The amination of aryl halides with palladium catalysts (Buchwald‐Hartwig amination) is a widely used transformation in synthetic and drug discovery chemistry. In this report, we demonstrate that a monometallic 2‐phosphinoimidazole Pd catalyst exhibits comparable or enhanced reactivity when compared to all ligands screened for room temperature amination of aryl chlorides with secondary amines. The di‐tert‐butylphosphine derivative showed extremely high reactivity while the di‐isopropyl variant led to almost complete loss of catalytic activity. Computational and experimental mechanistic and kinetic studies indicate that a monometallic Pd structure rather than a bimetallic Pd structure is key to fast catalysis. The di‐tert‐butylphosphine ligand has fast catalysis because it thermodynamically disfavors the formation of a much less active bimetallic Pd complex. A wide substrate scope is demonstrated for the arylation of secondary amines with aryl chlorides using our new catalyst system.
Amine-functionalized carbon nanotubes supported palladium nanoparticles in Buchwald-Hartwig amination
Buchwald-Hartwig amination is a cross-coupling reaction between aryl halides or pseudohalides and primary or secondary amines to produce aryl amines. The reaction has become a fundamental tool in organic synthesis for the formation of carbon-nitrogen bonds in a variety of biologically active molecules, natural products, pharmaceuticals, and material science. These reactions usually employ a palladium complex in homogeneous form along with a ligand to stabilize the metal center. In this regard, there are many disadvantages for using homogeneous catalysis including the potential contamination of the metal in the final product and lack of recyclability of the catalyst. Heterogeneous catalysis is an alternative attractive approach to construct carbon-nitrogen bonds in which the metal is fixed on variety of solid supports such as zeolites, polymers, mesoporous silica, and carbon materials. This would allow for ease of separation of the catalyst from the reaction and reusability for the subsequent runs. In this presentation, we will introduce the synthesis of amine-functionalized carbon nanotubes (CNTs) supported Pd nanoparticles (Pd/MWCNTs-NH2) via simple dry mixing of the corresponding palladium salts and amine-functionalized CNTs using the mechanical energy of a ball-mill mixer. The method is very straightforward and rapid and does not require any solvent or reducing agents, a feature that allows for large-scale preparation of these materials. The as-prepared catalyst demonstrated excellent catalytic activity for the Buchwald-Hartwig carbon–nitrogen cross-coupling reactions of variety of aryl halides and functionalized amines under microwave irradiation conditions and short reaction time. The Pd/MWCNTs-NH2 nanoparticles prepared by this simple, solventless, and inexpensive preparation provide a more direct, cost-efficient, and streamlined means to accomplish often-challenging Buchwald-Hartwig amination reactions.
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- Award ID(s):
- 2101126
- PAR ID:
- 10528560
- Editor(s):
- NA
- Publisher / Repository:
- American Chemical Society (ACS)
- Date Published:
- ISSN:
- ID: 3970063
- Format(s):
- Medium: X
- Location:
- ACS Southeastern Regional Meeting (SERMACS) Fall 2023, October 25-28, 2023, Durham, NC
- Sponsoring Org:
- National Science Foundation
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