Novel Catalyst Systems Based on Cationic Palladium Cyclopentadienyl Complexes for the Polymerization of Norbornene and Norbornene Derivatives

Abstract

Results of studying the catalytic properties of systems based on complexes with [Pd(Cp)(L)_n]_m[BF₄]_m (where Cp = η⁵-C₅H₅; n = 2, m = 1: L = tris(ortho-methoxyphenyl)phosphine, triphenylphosphine, tris(2-furyl)phosphine (TFP); n = 1, m = 1: L = 1,1'-bis(diphenylphosphino)ferrocene, 1,3-bis(diphenylphosphino)propane, 1,4-bis(diphenylphosphino)butane, 1,5-bis(diphenylphosphino)pentane; n = 1, m = 2 or 3: L = 1,6-bis(diphenylphosphino)hexane) in the addition homo- and copolymerization of norbornene (NB) and NB derivatives have been described. It has been found that these complexes can be activated with Lewis acids (BF₃⋅OEt₂ or AlCl₃). The productivity of the [Pd(Cp)(PPh₃)₂][BF₄]/BF₃⋅OEt₂ catalyst system in NB polymerization can achieve 188 800 mol_NB \({\text{mol}}_{{{\text{Pd}}}}^{{ - 1}}\). The homopolymerization of 5-methoxycarbonylnorbornene and the copolymerization of NB with 5-methoxycarbonylnorbornene or 5-phenylnorbornene in the presence of BF₃⋅OEt₂ and [Pd(Cp)(L)₂][BF₄] (L = PPh₃ or TFP) has been studied. A hypothesis for the formation of the catalyst via the intramolecular rearrangement of the η⁵-Cp ligand into the η¹-Cp form upon interaction with a Lewis acid has been proposed. The structure of the [Pd(Cp)(TFP)₂]BF₄ complex (I) has been determined by X-ray diffraction (XRD) analysis. In the crystal structure of complex I, the coordination sphere of palladium is characterized by a slight distortion of the square planar geometry of the central atom, while the cyclopentadiyl moiety is in an eclipsed conformation. Based on XRD data, the steric hindrance of the TFP ligand has been determined (cone angle is 149°).