Convenient Synthetic Route to Palladium Complexes of Unconventional N‑Heterocyclic Carbenes Derived from Pyridazine and Phthalazine

Several Pd­(II) complexes with unconventional pyridazine- and phthalazine-derived carbene ligands were synthesized via direct oxidative addition of Cl derivatives of the alkylated diazine heterocycles to Pd(0) species. The alkylated ligand precursors are readily prepared from commercial starting materials, and oxidative addition is regioselective. DFT calculations confirm that the thermodynamically favored products are formed. Four complexes (1–4) have been fully characterized, including by X-ray crystallography. Attractive intramolecular π–π stacking between the electron-poor N-alkylated diazine heterocycles and adjacent phenyl groups of the PPh₃ coligands is revealed by the solid-state structures.