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

The reaction between CpRu(PPh)NCS (1a) and PMePh yields CpRu(PPh)(PMePh)NCS (2a) while CpRu(PPh)(PMePh)Cl reacts with SCN to form the S-bonded isomer, CpRu(PPh)(PMePh)SCN (2b). Compound 1a and the linkage isomers of 2 were characterized by X-ray crystallography. The kinetics of the reaction between 1a and PMePh 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: Δ = 15.7 ± 0.6 kcal mol and Δ = -35 ± 2 cal mol K in THF Δ = 24.8 ± 1.2 kcal mol and Δ = -6 ± 4 cal mol K in CHF. 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(PPh)SeCN (3b), crystallizes as the Se-bonded linkage isomer. Compound 3b reacts with PMePh under pseudo-first order conditions in fluorobenzene to form CpRu(PPh)(PMePh)SeCN (4b) at a much faster rate than 1a with activation parameters: Δ = 30.9 ± 4.8 kcal mol and Δ = 22.4 ± 15.9 cal mol K with no evidence for linkage isomerization to the N-bonded products.