Insertion Reactions of Alkynes into the Ru−H Bond of Indenylruthenium(II) Hydride Complexes. Mechanism of the Reaction of Phenylacetylene with [RuH(η<b>⁵</b>-C₉H₇)(dppm)] (dppm = Bis(diphenylphosphino)methane)

Abstract

The indenyl complexes [RuX(η 5 -C 9 H 7 )(dppm)] (dppm = bis(diphenylphosphino)methane, X = H, D) react with phenylacetylene to give the products of syn addition [Ru{( E )-CH CXPh}(η 5 -C 9 H 7 )(dppm)] in toluene, in the temperature range 40−80 °C. The indenyl complexes [RuH(η 5 -C 9 H 7 )LL‘] (L = L‘ = PMe 2 Ph; L = PPh 3, L‘ = PMe 2 Ph; L = PPh 3, L‘ = PMe 3; LL‘ = dppe) and [RuH(η 5 -Me 3 C 9 H 4 )(CO)(PPh 3 )] and the cyclopentadienyl complex [RuH(η 5 -C 5 H 5 )(dppm)] do not react with PhC⋮CH, even under more forcing conditions. The complexes [RuH(η 5 -C 9 H 7 )LL‘] (LL‘ = dppe; LL‘ = dppm; L = L‘ = PMe 2 Ph; L = PPh 3, L‘ = PMe 3; L = PPh 3, L‘ = PMe 2 Ph) and the indenyl-substituted complexes [RuH(η 5 -Me 3 C 9 H 4 )(CO)(PR 3 )] (PR 3 = PPh 3, P i Pr 3 ) react with dimethyl acetylenedicarboxylate to give the alkenyl derivatives [Ru{( E )-C(CO 2 Me) CH(CO 2 Me)}(η 5 -C 9 H 7 )LL‘] and [Ru{( E )-C(CO 2 Me) CH(CO 2 Me)}(η 5 -Me 3 C 9 H 4 )(CO)(PR 3 )], respectively, in diethyl ether under reflux. The reaction of [RuH(η 5 -C 9 H 7 )LL‘] with methyl propiolate yields the α-metalated alkenyl complexes [Ru{C(CO 2 Me) CH 2 }(η 5 -C 9 H 7 )LL‘] (LL‘ = dppe, dppm; L = L‘ = PMe 2 Ph; L = PPh 3, L‘ = PMe 3 ) in refluxing diethyl ether. A kinetic study has been carried out for the reaction of the complexes [RuX(η 5 -C 9 H 7 )(dppm)] with phenylacetylene in toluene, by 1 H and 31 P{ 1 H} NMR spectroscopy. The reactions are first order with respect to the ruthenium complex and to the alkyne. The hydride and the deuteride complexes react at the same rate; intermediates are not detectable neither by kinetic studies nor by spectroscopy. The activation parameters, from rate measurements in the range 40−60 °C, are as follows: Δ H ⧧ = 17 ± 2 kcal mol - 1, Δ S ⧧ = −21 ± 4 cal mol - 1 K - 1 . An associative mechanism is proposed for the reaction, which involves the formation of an intermediate from the ruthenium complex and the alkyne under rate-determining steady-state conditions, followed by fast hydride migration and product formation. Due to the lack of reactivity of the analogous cyclopentadienyl complex [RuH(η 5 -C 5 H 5 )(dppm)], the reaction represents a case of indenyl effect . On the other hand, the indenyl and the cyclopentadienyl complexes react at comparable rates with the activated alkyne methyl propiolate.