Vinyl Addition Polymerization of Norbornene Derivatives by Palladium(II) Catalytic System: Comparison of In Situ Versus Complex Catalysts

In this study, 2-(piperidin-1-ylmethyl)quinoline (L_A) and 1-(naphthalen-2-ylmethyl)piperidine (L_B) ligands were utilized alongside palladium(II) acetate [Pd(OAc)₂] and N,N-Dimethylanilinium tetrakis (pentafluorophenyl)borate as a cocatalyst for the in situ addition polymerization of norbornene (NB). The ligand L_B system demonstrated superior catalytic performance compared with that of the ligand L_A system, achieving 99% versus 94% conversion for NB to polynorbornene (PNB) at 25°C in chlorobenzene. To validate the catalytic activities of these in situ catalytic systems, Pd (II) complexes, [L_APd(OAc)₂] and [L_BPd(μ-OAc)]₂, were synthesized and characterized. X-ray structure analysis revealed that [L_APd(OAc)₂] adopted a square planar geometry, whereas [L_BPd(μ-OAc)]₂ exhibited a distinctive clamshell structure. These complexes were also employed for the vinyl addition polymerization of NB under the same conditions as in situ catalytic systems. The active real Pd(II) complexes demonstrated slightly lower conversions compared with those of the in situ catalytic systems, achieving over 90% conversions for both [L_APd(OAc)₂] and [L_BPd(μ-OAc)]₂. Furthermore, both catalytic systems were subsequently used for the (co)polymerization of NB and its derivatives, such as 5-butylbicyclo[2.2.1]hept-2-ene (Bu-NB), methyl bicyclo[2.2.1]hept-5-ene-2-carboxylate (Me-NB), and bicyclo[2.2.1]hept-5-en-2-ylmethyl acetate (AAc-NB), yielding relatively lower conversions.