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)

Abstract

The reactions of FeCl(dppe)Cp* and Ru(C≡CC≡CH)L 2Cp′ 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≡CC≡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, Mössbauer) 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≡CC≡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≡CC≡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)2Ru} (C≡CC≡C){Ru(PPh3)2Cp} (2) and {Cp*(dppe)Ru}-(C≡CC≡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. © 2005 American Chemical Society.