Hangyu Liu

Copper-catalyzed N-formylation of amines with CO2 under ambient conditions

We carried out work on N-formylation of amines with CO2 and PhSiH3 to produce formamides catalyzed by a copper complex. It was found that the Cu(OAc)2–bis(diphenylphosphino)ethane (dppe) catalytic system was very efficient for these kind of reactions at room temperature and 1 atm CO2 with only 0.1 mol% catalyst loading.

Synthesis of formamides containing unsaturated groups by N-formylation of amines using CO2 with H2

Formamides have wide applications in the industry and have been synthesized using CO2 as a carbon source and H2 as a reducing agent. However, previous systems required a noble catalyst and high temperature to achieve high efficiency, and the substrate scope was mostly limited to saturated amines. The selective N-formylation of amines containing unsaturated groups using CO2 and H2 is challenging because the efficient catalysts for the N-formylation are usually very active for hydrogenation of the unsaturated groups. Herein, we achieved for the first time a selective and efficient N-formylation of amines containing unsaturated groups using CO2 and H2 with a Cu(OAc)2–4-dimethylaminopyridine (DMAP) catalytic system. The substrates were converted to the desired formamides, while the unsaturated groups, such as the carbonyl group, the CC bond, CN bond and the ester group remained. The main reason for the excellent selectivity of the Cu(OAc)2–DMAP catalytic system was that it was very active for the N-formylation reaction, but was not active for the hydrogenation of the unsaturated groups.

Efficient hydrogenolysis of 5-hydroxymethylfurfural to 2,5-dimethylfuran over a cobalt and copper bimetallic catalyst on N-graphene-modified Al2O3

2,5-Dimethylfuran (DMF) is an important candidate for liquid fuels and can be produced from biomass derived 5-hydroxymethylfurfural (HMF). Efficient transformation of HMF to DMF has not been achieved over a non-noble catalyst under milder conditions. Herein, we developed a copper and cobalt bimetallic nanoparticle catalyst supported on N-graphene-modified Al2O3 (CuCo®/NGr/α-Al2O3). It was found that CuCo®/NGr/α-Al2O3 could catalyze the conversion of HMF to DMF effectively and the yield of DMF could reach 99%. The catalyst was completely not active for the hydrogenation of the CC bond in furan and thus no 2,5-bis(hydroxymethyl)tetrahydrofuran (DHTHF) and 2,5-dimethyltetrahydrofuran (DMTHF) were detected.

Heterogeneous Cobalt-Catalyzed Direct N-Formylation of Isoquinolines with CO2 and H2

Isoquinolines (IQs) are an abundant feedstock, and N‐formyl‐1,2,3,4‐tetrahydroisoquinolines (FTHIQs) are valuable fine chemicals and key intermediates. Herein, we report for the first time the Co0/ZnCl2‐catalyzed direct N‐formylation of IQs by using CO2 with H2 to produce FTHIQs. It was discovered that the Co catalyst and ZnCl2 worked synergistically in catalyzing the N‐formylation reactions, and moderate to high yields of the desired products could be obtained, depending on the nature of the substrates. The Co0 catalyst could be reused at least five times without a notable decrease in activity. A possible reaction mechanism is proposed on the basis of control experiments.

N-vinyl pyrrolidone promoted aqueous-phase dehydrogenation of formic acid over PVP-stabilized Ru nanoclusters

In this work, we fabricated the poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium(0) nanoclusters by reduction of RuCl3 using different reducing agents, and studied their catalytic activity in hydrogen generation from the decomposition of formic acid. It was demonstrated that N-vinyl-2-pyrrolidone (NVP), which is a monomer of PVP, could promote the reaction by coordination with Ru nanoparticles. The Ru nanoparticles catalyst reduced by sodium borohydride (NaBH4) exhibited highest catalytic activity for the decomposition of formic acid into H2 and CO2. The turnover of numenber (TOF) value could reach 26113 h–1 at 80 °C. We believe that the effective catalysts have potential of application in hydrogen storage by formic acid.

Selective Utilization of the Methoxy Group in Lignin to Produce Acetic Acid

Selective transformation of lignin into a valuable chemical is of great importance and challenge owing to its complex structure. Herein, we propose a strategy for the transformation of methoxy group (-OCH3 ) which is abundant in lignin into pure highly valuable chemicals. As an example to apply this strategy, a route to produce acetic acid with high selectivity by conversion of methoxy group of lignin was developed. It was demonstrated that the methoxy group in lignin could react with CO and water to generate acetic acid over RhCl3 in the presence of a promoter. The conversions of methoxy group in the kraft lignin and organosolv lignin reached 87.5 % and 80.4 %, respectively, and no by-product was generated. This work opens the way to produce pure chemicals using lignin as the feedstock.

Selective hydration of asymmetric internal aryl alkynes without directing groups to α-aryl ketones over Cu-based catalyst

Hydration of internal aryl alkynes to provide aryl carbonyl compounds is a class of important reactions and has been widely investigated. However, the hydration of asymmetric internal aryl alkynes without directing groups usually gives an aryl ketone or a mixture of aryl ketone and α-aryl ketone. High regioselectivity to α-aryl ketone is a great challenge and has not been reported. Herein, we found that CuBr and p-fluoroaniline had an excellent synergistic effect in catalyzing the hydration of internal aryl alkynes without directing groups to α-aryl ketones with regioselectivity up to more than 90%, which is much greater than those reported. The reaction mechanism was proposed, and the reason for the high selectivity was clarified by a combination of density functional theory (DFT) calculation, condensed dual descriptor (CDD) study, and experimental results. It was demonstrated that the formations of α-aryl ketone and aryl ketone were promoted by different catalytic active species, CuBr and CuBr[p-fluoroaniline], respectively. CuBr enlarged the difference of electron population on the two triple-bond carbon atoms, resulting in α-aryl ketones as the main products.

A new route to synthesize aryl acetates from carbonylation of aryl methyl ethers

Aryl acetates were synthesized efficiently for the first time by the carbonylation of aryl methyl ethers. Ether bond activation is very interesting because the synthesis of many valuable compounds involves conversion of ethers. Moreover, C–O bond cleavage is also very important for the transformation of biomass, especially lignin, which abundantly contains ether bonds. Developing efficient methods to activate aromatic ether bonds has attracted much attention. However, this is a challenge because of the inertness of aryl ether bonds. We proposed a new route to activate aryl methyl ether bonds and synthesize aryl acetates by carbonylation of aryl methyl ethers. The reaction could proceed over RhCl3 in the presence of LiI and LiBF4, and moderate to high yields of aryl acetates could be obtained from transformation of various aryl methyl ethers with different substituents. It was found that LiBF4 could assist LiI to cleave aryl methyl ether bonds effectively. The reaction mechanism was proposed by a combination of experimental and theoretical studies.