Journal
DALTON TRANSACTIONS
Volume 51, Issue 41, Pages 15703-15715Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/d2dt02866b
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- University of Pisa
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Dimetallic complexes are suitable platforms for the assembly of small molecular units, and the reactivity of bridging alkenyl ligands has been widely investigated to model C-C bond forming processes. The researchers in this study reported the unusual coupling of an alkenyl ligand with a series of alkynes, revealing two possible outcomes. Further experimental and computational studies demonstrated that the stability of the products is influenced by carboxylato substituents on the alkyne.
Dimetallic complexes are suitable platforms for the assembly of small molecular units, and the reactivity of bridging alkenyl ligands has been widely investigated to model C-C bond forming processes. Here, we report the unusual coupling of an alkenyl ligand, bridging coordinated on a diruthenium scaffold, with a series of alkynes, revealing two possible outcomes. The diruthenium complex [Ru2Cp2(Cl)(CO)(mu-CO) {mu-eta(1):eta(2)-C(Ph)=CH(Ph)}], 2, was prepared in two steps from [Ru2Cp2(CO)(2)(mu-CO){mu-eta(1):eta(2)-C(Ph)=CH (Ph)}]BF4, [1]BF4, in 69% yield. Then, the reaction of 2 with C-2(CO2Me)(2), promoted by AgCF3SO3 in dichloromethane, afforded in 51% yield the complex [Ru2Cp2(CO)(2){mu-eta(3):eta(2)-C(Ph)CH(Ph)C(CO2Me)C (CO2Me)}]CF3SO3, [3]CF3SO3, containing a ruthenacyclopentene-based hydrocarbyl ligand. On the other hand, 2 reacted with other alkynes and AgX salts to give the butadienyl complexes [Ru2Cp2(CO)(2){mu-eta(3):eta(2)-C(R)CH(R')C(Ph)C(Ph)}]X (R = R' = H, [4]BF4; R = R' = Me, [5]CF3SO3; R = R' = Ph, [6]CF3SO3; R = Ph, R' = H, [7]CF3SO3), in 42-56% yields. All products were characterized by IR and NMR spectroscopy, and by single crystal X-ray diffraction in the cases of 2, [3]CF3SO3 and [6]BF4. DFT calculations highlighted the higher stability of [4-7](+)- like structures with respect to the corresponding [3](+)-like isomers. It is presumable that [3](+)-like isomers initially form as kinetic intermediates, then undergo H-migration which is disfavoured in the presence of carboxylato substituents on the alkyne. Such hypothesis was supported by the computational optimization of the transition states for H-migration in the cases of R = R' = H and R = R' = CO2Me.
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