Phosphine substitution and linkage isomerization in cyclopentadienylruthenium bis(triphenylphosphine)thiocyanide and selenocyanide, CpRu(PPh3)2NCS and CpRu(PPh3)2SeCN

Abstract

The reaction between CpRu(PPh₃)₂NCS (1a) and PMePh₂ yields CpRu(PPh₃)(PMePh₂)NCS (2a) while CpRu(PPh₃)(PMePh₂)Cl reacts with SCN⁻ to form the S-bonded isomer, CpRu(PPh₃)(PMePh₂)SCN (2b). Compound 1a and the linkage isomers of 2 were characterized by X-ray crystallography. The kinetics of the reaction between 1a and PMePh₂ under pseudo-first order conditions in THF and in fluorobenzene to form 2a are consistent with a dissociative interchange mechanism. Activation parameters for the reaction are: ΔH^† = 15.7 ± 0.6 kcal mol⁻¹ and ΔS^† = –35 ± 2 cal mol⁻¹ K⁻¹ in THF vs. ΔH^† = 24.8 ± 1.2 kcal mol⁻¹ and ΔS^† = –6 ± 4 cal mol⁻¹ K⁻¹ in C₆H₅F. In the presence of added SCN⁻, the rate of phosphine substitution is unchanged but a mixture of 2a and 2b is observed. The selenocyanate derivative, CpRu(PPh₃)₂SeCN (3b), crystallizes as the Se-bonded linkage isomer. Compound 3b reacts with PMePh₂ under pseudo-first order conditions in fluorobenzene to form CpRu(PPh₃)(PMePh₂)SeCN (4b) at a much faster rate than 1a with activation parameters: ΔH^† = 30.9 ± 4.8 kcal mol⁻¹ and ΔS^† = 22.4 ± 15.9 cal mol⁻¹ K⁻¹ with no evidence for linkage isomerization to the N-bonded products.