Increasing the thermostability of alpha-diimine late-transition-metal complexes and therefore rendering them more active at higher temperatures is of great importance, yet challenging for the olefin polymerization field. In the present research, a new family of alpha-diimine palladium complexes that can promote norbornene polymerization at high temperatures (up to 140 degrees C) is disclosed. Because of the conformational restriction caused by increasing the axial and equatorial bulkiness as well as the presence of intraligand H center dot center dot center dot F hydrogen bonds, N-aryl rotations can be efficiently restricted, therefore circumventing the deactivation of the active species at high temperatures. At 80-140 degrees C, these complexes can efficiently catalyze norbornene homopolymerizations, giving high catalytic activities up to 5.65 x 10(7) g of PNB per mole Ni per hour and polymers with high molecular weights up to 37.2 x 10(4) g/mol, which are highly superior to catalytic systems mediated by CF3-free complexes. Moreover, these complexes could also afford medium catalytic activities in the presence of polar 5-norbornene-2-carboxylic acid methyl ester (NB-COOCH3).