Mechanism and Activation Parameters for the κ<i>O</i> to μ<i>,</i>κ²<i>O</i>,<i>O′</i> 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 κ<i>O</i> bonded. This slowly converted to [Os₃(μ-H)(CO)₁₀(μ-O₂CCHCHCO₂H)], in which the ligand adopted the more usual μ,κ²<i>O</i>,<i>O′</i> bonding mode. The conversion was followed by monitoring the metal hydride resonance in the ¹H NMR spectrum, and analysis of the data yielded Δ<i>H</i>^‡ = 110 ± 3 kJ mol^–1 and Δ<i>S</i>^‡ = 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.