SYNTHESIS AND REACTIVITY OF NEUTRAL AND IONIC PI-ADDUCTS OF FUNCTIONAL ARENES - X-RAY CRYSTAL-STRUCTURES OF ([(C5ME5)RU]2(ETA-6,ETA-6-PHC=CPH))(CF3SO3)2, (C5ME5)RU(ETA-6-PHCOO), AND [(C5ME5)(MECN)RU(MU-2-ETA-2,ETA-4-C4H2PH2)RU(C5ME5)](CF3SO3)

The protonation of [Cp*Ru(OMe)]2 (1) in the presence of functional arenes, viz. diphenylacetylene, stilbene, benzophenone, phenol, or benzoic acid, yields the pi-arene adducts [Cp*Ru(eta-6-PhC = CPh)](CF3SO3) (5), [(Cp*Ru)2 (eta-6,eta-6-PhC = CPh)](CF3SO3)2 (6), [(Cp*Ru)2(eta-6,eta-6-PhCH = CHPh)](CF3SO3)2 (7), [(Cp*Ru)2-(eta-6,eta-6-PhCOPh)](CF3SO3)2 (9), [Cp*Ru(eta-6-PhOH)](CF3SO3) (11), and [Cp*Ru(eta-6-PhCOOH)](CF3SO3) (14). It is noteworthy that the monoadducts (5) and bis adducts (6) can be obtained with diphenylacetylene, whereas with stilbene and benzophenone the bis adducts (7 and 9) are preferentially obtained under the same conditions. This can be related both to the electron-releasing effect of the ''Cp*Ru+'' fragment and to the better transmission of electronic effects. 1 can be directly protonated by phenol and benzoic acid to yield [Cp*Ru(eta-5-C6H5O)] (12) and [Cp*Ru(eta-6-PhCOO)] (15). 15 shows a zwitterionic character ascertained by an X-ray crystal structure determination and its reactivity. 12 reacts with CH3I to give [Cp*Ru(eta-6-PhOCH3)]+ (13), obtained independently from Cp*Ru+ and PhOCH3 but not with a primary amine. Finally, the protonation of [Cp*Ru(OMe)]2 in the presence of benzonitrile or phenylacetylene leads to untractable mixtures containing both pi-aromatic and sigma-bonded (PhCN) or more complicated (PhC = CH) derivatives. However, the reaction of [Cp*Ru(MeCN)3](CF3SO3) (17) with phenylacetylene affords the paramagnetic complex [Cp*(MeCN)Ru(mu-2-eta-2,eta-4-C4H2Ph2)RuCp*](CF3SO3) (18) in high yield. The structures of 6, 15, and 18 have been ascertained by X-ray crystal structure determination.