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.