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

Abstract

Treatment of the <i>o</i>-hydroxyaryl imidazolium proligands (2-OH-3,5-^<i>t</i>Bu₂C₆H₂)­(R)­(C₃H₃N₂)⁺Br^– (R = ^<i>i</i>Pr (<b>1a</b>), ^<i>t</i>Bu (<b>1b</b>), Ph (<b>1c</b>), Mes (<b>1d</b>)) with 3 equiv of Ag₂O afforded the corresponding silver complexes <b>2a</b>–<b>d</b>. The subsequent metal-exchange reactions with [(<i>p</i>-cymene)­RuCl₂]₂ at room temperature yielded the desired <i>o</i>-aryloxide-N-heterocyclic carbene <i>p</i>-cymene ruthenium complexes <b>3a</b>–<b>d</b> 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 <b>3b</b> was determined by single-crystal X-ray diffraction analysis. The ring-opening metathesis polymerization (ROMP) of norbornene (NBE) with <b>3a</b>–<b>d</b> was studied. Among them, complex <b>3d</b> 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)