Phosphine substitution and linkage isomerization in cyclopentadienylruthenium bis(triphenylphosphine)thiocyanide and selenocyanide, CpRu(PPh 3 ) 2 NCS and CpRu(PPh 3 ) 2 SeCN.

The reaction between CpRu(PPh 3 ) 2 NCS (1a) and PMePh 2 yields CpRu(PPh 3 )(PMePh 2 )NCS (2a) while CpRu(PPh 3 )(PMePh 2 )Cl reacts with SCN - to form the S-bonded isomer, CpRu(PPh 3 )(PMePh 2 )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 2 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 H † = 15.7 ± 0.6 kcal mol -1 and Δ S † = -35 ± 2 cal mol -1 K -1 in THF vs. Δ H † = 24.8 ± 1.2 kcal mol -1 and Δ S † = -6 ± 4 cal mol -1 K -1 in C 6 H 5 F. 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 3 ) 2 SeCN (3b), crystallizes as the Se-bonded linkage isomer. Compound 3b reacts with PMePh 2 under pseudo-first order conditions in fluorobenzene to form CpRu(PPh 3 )(PMePh 2 )SeCN (4b) at a much faster rate than 1a with activation parameters: Δ H † = 30.9 ± 4.8 kcal mol -1 and Δ S † = 22.4 ± 15.9 cal mol -1 K -1 with no evidence for linkage isomerization to the N-bonded products.