Comparing the Isoelectronic Complexes [RuTp(CH3CN)3]PF6 (Tp = Hydridotris(pyrazolyl)borate) and [RuCp(CH3CN)3]PF6. Structure and Acetonitrile Exchange Kinetics

The cationic trisacetonitrile complex [RuTp(CH3CN)3]PF6 has been obtained in 70% isolated yield by the reaction of RuTp(COD)Cl with NH4PF6 in boiling DMF/CH3CN. The CH3CN exchange kinetics has been studied by 1H NMR as a function of temperature. The first-order rate constant of 1.2 × 10-8 s-1 (298 K) is very low compared to 5.6 s-1 for the isoelectronic [RuCp(CH3CN)3]PF6, essentially because of a much higher energy of activation (37.2 vs 20.7 kcal mol-1).