Diazo compounds are popular carbenoid precursors that can react with various transition metals to afford carbene species for further transformations. In this study, density functional theory calculations were used to reveal the mechanisms of silver-and scandium-catalyzed alkylation of diazo compounds to construct compounds with tertiary or quaternary carbon centers. The results show that, with a silver(I) salt as the catalyst, the reaction starts with carbenation of silver(I) to afford a Fishertype silver carbene. Nucleophilic addition of silver carbene complex yields an enolate intermediate, which is followed by annulation/retro-aldol reaction to give a dialkylation product. Meanwhile, scandium(III) salt behaves as Lewis acid to generate free carbene, which is followed by conjugate addition of free carbene to produce an enolate intermediate. Subsequent 1,4proton transfer to a synthesized monoalkylation product is more favorable than nucleophilic addition process. Computational studies show that formation of mono-or dialkylation products from enolate intermediates results from competition between the nucleophilicity and Brønsted basicity of the α-carbon in the enolate intermediate, which is mainly controlled by the transitionmetal catalyst. The global nucleophilicity and Laplacian of the electron density were evaluated to reveal factors affecting the nucleophilicity and Brønsted basicity.

Terminal alkynes have become one of the most versatile building blocks for C–C bond construction in the past few decades, and they are usually considered to convert to acetylides before further transformations. In this study, a novel direct nucleophilic addition mode for Cu­(I)-catalyzed cross-coupling of terminal alkynes and N-tosylhydrazones to synthesize chiral allenes is proposed, and it was investigated by density functional theory with the M11-L density functional. Three different reaction pathways were considered and investigated. The computational results show that the proposed reaction pathway, which includes direct nucleophilic attack of protonated acetylene, deprotonation of the vinyl cation, and catalyst regeneration, is the most favorable pathway. Another possible deprotonation–carbenation–insertion pathway is shown to be unfavorable. The direct nucleophilic addition step is the rate- and enantioselectivity-determining step in the catalytic cycle. Noncovalent interaction analysis shows that the steric effect between the methyl group of the carbene moiety and the naphthalyl group of the bisoxazoline ligand is important to control the enantioselectivity. In addition, calculation of a series of chiral bisoxazoline ligands shows that a bulky group on the oxazoline ring is favorable for high enantioselectivity, which agrees with experimental observations. Moreover, copper acetylides are stable, and their generation is a favorable pathway in the absence of chiral bisoxazoline ligands.

A three-layer chirality relay model is proposed for Rh­(I)-mediated enantioselective siletane activation. A chiral ligand in the back layer controls the position of the alkyne-coordinated metal center in the middle layer, which then provides a chiral environment for the incoming substrate at the front layer. A two-dimensional contour map analysis further clarified this model.

Nickel catalysis has recently emerged as an important addition to the suite of transition metal-catalysed C-H bond functionalization methods. Here we report density functional theory calculations to elucidate the mechanism of Ni(II)-catalysed C-H arylation with a diaryliodonium salt or a phenyliodide. The effect of the choice of oxidant on the order of oxidative addition and C-H bond cleavage is investigated. When the active catalyst is oxidized by the diaryliodonium salt oxidant, C-H bond cleavage occurs to give an alkyl-aryl-Ni (IV) species. Conversely, the relatively weak oxidant phenyliodide leads to an alternative reaction sequence. The active catalyst first undergoes C-H bond cleavage, followed by oxidative addition of the phenyliodide to give a Ni(IV) species. Frontier molecular orbital analysis demonstrates that the reaction sequence of oxidative addition and C-H bond cleavage is determined by the unoccupied C aryl-I bond antibonding orbital level of the oxidant.

As a C2 synthon, vinylene carbonate has been used instead of acetylene in transition-metal catalyzed-coupling reactions. In this study, the mechanism of the vinylene carbonate activation mode for the Rh­(III)-catalyzed 4 + 2 annulation of benzamide and vinylene carbonate reaction is proposed, and it was investigated by DFT with the M06 density functional. The computational results show that the proposed reaction pathway, which includes the insertion of vinylene carbonate into an Rh–C bond, decarboxylation of the seven-membered rhodacycle intermediate, protonation of the ketonate rhodium intermediate, deprotonation of the benzamide, and catalyst regeneration, is the most favorable pathway. The 1,2-rhodium migration process can assist decarboxylative activation of vinylene carbonate, which is the rate-determining step in the catalytic cycle. The IRC calculation clearly revealed a quasi-synchronized process to directly afford a cyclic ketonate rhodium intermediate by the release of carbon dioxide.