Highly Selective and Sensitive Turn-Off–On Fluorescent Probes for Sensing Al³⁺ Ions Designed by Regulating the Excited-State Intramolecular Proton Transfer Process in Metal–Organic Frameworks

The concept of high-performance excited-state intramolecular proton transfer (ESIPT)-based fluorescent metal–organic framework (MOF) probes for Al3+ is proposed in this work. By regulating the hydroxyl groups on the organic linker step by step, new fluorescent magnesium–organic framework (Mg–MOF) probes for Al3+ ions were established based on the ESIPT fluorescence mechanism. It is observed for the first time that the number of intramolecular hydrogen bonds between adjacent hydroxyl and carboxyl groups can effectively adjust the ESIPT process and lead to tunable fluorescence sensing performance. Together with the well-designed porous and anionic framework, the Mg–TPP–DHBDC probe decorating with a pair of intramolecular hydrogen bonds exhibits extra-high quantitative fluorescence response to Al3+ through an unusual turn-off (0–1.2 μM) and turn-on (4.2–15 μM) luminescence sensing mechanism. Notably, the 28 nM limit of detection value represents the lowest record among all reported MOF-based Al3+ fluorescent sensors up to now. Benefited from the unique turn–off–on ESIPT fluorescence detection process, the Mg–TPP–DHBDC MOF sensor exhibits single Al3+ detection compared with other 16 common metal ions including Ga3+, In3+, Fe3+, Cr3+, Ca2+, and Mg2+. Impressively, such an Al3+ selective sensing process can even be fulfilled by the reusable MOF test paper detected by naked eyes. Overall, the quantitative Al3+ detection, together with the extraordinary sensitivity, selectivity, fast response, and good reusability, strongly supports our concept of ESIPT-based fluorescent MOF Al3+ probes and makes Mg–TPP–DHBDC one of the most powerful Al3+ fluorescent sensors

Selectivity Enhancement in Dynamic Kinetic Resolution of Secondary Alcohols through Adjusting the Micro-Environment of Metal Complex Confined in Nanochannels: A Promising Strategy for Tandem Reactions

Dichloro­(η⁶-<i>p</i>-cymene) (1-butyl-3-cyclohexyl-imidazolin-2-ylidene) ruthenium­(II) (<b>RuL</b>) was synthesized and confirmed. Five heterogeneous catalysts with similar ruthenium cores were prepared by chemical immobilization method using various silica-based supports, including mesoporous silica SBA-15 of different pore sizes (<b>Ru/Si-9</b>, <b>Ru/Si-8</b>, and <b>Ru/Si-7</b>), nonporous silica particles (<b>Ru/SiO</b>_<b>2</b>), and surface trimethylsilylated SBA-15 (<b>Ru/SiMe</b>). The dynamic kinetic resolution (DKR) of 1-phenylethanol, which includes metal–enzyme bicatalytic racemization in tandem with stereoselective acylation, gave product in 99% yield and 0% ee with homogeneous catalyst <b>RuL</b>, whereas the heterogeneous <b>Ru/Si-8</b> exhibited high catalytic activity and enantioselectivity (up to 96% yield and 99% ee). The racemization and acylation abilities of different catalysts were analyzed. The influences of pore size and surface properties for heterogeneous catalysts were investigated, and the nanocage effect was found to be the key factor in stereoselectivity. The catalyst <b>Ru/Si-8</b> performed well in reactions with various substrates and can be reused for at least seven times

Imino-N-Heterocyclic Carbene Palladium(II) Complex-Catalyzed Direct Arylation of Electron-Deficient Fluoroarenes with “On and Off” Chelating Effect Assistance

An imino-N-heterocyclic carbene palladium­(II) complex with a bulky substituted group on the imino nitrogen was used to catalyze the direct arylation of electron-deficient fluoroarenes with aryl halides. A series of electron-poor substrates and aryl bromides could be coupled in good to excellent yields with satisfactory position selectivity (20 examples, up to 93%). These arylations could proceed at a relatively low temperature (80 °C, 20 examples, up to 95%) with mono-N-protected amino acid assistance. Some of them even gained higher yields than those at high temperature (110 °C). Otherwise, some aryl iodides can forge cross-coupling products in yields of nearly 30% under the optimized conditions. The rate profiles for arylation of electron-poor arenes were measured in the presence of the imino-N-heterocyclic carbene palladium­(II) complex or Pd­(OAc)₂ as the catalyst, which showed that the former could keep catalytic activity for a longer time. Computational studies indicated that the imino nitrogen in the imino-N-heterocyclic carbene ligand can detach from and attach to the central metal in the catalytic cycle. Thus, the coordination site could be protected, and this effect may be responsible for decreasing the rate of palladium black formation