Xingchao Dai

Methylation of amines, nitrobenzenes and aromatic nitriles with carbon dioxide and molecular hydrogen

CO2/H2 was successfully employed in alkylation reactions by performing CO2 reduction and amine N-methylation in one-pot. In the presence of a simple CuAlOx catalyst, N-methyl or N,N-dimethyl amines with different structures can be selectively synthesized with up to 96% yields by applying amine, nitrobenzene and nitrile as starting materials.

Development of a General Non‐Noble Metal Catalyst for the Benign Amination of Alcohols with Amines and Ammonia

The N-alkylation of amines or ammonia with alcohols is a valuable route for the synthesis of N-alkyl amines. However, as a potentially clean and economic choice for N-alkyl amine synthesis, non-noble metal catalysts with high activity and good selectivity are rarely reported. Normally, they are severely limited due to low activity and poor generality. Herein, a simple NiCuFeOx catalyst was designed and prepared for the N-alkylation of ammonia or amines with alcohol or primary amines. N-alkyl amines with various structures were successfully synthesized in moderate to excellent yields in the absence of organic ligands and bases. Typically, primary amines could be efficiently transformed into secondary amines and N-heterocyclic compounds, and secondary amines could be N-alkylated to synthesize tertiary amines. Note that primary and secondary amines could be produced through a one-pot reaction of ammonia and alcohols. In addition to excellent catalytic performance, the catalyst itself possesses outstanding superiority, that is, it is air and moisture stable. Moreover, the magnetic property of this catalyst makes it easily separable from the reaction mixture and it could be recovered and reused for several runs without obvious deactivation.

Carbon-catalysed reductive hydrogen atom transfer reactions

Generally, transition metal catalysts are essential for the reductive hydrogen atom transfer reaction, which is also known as the transfer hydrogenation reaction or the borrowing-hydrogen reaction. It has been reported that graphene can be an active catalyst in ethylene and nitrobenzene reductions, but no report has described carbon-based materials as catalysts for alcohol amination via the borrowing-hydrogen reaction mechanism. Here we show the results from the preparation, characterization and catalytic performance investigation of carbon catalysts in transition metal-free borrowing-hydrogen reactions using alcohol amination and nitro compound/ketone reduction as model reactions. XPS, XRD, SEM, FT-IR and N2 adsorption-desorption studies revealed that C=O group in the carbon catalysts may be a possible catalytically active site, and high surface area is important for gaining high activity. The activity of the carbon catalyst remained unchanged after reuse. This study provides an attractive and useful methodology for a wider range of applications.

Fermi surface dichotomy of the superconducting gap and pseudogap in underdoped pnictides

High-temperature superconductivity in iron-arsenic materials (pnictides) near an antiferromagnetic phase raises the possibility of spin-fluctuation-mediated pairing. However, the interplay between antiferromagnetic fluctuations and superconductivity remains unclear in the underdoped regime, which is closer to the antiferromagnetic phase. Here we report that the superconducting gap of underdoped pnictides scales linearly with the transition temperature, and that a distinct pseudogap coexisting with the superconducting gap develops on underdoping. This pseudogap occurs on Fermi surface sheets connected by the antiferromagnetic wavevector, where the superconducting pairing is stronger as well, suggesting that antiferromagnetic fluctuations drive both the pseudogap and superconductivity. Interestingly, we found that the pseudogap and the spectral lineshape vary with the Fermi surface quasi-nesting conditions in a fashion that shares similarities with the nodal-antinodal dichotomous behaviour observed in underdoped copper oxide superconductors.

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C–Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles.

A conjugated ketone as a catalyst in alcohol amination reactions under transition-metal and hetero-atom free conditions

Here, we show the results of a molecular-defined conjugated ketone catalyzed alcohol amination reaction. Under the optimized reaction conditions, the yields to the desired products reached 98%. The reaction mechanism and kinetic study supposed that carbonyl–hydroxyl groups are the catalytically active sites, and the transfer-hydrogenation reactions progress via the recycling of carbonyl and hydroxyl groups. The catalytic process shows promise as an efficient and economic route for alcohol amination reactions.

Cooperative transformation of nitroarenes and biomass-based alcohols catalyzed by CuNiAlOx

A simple CuNiAlOx catalyst was prepared for the cooperative transformation of nitrobenzene derivatives and biomass-based alcohols. Under the optimized reaction conditions, a range of nitrobenzene derivatives can be smoothly converted into the corresponding amines and glycerol was directly transformed into 1,3-dihydroxypropan-2-one.

Organic Ligand Free Carbonylation Reactions with Unsupported Bulk Pd as Catalyst

Herein, surprising results for bulk Pd-catalyzed carbonylation reactions are presented. Three types of carbonylation reactions can be realized efficiently under organic ligand-free conditions, namely, hydroaminocarbonylation of olefins, aminocarbonylation of aryl iodides and oxidative carbonylation of amines, which almost cover all the known mechanisms in carbonylation reactions. Notably, the bulk Pd catalyst system exhibited better catalytic activity than the classical homogeneous PdCl2/(2-OMePh)3P catalyst system. This study will create a momentous and new field of green carbonylation reactions.

Catalytic Synthesis of Formamides with Carbon Dioxide and Amines

Carbon dioxide is a green C1 resource that can be efficiently recycled by catalytic transformation into value-added chemicals. Formamides are important intermediates and solvents that are used extensively in pharmaceutical, daily-chemical, and petrochemical industry. Therefore, it is worthwhile to synthesize formamides with CO2 and amines. In this review, the main advancements in the synthesis of formamides by using CO2 as the C1 feedstock with noble metal catalysts (Ir, Pd, Pt, Ru, Rh, etc.), non-noble metal catalysts (Ni, Mo, Cu, Fe, Co, Zn, Al, etc.), organocatalysts, and catalyst-free systems have been summarized. In addition, the role of the reducing agents such as H2, silanes, and boranes involved in these transformations has also been reviewed. In addition, the reaction mechanisms with the different catalyst systems have been discussed.

Glycerol as a Building Block for Prochiral Aminoketone, N-Formamide, and N-Methyl Amine Synthesis

Prochiral aminoketones are key intermediates for the synthesis of optically active amino alcohols, and glycerol is one of the main biomass-based alcohols available in industry. In this work, glycerol was catalytically activated and purposefully converted with amines to generate highly valuable prochiral aminoketones, as well as N-formamides and N-methyl amines, over CuNiAlOx catalyst. The catalyst structure can be anticipated as nano-Ni species on or in CuAlOx via the formation of nano- Cu-Ni alloy particles. This concept may present a novel and valuable methodology for glycerol utilization.