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

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(-C₆H₄N)]Pd(C₇HMe)(NCMe)}(BF₄) (R = Pr (), Bu (), Ph (), 2,6-Me₂C₆H₃ (), 2,6-Pr₂C₆H₃ ()) were synthesized via single insertion of norbornene into the corresponding methylpalladium complexes -, 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 and , 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 -isomers, and ready geometric isomerization, cooperatively lead to a new mechanism that accounts for the novel catalytic formation of alternating COC.