Intermolecular hydrogenation of a C=C bond during pi-cyclopentadienyliron complexation of 1,8-dichloro-9,10-dihydro-9,10-etheneoanthracene

Reaction of 1,8-dichloro-9,10-dihydro-9,10-ethenoanthracene with ferrocene in the presence of Al and AlCl3 in cyclohexane affords the mono-iron comple x [endo-(eta(6)(1,8-dichloro-9,10-dihydro-9,10-ethanoanthracene))FeCp](PF6) as the only isolable iron-containing product. X-ray and NMR analysis of th is product confirms that the etheno bridge in the arene ligand has been hyd rogenated. The intramolecular mechanism previously proposed for this type o f hydrogenation accompanying pi complexation (i.e. involving an Fe-H interm ediate) is impossible for steric reasons; thus, an intermolecular process m ust be considered. The same reaction was attempted in methylcyclohexane-cyc lohexane mixtures, in order to improve the complexation yield and favor the formation of diiron complexes. However, this led instead to the formation of [(eta(6)-toluene)FeCp](PF6), in which the coordinated toluene ligand ari ses from dehydrogenation of the methylcyclohexane solvent. (C) 1999 Elsevie r Science S.A. All rights reserved.