•Ligand effect on cymene Ru complexes-catalyzed racemization of sec-alcohols.•16- and 18-electron complexes bearing a weak ligand are excellent catalysts.•The dissociation of ligands to form vacant sites is crucial to 18-electron Ru complexes.•The optimized Ru complexes showed efficiency in alcohols DKR.A family of ruthenium complexes with different ligands was utilized in racemization of (R)-1-phenylethanol to investigate the potential influence of the ligands coordinated to the ruthenium center. Kinetic experiments showed that 16-electron cymene ruthenium complex with two chloro-bridge bonds and 18-electron ones with easily dissociative ligands are highly active for catalytic racemization of alcohols. Possible racemization mechanism for cymene ruthenium complexes was then proposed. Computational analysis of dissociation energy barrier, NBO analysis and reaction potential energy surface suggest that ligand-dissociation process is the vital step of the racemization catalyzed by cymene ruthenium complexes. Thereafter, these complexes were applied in the DKR of secondary alcohols to verify their efficiency and applicability.Kinetic profiles show that 16-electron cymene ruthenium complex and 18-electron ones with easily dissociative ligands are highly active for catalytic racemazition of alcohols. Computational analyses provide the evidence of ligand-dissociation process for 18-electron complexes to transform into 16-electron ones. The optimized Ru complexes showed good efficiency in alcohols DKR.

An imino-N-heterocyclic carbene palladium(II) complex with a bulky substituted group on the imino nitrogen was used to catalyze the direct arylation of electron-deficient fluoroarenes with aryl halides. A series of electron-poor substrates and aryl bromides could be coupled in good to excellent yields with satisfactory position selectivity (20 examples, up to 93%). These arylations could proceed at a relatively low temperature (80 °C, 20 examples, up to 95%) with mono-N-protected amino acid assistance. Some of them even gained higher yields than those at high temperature (110 °C). Otherwise, some aryl iodides can forge cross-coupling products in yields of nearly 30% under the optimized conditions. The rate profiles for arylation of electron-poor arenes were measured in the presence of the imino-N-heterocyclic carbene palladium(II) complex or Pd(OAc)2 as the catalyst, which showed that the former could keep catalytic activity for a longer time. Computational studies indicated that the imino nitrogen in the imino-N-heterocyclic carbene ligand can detach from and attach to the central metal in the catalytic cycle. Thus, the coordination site could be protected, and this effect may be responsible for decreasing the rate of palladium black formation.

The mechanism of the samarium-catalyzed 1,5-regioselective azide–alkyne [3 + 2]-cycloaddition (SmAAC) reaction has been examined with quantum mechanical calculations at the B3LYP/6-31+G(d,p) level of theory with ECP51MWB on Sm. Four stepwise pathways were located, with two leading to the 5-endocyclic 1,5-disubstituted 1,2,3-triazole product PSmL2 (paths 1 and 2) and the other two to the exocyclic product ExoPSmCl2 (path 3) as well as 1,4-disubstituted 1,2,3-triazole RegPSmL2 (path 4), respectively. Among them, path 2 (R-COM1–TS12–COM2–TS23–COM3–TS3P–PSmL2) is the most favored one both in the gas phase and in toluene solution, which is in good agreement with the experimental data. Moreover, 1,1-insertion forming COM2 in path 2 is the rate-determining step. The computational results also infer that the participation of samarium catalyst changes the distribution of the electrostatic potential on the reactants’ surface, which determines the polarization direction of the reactants and formation of different intermediates (COM1 and RegCOM1), and finally affects the regioselectivity. When solvent corrections for toluene are considered, the 1,1-insertion process is discouraged, while the intramolecular [1,3]-shift reaction is facilitated.

An oxidative nucleophilic cyclization of 2-alkynylanilines with thiophenols under metal-free conditions was developed. The one-pot two-step reaction involves a PhI(OAc)2-mediated oxidative dearomatization and a Brønsted acid promoted nucleophilic cyclization. DFT calculations were performed to understand the reaction pathway.

•Both NMR and DFT spectroscopic study has been carried out in fluorinated dendritic catalyst.•We report a novel interaction between fluorinated dendrimer and catalytic site.•A new homogeneous catalyst is designed and synthesized with excellent recycling ability.•Enhanced activity, high enantioselectivity and outstanding recycling ability have been achieved at high reaction temperature with fluorinated dendritic catalyst.A series of fluorinated dendritic chiral ligands have been designed and synthesized. These fluorinated dendrimers are capable of forming a well-defined semi-rigid structure, which was revealed to play a vital role in the ruthenium(II) bifunctional catalyst for asymmetric transfer hydrogenation of prochiral ketone substrates. In contrast to the classical non-fluorinated dendrimer carrier, both NMR and DFT study exhibit that the introduction of fluorine atoms leads to considerable intramolecular weak interactions such as π–π stacking and hydrogen bonding interactions, which make the dendritic backbone exist with a semi-rigid structure in the catalyst. This influences the performance of the catalytic center in terms of the stability and reusability. This concept was employed as a strategy to design a new Ru(II)-complex catalyst Ru-G-2′-F, which demonstrated obviously improved recycling ability up to fifteen times. Significantly enhanced activity, high enantioselectivity and outstanding recycling ability have also been achieved even at high reaction temperature with Ru-G-2-F.

Metal-controlled cycloaddition of 2-alkynyl-1,4-benzoquinones and electron-rich styrenyl systems were investigated. The density functional theory (DFT) calculations revealed that the regioselectivity of the cycloaddition results from the different activation modes of Bi(OTf)3 and AuCl.

The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions.

2-Alkynylcyclohexadienimines, derived from the oxidation of 2-alkynylanilines, react with aromatic amines leading to N-arylindoles with a 4-amino substitution. The reaction was metal-controlled, and Bi(OTf)3 proved to be the best catalyst. The resulting 4-amino N-arylindoles could be converted to azepino[4,3,2-cd]indoles through condensation with aldehydes.