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-tBu2C6H2)­(R)­(C3H3N2)+Br– (R = iPr (1a), tBu (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 1H and 13C 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 °C without the need for any cocatalyst, and polymers with very high molecular weight (>106) and narrow molecular weight distributions were obtained. This complex can also catalyze the alternating copolymerization of NBE and cyclooctene (COE).