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Synthetic and kinetic studies of the reactions between (Fe(1-5-eta-C6H7)(CO)3)+ (1) and X-substituted pyridines (X=H, 2-Me, 3-Me, 4-Me, 4-Ph, 2-Cl, 3-CN, 2,5-Me2, 2,6-Me2, 3,5-Me2, or 2,4,6-Me3) in CH3CN provide the first quantitative information on the importance of basicity and steric properties in controlling amine nucleophilicity towards co-ordinated ?-hydrocarbons.The products are pyridinium adducts of tricarbonyl(hexa-1,3-diene)iron.Similar pyridinium adduct formation occurs with cations (Fe(1-5-eta-2-MeOC6H6)(CO)3)+ (2) and (Fe(1-5-eta-C7H9)(CO)3)(BF4) (3).The general rate law rate = k1(Fe)(amine) is observed, except for the equilibrium reaction of (1) with 3-cyanopyridine which gives rate = k1 (Fe)(amine) + k-1 (Fe).The rate trend C6H7 > 2-MeOC6H6 > C7H9 found with several pyridines and the low DeltaH1<*> and large negative DeltaS1<*> values are consistent with direct addition to the dienyl rings.For attack of non-sterically crowded pyridines on (1), a Bronsted plot of log k1 versus pKa of the amine conjugate acid has a high slope alpha of 1.0, indicating a very marked dependence of rate on amine basicity.Successive blocking of the 2- and 6-positions of pyridine by methyl groups leads to marked non-additive steric retardation.
The design and synthesis of related molecules that are more effective, more selective, and less toxic than aspirin are important objectives of biomedical research.Recommanded Product: 108-47-4, If a proposed mechanism predicts the wrong experimental rate law, however, the mechanism must be incorrect.Welcome to check out more blogs about 108-47-4, in my other articles.
Reference：
Chiral nitrogen ligands in late transition metal-catalysed asymmetric synthesis—I. Addressing the problem of ligand lability in rhodium-catalysed hydrosilations,
Nitrogen-Containing Ligands for Asymmetric Homogeneous and Heterogeneous Catalysis