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

The reaction between CpRu(PPh3)(2)NCS (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:Delta H-dagger = 15.7 +/- 0.6 kcal mol(-1) and Delta S-dagger = -35 +/- 2 cal mol(-1) K-1 in THF vs.Delta H-dagger = 24.8 +/- 1.2 kcal mol(-1) and Delta S-dagger = -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)(2)SeCN (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:Delta H-dagger = 30.9 +/- 4.8 kcal mol(-1) and Delta S-dagger = 22.4 +/- 15.9 cal mol(-1) K-1 with no evidence for linkage isomerization to the N-bonded products.