Synthesis, Structures, and Norbornene ROMP Behavior of o-Aryloxide-N-Heterocyclic Carbene p-Cymene Ruthenium Complexes

Treatment of the o-hydroxyaryl imidazolium proligands (2-OH-3,5-(Bu2C6H2)-Bu-t)(R)(C3H3N2)Br-+(-) (R = Pr-i (Ia), Bu-t (1b), Ph (1c), Mes (1d)) with 3 equiv of Ag2O afforded the corresponding silver complexes 2a-d. The subsequent metal-exchange reactions with [(p-cymene)-RuCl2](2) at room temperature yielded the desired o-aryloxide-N-heterocyclic carbene p-cymene ruthenium complexes 3a-d in nearly quantitative yields. All the complexes were characterized by H-1 and C-13 NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. The molecular structure of complex 3b was determined by single-crystal X-ray diffraction analysis. The ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with 3a-d was studied. Among them, complex 3d showed high activity and efficiency toward ROMP of NBE at 85 degrees C without the need for any cocatalyst, and polymers with very high molecular weight (>10(6)) and narrow molecular weight distributions were obtained. This complex can also catalyze the alternating copolymerization of NBE and cyclooctene (COE).