Synthesis, Structure, and Reactivity of Triosmium Clusters Bearing a Metalated Dialkyl-substituted Pyrazine Ligand

Reactions of two dialkyl-substituted pyrazine ligands with a triosmium cluster are described. Both 2-ethyl-3-methylpyrazine (C₄H₂N₂MeEt) and 2,5-dimethylpyrazine (C₄H₂N₂Me₂) react with the labile triosmium cluster [Os₃(CO)₁₀(NCMe)₂] at 80 °C to afford [HOs₃(CO)₁₀(µ-C₄HN₂MeEt)] (1) and [HOs₃(CO)₁₀(µ-C₄HN₂Me₂)] (2), respectively. Clusters 1 and 2 are formed via C–H bond activation at the α-carbon of the corresponding pyrazine ligand. Cluster 2 reacts with PPh₃ at room temperature in the presence of Me₃NO‧2H₂O to yield the mono- and diphosphine-substituted clusters [HOs₃(CO)₉(PPh₃)(µ-C₄HN₂Me₂)] (3) and [HOs₃(CO)₈(PPh₃)₂(µ-C₄HN₂Me₂)] (4), respectively, both of which exist in more than one isomeric form in solution. All new clusters have been characterized using spectroscopic methods together with single-crystal X-ray diffraction studies for 1, 2, and 4. The bonding in these clusters have been investigated by electronic structure calculations.

Graphical Abstract

Two new triosmium clusters bearing a metalated pyrazine ligand have been synthesized and structurally characterized. The reactivity of one of these newly synthesized clusters towards PPh₃ has also been investigated.