Insertion Reactions of Alkynes into the Ru−H Bond of Indenylruthenium(II) Hydride Complexes. Mechanism of the Reaction of Phenylacetylene with [RuH(η5-C9H7)(dppm)] (dppm = Bis(diphenylphosphino)methane)

Abstract

The indenyl complexes [RuX(η5-C9H7)(dppm)] (dppm = bis(diphenylphosphino)methane, X = H, D) react with phenylacetylene to give the products of syn addition [Ru{(E)-CHCXPh}(η5-C9H7)(dppm)] in toluene, in the temperature range 40−80 °C. The indenyl complexes [RuH(η5-C9H7)LL‘] (L = L‘ = PMe2Ph; L = PPh3, L‘ = PMe2Ph; L = PPh3, L‘ = PMe3; LL‘ = dppe) and [RuH(η5-Me3C9H4)(CO)(PPh3)] and the cyclopentadienyl complex [RuH(η5-C5H5)(dppm)] do not react with PhC⋮CH, even under more forcing conditions. The complexes [RuH(η5-C9H7)LL‘] (LL‘ = dppe; LL‘ = dppm; L = L‘ = PMe2Ph; L = PPh3, L‘ = PMe3; L = PPh3, L‘ = PMe2Ph) and the indenyl-substituted complexes [RuH(η5-Me3C9H4)(CO)(PR3)] (PR3 = PPh3, PiPr3) react with dimethyl acetylenedicarboxylate to give the alkenyl derivatives [Ru{(E)-C(CO2Me)CH(CO2Me)}(η5-C9H7)LL‘] and [Ru{(E)-C(CO2Me)CH(CO2Me)}(η5-Me3C9H4)(CO)(PR3)], respectively, in diethyl ether under reflux. The reaction of [RuH(η5-C9H7)LL‘] with methyl propiolate yields the α-metalated alkenyl complexes [Ru{C(CO2Me)CH2}(η5-C9H7)LL‘] (LL‘ = dppe, dppm; L = L‘ = PMe2Ph; L = PPh3, L‘ = PMe3) in refluxing diethyl ether. A kinetic study has been carried out for the reaction of the complexes [RuX(η5-C9H7)(dppm)] with phenylacetylene in toluene, by 1H and 31P{1H} 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: ΔH⧧ = 17 ± 2 kcal mol-1, ΔS⧧ = −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(η5-C5H5)(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.