Kinetics Study and Theoretical Modeling of the Diels−Alder Reactions of Cyclopentadiene and Cyclohexadiene with Methyl Vinyl Ketone. The Effects of a Novel Organotungsten Catalyst

Abstract

The Diels-Alder reaction rate constants of methyl vinyl ketone with cyclopentadiene and cyclohexadiene in the presence of a novel organotungsten catalyst, [P(2-py)(3)W(CO)(NO)(2)](2+), have been measured experimentally and modeled theoretically at several temperatures. The uncatalyzed systems were also studied for direct comparison. When 0.0022 M of catalyst is present at room temperature, the rate constants were found to be approximately 5.3 and 5300 times higher than the corresponding uncatalyzed reactions for cyclopentadiene and cyclohexadiene systems, respectively. Experimental data suggested that the catalyst reduced the activation energies by 5-10 kcal/mol. However, the preexponential factors showed reduction of more than 3 orders of magnitude upon catalysis due to the entropic effects. The energy barriers and the rate constants of the uncatalyzed systems were accurately modeled by correlated electronic structure and dual-level variational transition state theory calculation. The calculated endo selectivity is in good agreement with the observed product distribution. Theoretical calculation also suggested the catalyzed reactions proceeded in a highly asynchronous or even stepwise fashion.

Origins of Stereoselectivity in Diels−Alder Cycloadditions Catalyzed by Chiral Imidazolidinones

“…Previous studies of the Diels-Alder reaction of cyclopentadiene with methyl vinyl ketone predicted an 1.2:1 endo:exo ratio in the gas phase, and 3.7:1 in nitromethane at 0 °C. 23 According to preceding experimental results, in most of the cases an endo orientation of the carbonyl group is preferred, and this preference increases in polar solvents. [23][24][25] In water the endo selectivity enhancement is accompanied by a considerable reaction acceleration due to enforced hydrophobic interactions between diene and dienophile.…”

“…23 According to preceding experimental results, in most of the cases an endo orientation of the carbonyl group is preferred, and this preference increases in polar solvents. [23][24][25] In water the endo selectivity enhancement is accompanied by a considerable reaction acceleration due to enforced hydrophobic interactions between diene and dienophile. [28][29][30][31] The introduction of an alkyl group at R 2 slightly decreases the endo selectivity, 26 while an inversion of the endo orientation is observed when the hydrogen atom at R 3 is substituted by an alkyl group.…”

Asymmetric hetero-Diels–Alder reaction catalyzed by dirhodium(II) carboxamidates

“…Coordination of catalyst (Rh 2 L 4 ) with the lone pair of electrons on the carbonyl oxygen of the aldehyde (A) lowers the energy barrier for addition of the diene (D) to the catalyst complex to give the HDA adduct (P) and regenerate the catalyst (36). The values for both the association constant and the rate constant for five aromatic aldehydes, catalyzed by Rh 2 (4S-MPPIM) 4 , are shown in Table 3.…”

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

“…We evaluated Lewis acidity based on rate enhancement, as well as selectivity between exo-and endo-products. Although subtle solvent effects have been noted in the literature [224][225][226][227][228][229][230], we did not consider these factors in our calculations.…”