The Ni-catalyzed C(sp2)¢H/C(sp3)¢H coupling of benzamides with toluene derivatives was recently successfully achieved with mild oxidant iC3F7I. Herein, we employ density functional theory (DFT) methods to resolve the mechanistic controversies. Two previously proposed mechanisms are excluded, and our proposed mechanism involving iodine-atom transfer (IAT) between iC3F7I and the NiII intermediate was found to be more feasible. With this mechanism, the presence of a carbon radical is consistent with the experimental observation that (2,2,6,6-tetramethylpiperidin- 1-yl)oxyl (TEMPO) completely quenches the reaction. Meanwhile, the hydrogen-atom abstraction of toluene is irreversible and the activation of the C(sp2)¢H bond of benzamides is reversible. Both of these conclusions are in good agreement with Chatani’s deuterium-labeling experiments.

Recently, the Li group reported the first Ag-catalyzed hydrogenation of aldehydes in water, demonstrating the utility of Ag complexes in homogeneous catalytic transformations through hydrogen activation. In the present study, density functional theory methods have been used to study the mechanism of Ag-catalyzed hydrogen activation. Three possible pathways, including base-assisted hydrogen activation, ligand-assisted hydrogen activation, and oxidative addition were investigated. The ligand-assisted hydrogen activation is disfavored because the neutral biaryl phosphine ligand XPhos is not a competent proton acceptor and results in the destruction of the aromaticity of an aryl group. Oxidative addition of H2 on AgI complexes was also found to be unlikely. The resulting AgIII hydride complexes are highly unstable and can undergo spontaneous reduction due to the weakly electron-donating ligand and the relatively low electronegativity of hydrogen. By contrast, the base-assisted hydrogen act

Rhodium-catalyzed cross-coupling reactions of unactivated primary alkyl chlorides with diboron reagents have been developed as practical methods for the synthesis of alkylboronic esters. These reactions expand the concept and utility of Rh(I)-catalyzed cross-coupling of aliphatic electrophiles.

Recently the Chatani group reported the Rh(I)-catalyzed borylation of nitriles, which provided an efficient protocol for transformation of the C−CN bond to the C−B bond (J. Am. Chem. Soc. 2012, 134, 115). Although an unconventional β- carbon elimination mechanism was proposed in their study, the other previously proposed mechanisms, i.e., oxidative addition, deinsertion, and initial C−H bond activation, cannot be excluded. To clarify the dominant mechanism of this reaction, a density functional theory study on borylation of PhCN and BnCN catalyzed by [Rh(XantPhos)(B(nep))] (nep = neopentylglycolate, XantPhos = 4,5-Bis- (diphenylphosphino)-9,9-dimethylxanthene) was conducted. The computational results indicated that the deinsertion mechanism (2,1-insertion of the Rh−B bond into the C−N bond occurs first, followed by the insertion of the metal center into C−CN bond) is favored over oxidative addition, β-carbon elimination, and the initial C−H bond activation mechanism within all the inve

Here, an unpresented non-C1 synthon function of CO2 is reported to facilitate electrochemical defluorination. The introduction of CO2 modulates the electron distribution of the radical anion intermediate generated through one-electron reduction, thereby weakening the reduction potential and facilitating reduction and defluorination. CO2 is released subsequently via spontaneous decarboxylation to complete its promotion role. The presented results shed light on a distinctive utilization of CO2, which may stimulate interest in developing non-C1 synthon functions of CO2.

A KOtBu-mediated C2-benzylation of quinoline N-oxides with benzylboronates under mild reaction conditions has been developed. The reaction shows broad scope for both of the quinoline N-oxides and benzylboronates, especially, secondary and tertiary benzylboronates are also compatible with this reaction. DFT calculations indicate that the reaction is promoted by the nucleophilic addition of KOtBu to boronate rather than the deprotonation of benzylic C−H bond with KOtBu.

A 1,1-hydroboration of alkynylgermanes with unique transGe/B stereochemistry under transition-metal-free conditions is reported. Mechanistic studies suggest that a pathway involving α boration followed by a stepwise 1,2-Ge/H shift on the intermediate structurally lies between an alkyne−Ge+ π complex and a typical vinyl cation. The resulting Ge/B bimetallic modules, along with a Ge*/Ge/B trimetallic variant, can be conveniently transformed into trisubstituted olefins through iterative divergent cross-coupling. This work demonstrates that incorporating metalloids into classical organic reactions may offer unconventional chemical selectivity and efficient synthetic applications.

Nickel/photoredox dual catalyzed cross-coupling of aryl halides with alkylboron compounds is one of the effective methodologies for the construction of C(sp2) C(sp3) bonds. Although elegant results have been achieved by using alkyl trifluoroborates as alkyl radical precursors, the generation of alkyl radicals from readily available alkyl boronic esters is still limited due to their high oxidation potential. We disclosed here that activation of alkyl boronic esters by MeOLi is highly efficient for the generation of alkyl radicals under photocatalysis conditions. The reaction featured with a wide substrate scope, high functional group tolerance, and late-stage modification of bioactive substances. In addition, the method was also successfully extended to alkyl boronic acids. Experimental and computational mechanistic studies indicated that the crosscoupling likely proceeds via a Ni(I)-catalyzed pathway.

Here, an unpresented non-C1 synthon function of CO2 is reported to facilitate electrochemical defluorination. The introduction of CO2 modulates the electron distribution of the radical anion intermediate generated through one-electron reduction, thereby weakening the reduction potential and facilitating reduction and defluorination. CO2 is released subsequently via spontaneous decarboxylation to complete its promotion role. The presented results shed light on a distinctive utilization of CO2, which may stimulate interest in developing non-C1 synthon functions of CO2.

A KOtBu-mediated C2-benzylation of quinoline N-oxides with benzylboronates under mild reaction conditions has been developed. The reaction shows broad scope for both of the quinoline N-oxides and benzylboronates, especially, secondary and tertiary benzylboronates are also compatible with this reaction. DFT calculations indicate that the reaction is promoted by the nucleophilic addition of KOtBu to boronate rather than the deprotonation of benzylic C−H bond with KOtBu.

A 1,1-hydroboration of alkynylgermanes with unique transGe/B stereochemistry under transition-metal-free conditions is reported. Mechanistic studies suggest that a pathway involving α boration followed by a stepwise 1,2-Ge/H shift on the intermediate structurally lies between an alkyne−Ge+ π complex and a typical vinyl cation. The resulting Ge/B bimetallic modules, along with a Ge*/Ge/B trimetallic variant, can be conveniently transformed into trisubstituted olefins through iterative divergent cross-coupling. This work demonstrates that incorporating metalloids into classical organic reactions may offer unconventional chemical selectivity and efficient synthetic applications.

Nickel/photoredox dual catalyzed cross-coupling of aryl halides with alkylboron compounds is one of the effective methodologies for the construction of C(sp2) C(sp3) bonds. Although elegant results have been achieved by using alkyl trifluoroborates as alkyl radical precursors, the generation of alkyl radicals from readily available alkyl boronic esters is still limited due to their high oxidation potential. We disclosed here that activation of alkyl boronic esters by MeOLi is highly efficient for the generation of alkyl radicals under photocatalysis conditions. The reaction featured with a wide substrate scope, high functional group tolerance, and late-stage modification of bioactive substances. In addition, the method was also successfully extended to alkyl boronic acids. Experimental and computational mechanistic studies indicated that the crosscoupling likely proceeds via a Ni(I)-catalyzed pathway.