Recombinant Peptide Fusion Protein‐Templated Palladium Nanoparticles for Suzuki‐Miyaura and Stille Coupling Reactions

Derivatization of 2,1,3-Benzothiadiazole via Regioselective C-H Functionalization and Aryne Reactivity

Despite growing interest in 2,1,3-benzothiadiazole (BTD) as an integral component of many functional molecules, methods for the functionalization of its benzenoid ring have remained limited, and many even simply decorated BTDs have required de novo synthesis. We show that regioselective Ir-catalyzed C-H borylation allows access to versatile 5-boryl or 4,6-diboryl BTD building blocks, which undergo functionalization at the C4, C5, C6, and C7 positions. The optimization and regioselectivity of C-H borylation are discussed. A broad reaction scope is presented, encompassing ipso substitution at the C-B bond, the first examples of ortho-directed C-H functionalization of BTD, ring closing reactions to generate fused ring systems, as well as the generation and capture reactions of novel BTD-based heteroarynes. The regioselectivity of the latter is discussed with reference to the Aryne Distortion Model.

Palladium Supported on Bioinspired Materials as Catalysts for C–C Coupling Reactions

In recent years, the immobilization of palladium nanoparticles on solid supports to prepare active and stable catalytic systems has been deeply investigated. Compared to inorganic materials, naturally occurring organic solids are inexpensive, available and abundant. Moreover, the surface of these solids is fully covered by chelating groups which can stabilize the metal nanoparticles. In the present review, we have focused our attention on natural biomaterials-supported metal catalysts applied to the formation of C–C bonds by Mizoroki–Heck, Suzuki–Miyaura and Sonogashira reactions. A systematic approach based on the nature of the organic matrix will be followed: (i) metal catalysts supported on cellulose; (ii) metal catalysts supported on starch; (iii) metal catalysts supported on pectin; (iv) metal catalysts supported on agarose; (v) metal catalysts supported on chitosan; (vi) metal catalysts supported on proteins and enzymes. We will emphasize the effective heterogeneity and recyclability of each catalyst, specifying which studies were carried out to evaluate these aspects.

Developing a rational approach to designing recombinant proteins for peptide-directed nanoparticle synthesis

The controlled formation of nanoparticles with optimum characteristics and functional aspects has proven successful via peptide-mediated nanoparticle synthesis. However, the effects of the peptide sequence and binding motif on surface features and physicochemical properties of nanoparticles are not well-understood. In this study, we investigate in a comparative manner how a specific peptide known as Pd4 and its two known variants may form nanoparticles both in an isolated state and when attached to a green fluorescent protein (GFPuv). More importantly, we introduce a novel computational approach to predict the trend of the size and activity of the peptide-directed nanoparticles by estimating the binding affinity of the peptide to a single ion. We used molecular dynamics (MD) simulations to explore the differential behavior of the isolated and GFP-fused peptides and their mutants. Our computed palladium (Pd) binding free energies match the typical nanoparticle sizes reported from transmission electron microscope pictures. Stille coupling and Suzuki-Miyaura reaction turnover frequencies (TOFs) also correspond with computationally predicted Pd binding affinities. The results show that while using Pd4 and its two known variants (A6 and A11) in isolation produces nanoparticles of varying sizes, fusing these peptides to the GFPuv protein produces nanoparticles of similar sizes and activity. In other words, GFPuv reduces the sensitivity of the nanoparticles to the peptide sequence. This study provides a computational framework for designing free and protein-attached peptides that helps in the synthesis of nanoparticles with well-regulated properties.

Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

This Review examines parts per million (ppm) palladium concentrations in catalytic cross-coupling reactions and their relationship with mole percentage (mol %). Most studies in catalytic cross-coupling chemistry have historically focused on the concentration ratio between (pre)catalyst and the limiting reagent (substrate), expressed as mol %. Several recent papers have outlined the use of “ppm level” palladium as an alternative means of describing catalytic cross-coupling reaction systems. This led us to delve deeper into the literature to assess whether “ppm level” palladium is a practically useful descriptor of catalyst quantities in palladium-catalyzed cross-coupling reactions. Indeed, we conjectured that many reactions could, unknowingly, have employed low “ppm levels” of palladium (pre)catalyst, and generally, what would the spread of ppm palladium look like across a selection of studies reported across the vast array of the cross-coupling chemistry literature. In a few selected examples, we have examined other metal catalyst systems for comparison with palladium.

