Mechanism and Activation Parameters for the κO to μ,κ2 O,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,κ2 O,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 ID mechanism. The calculated values are in good agreement with the experimental values.