TRANSITION-METAL STABILIZED ORTHO-XYLYLENES - REACTIVITY OF THE NOVEL ORTHO-XYLYLENE COMPLEX RU(ETA-6-C6ME6)[ETA-4-C6ME4(CH2)2]

The title complex was prepared in 87% yield from the deprotonation of [Ru(C6Me6)2] (BF4)2 with excess potassium tert-butoxide in THF at -78-degrees-C. Treatment of the mixed-sandwhich complex [Ru(1,2-C6H4Me2)(C6Me6)](PF6)2 with excess potassium tert-butoxide resulted in preferential deprotonation of the hexamethylbenzene ligand, giving o-xylylene complex Ru(eta-6-1,2-C6H4Me2)[eta-4-C6Me4(CH2)2]. Attempts to prepare o-xylylene complexes bearing no ring methyl groups by deprotonation of [Ru(o-xylene)2]2+ or [Ru(benzene)(o-xylene)2+ failed to give isolable complexes. The cyclohexadienyl complex Ru(eta-6-C6Me6)(eta-C6Me5CH2)]+ was prepared as the PF6-, BPh4-, or CF3SO3-salt by monodeprotonating [Ru(C6Me6)2](PF6)2 with 1 equiv of potassium tert-butoxide, by treating the title complex with 1 equiv of trifluoromethanesulfonic acid, or by stirring an equimolar mixture of [Ru(C6Me6)2](BF4)2 and the title complex m acetonitrile. The exomethylene carbons of the coordinated o-xylylene were alkylated with excess CF3SO3Me to give [Ru(C6Me6)(1,2-C6Me4Et2)]2+ or were hydrogenated under catalytic conditions to give the single or doubly hydrogenated complexes Ru(eta-4-C6HMe5CH2)(eta-6-C6Me6) and Ru(eta-4-5,6-C6Me6H2)(eta-6-C6Me6). The singly hydrogenated product is a tautomer of the known 18-electron complex Ru(C6Me6)2 but is much more stable toward oxidation. Treatment with Fe(CO)4(NMe3) gave a product bearing an Fe(CO)3 group coordinated to the exomethylene diene system, along with an unexpected product characterized as a complex in which an iron acylate strap connects the two dissimilar hexamethylbenzene ligands. The coordinated o-xylylene ligand failed to undergo cycloaddition reactions when treated with dienophiles.