Frustrated Lewis Pair-Type Reactivity of Intermolecular Rare-Earth Aryloxide and N-Heterocyclic Carbene/Olefin Combinations.

This work reports the cooperative reactivity of rare-earth aryloxide complexes with N-heterocyclic carbene (NHC) or N-heterocyclic olefin (NHO), showcasing their synergistic effect on the activation of H2 and diverse organic substrates. Reactions of RE(OAr)3 (RE=La, Sm, and Y; Ar=2,6-tBu2-C6H3) with unsaturated NHC ItBu (:C[N(R)CH]2, R=tBu) isolated abnormally bound RE metal NHC complexes RE/aNHC. In contrast, no metal-NHO adducts were formed when RE(OAr)3 were treated with NHO (R2C=C[N(R)C(R)]2, R=CH3). Both RE/aNHC and RE/NHO Lewis pairs enabled cooperative H2 activation. Furthermore, RE(OAr)3 were found to catalyze the hydrogenation of the exocyclic C=C double bond of NHO under mild conditions. Moreover, treatment of the La/aNHC complex with benzaldehyde produced a La/C4 1,2-addition product. The La/NHO Lewis pair could react with (trimethylsilyl)diazomethane and α, ß-conjugated imine, affording an isocyanotrimethylsilyl lanthanum amide complex and a La/C 1,4-addition product, respectively.

Synthesis of a pyridine-based covalent organic framework as an efficient adsorbent for rhodamine B removal.

Covalent organic frameworks (COFs), featured with crystalline structures, permanent porosity, and designable organic skeletons, are good candidates for serving as adsorbents. Herein, a new pyridine-based two-dimensional COF (TAPP-DBTA-COF) was constructed via the condensation of 2,4,6-tris(4-aminophenyl)pyridine and 2,5-dibromobenzene-1,4-dicarbaldehyde. TAPP-DBTA-COF displayed high-performance for the removal of rhodamine B (Rh B) from water with high capacity, good adaptability and reusability. The maximum adsorption capacity for Rh B can reach up to 1254 mg g-1, and the kinetic constant was determined as k2 = 0.00244 g mg-1 min-1. Moreover, the corresponding amorphous polymer of TAPP-DBTA-COF, termed as TAPP-DBTA-COP, was synthesized from the same starting materials. The lower efficiency of TAPP-DBTA-COP in capture of Rh B revealed that the ordered pore structure, large specific surface area and rich adsorption sites play an important role in adsorption.

Synthesis and Properties of Short-Lifetime Thermally Activated Delayed Fluorescence Materials.

Compounds MBZ-mPXZ, MBZ-2PXZ, MBZ-oPXZ, EBZ-PXZ, and TBZ-PXZ were conveniently synthesized, and they were found to exhibit TADF properties with lifetimes of 857, 575, 561, 768, and 600 ns, respectively. These short lifetimes of the compounds might be due to the combination of small singlet-triplet splitting energy (ΔEST) and benzoate group, which could be an efficient strategy for the further design of short-lifetime TADF materials.

Rational Design of High-Performance Cationic Organic Network Adsorbents.

Development of high-performance ionic organic network (ION) adsorbents is of great importance for water remediation. However, the research on IONs is still nascent, especially, the design philosophy regarding contaminant adsorption has rarely been explored. In this contribution, we optimized the adsorption efficiency of IONs by increasing the density of charged sites and improving their accessibility. We first produced a new cationic organic network (CON), CON-LDU4, with a high density of positive sites via synthesis from tetra(4-pyridyl)ethene. Compared to the analogue CON-LDU2 that synthesized from tetra(4-(4-pyridyl)phenyl)ethene, CON-LDU4 exhibited higher efficiency in adsorption of methyl blue, indicating that the higher ionic density results in the higher adsorption efficiency. To further improve the accessibility of the active sites, another new CON material (CON-LDU5) was synthesized by employing a hard template. CON-LDU5 exhibited a larger specific surface area than CON-LDU4, with clearly enhanced adsorption efficiency. Finally, CON-LDU5 was used to capture CrO42- ions in water with fast adsorption kinetics (k2 = 0.0328 g mg-1 min-1) and high adsorption capacity (369 mg g-1).

Matrix Solid-Phase Dispersion Coupled with HPLC-UV for Simultaneous Extraction, Purification and Determination of Six Lignans in Schisandra chinensis Fruits.

An efficient method for simultaneous extraction, purification and determination of six lignans in Schisandra chinensis Baill was developed by employing matrix solid-phase dispersion (MSPD) extraction followed by HPLC-UV determination analysis. Several sorbent and desorption solvent that affected the extraction yield of lignans were investigated; neutral alumina and absolute ethanol were selected as the best dispersing material and desorption agent, respectively. Other extraction conditions for MSPD were optimized as follows: 1:2 of S. chinensis raw material to neutral aluminum oxide mass ratio, 1:30 (g/mL) of sample to absolute ethanol, 2.5 h of desorption time and 50°C of desorption temperature. Under the above conditions, the total extraction yield for six lignans have reached (16.99 ± 0.33) x 103 mg/kg with a higher content of 6.88 ± 0.25% in the extracts. Comparative studies were explored by conducting other six extraction approaches including Soxhlet extraction, heat reflux extraction, smashing tissue extraction, microwave-assisted extraction, ultrasonic-assisted extraction and ultrasonic-microwave synergistic extraction. Results showed MSPD technique not only improved the extraction yield, but also improved the purity of lignans, it can be generalized to more extraction of natural compounds. In addition, the validated HPLC-UV method had been successfully applied to analysis of lignans from 10 real S. chinensis samples.

