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.