FeCl(dppe)Cp* and Ru(C equivalent to CC equivalent to CH)L2Cp' with Na[BPh4] and 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu; 2 equiv) in a mixed thf/NEt3 solvent afford {Cp*(dppe)-Fe}(C equivalent to CC equivalent to C){Ru(PP)Cp'} (PP = dppe, Cp' = Cp*, 7; PP = (PPh3)(2), Cp' = Cp, 8). Cyclic voltammetry shows that these mixed Fe/Ru complexes undergo sequential loss of up to three electrons, with the mono- and dioxidized species being isolated following chemical oxidation. Computational (DFT) and spectroscopic (IR, NMR, ESR, Mossbauer) studies are consistent with a polarized ground-state structure with oxidation leading to the gradual evolution of cumulenic character in the FeC4Ru moiety and a greater degree of orbital mixing between the Fe, C, and Ru centers than found in the related heterometallic complex [{Cp*(dppe)-Fe}(C equivalent to CC equivalent to C){Re(NO)(PPh3)Cp*}](n+) ([6](n+)). In contrast to the two-electron oxidation products derived from the diiron complex {Cp*(dppe)Fe}(C equivalent to CC equivalent to C){Fe(dppe)Cp*} (1) and iron/rhenium complex 6, the dications [7](2+) and [8]2+ feature a dominant contribution from a singlet ground state. Thus, while 6 behaves in a manner closely related to 1, 7 and 8 are more closely related to {Cp(Ph3P)(2)Ru}(C equivalent to CC equivalent to C){Ru(PPh3)(2)Cp} (2) and {Cp*(dppe)Ru}-(C equivalent to CC equivalent to C){Ru(dppe)Cp*} (3), clearly demonstrating the pronounced role that choice of metal as well as formal electron count can play in tuning the electronic and magnetic properties of this fascinating class of compound.