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

A new bi-oxo capped molybdenum carboxylate, [Mo-3(mu(3)-O)(2)(mu-O2CCH2Cl)(6)(H2O)(2)(OH)](+), was synthesized by refluxing [Mo-3(mu(3)-O)(2)(mu-O2CCH3)(6)(H2O)(3)](2+) in chloroacetic add for 20 h (T = 110 degrees C). Using ion-exchange chromatography (0.5 M NaClO4 eluant), the trinuclear molybdenum ion was isolated and allowed to crystallize slowly (T = 4 degrees C) as the perchlorate salt (yield 23%). Upon dissolution of the compound in methanol-d(4) substitution of the terminal ligands for solvent occurs readily in which the observed exchange rate constant is k(obs)(298K) = 5.3 x 10(-5) (+/- 0.3) s(-1) and activation parameters equal to Delta H-double dagger = 130 (+/- 10) kJ mol(-1) and Delta S-double dagger = 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. (C) 2014 Elsevier B.V. All rights reserved.