N-Heterocyclic Carbene-Palladium Complexes [(NHC)Pd-(acac)Cl]: Improved Synthesis and Catalytic Activity in Large-Scale Cross-Coupling Reactions

From two commercially available starting materials, improved one-step, multigram-scale syntheses of [(IPr)Pd(acac)Cl] [IPr=N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene; acac=acetylacetonate] and [(IMes)Pd(acac)Cl] [IMes=N,N-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene] are described. The catalytic activity of both complexes in cross-coupling reactions has been examined. The most active pre-catalyst, [(IPr)Pd(acac)Cl], has allowed for efficient large-scale (10 mmol) Buchwald-Hartwig and -ketone arylation reactions to be carried out.