Search

A novel sulfonated CNN pincer ligand has been designed to support CH and O2 activation at a Pt(II) center. The derived cycloplatinated aqua complex 7 was found to be one of the most active reported homogeneous Pt catalysts for H/D exchange between studied arenes (benzene, benzene-d 6, toluene-d 8, p-xylene, and mesitylene) and 2,2,2-trifluoroethanol (TFE) or 2,2,2-trifluoroethanol-d; the TON for C6D6 as a substrate is >250 after 48 h at 80 °C. The reaction is very selective; no benzylic CH bond activation was observed. The per-CH-bond reactivity diminishes in the series benzene (19) > toluene (p-CH:m-CH:o-CH = 1:0.9:0.2) > xylene (2.9) > mesitylene (1.1). The complex 7 reacts slowly in TFE solutions under ambient light but not in the dark with O2 to selectively produce a Pt(IV) trifluoroethoxo derivative. The H/D exchange reaction kinetics and results of the DFT study suggest that complex 7, and not its TFE derivatives, is the major species responsible for the arene CH bond activation. The reaction deuterium kinetic isotope effect, k H/k D = 1.7, the reaction selectivity, and reaction kinetics modeling suggest that the CH bond cleavage step is rate-determining. [ABSTRACT FROM AUTHOR]

The first examples of catalysis of aliphatic C-H hydroxylation by an iminium salt are presented. The method allows the selective organocatalytic hydroxylation of unactivated 3° C-H bonds at room temperature using hydrogen peroxide as the terminal oxidant. Hydroxylation of an unactivated 2° C-H bond is also demonstrated. Furthermore, improved functional group compatibility over other catalytic methods is reported in the form of selectivity for aliphatic C-H hydroxylation over alcohol oxidation. On the basis of initial mechanistic studies, an oxaziridinium species is proposed as the active oxidant. [ABSTRACT FROM AUTHOR]

Floods can cause masonry buildings to become immersed for a long period of time, which causes the building materials to deteriorate and thus affects the safety performance of the structure. In this study, a long-term-immersed masonry wall was considered as the research object and a cohesive element containing damage evolution was used to simulate the mortar layer, establish a finite-element model of the separated masonry wall and perform numerical loading experiments. Data on crack width variation in the masonry wall was extracted using Python. The effect of a long-termwater-immersion environment on the shear performance of masonry walls was analyzed considering material deterioration. The results show that long-term flooded masonry walls are characterized by low shear capacity and low stiffness and safety reserves cannot be guaranteed. A partially immersed masonry wall is prone to damage from the weak parts and has a high risk coefficient. The macro-damage degree of a masonry wall immersed by a flood is not as serious as that of the original wall in the early stage, but it suddenly increases in the collapse stage and the warning effect of cracks is reduced, which requires special attention in safety assessments. [ABSTRACT FROM AUTHOR]