Phosphine substitution reactions of (η5-cyclopentadienyl)ruthenium bis(triarylphosphine) chloride, CpRu(PAr3)2Cl {PAr3 = PPh3, P(p-CH3C6H4)3, P(p-FC6H4)3, P(p-CH3OC6H4)3, and PPh2(p-CH3C6H4)}: a tale of two mechanisms

Abstract

The kinetics of phosphine substitution in CpRu(PAr₃)₂Cl by PMePh₂ under pseudo-first order conditions in CDCl₃ have been measured for PAr₃ = PPh₃, 1a, PPh₂(p-tol), 1b, P(p-tol)₃, 1c, P(p-CH₃OC₆H₄)₃, 1d, and P(p-FC₆H₄)₃), 1e. Activation parameters characteristic of a dissociative pathway (ΔH^† = 110–124 ± 2 kJ mol⁻¹, ΔS^† = 16–44 ± 5–12 J mol⁻¹ K⁻¹) are observed for all five compounds. The rate of substitution in CpRu(PAr₃)₂Cl (1a) and CpRu[P(p-FC₆H₄)₃]₂Cl (1e) is independent of added chloride ion and decreases in the presence of excess PAr₃, however, the rate of substitution in CpRu[P(p-CH₃OC₆H₄)₃]₂Cl (1d) is first order in added chloride ion and is less dependent on added PAr₃. A mechanism involving [CpRu(PAr₃)₂(PMePh₂)]⁺[Cl]⁻ intermediates contributes to the substitution in 1b–d.