Synthesis and Electronic Structure of Dissymmetrical, Naphthalene-Bridged Sandwich Complexes [Cp′Fe(μ-C10H8)MCp*]x (x=0,+1; M = Fe, Ru; Cp′ = η5-C5H2-1,2,4-tBu3; Cp* = η5-C5Me5)

The dissymmetrical naphthalene-bridged complexes [Cp'Fe(mu-C10H8)FeCp*] (3; Cp* = eta(5)-C5Me5, Cp' = eta(5)-C5H2-1,2,4-tBu(3)) and [Cp'Fe(mu-C10H8)RuCp*] (4) were synthesized via a one-pot procedure from FeCl2(thf)(1.5), Cp'K, KC10H8, and [Cp*FeCl(tmeda)] (tmeda = N,N,N',N'-tetramethylethylenediamine) or [Cp*RuCl](4), respectively. The symmetrically substituted iron ruthenium complex [Cp*Fe(mu-C10H8)RuCp*] (5) bearing two Cp* ligands was prepared as a reference compound. Compounds 3-5 are diamagnetic and display similar molecular structures, where the metal atoms are coordinated to opposite sides of the bridging naphthalene molecule. Cyclic voltammetry and UV/vis spectroelectrochemistry studies revealed that neutral 3-5 can be oxidized to monocations 3(+)-5(+) and dications 3(2+)-5(2+). The chemical oxidation of 3 and 4 with [Cp2Fe]PF6 afforded the paramagnetic hexafluorophosphate salts [Cp'Fe(mu-C10H8)FeCp*]PF6 ([3]PF6) and [Cp'Fe(mu-C10H8)RuCp*]PF6 ([4]PF6), which were characterized by various spectroscopic techniques, including EPR and Fe-57 Mossbauer spectroscopy. The molecular structure of [4]PF6 was determined by X-ray crystallography. DFT calculations support the structural and spectroscopic data and determine the compositions of frontier molecular orbitals in the investigated complexes. The effects of substituting Cp* with Cp' and Fe with Ru on the electronic structures and the structural and spectroscopic properties are analyzed.