Synthetic and Structural Studies of (NHC)Pd(allyl)Cl Complexes (NHC = <i>N</i>-heterocyclic carbene)

The synthesis and structural characterization of a series of palladium complexes bearing
N-heterocyclic carbenes (NHC) as supporting ligands are described. The reaction of
commercially available [Pd(allyl)Cl]2 and isolated or in situ generated NHC leads to
monomeric palladium complexes where one NHC is bound to the metal center, as indicated
by spectroscopic and single-crystal X-ray diffraction studies. The relative reactivity trend
for these complexes as catalysts in aryl amination is discussed in terms of ligand steric
properties, which vary as a function of imidazole-nitrogen substituents and perturbation
resulting in modulation of ring planarity. The concept of buried volume is used to quantify
the steric demand of each NHC in the corresponding complexes.