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

The labile compound [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. Complexes [RuCl2(NCR)2(cod)] spontaneously transform into the dimer compounds [Ru2Cl(μ-Cl)3(cod)2(NCR)] (R = Me, Ph). H NMR kinetic experiments for these transformations evidenced a first-order type kinetic. [RuCl2(NCPh)2(cod)] dimerizes slower than [RuCl2(NCCH3)2(cod)] by a factor of ten. The following activation parameters, ΔH = 114 ± 3 kJmol and ΔS = 66 ± 9 JKmol for R = CH3CN (ΔG = 94 ± 5 kJmol, 298.15 K) and ΔH = 122 ± 2 kJmol and ΔS = 75 ± 6 JKmol for R = Ph (ΔG = 100 ± 4 kJmol, 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 the dissociation of acetonitrile as the rate-determining step. The molecular structure of compounds [Ru2Cl(μCl)3(cod)2(NCR)] (R = Me, Ph) have been determined by X-ray diffraction.