Ruthenium Ring-Opening Metathesis Polymerization Catalysts Bearing o- Aryloxide-N-Heterocyclic Carbenes

A series of o-aryloxide-N-heterocyclic carbene ruthenium complexes 24 is synthesized via sequential reactions of the o-hydroxyaryl imidazolium proligands (2-OH-3,5-tBu2C6H2)(R)(C3H3N2)+Br (R = Me (1a), iPr (1b), Mes (1c)) with Ag2O and [(C6H6)RuCl2]2. All of the complexes are characterized by 1H and 13C NMR spectroscopy, high-resolution mass spectrometry (HRMS), and elemental analysis. The molecular structure of 2 is determined by single-crystal X-ray diffraction analysis. The ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with 24 is studied. Among them, complex 4 exhibits the highest activity and efficiency toward ROMP of NBE at 85 degrees C without any cocatalyst, and the resultant polymers have very high molecular weight (>106 Da) and narrow molecular weight distributions. This complex can also efficiently catalyze the alternating copolymerization of NBE and cyclooctene.