Mechanism and Activation Parameters for the κO to μ,κ²O,O′ Bonding Mode of the Maleic Acid Ligand on an Osmium Carbonyl Cluster

The reaction of maleic acid and [Os₃(CO)₁₀(NCCH₃)₂] afforded initially the cluster [Os₃(μ-H)(CO)₁₀(O₂CCHCHCO₂H)(CH₃CN)], in which the maleic acid was κO bonded. This slowly converted to [Os₃(μ-H)(CO)₁₀(μ-O₂CCHCHCO₂H)], in which the ligand adopted the more usual μ,κ²O,O′ bonding mode. The conversion was followed by monitoring the metal hydride resonance in the ¹H NMR spectrum, and analysis of the data yielded ΔH^‡ = 110 ± 3 kJ mol^–1 and ΔS^‡ = 14 ± 10 J mol^–1 K^–1 for this process, thus suggesting an I_D mechanism. The calculated values are in good agreement with the experimental values.