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)

Article abstract of DOI:10.1021/om970489d

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)-CH=CXPh)(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)(PPh ₃)] 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)(PR ₃)] (PR₃ = PPh₃, PⁱPr₃) react with dimethyl acetylenedicarboxylate to give the alkenyl derivatives [Ru{(E)-C(CO₂Me)=CH(CO₂Me)}(η⁵-C ₉H₇)LL′] and [Ru{(E)-C(CO₂-Me)=CH(CO₂Me)}(η⁵-Me ₃C₉H₄)(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-C₉H ₇)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 deutende 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.