92 research outputs found
Phosphine Ligand-Free Bimetallic Ni(0)Pd(0) Nanoparticles as a Catalyst for Facile, General, Sustainable, and Highly Selective 1,4-Reductions in Aqueous Micelles
No full textBy harnessing the synergy between Ni(0), Pd(0), and aqueous micelle of proline-derived PS-750-M amphiphile,
phosphine ligand-free ultrasmall nanoparticles (NPs) of Ni(0)-Pd(0) are developed for highly selective 1,4-reductions of
enones. In NP, Ni(0)-bound Pd(0) atom found to only react with most electron-deficient double bond due to electron-rich
character of Pd and fine-tuning of its d-band. Most notably, NPs contain a minimal amount of Pd (Ni:Pd = 25:1) and are highly selective without affecting the different types of N-and O-benzyl, aldehyde, nitrile, and nitro functional groups. The catalytic selectivity is investigated on a broad range of substrates, including the gram scale reaction. Control experiment reveals Ni, Pd, and micelle of PS-750-M are required for higher selectivity. The metal-micelle binding was supported by a surface-enhanced Raman spectroscopy study of NPs and their components. Optical imaging, high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX) analyses were performed to reveal the formation of NPcontaining micelle or vesicles, NPs morphology, particle size distribution, and chemical composition, while X-ray photoelectron spectroscopy (XPS) measurements unveiled the oxidation state of each metal in bimetallic NP
EvanPhos. A New Ligand for ppm Level Pd-Catalyzed Suzuki-Miyaura Couplings in Either Organic Solvent or Water
No full textIn only two chemical steps, a new biaryl platform can be constructed that complexes Pd(OAc)2 forming a precursor to a very active catalyst useful for Suzuki-Miyaura cross-couplings. By a combination of catalyst pre-activation, used together with the uncommon solvent EtOAc, this catalyst system is effective at loadings in the ppm (0.1-0.5 mol %) range with highly functionalized reaction partners. Similar reactions run in water containing nanomicelles are as fast or faster. The
stability of this new ligand, EvanPhos, as its derived Pd catalyst, is also shown to have considerable stability at r
N2Phos. An easily made, highly effective ligand designed for ppm level Pd-catalyzed Suzuki-Miyaura cross couplings in water
No full textA new biaryl phosphine-containing ligand from an active palladium catalyst for ppm level Suzuki-Miyaura couplings, enabled by an aqueous micellar reaction medium. A wide array of functionalized substrates including aryl/hetroaryl bromides is amenable, as are, notably, chlorides. The catalytic system is both general and highly effective at low palladium loadings (1000-2500 ppm or 0.10-0.25 mol %). Density funtional theory calculations suggest that greater steric congestion in N2Phos induces increased steric crowding around the Pd center, preventing formation of a 2:1 ligand-Pd complex found with EvanPhos (and less bulky ligands) that could slow oxidative addition to aryl chlorides
A sustainable 1-pot, 3-step synthesis of boscalid using ppm level Pd catalysis in water
No full textBoscalid is an active ingredient in fungicides marketed by BASF. The approach
used currently for its production is unsustainable. Herein is disclosed a 3-step route using only
water as the reaction medium, and a very low loading (700 ppm or 0.07 mol %) of costly and
endangered Pd. Furthermore, the overall, isolated yield is 83%
First Pd-catalyzed C(sp2)–H / C(sp2)–H coupling of Limonene
No full textLimonene undergoes a regioselective Pd(II)-catalyzed C(sp2)–H / C(sp2)–H coupling with acrylic acid esters and amides, ,β-unsaturated ketones, styrenes and allyl acetate, affording novel 1,3-dienes. DFT computations gave results in accord with the experimental results and allowed to formulate a plausible mechanism. The post-functionalization of one of the coupled products was achieved via a large scale Sonogashira reaction conducted under micellar catalysis
Mild and Robust Stille Reactions in Water using Parts Per Million Levels of a Triphenylphosphine‐Based Palladacycle
