Reaction of anhydrous ErCl 3 with sodium salt of carbon-bridged biphenolate, MBMPNa 2 (MBMP 2−=2,2′-methylene-bis (6- tert-butyl-4-methyl-phenoxo)), in 1:2 molar ratio in THF at room temperature gave the lanthanide ‘ate’ complexes (THF)Er(MBMP) 2Na(THF) 2 ( 1) in high isolated yield. Similarly reaction of anhydrous SmCl 3 with 2 equiv. of MBMPNa 2 in THF, then crystallization from toluene in the presence of TMEDA, afforded the final product (THF)Sm(MBMP) 2Na(TMEDA) ( 2). Both complexes 1 and 2 were well characterized by elemental analysis, IR spectra, and X-ray diffraction analysis. Preliminary results revealed that these complexes are able to act as Lewis acid to catalyze the Diels–Alder reaction of cyclopentadiene with methyl acrylate in good activity and stereoselectivity.