A Comparative Study on (NHC)Pd(acac)Cl Complexes (NHC = N-heterocyclic carbene): Indications for the Origin of the Different Reactivity of Saturated and Unsaturated NHC in Cross-Coupling Reactions

The synthesis of the new well-defined and air-stable complex (SIPr)Pd(acac)Cl (SIPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) is described, and the catalytic activity of this new complex has been tested in the α-arylation of ketones and in Buchwald−Hartwig amination reactions. The significant differences in catalytic performance when compared to the previously reported, unsaturated counterpart (IPr)Pd(acac)Cl (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) are discussed by means of X-ray crystallography and on the basis of their varying solution dynamics, observed by 1H NMR spectroscopy.