Kinetics of nucleophilic attack on co-ordinated organic moeities. Part 3. Effect of solvent on addition of pentane-2,4-dione to complexes of cyclic dienyls

Abstract

The kinetics of addition of pantane-2.4-dione (Hpd) to [Fe(C₆H₇)(CO)₁][BF₄] and related dienyl salts have been studied in the solvents nitromethane. acetone.and dichloromethane. Comparison with previous data in acetonitrile shows that the reactions are not sensitive to solvent changes, and indicate the general rate law –d[R]/dt=k[R][ Hpd](R = dienyl cation). These solvent effects. together with the effects of added acid, added base, and deuteriation of Hpd. are explained in terms of a common mechanism involving rapid pre-equilibrium dissociation of Hpd to give the pd^– carbanion which then adds directly to the dienyl rings. The analogous reaction of [Ru ( C₆H₇)(CO)₃][BF₄] with Hpd is considerably slower.