Synthesis, structure, and kinetic studies on [RuCl2(NCCH3)2(cod)

Abstract

[RuCl2(NCCH3)2(cod)], an alternative starting material to [RuCl2(cod)] n for the preparation of ruthenium(II) complexes, has been prepared from the polymer compound and isolated in yields up to 87% using a new work-up procedure. The compound has been obtained as a yellow solid without water of crystallization. The complexes [RuCl2(NCR)2(cod)] spontaneously transform into dimers [Ru2Cl(μ-Cl)3(cod)2(NCR)] (R = Me, Ph). 1H NMR kinetic experiments for these transformations evidenced first-order behavior. [RuCl2(NCPh)2(cod)] dimerizes slower by a factor of ten than [RuCl2(NCCH3)2(cod)]. The following activation parameters, ΔH # = 114 ± 3 kJ mol−1 and ΔS # = 66 ± 9 J K−1 mol−1 for R = CH3CN (ΔG # = 94 ± 5 kJ mol−1, 298.15 K) and ΔH # = 122 ± 2 kJ mol−1 and ΔS # = 75 ± 6 J K−1 mol−1 for R = Ph (ΔG # = 100 ± 4 kJ mol−1, 298.15 K), have been calculated from the first-order rate constants in the temperature range 294–323 K. The kinetic parameters are in agreement with a two-step mechanism with dissociation of acetonitrile as the rate-determining step. The molecular structures of [Ru2Cl(μ-Cl)3(cod)2(NCR)] (R = Me, Ph) have been determined by X-ray diffraction.