Project description:Suzuki cross-coupling reactions catalyzed by palladium are powerful tools for the synthesis of functional organic compounds. Excellent catalytic activity and stability require negatively charged Pd species and the avoidance of metal leaching or clustering in a heterogeneous system. Here we report a Pd-based electride material, Y3Pd2, in which active Pd atoms are incorporated in a lattice together with Y. As evidenced from detailed characterization and density functional theory (DFT) calculations, Y3Pd2 realizes negatively charged Pd species, a low work function and a high carrier density, which are expected to be beneficial for the efficient Suzuki coupling reaction of activated aryl halides with various coupling partners under mild conditions. The catalytic activity of Y3Pd2 is ten times higher than that of pure Pd and the activation energy is lower by nearly 35%. The Y3Pd2 intermetallic electride catalyst also exhibited extremely good catalytic stability during long-term coupling reactions.
Project description:A protocol for forming a highly active Pd(0) catalyst from Pd(OAc) 2, water, and biaryldialkylphosphine ligands has been developed. This protocol generates a catalyst system, which exhibits excellent reactivity and efficiency in the coupling of a variety of amides and anilines with aryl chlorides.
Project description:Solid-supported catalysts play efficient and crucial roles in organic synthesis. A solid-supported palladium(II) complex based on chitosan was synthesized and fully characterized using all possible tools (Fourier transform infrared spectroscopy, thermogravimetry analysis, differential scanning calorimetry, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller analysis). The catalytic activity of the solid-phase catalyst in Suzuki cross-coupling reactions was evaluated in aqueous solvents under both conventional heating and microwave irradiation conditions. The recyclability and thermal stability of the prepared catalyst were also examined, and the catalyst was found to be active till five consecutive runs without a notable loss of activity under the microwave condition, with the turnover number and turnover frequency values reaching 19,019 and 114,114 h-1, respectively.
Project description:In this work, we applied commercially available 2-pyridinecarboxylic acid to modify cellulose by simple manipulations, and then anchored low-toxicity metal nickel onto the modified cellulose to prepare the heterogeneous catalyst (CL-AcPy-Ni). The obtained catalyst was characterized by FT-IR, TG-DSC, BET, XRD, SEM-EDS, ICP-OES, XPS, and GPC. The catalytic performance of CL-AcPy-Ni in the Suzuki cross-coupling reaction was investigated using 4-methyl iodobenzene and phenylboronic acid as the model substrates reacting in THF under 120 °C for 24 h. The catalytic ability of CL-AcPy-Ni for various halobenzenes and phenylboronic acid derivatives was also further investigated under optimal conditions and demonstrated good catalytic activity, and a series of diaryls were successfully synthesized. Finally, this green nickel-based catalyst could be reused for five successive cycles by simple centrifugation.
Project description:Developing non-noble catalysts with superior activity and durability for oxygen evolution reaction (OER) in acidic media is paramount for hydrogen production from water. Still, challenges remain due to the inadequate activity and stability of the OER catalyst. Here, we report a cost-effective and stable manganese oxybromide (Mn7.5O10Br3) catalyst exhibiting an excellent OER activity in acidic electrolytes, with an overpotential of as low as 295 ± 5 mV at a current density of 10 mA cm-2. Mn7.5O10Br3 maintains good stability under operating conditions for at least 500 h. In situ Raman spectroscopy, X ray absorption near edge spectroscopy, and density functional theory calculations confirm that a self-oxidized surface with enhanced electronic transmission capacity forms on Mn7.5O10Br3 and is responsible for both the high catalytic activity and long-term stability during catalysis. The development of Mn7.5O10Br3 as an OER catalyst provides crucial insights into the design of non-noble metal electrocatalysts for water oxidation.
Project description:Electron poor benzimidazole substrates were arylated via an intramolecular cross-dehydrogenative coupling (CDC) reaction. These CDC reactions were catalyzed by a Pd(II)/Cu(I) catalyst system, capable of producing moderate yields on a large library of substrates. The substrate scope consisted of tethered arene-benzimidazoles that upon coupling, produced a fused polycyclic motif.
Project description:Electroreductive cross-electrophile coupling (eXEC) represents an attractive approach for the direct C-C coupling of two electrophiles but generally suffers from limited scope compared to reactions with chemical reductants. This work demonstrates that mediator-assisted electrocatalysis is a general strategy for the enhancement of eXEC reactions. While eXEC reactions catalyzed by a variety of widely available ligand-nickel complexes are low yielding when applied to reductive couplings of challenging substrates, reactions with the same complexes generate products in near-quantitative yield when a redox-matched mediator is included. We identify a library of catalyst-mediator systems that provide complementary reactivity and enable coupling of a range of substrate classes in high yields. These catalyst systems are applicable to both chemical and electrochemical reduction, but some require electroreduction due to the low potentials required for activation. Finally, mechanistic studies offer insights that facilitate catalyst-mediator pairing.
Project description:Following a rational design, three novel palladium(ii) complexes bearing galactopyranoside-based N-heterocyclic carbene ligands have been synthesized via transmetalation of the corresponding Ag(i) complexes. Palladium(ii) complexes have been characterized by NMR, FT-IR and elemental analysis. Catalytic studies, using the Stille and Suzuki-Miyaura cross-coupling reactions as model C-C coupling, reveal that the complexes are active and reusable. The best results in terms of TON values were achieved in aqueous medium using either the in situ deacetylation of the catalyst or the previously deacetylated catalyst. The catalytic condition using in situ deacetylation was more efficient because it avoids an additional deprotection step.
Project description:Herein we report a general synthesis of 1,3-diarylsubstituted indazoles utilizing a two-step Suzuki cross-coupling/deprotection/N-arylation sequence. This procedure proceeds in excellent overall yield starting from the 3-iodo-N-Boc indazole derivative allowing for rapid access to these compounds.
Project description:The combination of aryl bromides, allylbenzene, base and a palladium catalyst usually results in a Heck reaction. Herein we combine these same reagents, but override the Heck pathway by employing a strong base. In the presence of LiN(SiMe3)2, allylbenzene derivatives undergo reversible deprotonation. Transmetalation of the resulting allyllithium intermediate to LPdAr(Br) and reductive elimination provide the 1,1-diarylprop-2-enes, which are not accessible by the Heck reaction. The regioselectivity in this deprotonative cross-coupling process is catalyst-controlled and very high.