142246-11-5Relevant academic research and scientific papers
Facile decarboxylation of propiolic acid on a ruthenium center and related chemistry
Bowie, John H.,Bruce, Michael I.,Buntine, Mark A.,Gentleman, Alexander S.,Graham, David C.,Low, Paul J.,Metha, Gregory F.,Mitchell, Cassandra,Parker, Christian R.,Skelton, Brian W.,White, Allan H.
, p. 5262 - 5273 (2012/11/07)
Spontaneous decarboxylation of RC≡CCO2H (R = H, Ph) occurs in reactions with RuCl(PP)Cp (PP = (PPh3)2, dppe) to give [Ru(=C=CHR)(PP)Cp]+. Computational studies (DFT) of possible decarboxylation mechanisms suggest that the reaction that leads to extrusion of CO2 and formation of [Ru(=C=CH2)(dppe)Cp]+ most likely occurs by initial interaction of the anion HC≡CCO2 - with RuCl(dppe)Cp by coordination of carboxylate to Ru, followed by formation of an η2-alkyne intermediate which rearranges to the η1-ethynyl species with loss of CO2. Protonation of the ethynyl group affords the parent vinylidene. In contrast, reactions of HC≡CCO2R (R = Me, Et) with RuCl(PP)Cp and [NH 4]PF6 in MeOH have given [Ru{=C(OMe)CH2(CO 2R)}(PP)Cp]+, formed by attack of MeOH at C α of the intermediate vinylidenes [Ru{=C=CH(CO 2R)}(PP)Cp]+. Deprotonation of the carbenes affords Ru{C(OMe)=CH(CO2R)}(PP)Cp as mixtures of cis and trans isomers. The vinylidenes, which are obtained directly from RuCl(PP)Cp and HC≡CCO 2R in the presence of [NH4]PF6 in Bu tOH, can be deprotonated (Na/PriOH) to the corresponding alkynyls. Attempted deprotonation of [Ru(=C=CH2)(dppe)Cp]+ with LiBu gave the binuclear cyclobutenylidinium complex [{Ru(dppe)Cp} 2(μ-C4H3)]+. The X-ray diffraction molecular structures of [{Ru(dppe)Cp}2(μ-C 4H3)]PF6 (11), [Ru{=C(OMe)CH 2(CO2Me)}(dppe)Cp]PF6 (13), Ru{C(OMe)=CH(CO2R)}(dppe)Cp (R = Me (15), Et (16)) and Ru(C≡CCO2R)(dppe)Cp (R = Me (21), Et (22)) are described.
Kinetics and thermodynamics of proton transfer to Cp*Ru(dppe)H: Via dihydrogen bonding and (η2-H2)-complex to the dihydride
Belkova, Natalia V.,Dub, Pavel A.,Baya, Miguel,Houghton, Jennifer
, p. 149 - 162 (2008/10/09)
The interaction between Cp*RuH(dppe) and a series of proton donors (HA) of increasing strength: CFH2CH2OH (MFE), CF3CH2OH (TFE), (CF3)2CHOH (HFIP), p-nitrophenol, CF3COOH and HBF4 has been investigated spectroscopically by variable-temperature IR, UV-Vis, and NMR spectroscopy in solvents of differing polarity (n-hexane, dichloromethane and their mixture). The low-temperature IR study shows the establishment of a hydrogen-bond which involves the hydride ligand as the proton accepting site. The basicity factor Ej for the hydride was found to be 1.39. All techniques indicate that an equilibrium exists between the dihydrogen-bonded complex and the cationic dihydrogen complex, [Cp*Ru(η2-H2)(dppe)]+, the formation of which is shown here for the first time. The proton transfer from HFIP is characterized by ΔH{ring operator} = -8.1 ± 0.6 kcal mol-1 and ΔS{ring operator} = -17 ± 3 eu. The activation parameters for the subsequent irreversible isomerization leading to the classical dihydride complex, [Cp*Ru(H)2(dppe)]+, are ΔH? = 20.9 ± 0.8 kcal mol-1 and ΔS? = 9 ± 3 eu as determined from 1H NMR spectroscopy for protonation by HBF4. Computational results at the DFT/B3PW91 level confirm the experimentally observed hydride basicity increase on descending the Group from iron to ruthenium and also the formation of the non-classical complex as an intermediate, prior to the thermodynamically favored dihydride.
