Recent Advances of Pd/C-Catalyzed Reactions

Sustainable carbonaceous nanomaterial supported palladium as an efficient ligand-free heterogeneouscatalyst for Suzuki-Miyaura coupling

A novel ligand-free heterogeneous catalyst was synthesized via pyrolysis of Samanea saman pods to produce carbon nanospheres (SS-CNSs), which served as a carbon support for immobilizing palladium nanoparticles through an in situ reduction technique (Pd/SS-CNS). The SS-CNSs effectively integrated 3% of Pd on their surfaces with no additional activation procedures needed. The nanomaterials obtained underwent thorough characterization employing various techniques such as FT-IR, XRD, FE-SEM, TEM, EDS, ICP-AES, and BET. Subsequently, the efficiency of this Pd/SS-CNS catalyst was assessed for the synthesis of biaryl derivatives via Suzuki coupling, wherein different boronic acids were coupled with various aryl halides using an environmentally benign solvent mixture of EtOH/H2O and employing only 0.1 mol% of Pd/SS-CNS. The catalytic system was conveniently recovered through centrifugation and demonstrated reusability without any noticeable decline in catalytic activity. This approach offers economic viability, ecological compatibility, scalability, and has the potential to serve as an alternative to homogeneous catalysis.

Regioselective Partial Hydrogenation and Deuteration of Tetracyclic (Hetero)aromatic Systems Using a Simple Heterogeneous Catalyst

The introduction of added '3-dimensionality' through late-stage functionalisation of extended (hetero)aromatic systems is a powerful synthetic approach. The abundance of starting materials and cross-coupling methodologies to access the precursors allows for highly diverse products. Subsequent selective partial reduction can alter the core structure in a manner of interest to medicinal chemists. Herein, we describe the precise, partial reduction of multicyclic heteroaromatic systems using a simple heterogeneous catalyst. The approach can be extended to introduce deuterium (again at late-stage). Excellent yields can be obtained using simple reaction conditions.

Pd/C Catalyzed Dehalogenation of (Hetero)aryls Using Triethyl­silane as Hydrogen Donor

(Hetero)aryl dehalogenation is a classical transformation usually performed using hydrogen gas and a metal supported on carbon, notably palladium (Pd/C). Though efficient, the need for a milder and operationally simple dehalogenation can arise. We found that the combination of Pd/C as catalyst and triethylsilane (TES) as hydrogen donor in THF resulted in a broadly applicable, easy to set up, and scalable debromination and deiodination. Optimization of the reaction showed that 1 mol% of Pd/C and 4 equiv of TES at room temperature were sufficient to obtain full conversion of most synthons of pharmaceutical interest in 4–24 h. The newly found conditions were applied to a large range of aromatic and heteroaromatic substrates, affording the desired targets in good to excellent yields with an exceptional functional group tolerance.

Automated Recognition of Nanoparticles in Electron Microscopy Images of Nanoscale Palladium Catalysts

Automated computational analysis of nanoparticles is the key approach urgently required to achieve further progress in catalysis, the development of new nanoscale materials, and applications. Analysis of nanoscale objects on the surface relies heavily on scanning electron microscopy (SEM) as the experimental analytic method, allowing direct observation of nanoscale structures and morphology. One of the important examples of such objects is palladium on carbon catalysts, allowing access to various chemical reactions in laboratories and industry. SEM images of Pd/C catalysts show a large number of nanoparticles that are usually analyzed manually. Manual analysis of a statistically significant number of nanoparticles is a tedious and highly time-consuming task that is impossible to perform in a reasonable amount of time for practically needed large amounts of samples. This work provides a comprehensive comparison of various computer vision methods for the detection of metal nanoparticles. In addition, multiple new types of data representations were developed, and their applicability in practice was assessed.

A Novel Utilization of Water Extract of Suaeda Salsa in the Pd/C Catalyzed Suzuki-Miyaura Coupling Reaction

Using biomass-derived solvents in various organic reactions is challenging for the fine chemicals industry. We herein report a Pd/C catalyzed Suzuki-Miyaura reaction in water extract of suaeda salsa (WES) without using external phosphine ligand, base, and organic solvent. The cross-coupling reactions were carried out in a basic WES medium with a broad substrate scope and wide functional group tolerance. Furthermore, the high purity of solid biaryl products can be obtained by column chromatography or filtration.

Homogeneous and Heterogeneous Pd-Catalyzed Selective C-P Activation and Transfer Hydrogenation for "Group-Substitution" Synthesis of Trivalent Phosphines

A "group-substitution" synthesis of trivalent phosphines via a C-P activation of phosphonium salts is reported. The alkyl groups were introduced by alkylation of phosphines to form phosphonium salts. The "de-arylation" of phosphonium salts was achieved by C-P activation and transfer hydrogenation with homogeneous or heterogeneous Pd (0) catalysts. With this method, a series of trivalent phosphines were prepared from commercially available triarylphosphines. A chiral monophosphine ligand could be prepared from BINAP in a "de-phosphination" process.

Transfer hydrogenation of nitroarenes using cellulose filter paper-supported Pd/C by filtration as well as sealed methods

A reductive filter paper for selective nitro reduction has been prepared by modification of a pristine cellulose filter paper by Pd/C nanoparticles, as a portable catalyst. The reaction was performed in two different set-ups including (i) filtration and (ii) sealed systems, in the presence of ammonium formate and ex situ generated hydrogen gas reducing agents, respectively. In the sealed system in the presence of H₂ gas, the halogenated nitroarenes were completely reduced, while in the filtration system, different derivatives of the nitroarenes were selectively reduced to aryl amines. In both systems, the reduction of nitroarenes to aryl amines was performed with high efficiency and selectivity, comparable to a heterogeneous system. Reaction parameters were comprehensively designed using Design Expert software and then studied. The properties of the catalytic filter paper were studied in detail from the points of view of swellability, shrinkage, reusability, and stability against acidic, alkaline, and oxidative reagents.

A novel and efficient catalytic filtration has been developed for the selective reduction of nitro compounds on a Pd/C-doped cellulose filter paper.