Ru/Pd Complex and Its Monometallic Fragments as Catalysts for Norbornene Polymerization via ROMP and Addition

The [Ru(PPh3)2Cl-piperidine(4-aminomethyl)] complex (mono-Ru) was synthesized from [Ru(PPh3)3Cl2] and 4-(aminomethyl)piperidine, whereas the [(PPh3)PdCl(Shiff-pip)] complex (mono-Pd) was obtained by reacting [Pd(PPh3)2Cl2] with its respective Schiff base ligand, both at a 1:1 molar ratio. The heterobimetallic [RuCl2(PPh3)2](μ-Schiff)Pd(PPh3)Cl] complex (Ru/Pd) was synthesized via a one-pot, three-component reaction of mono-Ru, [(Pd(PPh3)2Cl2] and salicylaldehyde. All complexes were fully characterized by FTIR, UV-Vis, and NMR spectroscopy, as well as elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, and computational studies. Ru/Pd was able to polymerize norbornene (NBE) by two different mechanisms: ROMP and vinyl polymerization. The Ru fragment was active for ROMP of NBE, reaching yields of 68 and 31% for mono-Ru and Ru/Pd, respectively, when the [NBE]/[Ru] = 3000 molar ratio and 5 μL EDA addition were employed at 50 °C. The poly(norbornene) (polyNBE) obtained presented an order of magnitude of 104 g mol−1 and Ð values between 1.48 and 1.79. For the vinyl polymerization of NBE, the Pd fragment was active using MAO as a cocatalyst, reaching a yield of 47.0% for Ru/Pd and quantitative yields for mono-Pd when [Al]/[Pd] = 2500 and [NBE]/[Pd] = 20,000 molar ratios were employed, both at 60 °C.

Tertiary arsine ligands for the Stille coupling reaction

The Stille coupling reaction is one of the most important coupling reactions. It is well known that the triphenylarsine ligand can accelerate the reaction rate of Stille coupling. However, other arsine ligands have never been investigated for the Stille coupling reaction so far. In this work, we prepared 13 kinds of C₃-symmetrical tertiary arsine ligands and discovered that tri(p-anisyl)arsine is the best ligand for the reaction of tributylvinyltin and p-iodoanisole. The reaction mechanism was studied by dispersion-corrected density functional theory calculations to demonstrate the energetic feasibility of the Stille coupling reactions mediated by tri(p-anisyl)arsine.

CO Activation Using Nitrogen-Doped Carbon Nanotubes for Reductive Carbonylation of Nitroaromatics to Benzimidazolinone and Phenyl Urea

Carbonylation of nitroaromatics with CO is extensively investigated with efficient but precious group 8-10 metal-based catalysts for the productions of both industrially and academically important chemicals such as isocyanates, formamides, carbamates, ureas and several types of heterocyclic compounds. Herein, we report that rationally designed nitrogen-doped carbon nanotubes (N-CNTs) exhibit catalytic activity toward CO activation for carbonylation of nitroaromatics to benzimidazolinones and ureas. Under the optimal conditions, N-CNT-promoted intramolecular carbonylation of 2-nitroaniline (1a) with CO leads to formation of 1,3-dihydro-2H-benzo[d]imidazol-2-one in 90% yield. Moreover, an intermolecular carbonylation of nitrobenzene and aniline with CO in the presence of the N-CNT gives 70% yield of N,N'-diphenylurea. The N-CNT is also applicable to various benzimidazolinones and phenyl ureas; moreover, it can be readily reused at least 9 times for the carbonylation. The theoretical investigation based on density functional theory calculations indicates that the graphitic N of the N-CNT plays a crucial step in the 1a reduction with CO. The correlation between the structural defect and catalytic performance of the N-CNT reveals an enhanced catalytic activity of the N-CNT with its increased structural defects. This research thus represents a major breakthrough in CO activation for nitroaromatic carbonylation with environmental-friendly, low-cost, and carbon-based catalysts as a potential alternative to expensive and scarce noble-metal-based catalysts.

Pd Nanoparticles and Mixture of CO2/CO/O2 Applied in the Carbonylation of Aniline

CO2 is a compound of high stability which proves useful in some organic syntheses as a solvent or component decreasing explosivity of gases. It is also a good carbonylating agent for aliphatic amines although not for aromatic ones, the latter being carbonylated with phosgene or, as in our previous works, with CO/O2 in the presence of Pd(II) complexes. In this work we have used the mixture of CO/O2 and CO2 for carbonylation of aniline to N,N’-diphenylurea. After optimization of the reaction conditions (56% of CO2 in CO2/CO mixture) we studied the activity of three kinds of pre-catalysts: (a) Pd(II) complexes, (b) Pdblack, and (c) palladium nanoparticles (PdNPs) in the presence of derivatives of pyridine (XnPy). The highest conversion of aniline (with selectivity towards N,N-diphenylurea ca. 90%) was observed for PdNPs. The results show that catalytic cycle involves Pd(0) stabilized by pyridine ligand as active species. Basing on this observation, we put the hypothesis that application of PdNPs instead of Pd(II) complex can efficiently reduce the reaction time.