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 PdCl(2)(PhCN)(2), they form 2:1 PdCl(2) 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.