Kinetics of phosphine substitution in CpRu(PPh₃)₂X (X = Cl, Br, I, N₃, and NCO)

Abstract

The kinetics of phosphine substitution in CpRu(PPh3)2X (X = Cl, Br, I, N3, and NCO) is consistent with a dissociative mechanism. The complexes react with chloroform to yield CpRu(PPh3)2Cl by a mechanism that involves phosphine loss.

Mechanism of halide exchange in reactions of CpRu(PPh3)2Cl with haloalkanes

“…2 The phosphine substitution rate is significantly greater than halide exchange with bromobutane so formation of CpRu(PPh 3 )Cl is not the rate determining step. At first glance, the effect of radical traps and initiators on k obs suggest the presence of d 5 Ru III intermediates in solution similar to those reported for the reaction between 1a and CH 3 C(O)Br 4 and in ATRA reactions. 2 The success of the Cp*Ru(PPh 3 ) 2 Cl and CpRu(PPh 3 ) 2 Cl catalyzed Kharasch reactions depends on the organic radical R escaping the radical cage and adding to the olefin before decomposition or undergoing other reactions.…”

“…4 A combination of experimental and computational experiments suggest that single electron transfer and formation of radical pairs are the lowest energy pathway in the latter case. In our earlier work on phosphine substitution in CpRu(PPh 3 ) 2 X (X = Br, I, N 3 , NCO) we observed halide exchange when the reactions were carried out in chloroform, 5 but found no evidence for radical pathways. In a related reaction, the rate and selectivity of the [2 + 2] cycloaddition of alkynes to norbornenes increases when a mixture of iodomethane and 1a are used as the catalyst in place of 1a alone.…”

Physical properties, ligand substitution reactions, and biological activity of Co(iii)-Schiff base complexes

“…52,53 Eyring analysis of the ligand exchange reactions was performed by measuring the rate constants for each reaction at different temperatures. In all cases, the entropies of activation are positive, a feature that is consistent with a dissociative ligand substitution mechanism 89,113,114 The magnitude of the enthalpies of activation are also consistent with a dissociative mechanism, where the Co-N bond is weakened in the transition state. 115 These values for ΔH ‡ and ΔS ‡ are similar to those reported for structurally related Co(III) haloammine complexes and Co(III)-trans dioximes, [116][117][118] which are known to undergo dissociative ligand substitution.…”

Observation of a new type of aggregation-induced emission in nanoclusters

“…Accordingly, the TPP ligands on the Ag 29 (BDT) 12 (TPP) 4 NC are in dynamic dissociation/aggregation. It is suggested that the breaking of coordination bonds would consume energy, 46 and thus the energy loss with non-radiative transitions would influence the energy release with the radiative transition. Specifically, the TPP dissociation process would consume vast amounts of energy, which could be used to explain the result of low PL of the photo-excited Ag 29 (BDT) 12 (TPP) 4 NC in the solution state.…”