Kinetics, Mechanism and Theoretical Studies of Norbornene-Ethylene Alternating Copolymerization Catalyzed by Organopalladium(II) Complexes Bearing Hemilabile α-Amino–pyridine

Abstract

Cationic methylpalladium complexes bearing hemilabile bidentate α-amino–pyridines can serve as effective precursors for catalytic alternating copolymerization of norbornene (N) and ethylene (E), under mild conditions. The norbornyl palladium complexes in the formula of {[RHNCH2(o-C6H4N)]Pd(C7H10Me)(NCMe)}(BF4) (R = iPr (2a), tBu (2b), Ph (2c), 2,6-Me2C6H3 (2d), 2,6-iPr2C6H3 (2e)) were synthesized via single insertion of norbornene into the corresponding methylpalladium complexes 1a–1e, respectively. Both square planar methyl and norbornyl palladium complexes exhibit facile equilibria of geometrical isomerization, via sterically-controlled amino decoordination–recoordination of amino–pyridine. Kinetic studies of E-insertion, N-insertion of complexes 1 and 2, and the geometric isomerization reactions have been examined by means of VT-NMR, and found in excellent agreement with the results estimated by DFT calculations. The more facile N-insertion in the cis-isomers, and ready geometric isomerization, cooperatively lead to a new mechanism that accounts for the novel catalytic formation of alternating COC.

Single‐Component Catalysts for the Vinyl‐Addition Polymerization of Norbornene and its Derivatives

“…Chen et al and Suslov et al evaluated Pd complexes bearing a hemilabile bidentate α-amino-pyridine moiety (Pd90 and Pd91, Figure 19) in norbornene polymerization. [88,89] Acetylacetonate Pd complexes (Pd91) did not catalyze the VAP of NB without a cocatalyst. However, oligomerization of NB was observed in the presence of methylpalladium complexes with a labile MeCN ligand (Pd90).…”

“…Considering the possible ways of linking norbornene units, three types of such links are expected: exoexo-, endo-endo-, and exo-endo-enchainment (Figure 25a-C). Xray analysis of both intermediates with inserted norbornene molecule(s) into the metalÀ C bond [46,55,74,[82][83]86,88] and crystalline oligomers of norbornene derivatives [94] obtained in VAP clearly indicated exo-exo-linking of norbornene units. No experimental proof of endo-endo-or exo-endo-linking of norbornene units has been reported thus far.…”

Air-Stable Single-Component Pd-Catalysts for Vinyl-Addition Polymerization of Functionalized Norbornenes

“…N−N-and N−O-ligated cationic Pdcomplexes of a similar structure were found to be singlecomponent catalysts for VAP of unsubstituted norbornenes. 51,52 Chen and co-workers showed that a zwitterionic phospine-sulfonate Ni-complex is a latent catalyst for norbornene polymerization. 53 Recently, Peŕez-Ortega and Albeniz reported cationic benzylic Pd-complexes as onecomponent catalysts for VAP.…”

Approaching new biomaterials: copolymerization characteristics of vinyl esters with norbornenes, allyl esters and allyl ethers

“…The rigid repeat unit can contribute to useful physical properties 24,25 . Copolymerization of norbornene with ethylene or propylene initiated by metal complexes affords cyclic olefin copolymers with unique properties 26,27 . Furthermore, norbornenes have been copolymerized with methacrylates to achieve useful optical properties 25 …”