NEW CATIONIC BIS(ETA(3)-ALLYL)RUTHENIUM(IV) COMPLEXES FROM ALLYLIC C-H BOND ACTIVATION OF ALKENES

When (allyl)Ru(IV) complex CpRuBr2(eta3-C3H5) (1) was treated with silver trifluoromethane-sulfonate (silver triflate, AgOTf) followed by the reaction with propene (1 atm), new bis-allylic Ru(IV) cationic complex [CpRu(eta3-C3H5)2]OTf) (2) was obtained in 95% yield as a mixture of two isomers, in which the allyl ligands had different configurations; exo,endo form 2a and endo,endo isomer 2b. The former stereoisomer is predominant (70:30) in dichloromethane, whereas the latter prevails in the presence of alcohols (2a:2b = 15:85) or catalytic triethylamine (26:74). Interconversion between 2a and 2b did not occur in solution at ambient temperatures. 2-Butene gave an allyl-crotyl analogue (3; 96% yield), which takes an endo,endo configuration selectively. Such intermolecular allylic C-H bond activation of propene did not occur in the case of pentamethylcyclopentadienyl (Cp*) analogues. Intramolecular allylic C-H bond activation, however, takes place readily in the case of the (eta3-allyl)ruthenium(IV) complex 4, obtained from 1,5-dimethyl-1,5-cyclooctadiene and [Cp*RuCl2]2, to result in the formation of the new bis-allylic complex [Cp*Ru(eta3,eta3-C10H14)]OTf (5).