A DFT Study on the Binuclear Copper(I)-Catalyzed Synthesis Mechanism of 1,2,3-Triazolo[1,5-c]Pyrimidine via Interrupted Click and Ketenimine Rearrangement.

In this paper, the mechanism of the full catalytic cycle for binuclear Cu(I)-catalyzed sulfonyl azide-alkyne cycloaddition reaction for the synthesis of triazolopyrimidines was rationalized by density functional theoretical (DFT) calculations. The computed reaction route consists of: (a) formation of dicopper intermediates, including C-H activation of terminal alkyne, 3+2 ring cycloaddition and ring-reducing reaction and transmetalation, (b) interrupted CuAAC reaction, including di-copper catalyzed ring-opening of 2H-azirines and C-C bond formation to generate the copper-triazoles and -ketenimines, (c) two-step C-N cross-coupling and following (d) multi-step hydrogen transfer by the hydrogen bonding chain of water to promote the C-N formation and another C-N cleavage through the removal of p-tolyl sulfonamides. Our DFT results indicate that the multi-step hydrogen transfer process is the rate-determining step along the potential energy surface profile. The explicit water model was used for systematic determination of barrier for C-C cross-coupling, C-N bond formation and cleavage, and p-tolylsulfonamide removal. A critical insight in the interrupted CuAAC reaction was proposed. Further prediction interprets H2 O hydrogen bond chain plays an important role in C-N bond formation and cleavage, and the removal of p-tolylsulfonamide. This may have fundamental guidance on the design of 1, 5-herterocyclic functionalized triazolopyrimidines via interrupted CuAAC rearrangement reaction, as well as hydrogen bond chain of water.

Simultaneous Formation of cis- and trans-CH3OCu(OH) Intermediates in Methane Activation by Cu in Solid Ar.

Understanding the mechanisms of methane activation is an important and active research area of the contemporary catalyzed conversion of hydrocarbons to shippable, valuable feedstock and has invoked close collaborations between experimentalists and theorists. This article describes the trapping of reaction intermediates in a copper-catalyzed direct methane-to-methanol conversion. Specifically, two hydroxy(methoxy)copper(I) [CH3OCu(OH)] isomeric intermediates were distinguished and characterized by matrix isolation infrared spectroscopy and 18O2, CD4, and 13CH4 isotopic substitution experiments combined with quantum chemical calculations. Initially, laser-evaporated copper reacted with oxygen to form CuO2. Upon successive broadband UV irradiation, methane activation via the insertion of CuO2 into one of the C-H bonds produced both cis- and trans-CH3OCu(OH). All possible structures of the reactants, intermediates, transition states, minimum-energy crossing points, and products were optimized. The results indicated that the two CH3OCu(OH) isomers are not thermodynamically distinguishable, although both have different frequencies, which agrees with experimental observation. The proposed reaction mechanism involved (i) O-O bond cleavage, (ii) C-H bond activation, and (iii) H and CH3 competitive transfer. The small energy barrier for cis to trans conversion accounts for the simultaneous formation of cis- and trans-CH3OCu(OH). These findings indicate that the CH3OCu(OH) species would be a potent precursor in other families of copper-cored oxidants that can trigger methanol formation.

Noble Gas-Tungsten Peroxide Complexes in Noble Gas Matrixes: Infrared Spectroscopy and Density Functional Theoretical Study.

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that tungsten oxo and mono-superoxide, WO3 and (η2-O2)WO2, coordinate noble gas atoms in forming noble gas-tungsten oxide complexes. The results showed that both WO3 and (η2-O2)WO2 oxides can coordinate one Ar or Xe atom in solid noble gas matrixes; otherwise, tungsten mono- and dioxides cannot. Hence, the WO3 and (η2-O2)WO2 molecules trapped previously in solid argon noble gas matrixes should be regarded as the WO3(Ar) oxide and (η2-O2)WO2(Ar) peroxide complexes. When annealing, the lighter Ar atom can be replaced by a heavier xenon atom to form WO3(Xe) and (η2-O2)WO2(Xe) complexes. What's more, upon UV photolysis, both Ar and Xe atoms can be replaced by oxygen to form a tungsten disuperoxide (η2-O2)2WO2 complex. The binding energies were predicted to be 25.7, 16.6, 9.4, 14.7, and 8.1 kcal/mol for the (η2-O2)2WO2, WO3(Xe), WO3(Ar), (η2-O2)WO2(Xe), and (η2-O2)WO2(Ar) complexes at the CCSD(T)//M06-2X-D3//def2-TZVP/DGDZVP/SDD level. The substitution law, O2 > Xe > Ar, can be interpreted according to the chemical reaction energies calculated to be -6.6 and +11.0 kcal/mol, respectively, for the equation formulas Xe + (η2-O2)WO2(Ar) = (η2-O2)WO2(Xe) + Ar and O2 + (η2-O2)WO2(Xe) = (η2-O2)2WO2 + Xe at the same level.

DFT and AFIR study on the copper(i)-catalyzed mechanism of 5-enamine-trisubstituted-1,2,3-triazole synthesis via C-N cross-coupling and the origin of ring-opening of 2H-azirines.

Understanding the synthesis mechanism of substituted 1,2,3-triazoles is an important and state-of-the-art research area of contemporary copper(i)-catalyzed terminal alkyne and organic azide click reaction (CuAAC), which has invoked increasing close collaborations between experiment and theory including copper catalyzed interrupted click reaction. In this study, the mechanism of Cu(i)-catalyzed 5-enamine-functionalized fully substituted 1,2,3-triazole synthesis was rationalized via density functional theory (DFT) and multicomponent artificial force-induced reaction (MC-AFIR) methods. The reasonable reaction route consists of (a) di-copper catalyzed ring-opening of 2H-azirines, (b) alkyne hydrogen atom transfer, (c) [3 + 2] ring cycloaddition, and (d) C-N bond formation through reductive elimination. The MC-AFIR method was used for the systematic determination of transition states for the C/N-Cu bond formation, C-N bond coupling and crossing points between singlet and triplet states. Our survey on the prereactant complexes suggested that the dicopper-catalyzed 2H-azirine ring-opening and alkyne hydrogen activation are both thermodynamically feasible via a singlet/triplet crossing point. This explains why Et3N is critical for alkyne hydrogen transfer (HT) before the [3 + 2] cycloaddition reaction, and the C-N cross-coupling product instead of the click product (byproduct). Our DFT results indicate that the transmetalation process is the rate determination step along the triplet state potential energy surface. This study provides important mechanistic insights for the interrupted CuAAC reaction to form 5-enamine-fully-substituted-1,2,3-triazoles. Further insight prediction interprets that solvent and extra strong ligand coordination play a certain role in competitive reactions.