Organometallics zyxwvu 1989, 8, zyxwvu 2233-2242 2233 Complexation of Polyaromatics by C,H,Fe+ and C,Me,Fe+ and Electronic Structures of the Monoreduced Complexes Marc Lacoste,t Hassan Rabaa,$ Didier Astruc, *vt Albert Le Beuze,$ Jean-Yves Saillard, zyx *2 Gilles Prbcigoux,§ Christian Courseille,§ Nicole Ardoin,t and Walter Bowyert Laboratoire de Chimie Organique et OrganomBtallique, U.A. CNRS No. 35, Universitg de Bordeaux I, 351, Cows de la Libgation, 33405 Talence Cgdex, France, Laboratoire de Chimie du Solide et Inorganique Mol6culaire, UniversitB de Rennes I, Campus Beaulieu, 35042 Rennes C a e x , France, and Laboratoire de Cristallographie, UniversitB de Bordeaux I, 35 1, Cours de la Libgration, 33405 Talence CBdex, France Received October 7, 1988 The synthesis of a number of known complexes [FeCp(n6-polyaromatic)Il+PF6- has been reproduced or improved in order to examine their cathodic and LiAlH, reduction to Fe or the monoreduced state. It is found that the phenanthrene and pyrene complexes are not hydrogenated during the ligand exchange reaction with ferrocene and AlCl, 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 zyxwv [FeCp*(~6-polyaromatic)]+PF6- (cp* = n5-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 polyaromatics 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)+/O with those of the free ligand system (polyAr)O/-provides, according to VlEek'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 zyxwvuts 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(1) 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-Xa formalisms have been performed on a series of complexes. The results concerning the spin densities are in reasonable (EH) or good (Xa) 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 Fen complexes react with LiAlH, in THF at low temperature to give the neutral electron-transfer products. The ESR spectra of the latter also show a d7Fe' state for n < 4 (three g values around 2) and a single line attributed to the radical anionic ligand if n > 4. Introduction There is an increasing interest in the use of poly- aromatics as molecular materials.l" For instance, deriv- atives of triphenylene are used as discotic liquid crystals? perylene can be doped with oxidants to provide organic conductor^,^^^ and several fused polyaromatics are fluor- escent and luminescent agents and are used as photo- chromics.' The T complexation of polyaromatics by a transition metal brings about a tridimensionality which should have a dramatic influence on the physical properties and could open new synthetic routes. As compared to simple arene complexes, fused polyaromatic complexes can have a weaker arene-metal bond, which is useful in cata- lysis or for any purpose requiring free coordination sites. A number6 of chromium tricarbonyl complexes of poly- aromatics are known, and Cr($-naphthalene)(CO), was shown by Cais to be a catalyst for the hydrogenation of diene^.^ In the FeCp+ series, the situation is confusing. Several publications have reported studiesg15 of what were believed to be complexes of fused polyaromatics; in fact, it was shown later that these complexes are hydrogenated during their complexation with FeCp, + AlC1, + A1 (naphthalene, anthracene, phenanthrene, pyrene). Some Laboratoire de Chimie Organique et Organomgtallique, * Laboratoire de Chimie du Solide et Inorganique MolBculaire, * Laboratoire de Cristallographie, Universit6 de Bordeaux I. Universit6 de Bordeaux I. Universit6 de Rennes I. 0276-7333/89/ 2308-2233$01.5O/O true complexes are known, however (naphthalene, coron- ene,14a cyclophane~l~~~), but we have reinvestigated the synthetic problem. We were also interested in knowing (1) Ewald, M.; Lamotte, M.; Garrigues, P.; Rima, J.; Veyres, A.; La- pouyade, R.; Bourgeois, G. Adu. Org. Geochem. 1983,705. (2) (a) Donn, B. Astrophys. J. 1968,152,L129. (b) Basile, B.; Mid- deditch, B.; Oro, J. Org. Geochem. 1983,5, 211. (3) (a) Clar, E. Polycyclic Hydrocarbons; Academic Press: New York, 1964; Vols. 1 and 2. (b) Destrade, C.; Gasparoux, H.; Foucher, P.; Nguyeyn Hun Tinh; Malthete, J.; Jacques, J. J. Chim. Phys. Biol. 1983, 80, 137. (c) Levelut, A. M. Ibid. 1983, 80, 149. (4) Dias, J. R. Acc. Chem. Res. 1985,18,241. (5) Clar, E. The Aromatic Sextet; Wiley: London, 1972. (6) (a) Kirss, R. V.; Treichel, P. M. J. Am. Chem. SOC. 1986,108,853. (b) Rogers, R. D.; Atwood, J. L.; Albright, T. A.; Lee, W. A.; Rausch, M. D. organometallics 1984,3,263. 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