A Theoretical Study on the Kinetics and Thermodynamic Parameters of Chelotropic Reactions: Dienes with Dichlorophenylphosphine

The kinetics and thermodynamic parameters of the chelotropic reactions between dichlorophenylphosphine and the conjugated hydrocarbon dienes [1] (see Fig1) have been theoretically investigated. The geometries of reactants, products, intermediates, and transition states involved in the reactions were optimized at the M062x/6–311++G (2d,2p) level of theory [2,3]. The ground and transition states were confirmed by the frequency calculations. The kinetic parameters were calculated with the transition state theory. The comparison showed that the reaction rates in the presence of dienes such as isoprene (k = 5.88×10-26cm3molecule-1s-1), phenoprene (k = 6.63×10- 24cm3molecule-1s-1), and 2,3-dimethylbutadiene (k = 3.58×10-25cm3molecule-1s-1) were increased, while chloroprene (k = 1.48×10-26cm3molecule-1s-1) and 2-bromobutadiene (k = 2.23×10-26cm3molecule-1s-1) decreased the reaction rate. The rate constant of the butadiene was k= 4.03×10-26cm3molecule-1s-1.The free energies for dienes such as isoprene (ΔG = 26.98kJmol-1), phenoprene (ΔG =19.63kJmol-1), and 2,3- dimethylbutadiene (ΔG = 23.38kJmol-1) were lower than butadiene (ΔG = 33.04kJmol- 1) while chloroprene (ΔG = 33.52kJmol-1) and 2-bromobutadiene (ΔG = 35kJmol-1) had a larger amount of free energy. As a result, dienes include butadiene, isoprene, phenoprene and 2,3-dimethylbutadiene were thermodynamically and kinetically more favorable than chloroprene and 2-bromobutadiene.