Synthesis, structure, and substitution reactivity of a new bi-oxo capped molybdenum cluster: [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+

• Ligand substitution at the [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+ complex
• Faster reaction rate when compared to the molybdenum acetate analog
• Enhanced rates due to bound hydoxo ligand
• Activation parameters suggest a dissociative (D) mechanism for substitution

A new bi-oxo capped molybdenum carboxylate, [Mo3(μ3-O)2(μ-O2CCH2Cl)6(H2O)2(OH)]+, was synthesized by refluxing [Mo3(μ3-O)2(μ-O2CCH3)6(H2O)3]2 + in chloroacetic acid for 20 h (T = 110 °C). Using ion-exchange chromatography (0.5 M NaClO4 eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 °C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d4, substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is kobs298K = 5.3 × 10− 5 (± 0.3) s− 1 and activation parameters equal to ΔH‡ = 130 (± 10) kJ mol− 1 and ΔS‡ = 111 (± 33) J mol− 1 K− 1. From the kinetic data, we find that ligand substitution follows a dissociative pathway and that rates of substitution are faster than expected when compared to the molybdenum acetate analog. Herein, we report the synthesis, crystallographic study, and substitution reactivity of a new molybdenum bi-oxo capped cluster with bridging chloroacetate ligands.