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

ABSTRACT: Cationic methylpalladium complexes bearing hemilabile bidentate ?-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 {[RHNCH?(o-C?H?N)]Pd(C?H10Me)(NCMe)}(BF?) (R = iPr (2a), tBu (2b), Ph (2c), 2,6-Me?C?H? (2d), 2,6-iPr?C?H? (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.

SUBMITTER: Yu KH 

PROVIDER: S-EPMC6152412 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature