N-Acylamidine Palladium(II) Complexes. Synthesis, Structures, and Catalytic Activity for Suzuki−Miyaura Cross-Coupling Reactions:  Experiments and DFT Calculations

N-Acylamidines 2 are easily prepared by acylation of amidines 1. Upon treatment with PdCl₂(PhCN)₂, they form 2:1 PdCl₂ complexes 3 with trans configuration, acting as monodentate ligands via the nitrogen atom remote from the carbonyl group. The structures of the complexes 3a−c in the solid state were obtained by X-ray crystallography. As studied by DFT calculations on 2:1 model complexes, many isomeric structures 6 with different conformations and configurations are associated with local minima on the energy hyperface within an energy range of 4 kcal/mol. The complexes 3 show very high catalytic activity in Suzuki−Miyaura cross-coupling reactions, either as isolated crystals or prepared in situ without isolation.