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The chemical reactivity of the first- and second-generation Grubbs catalysts has always been a significant issue in olefin metathesis. In the present work, we study the [2+2] cycloreversion/cycloaddition and the alkylidene rotation involved into the interconversion of the ruthenacyclobutane intermediate, through the reaction force and reaction force constant analysis. It has been found that the structural contribution controls the barrier energy in the interconversion of ruthenacyclobutane via [2+2] cycloreversion/cycloaddition, which is slightly lower in the second generation of Grubbs catalysts while its electronic contribution is slightly higher, which unveils a major rigidity and donor/acceptor properties of the NHC. This finding explains a greater structural contribution in the rate constant. Moreover, on the basis of the reaction force constant, the process can be classified as "two-stage"-concerted reactions, noting a more asynchronous process when the first generation is used as a catalyst. Finally, a similar analysis into the alkylidene rotation was performed. It was determined that [2+2] cycloreversion and alkylidene rotations take place in a sequential manner, the energy barrier is again controlled by structural reorganization, and the pathway is less asynchronous. [ABSTRACT FROM AUTHOR]

New 4-amino-3-iminoquinoline derivative ligands (L1–4) were synthesized through an intramolecular exo-dig cyclization of anionic β-diketiminates, containing an N-benzonitrile moiety. The effect of the alkali-metal in this reaction was investigated and an inverse effect between the size of the cation and the cyclization rate was revealed. The effect of the reaction temperature was also studied, in which a direct dependence was observed. Kinetic and theoretical studies were performed in an attempt to clarify the reaction mechanism, obtaining a first-order reaction rate dependence with an activation energy of 20.6 kcal mol−1, with DFT-based calculations supporting the proposed mechanism. In addition, four new aluminium complexes were isolated in high yields (C1–4), which were evaluated as catalysts for the preparation of cyclic carbonates from epoxides and CO2, thus becoming the first examples of the use of β-diketiminate ligands in this catalytic process. The reactions were performed at 80 °C and 1 bar CO2 pressure under solvent-free conditions. We were able to prepare a large variety of cyclic carbonates in excellent selectivities and yields, employing the aluminium complex C3. The L1–4 ligands and C1–4 complexes were characterized using NMR, FT-IR, HRMS, and X-ray diffraction methods. [ABSTRACT FROM AUTHOR]

We have analyzed the variation of the reaction force F( ξ) and the reaction force constant κ( ξ) along the intrinsic reaction coordinates ξ of the water-assisted proton transfer reactions of HX-N = Y (X,Y = O,S). The profile of the force constant of the vibration associated with the reactive mode, k( ξ), was also determined. We compare our results to the corresponding intramolecular proton transfers in the absence of a water molecule. The presence of water promotes the proton transfers, decreasing the energy barriers by about 12 - 15 kcal mol. This is due in part to much smaller bond angle changes being needed than when water is absent. The κ( ξ) profiles along the intrinsic reaction coordinates for the water-assisted processes show striking and intriguing differences in the transition regions. For the HS-N = S and HO-N = S systems, two κ( ξ) minima are obtained, whereas for HO-N = O only one minimum is found. The k( ξ) show similar behavior in the transition regions. We propose that this fine structure reflects the degree of synchronicity of the two proton migrations in each case. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]