Synthesis, Structures, and Norbornene Polymerization Behavior of o-Aryloxide-Substituted NHC-Ligated σ, π-Cycloalkenyl Palladium Complexes

Treatment of the pro-ligand (2-OH-3,5-tBu2C6H2)(Mes)(C3H3N2)+Br– (2a) with di[μ-chloro-2η2,5η1-(6-methoxy-endo-bicyclo[2.2.1]-hept-2-enyl)palladium(II)] (1a) and K2CO3 in dioxane, or reaction of the pro-ligand 2a subsequently with nBuLi and 1a in THF afforded the o-aryloxide-substituted NHC-ligated σ, π-cycloalkenyl palladium complex 3. Similarly, treatment of the pro-ligands (2-OH-3,5-tBu2C6H2)(R)(C3H3N2)+Br– [R = Mes (2a), Me (2b), iPr (2c), Ph (2d)] with bis[μ-chloro-1η2,5η1-(6-ethoxy-exo-5,6-dihydrodicyclopentadienyl)palladium(II)] (1b) and K2CO3 in dioxane afforded the desired products 4–9. All these complexes were fully characterized by 1H and 13C NMR, high-resolution mass spectrometry (HRMS), and elemental analysis. Single-crystal X-ray diffraction analysis results further confirmed the molecular structures of 3–6. With methylaluminoxane (MAO) as cocatalyst, these complexes showed excellent catalytic activities up to 107 g of PNB (mol of Pd) –1 h–1 in the addition polymerization of norbornene.