A study of acetylene and acetylide carbonyl and diphosphine substituted ruthenium trinuclear clusters: Synthesis and structural characterization

The synthesis and structural characterization of the acetylene and acetylide carbonyl ruthenium clusters: [Ru3(CO)9(μ-CO){μ3-η2-(//)-HCCR}] [R = C6H4-4-CH3 (1a), C6H3-2,5-(CH3)2 (1b), C6H2-2,4,5-(CH3)3 (1c), C6H4-4-tBu (1d), C6H4-4-COH (1e), C6H4-4-NH2 (1f)] and [Ru3(CO)9(μ-H){μ3-η2-(⊥)-CCR}] [R = C6H4-4-CH3 (2a), C6H3-2,5-(CH3)2 (2b), C6H2-2,4,5-(CH3)3 (2c), C6H4-4-tBu (2d), C6H4-4-COH (2e), C6H4-4-NH2 (2f)] are described. Compounds 1a–f were obtained under very mild conditions from the known [Ru3(CO)10(NCMe)2] activated cluster in the presence of the monosubstituted phenylacetylenes; in all cases, the alkynes are coordinated to the metallic fragment as acetylene groups in a μ3-η2 parallel fashion without breaking the C(sp)–H bond of the triple bond. In solution compounds of the 1 series slowly transformed to the acetylide derivatives (2), where the acetylene group undergoes an oxidative addition and a rearrangement of the –CC– coordinated fragment to a μ3-η2 perpendicular coordination mode of the C–C axis by breaking the C(sp)–H bond to give a hydride ligand in each case. The diphosphines substituted derivatives [Ru3(CO)7(μ-diphosphine)(μ-H){μ3-η2-(⊥)-CCR}] [diphosphine = dppe; R = C6H4-4-CH3 (3a), C6H3-2,5-(CH3)2 (3b), C6H2-2,4,5-(CH3)3 (3c) and diphosphine = dfppe; R = C6H4-4-CH3 (4a), C6H3-2,5-(CH3)2 (4b), C6H2-2,4,5-(CH3)3 (4c)] were obtained from the reaction of the [Ru3(CO)10(diphosphine)] cluster (diphosphine = dppe or dfppe) with the terminal alkyne, respectively. All compounds have been characterized in solution by infrared spectroscopy and multinuclear magnetic resonance. The solid state structures of the acetylide compounds 2b–d and 3b have been established by single crystal X-ray diffraction studies; the –CC– fragment was observed in a μ3-η2 perpendicular coordination mode.

Graphical abstractThe reaction of compound [Ru3(CO)10(NCMe3)2] with terminal alkynes HCCR, [R = C6H4-4-CH3 (a), C6H3-2,5-(CH3)2 (b), C6H2-2,4,5-(CH3)3 (c), C6H4-4-tBu (d), C6H4-4-COH (e), C6H4-4-NH2 (f)] under very mild conditions yielded isostructural parallel acetylene clusters [Ru3(CO)9(μ-CO)(μ3-η2-(//)-HCCR)] [R = C6H4-4-CH3 (1a), C6H3-2,5-(CH3)2 (1b), C6H2-2,4,5-(CH3)3 (1c), C6H4-4-tBu (1d), C6H4-4-COH (1e), C6H4-4-NH2 (1f)]. In solution, these compounds rapidly convert to compounds [Ru3(CO)9(μ-H)(μ3-η2-(⊥)-CCR)] [R = C6H4-4-CH3 (2a), C6H3-2,5-(CH3)2 (2b), C6H2-2,4,5-(CH3)3 (2c), C6H4-4-tBu (2d), C6H4-4-COH (2e), C6H4-4-NH2 (2f)], respectively; where the ligands are coordinated as acetylide fragments in a μ3-η2 perpendicular mode by breaking the C(sp)–H bond of the alkynes. In addition, diphosphine substituted derivatives [Ru3(CO)7(μ-diphosphine)(μ-H)(μ3-η2-(⊥)-CCR)] [diphosphine = dppe; R = C6H4-4-CH3 (3a), C6H3-2,5-(CH3)2 (3b), C6H2-2,4,5-(CH3)3 (3c) and diphosphine = dfppe; R = C6H4-4-CH3 (4a), C6H3-2,5-(CH3)2 (4b), C6H2-2,4,5-(CH3)3 (4c)] were obtained from the reaction of the cluster [Ru3(CO)10(μ-diphosphine)] with the corresponding terminal alkyne. All of these clusters have been characterized in solution by infrared spectroscopy and multinuclear magnetic resonance and the structures of compounds 2b–d and 3b have been established by single crystal X-ray diffraction studies.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Syntheses and characterization of [Ru3(CO)9(μ-CO)(μ3-η2-(//)-HCCR)] (1) complexes from terminal alkynes HCCR. ► In solution, acetylene compounds 1 are rapidly converted into the acetylides clusters. ► It was confirmed the low stability of the μ3-η2 alkyne coordination in a π:σ:σ ligand donation. ► The dppe or dfppe did not produce the stabilization of the μ3-η2-(//) parallel coordination of the acetylene. ► The solid state structures showed the thermodynamically stable μ3-η2-(⊥) perpendicular coordination mode of the acetylide.