Computational Study of the Migration of Rhenium from One Enantioface of an Olefin to the Other Facilitated by (C–H)···Re Interactions

Abstract

The migration of a metal atom in a metal−olefin complex from one π face of the olefin to the opposite π face has been rarely documented. Gladysz and co-workers showed that such a movement is indeed possible in monosubstituted chiral Re olefin complexes, resulting in diastereomerization. Interestingly, this isomerization occurred without dissociation, and on the basis of kinetic isotope effects, the involvement of a trans C−H bond was indicated. Either oxidative addition or an agostic interaction of the vinylic C−H(D) bond with the metal could account for the experimentally observed kinetic isotope effect. In this study we compute the free energy of activation for the migration of Re from one enantioface of the olefin to the other through various pathways. On the basis of DFT calculations at the B3LYP level we show that a trans (C−H)•••Re interaction and trans C−H oxidative addition provide a nondissociative path for the diastereomerization. The trans (C−H)•••Re interaction path is computed to be more favorable by 2.3 kcal mol −1 than the oxidative addition path. While direct experimental evidence was not able to discount the migration of the metal through the formation of a η 2 -arene complex (conducted tour mechanism), computational results at the B3LYP level show that it is energetically more expensive. Surprisingly, a similar analysis carried out at the M06 level computes a lower energy path for the conducted tour mechanism and is not consistent with the experimental isotope effects observed. Metal−(C−H) interactions and oxidative additions of the metal into C−H bonds are closely separated in energy and might contribute to unusual fluxional processes such as this diastereomerization.

Mechanistic insight into the tautomerization of histidine initiated by water-catalyzed N–H and C–H cleavages

“…It is worth mentioning that ruthenium complex could improve the terminal C sp2 -H bond cleavage in phenyl vinyl (Fig. 1) with a energy barrier of 27.3 kcal mol -1 , [29] although this bond is more prone to breakage than C sp2 -H at the active site in our system according to the values of bond dissociation energy, [30] the energy barrier is higher than that of present 6W-system (9.60 kcal mol -1 ), indicating the catalytic activity of water is better that the metallorganics. Moreover, it is well known transition metal ruthenium is biologically toxic, and could bring serious environmental pollution of water and soil.…”

Computational Investigation of Dichloromethane Ligand Substitution in the Enantiopure Cation [(η5-C5H5)Re(NO)(PPh3)(ClCH2Cl)]+, a Functional Equivalent of a Chiral Lewis Acid

“…All calculations were performed with the Gaussian 16 program, revision B.01 . As the choice of density functional theory (DFT) methodology is important, benchmark calculations involving chiral cyclopentadienyl rhenium complexes were conducted to select reasonable DFT functionals and basis sets . Details are provided in the Supporting Information.…”