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 a-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.