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We have developed an efficient method to generate highly active nickel–palladium bimetallic nanoparticles supported on multi-walled carbon nanotubes (Ni–Pd/MWCNTs) by dry mixing of the nickel and palladium salts utilizing the mechanical energy of a ball-mill. These nanoparticles were successfully employed in Sonogashira cross-coupling reactions with a wide array of functionalized aryl halides and terminal alkynes under ligand and copper free conditions using a Monowave 50 heating reactor. Notably, the concentration of palladium can be lowered to a minimum amount of 0.81% and replaced by more abundant and less expensive nickel nanoparticles while effectively catalyzing the reaction. The remarkable reactivity of the Ni–Pd/MWCNTs catalyst toward Sonogashira cross-coupling reactions is attributed to the high degree of the dispersion of Ni–Pd nanoparticles with small particle size of 5–10 nm due to an efficient grinding method. The catalyst was easily removed from the reaction mixture by centrifugation and reused several times with minimal loss of catalytic activity. Furthermore, the concentration of catalyst in Sonogashira reactions can be reduced to a minimum amount of 0.01 mol% while still providing a high conversion of the Sonogashira product with a remarkable turnover number (TON) of 7200 and turnover frequency (TOF) of 21 600 h −1 . The catalyst was fully characterized by a variety of spectroscopic techniques including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).
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This content will become publicly available on July 5, 2026
Synthetic and Mechanistic Evaluation of Palladium(II) Bis(Arylazoformamide) Precatalysts in the Sonogashira Reaction
The palladium-catalyzed sp-sp2 C−C bond forming the Sonogashira reaction has been both extensively studied mechanistically and widely used in organic synthesis. Herein, we describe an investigation into how a palladium(II) complex with arylazoformamide (AAF) ligands mediates these transformations. When mixed, two AAFs coordinate in a κ1-fashion with an equivalent of PdCl2, creating complexes of the form PdCl2(AAF)2. Under typical and optimized copper(I)-cocatalyzed Sonogashira conditions, using phenylacetylene and iodobenzene as reagents, these complexes (precatalysts) reduce to Pd(0) and afford the coupled diphenylacetylene product in high yields (i.e., 99%). A substrate scope explored the substitution on both rings, yielding 18 examples with yields varying from 38 to 99%. Mechanistically, from DFT studies, a formal Pd(I) open-shell singlet complex is suggested, along with an explanation of the need for DBU when employing CuI in toluene. Further DFT exploration provides insight into the copper-free Sonogashira reaction when utilizing Pd(AAF)2 complexes.
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- PAR ID:
- 10615113
- Editor(s):
- Fey, Natalie; Chirik, Paul
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- Organometallics
- ISSN:
- 0276-7333
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Nickel-palladium bimetallic nanoparticles supported on multi-walled carbon nanotubes (Ni-Pd/MWCNTs) were prepared by dry mixing of the nickel and palladium salts using the mechanical energy of a ball-mill. These nanoparticles demonstrated remarkable catalytic activity in Sonogashira cross-coupling reactions with a wide range of functionalized aryl halides and terminal alkynes under ligand and copper free conditions using Monowave 50 heating reactor. The catalyst is air-stable and can be easily removed from the reaction mixture by centrifugation and reused several times with minimal loss of catalytic activity. Furthermore, the concentration of catalyst in Sonogashira reactions can be lowered to a minimum amount of 0.01 mol%while still providing a high conversion of the Sonogashira product with an excellent turnover number (TON) of 7200 and turnover frequency (TOF) of 21600 h. The Ni-Pd/MWCNTs nanoparticles were fully characterized by a variety of spectroscopic techniques including X-ray diffraction (XRD), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy (XPS). The remarkable reactivity of the Ni-Pd/MWCNTs catalyst toward Sonogashira cross-coupling reactions is attributed to the high degree of the dispersion of Ni-Pdnanoparticles with small particle size of 5-10 nm due to an efficient grinding method. This work provides a facile, solventless and inexpensive method for large-scale preparation of Ni-Pd/MWCNTs to accomplish often-challenging Sonogashira cross coupling reactions.more » « less
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