Polymerization of 5-Alkylidene-2-norbornenes with Highly Active Pd–N-Heterocyclic Carbene Complex Catalysts: Catalyst Structure–Activity Relationships

Abstract

We studied the addition polymerization of readily available bifunctional norbornene derivatives, 5-alkylidene-2-norbornenes, in the presence of modified Pd complexes with N-heterocyclic carbene ligands activated by borates. The Pd−N-heterocyclic carbene complex/phosphine/borate systems selectively catalyze the addition polymerization of 5methylene-2-norbornene and 5-ethylidene-2-norbornene with the participation of the endocyclic norbornene double bond, whereas the exocyclic double bond remained intact. The catalysts exhibited extremely high activity and durability: the activity was higher than 1 × 10 8 g polymer / (mol Pd •h) and some catalysts were active at a very high monomer/Pd molar ratio of 2 × 10 7 or at a Pd complex concentration of 5 × 10 −6 mol %. The structure−catalytic activity relationships were established for Pd−N-heterocyclic carbene complexes: the Pd complexes bearing five-membered heterocyclic rings and/or less sterically hindered aryl groups at nitrogen atoms in carbene ligands exhibited the highest activity. The polymerization can be performed in an atmosphere of air and in wet solvents. The resulting polymers are amorphous and high-molecular-weight products consisting of rigid saturated main chains and reactive side groups. Thus, they can be considered as promising intermediates in the production of polymeric materials with high glass-transition temperatures and desired properties by targeted modifications.

Novel Strained Alicyclic Hydrocarbons Based on 5-Methylene-2-norbornene

“…The target 5-methylene-2-norbornene was isolated from the reaction mixture by vacuum distillation with a yield of 78% (56-58°C, 40 Torr). The MNB spectra agreed with the published data [15] (Scheme 1).…”

“…Moreover, MNB is an available compound produced by a Diels-Alder reaction between allyl bromide and cyclopentadiene followed by elimination under basic conditions. MNB has generally been used as a monomer or co-monomer to synthesize various polymers, so research on its transformations has mostly focused on the polymerization aspects [15].…”

5‐Ethylidene‐2‐norbornene Polymerization by α‐Diimine Nickel Catalyst: A Revealing Insight into the Pivotal Function of Binuclear and Mononuclear Catalyst Structure in Tailoring Polymer Architecture

“…[ 19 ] It was particularly understood that the application of Pd N ‐heterocyclic carbene complexes as a catalyst has been adjusted to provide a soluble high molecular weight poly 5‐ethylidene‐2‐norbornene (PENB). [ 20 ] Chemical modification via grafting different functional groups to polymer chains provides this category of cyclic polyolefin with atractive properties, such as improved transparency, greater adhesion as well as enhanced compatibility with other polymers. Transition‐metal‐based olefin polymerization catalysts, particularly early transition metal, seriously suffer from rapid poisoning/deactivation upon interaction with polar groups, due to the competition between polar monomers coordination and olefin π ‐interaction.…”

Highly efficient vinylic addition polymerization of 5-vinyl-2-norbornene using benzylic palladium complexes as precatalysts

“…Bermeshev et al have used a Pd(II)-N-heterocyclic carbene complex as palladium source with similar results. 13 This activity is far from that reached with the same system for ENB (efficient polymerization in high yield using an amount of catalyst of 10 low molecular weight VA-PVNB. 7 Other reported precatalytic mixtures showed less efficiency, or led to oligomers.…”