Bond dissociation is a fundamental chemical reaction, and the first principles modeling of the kinetics of dissociation reactions with a monotonically increasing potential energy along the dissociation coordinate presents a challenge not only for modern electronic structure methods but also for kinetics theory. In this work, we use multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) to compute the high-pressure limit dissociation rate constant of tetrafluoroethylene (C2F4), in which the potential energies are computed by direct dynamics with the M08-HX exchange correlation functional. To treat the pressure dependence of the unimolecular rate constants, we use the recently developed system-specific quantum Rice–Ramsperger–Kassel theory. The calculations are carried out by direct dynamics using an exchange correlation functional validated against calculations that go beyond coupled-cluster theory with single, double, and triple excitations. Our computed dissociation rate constants agree well with the recent experimental measurements.

In this paper, we used density functional theory (DFT) computations to study the mechanisms of the hydroacylation reaction of an aldehyde with an alkene catalyzed by Wilkinson’s catalyst and an organic catalyst 2-amino-3-picoline in cationic and neutral systems. An aldehyde’s hydroacylation includes three stages: the C-H activation to form rhodium hydride (stage I), the alkene insertion into the Rh-H bond to give the Rh-alkyl complex (stage II), and the C-C bond formation (stage III). Possible pathways for the hydroacylation originated from the trans and cis isomers of the catalytic cycle. In this paper, we discussed the neutral and cationic pathways. The rate-determining step is the C-H activation step in neutral system but the reductive elimination step in the cationic system. Meanwhile, the alkyl group migration-phosphine ligand coordination pathway is more favorable than the phosphine ligand coordination-alkyl group migration pathway in the C-C formation stage. Furthermore, the calculated results imply that an electron-withdrawing group may decrease the energy barrier of the C-H activation in the benzaldehyde hydroacylation.

In this paper, the origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH2(binap)(cydn) (cydn = trans-1,2-diaminocyclohexane) were discussed. Fifteen substrates involving aromatic, heteroaromatic, olefinic and dialkyl prochiral ketones were used to probe the catalytic mechanism and find an effective way to predict the chirality of the products. The calculated results demonstrate that the hydrogen transfer (HT) step from the Ru complex to the ketone substrate is the chirality-determining step in the H2-hydrogenation of ketones. The hydrogenation of aromatic-alkyl ketones can give higher enantiomeric excess (ee) values than that of dialkyl ketones. An interesting intermediate (denoted as ABS) could be formed if there is an α-hydrogen for R/R′ groups of the ketone due to the H2–Hα interaction. Two substituent groups of the ketone could rotate around the CO axis in two directions, clockwise or counter-clockwise. This rotation, with the big or conjugative substituent group away from/toward the closer binap ligand of the Ru catalyst, will form favorable/unfavorable chiral products with an Re-/Si- intermediate structure. On the contrary, if there is no such α-hydrogen in any substituent group of the ketone, ABS and another intermediate (denoted as INT) would not exist. This study indicates that the conjugative effect of the substituent groups of the ketone play an important role in differentiating the R/R′ groups of the ketone, while steric and electrostatic effects contribute to a minor extent. Furthermore, the disparity of the R and R′ groups of the ketone is of importance in the enantioselectivity and the favorable chiral alcohol is formed when the structure of the conjugative/big substituent group is away from the closer binap ligand of the RuH2(binap)(cydn) catalyst. According to the three factors of the substituent group and the fourth quadrant theory, the enantioselectivity of 91 prochiral ketones catalyzed by a series of Ru catalysts were predicted. All of the predictions are consistent with the experimental results.

In this paper, the origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH2(binap)(cydn) (cydn = trans-1,2-diaminocyclohexane) were discussed. Fifteen substrates involving aromatic, heteroaromatic, olefinic and dialkyl prochiral ketones were used to probe the catalytic mechanism and find an effective way to predict the chirality of the products. The calculated results demonstrate that the hydrogen transfer (HT) step from the Ru complex to the ketone substrate is the chirality-determining step in the H2-hydrogenation of ketones. The hydrogenation of aromatic-alkyl ketones can give higher enantiomeric excess (ee) values than that of dialkyl ketones. An interesting intermediate (denoted as ABS) could be formed if there is an α-hydrogen for R/R′ groups of the ketone due to the H2–Hα interaction. Two substituent groups of the ketone could rotate around the CO axis in two directions, clockwise or counter-clockwise. This rotation, with the big or conjugative substituent group away from/toward the closer binap ligand of the Ru catalyst, will form favorable/unfavorable chiral products with an Re-/Si- intermediate structure. On the contrary, if there is no such α-hydrogen in any substituent group of the ketone, ABS and another intermediate (denoted as INT) would not exist. This study indicates that the conjugative effect of the substituent groups of the ketone play an important role in differentiating the R/R′ groups of the ketone, while steric and electrostatic effects contribute to a minor extent. Furthermore, the disparity of the R and R′ groups of the ketone is of importance in the enantioselectivity and the favorable chiral alcohol is formed when the structure of the conjugative/big substituent group is away from the closer binap ligand of the RuH2(binap)(cydn) catalyst. According to the three factors of the substituent group and the fourth quadrant theory, the enantioselectivity of 91 prochiral ketones catalyzed by a series of Ru catalysts were predicted. All of the predictions are consistent with the experimental results.