Coupling Multiple Benzylic Activation of Simple Arenes by CpFe⁺ with Multiple Alkene Metathesis Using Grubbs Catalysts:  An Efficient Carbon−Carbon Bond Formation Strategy Leading to Polycycles, Cyclophanes, Capsules, and Polymeric Compounds and Their CpFe⁺ Complexes

The CpFe⁺-induced perallylation of arenes containing benzylic hydrogens in the complexes [FeCp(η⁶-arene)][PF₆] using a base and allyl bromide has been improved by using room-temperature conditions and KOH as a base, which simplifies the procedure and brings the selectivity when some benzylic hydrogens remain. This reaction has been combined with RCM metathesis of two allyl groups borne by the same benzylic carbon using the Grubbs catalyst [Ru(CHPh)(PCy₃)₂Cl₂] (1) in a few minutes at room temperature and with cross-metathesis (CM) in refluxing dichloroethane using the more efficient second-generation Grubbs catalyst [Ru(CHPh)(PCy₃)₂{C(NMesCH₂)₂Cl₂}] (2). The FeCp⁺ tag allows an easy separation of the product from the catalyst and slows down the CM reaction for steric reasons, providing selectivity for the RCM reaction. The iron-free polyallyl arenes undergo both RCM and CM metathesis, and catalysis can also be carried out in the ionic liquid 1-butyl-3-imidazolium hexafluorophosphate as the solvent at 80 °C. CM metathesis of the perallylated arenes gives organoiron and organic macrocycles, cyclophanes, capsules, and polymers, all these compounds being conveniently detected by MALDI-TOF mass spectroscopy, which also gives useful information concerning the advancement of the metathesis reaction and the purity or mixture of the metathesis products.