Green Synthesis of Pd Nanoparticles for Sustainable and Environmentally Benign Processes

Among transition metal nanoparticles, palladium nanoparticles (PdNPs) are recognized for their high catalytic activity in a wide range of organic transformations that are of academic and industrial importance. The increased interest in environmental issues has led to the development of various green approaches for the preparation of efficient, low-cost and environmentally sustainable Pd-nanocatalysts. Environmentally friendly solvents, non-toxic reducing reagents, biodegradable capping and stabilizing agents and energy-efficient synthetic methods are the main aspects that have been taken into account for the production of Pd nanoparticles in a green approach. This review provides an overview of the fundamental approaches used for the green synthesis of PdNPs and their catalytic application in sustainable processes as cross-coupling reactions and reductions with particular attention afforded to the recovery and reuse of the palladium nanocatalyst, from 2015 to the present.

Recoverable Palladium-Catalyzed Carbon-Carbon Bond Forming Reactions under Thermomorphic Mode: Stille and Suzuki-Miyaura Reactions

The reaction of [PdCl₂(CH₃CN)₂] and bis-4,4′-(R_fCH₂OCH₂)-2,2′-bpy (1a–d), where R_f = n-C₁₁F₂₃ (a), n-C₁₀F₂₁ (b), n-C₉F₁₉ (c) and n-C₈F₁₇ (d), respectively, in the presence of dichloromethane (CH₂Cl₂) resulted in the synthesis of Pd complex, [PdCl₂[4,4′-bis-(R_fCH₂OCH₂)-2,2′-bpy] (2a–d). The Pd-catalyzed Stille arylations of vinyl tributyltin with aryl halides were selected to demonstrate the feasibility of recycling usage with 2a as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent at 120–150 °C. Additionally, recycling and electronic effect studies of 2a–c were also carried out for Suzuki-Miyaura reaction of phenylboronic acid derivatives, 4-X-C₆H₄-B(OH)₂, (X = H or Ph) with aryl halide, 4-Y-C₆H₄-Z, (Y = CN, H or OCH₃; Z = I or Br) in dimethylformamide (DMF) at 135–150 °C. At the end of each cycle, the product mixtures were cooled to lower temperature (e.g., −10 °C), and then catalysts were recovered by decantation with Pd leaching less than 1%. The products were quantified by gas chromatography/mass spectrometry (GC/MS) analysis or by the isolated yield. The complex 2a-catalyzed Stille reaction of aryl iodides with vinyl tributyltin have good recycling results for a total of 8 times, with a high yield within short period of time (1–3 h). Similarly, 2a–c-catalyzed Suzuki-Miyaura reactions also have good recycling results. The electronic effect studies from substituents in both Stille and Suzuki-Miyaura coupling reactions showed that electron withdrawing groups speed up the reaction rate. To our knowledge, this is the first example of recoverable fluorous long-chained Pd-catalyzed Stille reactions under the thermomorphic mode.

Peptide-directed Pd-decorated Au and PdAu nanocatalysts for degradation of nitrite in water

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency. Pd-on-Au NPs with 20% to 300% surface coverage (sc%) of Au showed catalytic activity commensurate with sc%. Additionally, the catalytic activity of Pd_xAu_100−x alloy NPs varied based on palladium composition (x = 6–59). The maximum nitrite removal efficiency of Pd-on-Au and Pd_xAu_100−x alloy NPs was obtained at sc 100% and x = 59, respectively. The synthesized peptide-directed Pd-on-Au catalysts showed an increase in nitrite reduction three and a half times better than monometallic Pd and two and a half times better than Pd_xAu_100−x NPs under comparable conditions. Furthermore, peptide-directed NPs showed high activity after five reuse cycles. Pd-on-Au NPs with more available activated palladium atoms showed high selectivity (98%) toward nitrogen gas production over ammonia.

In this work, a palladium binding peptide, Pd4, has been used for the synthesis of catalytically active palladium-decorated gold (Pd-on-Au) nanoparticles (NPs) and palladium–gold (Pd_xAu_100−x) alloy NPs exhibiting high nitrite degradation efficiency.