Hydrosilylative reduction of carbon dioxide by a homoleptic lanthanum aryloxide catalyst with high activity and selectivity.

An efficient tandem hydrosilylation of CO2, which uses a combination of a simple, homoleptic lanthanum aryloxide and B(C6F5)3, was performed. Use of a less sterically hindered silane led to an exclusive reduction of CO2 to CH4, with a turnover frequency of up to 6000 h-1 at room temperature. The catalytic system is robust, and 19 400 turnovers could be achieved with 0.005 mol% loading of lanthanum. The reaction outcome depended highly on the nature of the silane reductant used. Selective production of the formaldehyde equivalent, i.e., bis(silyl)acetal, without over-reduction, was observed when a sterically bulky silane was used. The reaction mechanism was elucidated by stoichiometric reactions and DFT calculations.

Hydroboration of carbon dioxide enabled by molecular zinc dihydrides.

Neutral molecular zinc(ii) dihydrides supported by N-heterocyclic carbene ligands bearing a pendant phosphine group were synthesized and then reacted with carbon dioxide to afford zinc diformates. The zinc dihydrides were found to be active catalysts for hydroboration of carbon dioxide under mild conditions, selectively giving boryl formate, bis(boryl)acetal, or methoxy borane compounds by changing the nature of the borane reductant.

Dihydrogen activation by intermolecular rare-earth aryloxide/N-heterocyclic carbene Lewis pairs.

Dihydrogen was readily activated by combination of homoleptic rare-earth metal aryloxides, RE(OAr)3 (RE = La, Sm, and Y) with N-heterocyclic carbenes (NHCs) under mild conditions. RE(OAr)3 were found to be active catalysts for the reductive hydrogenation of NHCs to aminals under 1 bar of H2. In addition, the La/NHC pair also exhibited frustrated Lewis pair (FLP)-like reactivity towards carbon dioxide and phenylacetylene, affording 1,2-addition and deprotonation products, respectively.

Reactions of Neutral Scandium/Phosphorus Lewis Pairs with Small Molecules.

Treating a scandium mixed alkyl/diaryloxide complex with phosphino-substituted alcohols resulted in the formation of scandium mixed alkoxyl/diaryloxide complexes Sc[OC(CH3)2CH2PR2][O-2,6- tBu2-C6H3]2[THF] (6, R = Ph; 8, R = tBu). The reactivity of Sc-based Lewis pair complexes 6 and 8 toward a wide range of substrates was investigated. A ligand substitution reaction occurred when complex 6 was treated with benzophenone. The reaction of complex 6 with sulfur afforded a phosphane oxidative product. Complexes 6 and 8 also exhibited typical Sc/P frustrated Lewis pair (FLP) reactivity. They added to the carbonyl group of phenyl isocyanate to form seven-membered metallacycles. Complex 6 underwent selective Sc/P 1,4-addition reactions with α,ß-unsaturated carbonyl compounds to give the corresponding nine-membered metallacyclic products. The reaction of 6 with 0.5 mol of dimethyl acetylenedicarboxylate led to the formation of bicyclo[7.7.0]cetane-derived metallacycle 16 in a distinctive double 1,4-addition pattern. With benzil complex 6 underwent a 1,4-addition reaction to afford a cis-enediolate which was coordinated to the Sc/P FLP through Sc-O and P-O bonds. Treatment of complex 6 with cyclopropyl phenyl ketone afforded the 10-membered metallaheterocycle 18, in which a scandium Lewis acid added to the oxygen atom and the phosphine Lewis base attacked the cyclopropyl group with ring opening. A ring-opening reaction also took place when epoxycyclohexane was employed as a substrate. Complex 6 successfully cleaved the C-Br bond of benzyl bromide to give zwitterionic complex 20 with newly formed Sc-Br and P-C bonds. Scandium phosphazine complex 21 was generated by a Sc/P 1,1-addition to the terminal nitrogen atom of (trimethylsilyl)diazomethane. Aided by the phosphorus Lewis base, scandium Lewis acid was able to abstract chloride from (Ph3P)AuCl to produce heterobimetallic Sc/Au complexes 22 and 23. Many complexes in this study were characterized by single-crystal X-ray diffraction.

Frustrated Lewis pair behavior of a neutral scandium complex.

An easily-accessible neutral scandium complex Sc[OC(CH3)2CH2PPh2][O-2,6-tBu2-C6H3]2[THF] behaves as a reactive Sc/P frustrated Lewis pair, which when added to organic and inorganic substrates e.g. carbonyl compounds, transition-metal chlorides, and diazoalkane compounds, yields unique and intriguing addition products such as a Sc/Rh heterobimetallic complex and a Sc phosphazine complex.