Stoichiometric C−H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C−H transformations have not been developed. Herein, an iron-catalyzed annulation of N−H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C−H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C−H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C−H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step.

To enable the selection of more accurate computational methods for the future theoretical exploration of the reaction mechanism of Ir-catalyzed olefin hydrogenation, we compared high-level ab initio coupled cluster and DFT calculations with a simplified model of Pfaltz's Ir/P,N-type catalyst for all four previously proposed Ir^I/Ir^III and Ir^III/Ir^V mechanisms. Through the systematic assessment of the DFT performances, the DFT empirical dispersion correction (DFT-D3) is found to be indispensable for improving the accuracy of relative energies between the Ir^I/Ir^III and Ir^III/Ir^V mechanisms. After including the DFT-D3 correction, the three best performing density functionals (DFs) are B2-PLYP, BP86, and TPSSh. In these recommended DFs, the computationally more expensive double-hybrid functional B2-PLYP-D3 has a balanced and outstanding performance for calculations of the reaction barriers, reaction energies, and energy gaps between different mechanisms, whereas the less costly BP86-D3 and TPSSh-D3 methods have outstanding, but relatively less uniform performances.

Stoichiometric C−H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C−H transformations have not been developed. Herein, an iron-catalyzed annulation of N−H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C−H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C−H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C−H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step.

The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z-alkenes, the hydrogenation of alkynes to give E-alkenes is still not well resolved. In particular, selective preparation of both Z- and E-alkenes by the same catalytic hydrogenation system using molecular H₂ has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C₆F₅)₂-catalyzed metal-free hydrogenation of alkynes was adopted. Significantly, both Z- and E-alkenes can be furnished by hydrogenation with molecular H₂ in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H₂ play an essential role in promoting the hydrogenolysis reaction.

Although early transition metal (ETM) carbides can activate CH bonds in condensed-phase systems, the electronic-level mechanism is unclear. Atomic clusters are ideal model systems for understanding the mechanisms of bond activation. For the first time, CH activation of a simple alkane (ethane) by an ETM carbide cluster anion (MoC₃⁻) under thermal-collision conditions has been identified by using high-resolution mass spectrometry, photoelectron imaging spectroscopy, and high-level quantum chemical calculations. Dehydrogenation and ethene elimination were observed in the reaction of MoC₃⁻ with C₂H₆. The CH activation follows a mechanism of oxidative addition that is much more favorable in the carbon-stabilized low-spin ground electronic state than in the high-spin excited state. The reaction efficiency between the MoC₃⁻ anion and C₂H₆ is low (0.23±0.05) %. A comparison between the anionic and a highly efficient cationic reaction system (Pt⁺+C₂H₆) was made. It turned out that the potential-energy surfaces for the entrance channels of the anionic and cationic reaction systems can be very different.

Herein, a Rh^III-catalyzed stereocontrolled synthesis of benzo[k]fluoranthenes is reported. It was found that the unexpected E/Z isomerization was highly sensitive to the electronic effects of the substituents on the aryl groups. Theoretical calculations revealed that this controllable stereochemistry originates from the mediation of rhodacyclopentadiene intermediates during the isomerization. The fact that similar stereochemistry was observed when using an Ir^III catalyst further suggests a certain generality of this discovery toward some other transition metals.

A series of tunable G₀–G₃ dendritic 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) ligands was prepared by attaching polyaryl ether dendrons onto the four phenyl rings on the P atoms. Their ruthenium complexes were employed in the asymmetric hydrogenation of β-ketoesters, α-ketoesters, and α-ketoamides to reveal the effects of dendron size on the catalytic properties. The second- and third-generation catalysts exhibited excellent enantioselectivities, which are remarkably higher than those obtained from the small molecular catalysts and the first-generation catalyst. Molecular modeling indicates that the incorporation of bulky dendritic wedges can influence the steric environments around the metal center. In addition, the ruthenium catalyst bearing a second-generation dendritic ligand could be recycled and reused seven times without any obvious decrease in enantioselectivity.

Hyperhalogens were recently identified as a new class of highly electronagative species which are composed of metals and superhalogens. In this work, high-level theoretical calculations and photoelectron spectroscopy experiments are systematically conducted to investigate a series of coinage-metal-containing hyperhalogen anions, Cu(BO₂)₂⁻, Ag(BO₂)₂⁻, and Au(BO₂)₂⁻. The vertical electron detachment energy (VDE) of Ag(BO₂)₂⁻ is anomalously higher than those of Au(BO₂)₂⁻ and Cu(BO₂)₂⁻. In quantitative agreement with the experiment, high-level ab initio calculations reveal that spin–orbit coupling (SOC) lowers the VDE of Au(BO₂)₂⁻ significantly. The sizable magnitude of about 0.5 eV of SOC effect on the VDE of Au(BO₂)₂⁻ demonstrates that SOC plays an important role in the electronic structure of gold hyperhalogens. This study represents a new paradigm for relativistic electronic structure calculations for the one-electron-removal process of ionic Au^IL₂ complexes, which is characterized by a substantial SOC effect.