No full textAn inexpensive and new triphenylphosphine‐based palladacycle has been developed as a pre‐catalyst leading to highly effective Stille cross coupling reactions in water under mild conditions. Only 500‐1000 ppm of Pd suffices for couplings involving a variety of aryl/heteroaryl halides with aryl/hetaryl stannanes. Several drug intermediates can be prepared using this catalyst in aqueous nanoreactors formed by 2 wt % Brij‐30 in water
First Pd-catalyzed C(sp2)–H / C(sp2)–H coupling of Limonene
No full textLimonene undergoes a regioselective Pd(II)-catalyzed C(sp2)–H / C(sp2)–H coupling with acrylic acid esters and amides, alpha,beta-unsaturated ketones, styrenes and allyl acetate, affording novel 1,3-dienes. DFT computations gave results in accord with the experimental results and allowed to formulate a plausible mechanism. The post-functionalization of one of the coupled products was achieved via a large-scale Sonogashira reaction conducted under micellar catalysis
Continuous Flow Suzuki-Miyaura Couplings Under Aqueous Micellar Conditions in a CSTR Cascade Catalyzed by Fe/ppm Pd Nanoparticles
No full textChemistry in water, enabled by tailor-made surfactants that form nanomicelles of a particular size and shape, has been developed to accommodate flow conditions using Fe/ppm Pd nanoparticles as catalyst for Suzuki-Miyaura reactions. Cross-couplings of this type that are heterogeneous in terms of both the substrate and catalyst are particularly troublesome under flow conditions, and pose a major challenge in continuous manufacturing of pharmaceuticals and fine chemicals. To address this major issue, a new continuous stirred-tank reactor (CSTR) cascade has been engineered that can handle slurries/solids at any point during a chemical transformation in flow. Solid starting materials are now simply suspended in water and pumped into the CSTR as a heterogeneous slurry, minimizing the upstream need for organic solvents, thereby leading to a far more environmentally friendly process. The ability of CSTR cascade to handle solids continuously was demonstrated over hours, without clogging, by examining several couplings which involve both initial solid catalyst and substrates, while generating solids products, some of which are key intermediates in pharmaceuticals currently in use
Transition Metal Synergy in Fe Nanoparticles Doped with ppm Levels of (Pd + Ni). A New Catalyst for Nitro Group Reductions under Environmentally Responsible Conditions
No full textA remarkable synergistic effect has been uncovered between ppm levels of Pd and Ni embedded within iron nanoparticles that leads to mild and selective catalytic reductions of nitro-containing aromatics and heteroaromatics in water at room temperature. NaBH4 serves as the source of hydride. Broad substrate scope is documented, along with several other features, including low catalyst loading, low residual metal in the products, and recycling of the catalyst and reaction medium, highlight the green nature of this new technology
The impact of earth-abundant metals as a replacement for Pd in cross coupling reactions
No full textSubstitution of one metal catalyst for another is not straightforward as simply justifying this change based on the availability and/or cost of the metals. A life cycle-like assessment was performed leading to the conclusion that the commonly held view that use of earth-abundant metals (and in this case study, Ni) are replacements for palladium most notably in cross coupling reactions, and Suzuki-Miyaura couplings, in particular, is an incomplete analysis of the entire picture. This notion can be misleading, and unfortunately derives nowadays mainly from the standpoint of cost, and to some degree, the relative natural abundance and mining impact of each metal. However, a more realistic appreciation emerges when several additional reaction parameters involved in the couplings are considered. Such an analysis unequivocally points to the major impact on climate change brought about by use of organic solvents, while the metals actually play subordinate roles in terms of CO2-release into the environment. Clearly, this study reveals that several factors contribute in various ways to the overall carbon footprint. Hence, a far more detailed analysis is required than that typically being utilized
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