Some Ni (Ⅱ) salicyladimine complexes are neutral single component polymerization catalysts which can tolerate many functional groups．They can catalyze polymerization of olefins even olefins with polar groups The catalytic polymerization mechanism was modeled by the reaction of ethylene with (NH=CH—CH=CH—O) NiCH3R The neutral reaction mechanism and the cationic reaction mechanism of ethylene polymerization were studied based on DFT method at B3LYP

LANL2MB level．The result shows that the insertion is initiated by the complexation of the incoming ethylene with the electron-deficient metal center to form a π-complex．This complexation assists the insertion of the ethylene into the metal-carbon bond via a four member cyclic transition state．After insertion

a product with γ-agostic interaction is formed．Finally

a product is formed with the β-agostic interaction species resembling the starting material

so a new vacant coordination site is available for the next ethylene to coordinate and propagate the chain．Moreover

the calculation results indicate that the neutral reaction mechanism is similar with the cationic reaction mecanism．Compared with the cationic reaction mechanism

the neutral reaction mechanism is easier to initialize．By comparing

it is shown that the interaction of ethylene with the cationic active center is stronger than that with the neutral active center The activation energy for the cationic mechanism is lower than that for the neutral mechanism It implies that the process of the cationic reaction mechanism is easier than that of the neutral mechanism．The β-agostic action plays an important role in the neutral catalytic reaction mechanism

and it dominants the Ni charges in the alkyl complexes．