A 1H NMR study of the kinetics of the acetonitrile exchange in the complex decakis(acetonitrile)dirhenium(II,II)

The pseudo-first-order rate constant, k, for the substitution of the eight equatorial acetonitrile ligands in the complex [Re2(NCCH3)10]4+ with acetonitrile has been determined by 1H NMR in CD3CN solution in the temperature range 298–333 K. The results obtained were: k=(8.3±0.5)×10−7 s−1 (half-life: 9.6±0.5 days) at 298.0 K, ΔH‡=109±2 kJ mol−1 and ΔS‡=6±6 J mol−1 K−1. The exchange of the two axially coordinated acetonitrile ligands was found to be fast on the NMR time-scale.