Aquation of formato-, NN-dimethylformamide-, and fluoro-penta-amminechromium(III) complexes. Identification of reaction paths and kinetic studies

Abstract

The formato- and NN-dimethylformamide (DMF) complexes [Cr(NH₃)₅(O₂CH)]²⁺ and [Cr(NH₃)₅(OCHNMe₂)]³⁺ have been prepared and characterized. Ion-exchange separation of the aquation products in the case of the formato-complex indicates that ammonia loss features prominantly. With the DMF complex a single process corresponding to aquation of DMF is observed. Kinetic studies give k₁= 1.79 × 10^–4 s^–1 at 50 °C. I = 1.00M(LiClO₄),with activation parameters ΔH^‡= 20.2 ± 0.5 kcal mol^–1 and ΔS^‡=–13.5 ± 1.7 cal K^–1 mol^–1. Aquation of [Cr(NH₃)₅F]²⁺ yields [Cr(NH₃)₅(H₂O)]³⁺(k₂) and [Cr(NH₃)₄(H₂O)F]²⁺(k₃) with the latter predominating over the conditions [H+]= 0.01–1.00M investigated. From product analyses and kinetic studies at different [H+] rate constants have been obtained at 50 °C. I = 1.00M(LiClO₄). Aquation of fluoride is [H+]-dependent,k₂=a+b[H⁺] with a= 2.1 × 10^–6 s^–1 and b= 2.9 × 10^–6 l mol^–1 s_–1, while k₃ for ammonia loss is independent of [H⁺], k₃= 7.7 × 10^–6 s^–1.