RESUMO
The assembly of various azo dyes and pigments with inorganic layered materials could develop new types of intercalation materials. The electronic structures and photothermal properties of composite materials (AbS--LDH) constituted by azobenzene sulfonate anions (AbS-) and Mg-Al layered double hydroxide (LDH) lamella were theoretically studied at the M06-2X/def2-TZVP//M06-2X/6-31G(d,p) level using density functional theory and time-dependent density functional theory. Meanwhile, the influences of LDH lamella on the AbS- in AbS--LDH materials were investigated. The calculated results showed that the addition of LDH lamella could lower the isomerization energy barrier of CAbS- anions (CAbS- stands for cis AbS-). The thermal isomerization mechanisms of AbS--LDH and AbS were related to the conformational change of the azo group, out-of-plane rotation and in-plane inversion. The LDH lamella could reduce the energy gap of the n â π* and π â π* electronic transition and lead to a red-shift in the absorption spectra. When a polar solvent DMSO was applied, the excitation energy of the AbS--LDHs was increased, making its photostability stronger than in nonpolar solvent and solvent-free.
RESUMO
The mechanism and regioselectivity of the heterocyclic C-H arylation of benzofuran and benzothiophene catalyzed by Pd(OAc)2 complexes were investigated using the density functional theory (DFT) method. The Pd(0)L2(PhI) complex (L = HOAc) is proposed to be the catalytic species. Compared to the traditional Heck-type mechanism, concerted metalation-deprotonation (CMD) mechanism, and electrophilic aromatic substitution (SEAr) mechanism for the C-H arylation, a new hydride relay exchange mechanism was proposed for the benzoheterocyclic C-H arylation catalyzed by Pd complexes, which consists of two redox processes between Pd(II) and Pd(0) species to complete the regioselective C-H activation. The calculated results indicate that the reaction along the hydride relay exchange mechanism is more favorable than those along other mechanisms, including the traditional Heck-type mechanism and the base-assisted anti-H elimination mechanism. This agrees well with the experimental results. Meanwhile, the origin for the regioselective C-H arylation was unveiled in which the α-C-H arylation products are major for the heterocyclic C-H arylation of benzofuran, but the ß-C-H arylation products are major for that of benzothiophene. This study might provide a deep mechanistic understanding on the regioselective C-H activation and arylation of benzoheterocycle compounds catalyzed by transition-metal complexes.