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We report the first example of RhII-catalyzed chemoselective double C(sp3)H oxygenation, which can directly transform various toluene derivatives into highly valuable aromatic aldehydes with great chemoselectivity and practicality. The critical combination of catalyst Rh(OAc)2, oxidant Selectfluor, and solvents of TFA/TFAA promises the successful delivery of the oxidation with satisfactory yields. A possible mechanism involving a unique carbene-Rh complex is proposed, and has been supported by both experiments and theoretical calculations. [ABSTRACT FROM AUTHOR]

In this study, M11-L was used to evaluate the feasibility of the formation of rhodium(V) species using the rhodium(III)-catalyzed ortho-bromination of arenes as a model reaction. In most cases for these types of reactions, DFT calculations reveal that the bromination step involves a Br transfer from N-bromosuccinimide to the reacting arylrhodium to form a bromonium intermediate, followed by a Br shift to generate a new C−Br bond, which is more favorable than the previously proposed RhIII/RhV catalytic cycle. The rhodium catalyst remains in its +3 oxidation state throughout. The substituent effects of the reacting arene were studied, and computational results showed that the introduction of electron-donating groups on the reacting arene was favorable for this pathway. In contrast, the inclusion of a strong electron-withdrawing group on the aromatic ring would hinder the formation of a bromonium intermediate. Therefore, the RhIII/RhV catalytic cycle is favorable in cases that involve a RhV intermediate, which is generated by oxidative addition with NBS. In this pathway, the C−Br bond is formed by reductive elimination from the RhV intermediate. Additionally, a distortion-interaction analysis model along the reaction pathway was used to explain the directing-group effects. The results showed that the interaction energy controlled the reactivity because of the difference in electronic nature of various directing groups. [ABSTRACT FROM AUTHOR]

Metal-catalyzed CH activation not only offers important strategies to construct new bonds, it also allows the merge of important research areas. When quinoline N-oxide is used as an arene source in CH activation studies, the NO bond can act as a directing group as well as an O-atom donor. The newly reported density functional theory method, M11L, has been used to elucidate the mechanistic details of the coupling between quinoline NO bond and alkynes, which results in CH activation and O-atom transfer. The computational results indicated that the most favorable pathway involves an electrophilic deprotonation, an insertion of an acetylene group into a RhC bond, a reductive elimination to form an oxazinoquinolinium-coordinated RhI intermediate, an oxidative addition to break the NO bond, and a protonation reaction to regenerate the active catalyst. The regioselectivity of the reaction has also been studied by using prop-1-yn-1-ylbenzene as a model unsymmetrical substrate. Theoretical calculations suggested that 1-phenyl-2-quinolinylpropanone would be the major product because of better conjugation between the phenyl group and enolate moiety in the corresponding transition state of the regioselectivity-determining step. These calculated data are consistent with the experimental observations. [ABSTRACT FROM AUTHOR]