Highly efficient palladium precatalysts of homoscorpionate bispyrazolyl ligands for the more challenging Suzuki–Miyaura cross-coupling of aryl chlorides

Abstract

Highly efficient palladium precatalysts {[RN{-(CH₂)_n-pz^3,5-Me₂}₂]PdCl₂}_m [m = n = 1; R = 2,6-Me₂C₆H₃ (1), 2,4,6-Me₃C₆H₂ (2), CH₂Ph (3) and m = n = 2; R = CH₂Ph (4)] of a series of homoscorpionate bispyrazolyl ligands for the Suzuki–Miyaura cross-coupling of the more challenging aryl chloride substrates are reported. In particular, the palladium 1–4 precatalysts carried out the Suzuki–Miyaura cross-coupling of a wide variety of aryl chloride substrates bearing electron withdrawing, electron donating and heteroaryl substituents. Remarkably enough, the molecular structure determination of the 1–4 precatalysts by X-ray diffraction studies revealed the presence of anagostic [C–H⋯Pd] type interactions in the mononuclear 1–3 complexes of methylene bridged bispyrazolyl ligands whereas the ethylene bridged analog 4 yielded an interesting dimeric 20-membered macrometallacyclic complex devoid of any such interaction.