Regioselective Synthesis of Indenylruthenium(II) Vinylalkylidene Complexes via Proton Additions to Vinylalkenyl Derivatives

Vinylalkenyl complexes [Ru{( E )-CH CHCR CH 2 }(η 5 -C 9 H 7 )(dppm)] (dppm = bis(diphenylphosphino)methane; R = H ( 1a ), CH 3 ( 1b )) and ( n = 1 ( 2a ), 2 ( 2b ), 3 ( 2c )) have been prepared by the regio- and stereoselective reaction of the hydride complex [RuH(η 5 -C 9 H 7 )(dppm)] with propargylic alcohols HC⋮CC(OH)RCH 3 (R = H, CH 3 ) and cyclic alcohols. The reactions proceed through the regio- and stereoselective insertion of the alcohols in the ruthenium-hydride bonds leading to the transient hydroxyvinyl complexes [Ru{( E )-CH CHC(OH)RCH 3 }(η 5 -C 9 H 7 )(dppm)] and which undergo a rapid dehydration process to give the final products. The hydroxyalkenyl complex [Ru{( E )-CH CHCH 2 OH}(η 5 -C 9 H 7 )(dppm)] ( 3a ) is sufficiently stable toward the dehydration and can be isolated from the insertion reaction of [RuH(η 5 -C 9 H 7 )(dppm)] with HC⋮CCH 2 OH. Protonation at C δ of the vinylalkenyl moiety of complexes 1a, b and 2a, c with HBF 4 ·Et 2 O in diethyl ether affords the cationic vinylalkylidene complexes [Ru( CHCH CRCH 3 )(η 5 -C 9 H 7 )(dppm)][BF 4 ] (R = H ( 4a ), CH 3 ( 4b )) and ( n = 1 ( 4c ), 3 ( 4e )) in good yields. The analogous vinylalkylidene complexes [Ru( CHCH CRPh)(η 5 -C 9 H 7 )(dppm)][BF 4 ] (R = H ( 4f ), Ph ( 4g )) are obtained via one-pot synthesis by the reaction of [RuH(η 5 -C 9 H 7 )(dppm)] with HC⋮CCR(OH)Ph (R = H, Ph) in refluxing toluene followed by the addition of an stoichiometric amount of HBF 4 ·Et 2 O. However, the protonation of complex 2b is not regioselective, giving instead a mixture of the vinylalkylidene complex ( 4d ) and the π-olefin complex ( 5 ) in a 4/1 molar ratio. The mechanism of this process has been established by analyzing the 1 H NMR spectrum of the reaction of complex 2b with DBF 4 . It is shown that the π-olefin complex 5 is generated from the electrophilic addition at the C β atom of the vinylalkenyl complex 2b, which undergoes a favorable [1,2]-H shift to give 5 . 1 H, 31 P{ 1 H}, and 13 C{ 1 H} NMR spectroscopic data are discussed for all the novel vinylalkenyl and vinylalkylidene complexes.