Insertion reactions of alkynes into the Ru-H bond of indenylruthenium(II) hydride complexes. Mechanism of the reaction of phenylacetylene with [RuH(eta(5)-C9H7)(dppm)](dppm=bis(diphenylphosphino)methane)

The indenyl complexes [RuX(eta(5)-C9H7)(dppm)] (dppm = bis(diphenylphosphino)methane, X = H, D) react with phenylacetylene to give the products of syn addition [Ru{(E)CH=CXPh}(eta(5)-C9H7)(dppm)] in toluene, in the temperature range 40-80 degrees C. The indenyl complexes [RuH(eta(5)-C9H7)LL'] (L = L' = PMe2Ph; L = PPh3, L' = PMe2Ph; L = PPh3, L' = PMe3; LL'= dppe) and [RuH(eta(5)-Me3C9H4)(CO)(PPh3)] and the cyclopentadienyl complex [RuH(eta(5)-C5H5)(dppm)] do not react with PhC=CH, even under more forcing conditions. The complexes [RuH(eta(5)-C9H7)LL'] (LL' = dppe; LL'= dppm; L = L' = PMe2Ph; L = PPh3, L' = PMe3; L = PPh3, L' = PMe2Ph) and the indenyl-substituted complexes [RuH(eta(5)-Me3C9H4)(CO)(PR3)] (PR3 = PPh3, (PPr3)-Pr-i) react with dimethyl acetylenedicarboxylate to give the alkenyl derivatives [Ru{(E)-C(CO2Me)=CH(CO2Me)}(eta(5)-C9H7)LL'] and [Ru{(E)-C(CO2Me)=CH(CO2Me)}(eta(5)-Me3C9H4)(CO)(PR3)], respectively, in diethyl ether under reflux, The reaction of [RuH(eta(5)-C9H7)LL'] with methyl propiolate yields the alpha-metalated alkenyl complexes [Ru{C(CO2Me)=CH2}(eta(5)-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(eta(5)-C9H7)(dppm)] with phenylacetylene in toluene, by H-1 and P-31{H-1} 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 degrees C, are as follows: Delta H double dagger = 17 +/- 2 kcal mol(-1), Delta S double dagger = -21 +/- 4 cal mol(-1) K-1. An associative mechanism is proposed for the reaction, which involves the formation of arm 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(eta(5)-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.