Regioselective permethylation, perallylation and perbenzylation of the arene ligand in [Ru(η5-C5Me5)(η6-C6Me6)][PF6]:: a remarkable periodic effect

The reactions of [MCp*(eta(6)-C6Me6)][PF6], M = Fe: 1, Ru: 2, Cp* = eta(5)-C5Me5, with KOH (in DME) or tert-BuOK (in THF) and methyl iodide, allyl bromide or benzyl bromide are regioselective on the arene ligand only for 2, giving the complexes [RuCp*{eta(6)-C-6(CH2R)(6)}][PF6], R = methyl (3), allyl (4) or benzyl (5), although some formations of C-C bonds also occur on the Cp* ligand in the case of the reactions of allyl and benzyl bromides. This contrasts with the complete lack of regioselectivity formerly observed with the iron analogue I, and is best taken into account by the difference of steric effects which are less marked in 2 than in 1. (C) Academie des sciences/Elsevier, Paris.