Moderate Activity from Trace Palladium Alloyed with Copper for the Chemoselective Hydrogenation of –CN and –NO 2 with HCOOH

Porous Organic Polymers with Thiourea Linkages (POP-TUs): Effective and Recyclable Organocatalysts for the Michael Reaction

As novel porous organic polymers with thiourea linkages, POP-TUs were successfully synthesized with tris(4-aminophenyl) amine (TAA) and 1,4-phenylene diisothiocyanate (PDT) under different conditions. The as-synthesized POP-TUs possess distinctly different morphological characteristics and can effectively catalyze the Michael reaction of trans-β-nitrostyrenes to diethyl malonate. Particularly, the POP-TU-2-catalyzed Michael reaction can proceed smoothly even using an ultralow catalyst dosage of 0.03 mol %, whose turnover number (TON) and turnover frequency (TOF) can reach up to 2700 and 25 h^-1, respectively. Besides, POP-TU-2 also exhibits excellent recyclability and reusability. Only 2% decline in the isolated yield was found after five consecutive runs. This work shows a significant improvement over previously reported thiourea-based catalysts and can offer an effective strategy for developing highly efficient heterogeneous organocatalysts.

Heterogeneous Catalytic Hydrogenation of 3-Phenylpropionitrile over Palladium on Carbon

A previously developed and industrially feasible process for selective, Pd-mediated, liquid-phase heterogeneous catalytic hydrogenation of nitriles to primary amines was extended to the reduction of 3-phenylpropionitrile (PPN) to 3-phenylpropylamine (PPA). PPN, which belongs to the homologous series of benzonitrile (BN) and benzyl cyanide (BC), was hydrogenated under mild reaction conditions (30-80 °C, 6 bar), over Pd/C, in two immiscible solvents (dichloromethane/water) and using acidic additives (NaH₂PO₄ and H₂SO₄). Although relatively high conversion (76%) was achieved, the selectivity to PPA (26%) and its isolated yield (20%) were lesser than those in the case of the hydrogenation of BN or BC reported earlier. However, the purity of PPA was >99% without using any purification method. Quantum chemical calculations using a density functional theory (DFT) method were performed to compare the adsorption interactions of the different imine intermediates on palladium, as well as to clarify the differences observed in the primary amine selectivity. PPA is a valuable intermediate for the synthesis of carboxypeptidase B enzyme inhibitors, antimuscarinic drugs, or potential anticancer agents in the pharmaceutical industry.

Mild and selective hydrogenation of nitriles into primary amines over a supported Ni catalyst

The mesoporous Al₂O₃ supported Ni catalyst demonstrated a high activity and selectivity for the hydrogenation of nitriles into primary amines under the mild conditions (60–80 °C and 2.5 bar H₂) with ammonia as the additive.

Quasi Pd1Ni single-atom surface alloy catalyst enables hydrogenation of nitriles to secondary amines

Hydrogenation of nitriles represents as an atom-economic route to synthesize amines, crucial building blocks in fine chemicals. However, high redox potentials of nitriles render this approach to produce a mixture of amines, imines and low-value hydrogenolysis byproducts in general. Here we show that quasi atomic-dispersion of Pd within the outermost layer of Ni nanoparticles to form a Pd1Ni single-atom surface alloy structure maximizes the Pd utilization and breaks the strong metal-selectivity relations in benzonitrile hydrogenation, by prompting the yield of dibenzylamine drastically from ∼5 to 97% under mild conditions (80 °C; 0.6 MPa), and boosting an activity to about eight and four times higher than Pd and Pt standard catalysts, respectively. More importantly, the undesired carcinogenic toluene by-product is completely prohibited, rendering its practical applications, especially in pharmaceutical industry. Such strategy can be extended to a broad scope of nitriles with high yields of secondary amines under mild conditions.