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• 92-52-4 biphenyl 

Relevant academic research and scientific papers

Complexation of polyaromatics by C5H5Fe+ and C5Me5Fe+ and electronic structures of the monoreduced complexes

The synthesis of a number of known complexes [FeCp(η6-polyaromatic)]+PF6- has been reproduced or improved in order to examine their cathodic and LiAlH4 reduction to FeI or the monoreduced state. It is found that the phenanthrene and pyrene complexes are not hydrogenated during the ligand exchange reaction with ferrocene and AlCl3 and that pyrene does not give binuclear complexes, contrary to previous reports. The new complexes of triphenylene and of perylene have been made, and, although the latter is extremely light-sensitive, its X-ray crystal structure has been determined. It contains two different molecules in the unit cell where the two possibilities of relative conformations of the C5 ring/C6 ring are found. With FeCp*(CO)2Br + AlCl3, the new complexes [FeCp*(η6-polyaromatic)]+PF6 - (Cp* = η5-C5Me5) have been made with biphenyl, phenanthrene, dihydrophenanthrene, triphenylene, and pyrene. Syntheses in the melt are suitable for both Cp and Cp* series. The first cathodic wave is chemically reversible only for polyarornatics with less than four fused rings in the Cp series, but, with Cp*, the reduction of the pyrene complex becomes reversible. The comparison of the thermodynamic redox potentials corresponding to the system FeCp(polyAr)+/0 with those of the free ligand system (polyAr)0/- provides, according to Vlc?ek's theory, the spin density on the polyaromatic ligand of the monoreduced complexes. Values are found to depend markedly on the number n of fused rings of the polyaromatic in the Cp series so that significant spin density remains on Fe if n ≤ 4, whereas it is mainly located on the polyaromatic if n > 4. This is not the case in the Cp* series where the Fe(I) state is stabilized, with residual spin density on the polyaromatic being about 15-30%. In order to understand the electronic structure of those compounds, calculations using both the EH and MS-SCF-Xα formalisms have been performed on a series of complexes. The results concerning the spin densities are in reasonable (EH) or good (Xα) agreement with the experimental ones. However, the EH calculations on [FeCp(naphthalene)] lead to wrong results due to a poor level ordering of two a′ levels situated in the HOMO/LUMO region. All of the cationic FeII complexes react with LiAlH4 in THF at low temperature to give the neutral electron-transfer products. The ESR spectra of the latter also show a d7 FeI state for n ≤ 4 (three g values around 2) and a single line attributed to the radical anionic ligand if n > 4.