Polymerization of norbomene by palladium(II) complexes bearing ethylene-bridged bisindolinyl- or bis(1,2,3,4-tetrahydroquinolinyl) ligands

Novel moisture and air stable, cationic palladium(II) amine complexes (1-4) of the general type [Pd(N μ N)(X)₂](BF₄)₂, [N μ N = 1,2-bis(N-indolinyl)ethane (BIE) 1, 3; 1,2-bis(N-l,2,3,4-tetrahydroquinolinyl)ethane (BTQE) 2, 4; X = NCCH₃, H₂O] were found to catalyze the polymerization reaction of bicyclo[2.2.1]hept-2-ene at room temperature. The amorphous polymer products consist of 2,3-linked norbornene units; no indications for ring opened species could be observed. The polymerization activity of the diaqua-complexes 3, 4 is superior compared to their acetonitrile analogues due to a facile activation by a Wacker-type reaction. The cationic Pd(II)-compounds are inactive towards homo- and copolymerization reactions of polar monomers, like acrylates or carbon monoxide. However, addition of methylacrylate resulted in polynorbomene products with increased molecular weight and narrow molecular weight distributions.