From allenes to edge-bridging allyl ligands or face-capping alkenyl ligands on a triruthenium hydrido carbonyl cluster: An experimental and DFT computational study

Abstract

Terminal allenes, H2CCCR1R2 (R1 = R2 = Me; R1 = SiMe3, R2 = Me; R1 = CO2Et, R2 = H; R1 = Cy, R2 = H), react with the hydrazido-capped hydrido carbonyl triruthenium complex [Ru3(μ-H)(μ3-κ2-HNNMe2)(CO)9] (1) in THF at reflux temperature to give the allyl-bridged derivatives [Ru3(μ-κ3-H2CCHCR1R2)(μ3-κ2-HNNMe2)(μ-CO)2(CO)6], as mixtures of syn-allyl and anti-allyl isomers when R1 ≠ R2. These reactions also produce a small amount of an alkenyl-capped derivative, [Ru3(μ3-κ2-HNNMe2)(μ3-κ2-MeCCHR1)(μ-CO)2(CO)6], when monosubstituted allenes (R2 = H) are used. Density functional theory calculations have shown that the reactions that give edge-bridging allyl or face-capping alkenyl derivatives from compound 1 and allene are multistep processes. In both cases, the first step, a bimolecular allene for CO substitution, is rate-limiting. The way the allene approaches the cluster complex determines the formation of an allyl or alkenyl product, since this fact decides the final destiny of the hydride ligand, which can be transferred to the central C atom of the allene to give an allyl product or to the terminal CH2 fragment of the allene to give an alkenyl product.