Synthesis of Electron Deficient N-heterocyclic-carbenes and Activity of Imidazol-2-imine Thioureate Ligand on Group 10 Transition Metals

Abstract

Previous work in the Lavoie group has resulted in the synthesis of new imidazol-2-imine ligands that have low activity towards ethylene polymerization due to their electron rich nature. In an attempt to alleviate this an electron poor naphthalene-1,4-dione-IMes imidazol-2-imine ligand (L) was synthesized in 90% yield (14a) and coordinated to titanium (LTiCpCl2, 15). The resulting complex successfully polymerizes ethylene at a rate of 75 kg PE mol catalyst–1 h–1. A separate study focused on the coordination of functionalized imidazol-2-imine thioureate ligands (L’) to late transition metal. Three complexes were synthesized. Ni(methylallyl)L’ (7), Pd(allyl)L’ (8), and NiL’2 (9) were isolated in 85, 85, and 61% yields, respectively and all spectroscopically characterized. The X-ray crystallographic structure of 9 shows the unexpected N^S binding mode for the ligand. Complexes 7 and 8 have sparing activity towards ethylene polymerization, neither having productivity above 2 kg PE mol–1 h–1.