Palladium Catalysts for Norbornene Polymerization. A Study by NMR and Calorimetric Methods

Abstract

Neutral trans-[Pd(C 6 F 5 )XL 2 ] (X ) Cl, Br) and cationic trans-[Pd(C 6 F 5 )L 2 (NCMe)]BF 4 (L ) SbPh 3 , AsPh 3 , As(C 6 Cl 2 F 3 )Ph 2 , AsCyPh 2 , AsMePh 2 , PPh 3 ) complexes have been studied and tested for norbornene (NB) polymerization and copolymerization with 5-norbornene-2-carboxaldehyde (NB-CHO). The neutral complexes are almost inactive and produce only small amounts of oligomers, but the cationic complexes with arsines and stibines are very good for palladium-catalyzed norbornene polymerization. External coordinating molecules (e.g., ligands or monomers with O-donor groups) compete with the olefin function for the coordination sites on Pd and inhibit the reaction. In spite of this, copolymerization of norbornene and 5-norbornene-2-carboxaldehyde could be achieved, with lower yields and higher incorporations of the functionalized norbornene as the NB:NB-CHO ratio decreases. The complex with the fluorinated arsine AsPh 2 (C 6 Cl 2 F 3 ) is the most active catalyst and allows for easy spectroscopic study of the reacting systems by 19 F NMR. Calorimetry provides straightforward monitoring and detection of activation and deactivation processes in polymerization reactions that give insoluble products and cannot be followed by NMR spectroscopy.

η5-Cyclopentadienylpalladium(II) complexes: Synthesis, characterization and use for the vinyl addition polymerization of norbornene and the copolymerization with 5-vinyl-2-norbornene or 5-ethylidene-2-norbornene

“…The system 7/MAO generally yielded higher activities than 4/MAO. This is reasoned with a kinetic activation effect through a faster removal of the more weakly bound AsPh 3 ligand in 7 over the PPh 3 ligand in 4 upon reaction with MAO together with the C 6 F 5 ligand to give the active Pd species (see below) [77]. The weaker AsPh 3 bonding is based on the longer PdeAs (w2.36 A) over the shorter PdeP bond (2.23 A) [49].…”

“…In addition, the still present and stronger coordinating PPh 3 ligand can compete in equilibrium with the NB monomer for the free metal coordination site (Eq. (3)) which, as a consequence, slows the chain growth rate [77,69]. Such a PPh 3 /ethene competition is used in the Shell higher olefin process (SHOP) to control the oligomer chain length [70].…”

Insertion of CO and Strained Olefins into Organometallic (Ferrocenylmethyl)phosphane Palladium Complexes

“…This effect was interpreted to result from easy replacement of the weakly coordinated ligands by NBE along with the formation of the catalytically active species. [39] Hence, it seemed reasonable to check whether in our polymerization reaction the primary phosphane ligand remained coordinated to palladium. To this purpose, we analyzed, by multinuclear NMR spectroscopic experiments, two different polymerization reactions carried out at low temperature in an NMR tube.…”

Palladium-Mediated Organofluorine Chemistry

“…In this way the Pd-fluoroaryl moiety has been used as a reporter of the symmetry of the molecule and has allowed the study of a variety of complex fluxional processes, isomerization, and ligand substitution and exchange reactions, 25 as well as the study of palladium-catalyzed polymerization reactions. 26 A review covering the use of fluroraryl groups as reporter tools is available. 27 Also, the use of 19 F NMR has been very important in the study of other processes where the Pd-R F bond is cleaved and these examples will be discussed here.…”