Bimetallic Nanoshells as Platforms for Metallo- and Biometallo-Catalytic Applications

Expanding the Synthetic Toolbox through Metal-Enzyme Cascade Reactions

The combination of metal-, photo-, enzyme-, and/or organocatalysis provides multiple synthetic solutions, especially when the creation of chiral centers is involved. Historically, enzymes and transition metal species have been exploited simultaneously through dynamic kinetic resolutions of racemates. However, more recently, linear cascades have appeared as elegant solutions for the preparation of valuable organic molecules combining multiple bioprocesses and metal-catalyzed transformations. Many advantages are derived from this symbiosis, although there are still bottlenecks to be addressed including the successful coexistence of both catalyst types, the need for compatible reaction media and mild conditions, or the minimization of cross-reactivities. Therefore, solutions are here also provided by means of catalyst coimmobilization, compartmentalization strategies, flow chemistry, etc. A comprehensive review is presented focusing on the period 2015 to early 2022, which has been divided into two main sections that comprise first the use of metals and enzymes as independent catalysts but working in an orchestral or sequential manner, and later their application as bionanohybrid materials through their coimmobilization in adequate supports. Each part has been classified into different subheadings, the first part based on the reaction catalyzed by the metal catalyst, while the development of nonasymmetric or stereoselective processes was considered for the bionanohybrid section.

Copper-Containing Polyoxometalate-Based Metal-Organic Framework as a Catalyst for the Oxidation of Silanes: Effective Cooperative Catalysis by Metal Sites and POM Precursor

The oxidation of silanes into silanols is a very necessary transformation, and yet the rational fabrication of efficient catalysts for this reaction remains a challenging task. Here, a 3D polyoxometalate-based metal-organic framework (POMOF), [Cu^Ι₃(pz)₃{PMo₁₂O₄₀}]·H₂O (HENU-8, HENU = Henan University; pz = pyrazine) was consciously prepared and first employed in the oxidation of dimethylphenylsilane with tert-butyl hydroperoxide (TBHP) as an oxidant, achieving 89% yield at a production rate of 132 mmol·g^-1·h^-1. Control experiments indicated that polyoxometalates and Cu atoms together affected the ultimate outcome in this catalytic system, and the designed catalyst followed a free radical mechanism.

Mechanochemical Strategies for the Preparation of SiO2-Supported AgAu Nanoalloy Catalysts

Silver-gold nanoalloys were prepared from their metal salts precursors through bottom-up mechanochemical synthesis, using one-pot or galvanic replacement reaction strategies. The nanostructures were prepared over amorphous SiO₂ as an inert supporting material, facilitating their stabilization without the use of any stabilizing agent. The nanomaterials were extensively characterized, confirming the formation of the bimetallic nanostructures. The nanoalloys were tested as catalysts in the hydrogenation of 2-nitroaniline and exhibited up to 4-fold the rate constant and up to 37% increased conversion compared to the respective single metal nanoparticles. Our approach is advantageous to produce nanoparticles with clean surfaces with available catalytic sites, directly in the solid-state and in an environmentally friendly manner.

Selective and leaching-resistant palladium catalyst on a porous polymer support for phenol hydrogenation

Selective hydrogenation of phenol is promising for the utilization of renewable lignocellulose and production of cyclohexanone that usually relies on petroleum, but it is challenging to simultaneously achieve high activity and selectivity. Herein, we report an amino-functionalized nanoporous polymer stabilized palladium nanoparticle catalyst, which is prepared via a one-pot co-polymerization method, as highly active and selective catalysts for the phenol hydrogenation, giving cyclohexanone selectivity over 99.5% with full conversion of phenol under mild reaction conditions without any soluble additives. Importantly, the palladium leaching was efficiently hindered, maintaining the catalytic performances in continuously recycle tests. In contrast, the commercial palladium catalysts exhibit much lower selectivity and obvious deactivation because of the palladium leaching.

Green synthesis of Au decorated CoFe2O4 nanoparticles for catalytic reduction of 4-nitrophenol and dimethylphenylsilane oxidation

We present a cleaner chemical synthesis process of a magnetic recoverable Au/CoFe₂O₄ hybrid nanocomposite catalyst that has remarkable activity in catalytic reduction and oxidation, improved by surface plasmon resonance.

Directed evolution of cytochrome c for carbon-silicon bond formation: Bringing silicon to life

Enzymes that catalyze carbon-silicon bond formation are unknown in nature, despite the natural abundance of both elements. Such enzymes would expand the catalytic repertoire of biology, enabling living systems to access chemical space previously only open to synthetic chemistry. We have discovered that heme proteins catalyze the formation of organosilicon compounds under physiological conditions via carbene insertion into silicon-hydrogen bonds. The reaction proceeds both in vitro and in vivo, accommodating a broad range of substrates with high chemo- and enantioselectivity. Using directed evolution, we enhanced the catalytic function of cytochrome c from Rhodothermus marinus to achieve more than 15-fold higher turnover than state-of-the-art synthetic catalysts. This carbon-silicon bond-forming biocatalyst offers an environmentally friendly and highly efficient route to producing enantiopure organosilicon molecules.

Detoxification of organophosphates using imidazole-coated Ag, Au and AgAu nanoparticles

Organophosphate (OP) detoxification is a worldwide problem due to the high stability of P–O bonds.

Morphology evolution of Ag/Au nanocomposites via temperature-controlled galvanic exchange to enhance catalytic activity

Morphology-controlled Ag/Au nanocomposites have been fabricated facilely via a modified galvanic replacement reaction using Ag nanocubes as sacrificial templates.