Facile ruthenium(IV)-catalyzed single and double allylation of indole compounds using alcohols as substrates:: Aspects of ruthenium(IV) allyl chemistry

The dicationic Ru(IV) salt [Ru(Cp*)(eta(3) -C3H5)(CH3CN)(2)](PF6)(2) is shown to be an excellent and rapid catalyst for the C-allylation of indole compounds using allyl alcohols as substrates. Selective, one-pot N,C-double allylation is also possible. Preliminary experiments suggest that vinyl epoxides may be used as an allyl source. Stoichiometric reactions of CH2 = CHCH(OH)CH = CH2, CH2 = CHCH(OAc)CH = CH2, and CH2 = CHCH = CHCH2Br with [Ru(Cp*)(CH3CN)(3)] (PF6) afford new Ru(IV)) eta(3)-vinyl-allyl salts, two of which, [Ru(Cp*)(k(2)-OAc)(eta(3)-vinyl-allyl)](PF6) (13) and [Ru(Cp*)Br(eta(3)-vinyl-allyl)(CH3CN)](PF6) (14), have been studied by X-ray diffraction methods. In addition to the Ru(IV) eta(3)-vinyl-allyl bonding mode, we also find an isomer of the bromo salt 14 possessing a dynamic Ru(IV) S (rather than U)-shaped) eta(5)-pentadienyl moiety, 20. DFT computational results for 20 indicate that the S-shaped rather than the U-shaped form is the most stable Ru(IV) species and that the stability difference between these two forms is mainly due to interligand repulsion between the Br and pentadienyl ligands.