The most fundamental concepts in chemistry are structure, energetics, reactivity and their inter-relationships, which are indispensable for promoting chemistry into a rational science. In this regard, bond energy, the intrinsic determinant directly related to structure and reactivity, should be most essential in serving as a quantitative basis for the design and understanding of organic transformations. Although C-H activation/functionalization have drawn tremendous research attention and flourished during the past decades, understanding the governing rules of bond energetics in these processes is still fragmentary and seems applicable only to limited cases, such as metal-oxo-mediated hydrogen atom abstraction. Despite the complexity of C-H activation/functionalization and the difficulties in measuring bond energies both for the substrates and intermediates, this is definitely a very important issue that should be more generally contemplated. To this end, this review is rooted in the energetic aspects of C-H activation/functionalization, which were previously rarely discussed in detail. Starting with a concise but necessary introduction of various classical methods for measuring heterolytic and homolytic energies for C-H bonds, the present review provides examples that applied the concept and values of C-H bond energy in rationalizing the observations associated with reactivity and/or selectivity in C-H activation/functionalization.

Transfer of electrophilic NH to sulfides and a subsequent sulfimine‐promoted fast O transfer have been achieved in a one‐pot process unprecedentedly for the preparation of sulfoximines at ambient temperature under air. The transformations, which are metal‐, ligand‐, base‐, additive‐free, and operationally simple, proceed in just 5 min and furnish NH‐sulfoximines in good‐to‐excellent yields (up to 99 %) by treatment of sulfides with a combination of PhI(OAc)2 and ammonia source. A variety of commercially available and inexpensive electrophilic nitrogen sources are successfully used in the oxidative sulfide‐to‐sulfoximine conversions. This method features a high efficiency, excellent functional‐group tolerance, and broad substrate scope, which may facilitate its applications in medicinal chemistry area.

The mechanism of the aryl iodide-catalyzed asymmetric migratory geminal difluorination of β-substituted styrenes (Banik et al. Science 2016, 353, 51) has been explored with density functional theory computations. The computed mechanism consists of (a) activation of iodoarene difluoride (ArIF2), (b) enantiodetermining 1, 2-fluoroiodination, (c) bridging phenonium ion formation via SN2 reductive displacement, and (d) regioselective fluoride addition. According to the computational model, the ArIF2 intermediate is stabilized through halogen-π interactions between the electron-deficient iodine(III) center and the benzylic substituents at the catalyst stereogenic centers. Interactions with the catalyst ester carbonyl groups (I(III)+⋯O) are not observed in the unactivated complex, but do occur upon activation of ArIF2 through hydrogen bonding interactions with external Brønsted acid (HF). The 1, 2-fluoroiodination occurs via alkene complexation to the electrophilic, cationic I(III) center followed by C−F bond formation anti to the forming C−I bond. The bound olefin and the C−I bond of catalyst adopt a spiro-arrangement in the favored transition structures but a nearly periplanar arrangement in the disfavored transition structures. Multiple attractive non-covalent interactions, including slipped π⋯π stacking, C–H⋯O, and C–H⋯π interactions, are found to underlie the high asymmetric induction. The chemoselectivity for 1,1-difluorination versus 1,2-difluorination is controlled mainly by 1) the steric effect of the substituent on the olefinic double bond, and 2) the nucleophilicity of the carbonyl oxygen of substrate.

The conventional oxidative Heck reaction between aryl boronic acids and alkenes typically involved the PdII/Pd0/PdII catalytic cycle incorporating an external oxidant and often suffered C=C bond isomerization for internal alkyl-substituted alkenes via chain-walking. Herein, we demonstrate that the regioselectivity (γ-selectivity vs. δ-selectivity) and pathway selectivity (hydroarylation vs. oxidative Heck coupling) of a directed Ni-catalyzed alkene arylation can be controlled by judicious tuning of the coordination environment around the nickel catalyst via optimization of an appropriate phosphine ligand and directing group. In this way, the Ni(0)-catalyzed oxidative Heck arylation that relies on transfer hydrogenation of an acceptor olefin is developed with excellent E/Z selectivity and regioselectivity. Mechanistic investigations suggest that the addition of the acceptor is crucial for lowering the energy for carbometalation and for enabling catalytic turnover.

The mechanism and origin of the unexpected chemoselectivity in fluorocyclization of o-styryl benzamide with a cyclic hypervalent fluoroiodane reagent were explored with DFT calculations. The calculations suggested an alternative mechanism that is broadly similar to, but also critically different from, the previously proposed mechanism for the formation of an unexpected structurally novel seven-membered 4-fluoro-1,3-benzoxazepine. The amide group of o-styryl benzamide was revealed to be crucial for activating the fluoroiodane reagent and facilitating C-F bond formation. In contrast to the popular electrophilic N-F reagent Selectfluor, the F atom in the fluoroiodane reagent is nucleophilic, and the I(III) atom is the most electrophilic site, thus inducing a completely different reactivity pattern. The insights reported here will be valuable for the further development of new reactions based on the hypervalent fluoroiodane reagent.