Synthesis, structures, and norbornene polymerization behavior of palladium methyl complexes bearing N-heterocyclic carbene-sulfonate ligands

Abstract

A series of N-heterocyclic carbene-sulfonate (NHC-sulfonate) palladium methyl complexes 2a−d were synthesized from the reaction of NHC-sulfonate ligands with Ag2O and Pd2(μ-Cl)2Me2(2,6-lutidine)2 in good yields. All these complexes were fully characterized by 1H and 13C NMR, elemental analysis, and high-resolution mass spectrometry (HRMS). The molecular structure of the representative complex 2a was also determined by single-crystal X-ray diffraction analysis. Upon activation with either methylaluminoxane (MAO) or [Ph3C]+[B(C6F5)4]−, all the palladium methyl complexes showed excellent catalytic activities [up to 108 g of polynorbornene (PNB) (mol of Pd)−1 h−1] in the vinyl polymerization of norbornene.