Reactivity of indenyl-ruthenium(II) vinylidene complexes:: Selective synthesis of alkenyl-phosphonio derivatives via nucleophilic addition of triphenylphosphine on their η2-alkyne tautomers.: Theoretical study of the η1-vinylidene-η2-alkyne tautomerization

The activation of terminal alkynes with the halide derivatives [RuX eta (5)-1,2,3-R3C9H4)(CO)- (PR3)] (R = Me, X = Br, PR3 = PPh3 (1), (PPr3)-Pr-i (3); R = H, X = I, PR3 = (PPr3)-Pr-i (2)) and AgBF4 affords, in dichloromethane at room temperature, equilibrium mixtures containing the corresponding eta (1)-vinylidene and eta (2)-alkyne tautomers [Ru{=C=C(H)R'}(eta (5)-1,2,3-R3C9H4)-(CO)(PR3)][BF4] (4a-c) and [Ru(eta (2)-HC drop CR')(eta (5)-1,2,3-R3C9H4)(CO)(PR3)][BF4] (5a-c), respectively. The reaction of 1 with AgBF4 and phenylacetylene has been studied by variable-temperature P-31{H-1}and H-1 NMR spectroscopy: at low temperature (-60 degreesC) the vinylidene complex [Ru{=C=C(H)Ph}(eta (5)-1,2,3-Me3C9H4)(CO)(PPh3)][BF4] (4a) is initially observed which upon warming (14 degreesC) forms an equilibrium with the pi -alkyne derivative [Ru(eta (2)-HC drop CPh)-romethane at room temperature selectively yields the neutral sigma -alkynyl derivative [Ru(C drop CPh)(eta (5)-1,2,3-Me3C9H4)(CO)(PPh3)] (6) by displacement of the aforementioned equilibrium via deprotonation of the acidic vinylidene proton in 4a, while the addition of PPh3 to this C(PPh3)Ph}(eta (5)-1,2,3-Me3C9H4)(CO)(PPh3)][BF4] [(E)-7] via the nucleophilic attack of PPh3 on the coordinated pi -alkyne in 5a. In a similar fashion, compounds (E)-[Ru{C(H)=C(PPh3)-R'}(eta (5)-1,2,3-R3C9H4)(CO)(PR3)][BF4] (R = Me, PR3 = PPh3, R' = 1-cycloctenyl [(E)-13]; R = H, PR3 = (PPr3)-Pr-i, R' = Ph [(E)-8], 1-cyclooctenyl [(E)-14] can be selectively obtained by addition of PPh3 to the corresponding reaction mixture. The monosubstituted alkenyl-vinylidene complexes [Ru{=C=C(H)CH=CRR'}(eta (5)-C9H7)(PPh3)(2)][BF4] (R = R' = Ph (11a); R = H, R' = (eta (5)-C5H4)Fe(eta (5)-C5H5) [(E)-11b], 4-OMe-C6H4 [(Z)-11c]) also react with triphenylphosphine, but in refluxing methanol, to afford the alkenyl-phosphonio derivatives (EE)-[Ru{C(H)=C(PPh3)CH=CRR'}(eta (5)-C9H7)(PPh3)(2)][BF4] (12a-c) stereoselectively. The process also proceeds via an initial eta (1)-vinylidene-eta (2)-alkyne tautomerization followed by the nucleophilic attack of PPh3 on the coordinated pi -alkyne. The crystal structures of (E)-[Ru{C(H)=C(PPh3)Ph}-(eta (5)-1,2,3-Me3C9H4)(CO)(PPh3)][BF4] ((E)-7) and (EE)-[Ru{C(H)=C(PPh3)(CH=CH(eta (5)-C5H4-Fe(eta (5)-C5H5)}(eta (5)-C9H7)(PPh3)(2)][BF4] ((EE)-12b) have been determined by X-ray diffraction methods. Ab initio molecular orbital calculations on the eta (1)-vinylidene to eta (2)-alkyne tautomerization on the models [Ru(eta (5)-C9H7)(PH3)L(C2H2)](+) (L = CO, PH3) are also reported.