Kinetics of Nucleophilic Attack on Co-ordinated Organic Moieties. Part 19. Addition of Anilines to Tricarbonyl(1-5-η-dienyl)iron Cations

Article abstract of DOI:10.1039/DT9810002489

Spectroscopic and kinetic studies of the reactions below (X=H, 2-Me, 3-Me, 4-Me, 2-Cl, 3-Cl, 4-Cl, 4-OMe, or 4-NO2) in CH3CN have provided quantitative information on the importance of basicity and steric factors in controlling amine nucleophilicity towards co-ordinated ?-hydrocarbons.Similar reactions with cations (+) (1a) and (+) (1c) have also been investigated.For the reactions of 4-methoxy- and 4-methyl-aniline with (1b), which proceed to completion, k_obs.=k₁.However, for the equilibrium reactions of the other less basic amines with cations (1a)-(1c) the two-term expression k_obs.=k₁ + k_-1/(+K₂K_a) is indicated.The general rate trend C6H7 > 2-MeOC6H6 > C7H9 and the low ΔH^%₁ and large negetive ΔS^%₁ values are consistent with direct addition to the dienyl rings.For attack by non-sterically crowded anilines on (1b), a Broensted plot of log k₁ versus pK_a of the amine conjugate acid (in H2O) has a high slope of 1.0, indicating a very strong dependence of k₁ on amine basicity.A Hammett plot for this reaction gives a slope of -2.7, indicating significant bond formation and build-up of positive charge on the aniline nitrogen atom in the transition state.The steric retardation of k₁ caused by blocking substituents in the 2-position of the anilines is considerably smaller than that previously found for the related additions of pyridines to cations (1a)-(1c).

Full text of DOI:10.1039/DT9810002489

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