Abstract
A series of (NHC)Pd(R-allyl)CI complexes [NHC: IPr = N,N'-bis(2,6-diisopropylphenyl)imidazol2-ylidene, SIPr = N,N'-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me-2, Ph] have been synthesized and fully characterized. When compared to (NHC)Pd(allyl)CI, substitution at the terminal position of the allyl scaffold favors a more facile activation step. This translates into higher catalytic activity in the Suzuki-Miyaura and Buchwald-Hartwig reactions, allowing for the coupling of unactivated aryl chlorides at room temperature in minutes. In the Suzuki-Miyaura reaction, aryl triflates, bromides, and chlorides react with boronic acids using very low catalyst loading. In the N-aryl amination reaction, a wide range of substrates has been coupled efficiently; primary-, secondary-, alkyl-, or aryl-amines react in high yields with unactivated, neutral, and activated aryl chlorides and bromides. In both reactions, extremely hindered substrates such as tri-ortho-substituted biaryls and tetra-ortho-substituted diarylamines can be produced without loss of activity. Finally, the present catalytic system has proven to be efficient with as low as 10 parts-per-million (ppm) of precatalyst in the Buchwald-Hartwig reaction and 50 ppm in the Suzuki-Miyaura reaction.
Original language | English |
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Pages (from-to) | 4101-4111 |
Number of pages | 11 |
Journal | Journal of the American Chemical Society |
Volume | 128 |
Issue number | 12 |
DOIs | |
Publication status | Published - 29 Mar 2006 |
Keywords
- CROSS-COUPLING REACTIONS
- PALLADIUM-CATALYZED AMINATION
- HINDERED ARYL CHLORIDES
- HIGHLY-ACTIVE CATALYST
- ARYLBORONIC ACIDS
- C-N
- NUCLEOPHILIC CARBENES
- ELECTRON-TRANSFER
- STABLE CARBENES
- ENERGY-TRANSFER