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- t Bu 2 C 6 H 2 )(R)(C 3 H 3 N 2 ) + Br – (R = i Pr ( 1a ), t Bu ( 1b ), Ph ( 1c ), Mes ( 1d )) with 3 equiv of Ag 2 O afforded the corresponding silver complexes 2a – d . The subsequent metal-exchange reactions with [( p -cymene)RuCl 2 ] 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 1 H and 13 C 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 (>10 6 ) and narrow molecular weight distributions were obtained. This complex can also catalyze the alternating copolymerization of NBE and cyclooctene (COE).