Abstract
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 20h (T=110°C). Using ion-exchange chromatography (0.5M 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) kJmol−1 and ΔS‡=111 (±33) Jmol−1K−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.
•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