Understanding the Reactivity Difference of Isocyanate and Isothiocyanate toward a Ruthenium Silylene Hydride Complex

The detailed reaction mechanisms of the CO hydrosilylation of isocyanate and the CS bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex Cp*­(CO)­(H)­RuSi­(H)­{C­(SiMe₃)₃} have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between isocyanate and isothiocyanate toward the ruthenium silylene hydride complex has been examined and discussed. The different bond strengths and π-accepting abilities of CO and CS and the different degrees of affinity of O and S toward the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally

Understanding the Reactivity Difference of Isocyanate and Isothiocyanate toward a Ruthenium Silylene Hydride Complex

The detailed reaction mechanisms of the CO hydrosilylation of isocyanate and the CS bond cleavage of isothiocyanate mediated by the neutral ruthenium silylene hydride complex Cp*­(CO)­(H)­RuSi­(H)­{C­(SiMe₃)₃} have been investigated with the aid of density functional theory calculations. Through the investigation, the difference in reactivity between isocyanate and isothiocyanate toward the ruthenium silylene hydride complex has been examined and discussed. The different bond strengths and π-accepting abilities of CO and CS and the different degrees of affinity of O and S toward the Si center in the silylene ligand contribute to the different reactivities of the isocyanate and isothiocyanate substrates observed experimentally

Palladium(0)-Catalyzed Methylcyclopropanation of Norbornenes with Vinyl Bromides and Mechanism Study

An unusual methylcyclopropanation from [2 + 1] cycloadditions of vinyl bromides to norbornenes catalyzed by Pd­(OAc)₂/PPh₃ in the presence of CH₃ONa and CH₃OH has been established. A methylcyclopropane subunit was installed by a 3-fold domino procedure involving a key protonation course. Preliminary deuterium-labeling studies revealed that the proton came from methyl of CH₃OH and also exposed an additional hydrogen/deuterium exchange process. These two proton-concerned reactions were fully chemoselective

DFT Studies on the Palladium-Catalyzed Dearomatization Reaction between Chloromethylnaphthalene and the Cyclic Amine Morpholine

Density functional theory calculations have been performed to investigate the mechanisms of the Pd-catalyzed dearomatization reaction between chloromethylnaphthalene and the cyclic amine morpholine. The calculation results indicate that the reductive elimination leading to the formation of the dearomatic product takes place via an intramolecular C–N bond coupling between the para carbon of an η³-exo-(naphthyl)­methyl ligand and the nitrogen atom of the amide ligand. The free energy barrier is calculated to be only 13.1 kcal/mol, significantly lower than that (37.8 kcal/mol) through the η³-endo-(naphthyl)­methyl intermediate originally thought. For comparison, various C–N coupling reaction pathways leading to the formation of dearomatic and aromatic products have also been examined

One-Step Cyclization: Synthesis of <i>N</i>‑Heteroalkyl‑<i>N</i>′‑tosylpiperazines

Piperazine derivatives are important intermediates in organic synthesis and useful building blocks in pharmaceutical and fine chemical industries. Currently available synthetic routes for these heterocyclic compounds have limited scope owing to the harsh reaction conditions, low yields, and multistep process. Herein, we reported a practical method for synthesis of alkyl-, alcohol-, amine-, and ester-extended tosylpiperazines under mild conditions with moderate to high yields. This protocol exhibits potential applicability in the synthesis of pharmaceuticals and natural products because of the operational simplicity and the conveniently available reactants. On the basis of the experimental and theoretical results, a plausible mechanism of aliphatic nucleophilic substitution (S_N) in the cyclization has been postulated and evidence for the formation of a six-membered ring has also been confirmed by means of density functional theory (DFT) calculations

Mechanism of Carbon Monoxide Induced N–N Bond Cleavage of Nitrous Oxide Mediated by Molybdenum Complexes: A DFT Study

The detailed mechanism of CO-induced N–N bond cleavage of N₂O mediated by molybdenum complexes leading to the nitrosyl isocyanate complex has been investigated via density functional theory (DFT) calculations at the B3LYP level. On the basis of the calculations, we proposed a new reaction mechanism of CO-induced N–N bond cleavage of N₂O with an overall free energy barrier of 23.6 kcal/mol, significantly lower than that of the reaction mechanism (42.2 kcal/mol) proposed by Sita et al. The calculations also indicated that CO-induced N–N bond cleavage of N₂O is competitive with oxygen atom transfer (OAT) to carbon monoxide due to the comparable free energy barriers. The metal-bound carbonyl complex obtained from OAT can be recycled to give more nitrosyl isocyanate complexes. In addition, we demonstrated why the analogous tungsten complex cannot give the nitrosyl isocyanate complex via CO-induced N–N bond cleavage of N₂O. The calculations are consistent with experimental observations

