Three new bimetallic complexes were synthesized and crystalized by reactions of (CF~3CO~2)~3Ln with R^1 AlR~2(Ln=Nd and Y, R^1=H, R=i-C~4H~9; Ln=Eu, R=R^1=C~2H~5) in tetrahydrofuran solution, and their crystal structures were determined using a X-ray diffraction method. The structurres and the questions on valence state and noncoplanarity in the structures were confirmed and cracked by means of ^1H NMR and ^1^3C NMR spectra, especially by ^1^3C-^1H COSY 2D NMR technique. A general formula of molecules of the three rare earth complexes was defined as follows: A mechanism on the formation of the new complexes was also proposed through the following five steps: alkylating, β-elimination (or hydrogenation), hydrogen transfer, linkage and association. Both Y-Al and Eu-Al complexes function as a catalyst in polymerization of MMA and ECH. The polymer obtained from the first monomer is mainly syndiotactic chain structure and the polymerization of the last monomer shows higher catalytic activity. The Y-Al complex also capable of ring-opening polymerization of THF in case of adding vary small amount of ECH and a oxonium ion mechanism of THF polymerization was suggested from the analysis of THF polymer terminal.

Key words: SYNTHESIS, REACTION MECHANISM, COMPLEX COMPOUNDS, POLYMERIZATION, BIMETALS, CHARACTERIZATION