Mechanisms and Reactivity Differences for Cycloaddition of Anhydride to Alkyne Catalyzed by Palladium and Nickel Catalysts: Insight from Density Functional Calculations

Mechanisms and reactivity differences for the cycloaddition of anhydride to alkyne catalyzed by the palladium and nickel catalysts have been investigated by extensive density functional theory (DFT) calculations. The predicted free energy profiles for the Pd- and Ni-catalyzed reactions have been used to evaluate possible mechanisms for the formation of different products. Calculations show that the formation of isocoumarin via the decarbonylative addition of anhydride to alkyne is kinetically more favorable than the channel to indenone in the Ni-catalyzed reaction. On the contrary, the preparation of naphthalene through sequential liberation of CO₂ and CO is kinetically more favorable than that the formation of indenone in the Pd-catalyzed process. The bonding differences between Pd–C and Ni–C bonds, arising from the relativistic effect of late transition metals, play an important role in regulating their catalytic activity. The calculation results show good agreement with the experiments

Mechanism and Substrate-Dependent Rate-Determining Step in Palladium-Catalyzed Intramolecular Decarboxylative Coupling of Arenecarboxylic Acids with Aryl Bromides: A DFT Study

The mechanism of palladium-catalyzed intramolecular decarboxylative coupling of arenecarboxylic acids with aryl bromides has been studied computationally with the aid of density functional theory. Full free-energy profiles have been computed for all ether- and amine-containing substituted substrates. The calculations indicate that the rate-determining step is indeed substrate dependent, as reflected in free energy profiles; the oxidative addition, decarboxylation, or reductive elimination step can become the rate-determining step for the full catalytic cycle due to the different substituents on the substrates. In addition, we also demonstrate the preference of NCH₃- over NH-containing amine substrates for the decarboxylation process. The calculations are in good agreement with the experimental observations

Explore the Catalytic Reaction Mechanism in the Reduction of NO by CO on the Rh₇⁺ Cluster: A Quantum Chemical Study

Rhodium has been proved to possess unique reactivity to convert NO_<i>x</i> into N₂ with high conversion efficiency and selectivity. In this study, we have carried out DFT calculations on the reaction mechanism in the reduction of NO by CO on the surface of the Rh₇⁺ cluster. The calculated results suggest that the reaction proceeds via three steps. First, the NO and CO are adsorbed on the Rh₇⁺ cluster, then the adsorbed NO decomposes to N and O atoms. The O atom reacts with the adsorbed CO leading to the formation of CO₂ molecule. Second, another NO is adsorbed on the rhodium cluster and decomposes to N and O atoms, then the two N atoms couple with each other to yield N₂ molecule. Finally, the second CO can be adsorbed on the Rh₁ or Rh₇ atom of the Rh₇⁺ cluster and oxidized to CO₂ molecule. On the basis of present calculations from gas-phase Gibbs free energy profiles, the reaction path related to CO adsorption on the Rh₇ atom is energetically more favorable. The second adsorbed NO generating N and O atoms in the second step is the rate-limiting step of whole catalytic cycle. The high activation barrier (TS₆₇) of 56.6 kcal/mol can be driven by large exergonic reaction. Our work would provide some valuable fundamental insights into the reaction mechanism between NO and CO on the rhodium surface, which is vitally important to decrease NO emissions in automotive exhaust gas

Structure–Function Analysis of the Conserved Tyrosine and Diverse π‑Stacking among Class I Histone Deacetylases: A QM (DFT)/MM MD Study

Discovery of the isoform-selective histone deacetylases (HDACs) inhibitors is of great medical importance and still a challenge. The comparison studies on the structure–function relationship of the conserved residues, which are located in the linker binding channel among class I HDACs (including 4 isoforms: HDAC1/2/3/8), have been carried out by using <i>ab initio</i> QM/MM MD simulations, a state-of-the-art approach to simulate metallo-enzymes. We found that the conserved tyrosine (Y303/308/286/306 in HDAC1/2/3/8, respectively) could modulate the zinc-inhibitor chelation among all class I HDACs with different regulatory mechanisms. For HDAC1/2/3 selective-inhibitor benzamide, the conserved tyrosine could modulate the coordinative ability of the central atom (Zn²⁺), while for pan-inhibitor SAHA, the conserved tyrosine could increase the chelating ability of the ligand (SAHA). Moreover, it is first found that the conserved tyrosine is correlated with the intertransformation of π–π stacking styles (parallel shift vs T-shaped) by the aromatic ring in benzamide and the two conserved phenylalanine residues of HDACs. In addition, the catalytic roles of the conserved tyrosine in stabilizing the transition state and intermediate are further revealed. These findings provide useful molecular basis knowledge for further isoform-selective inhibitor design among class I HDACs