Carbon-bridged biphenolate lanthanide complexes: synthesis and their catalytic activity for the Diels–Alder reaction

Reaction of anhydrous ErCl3 with sodium salt of carbon-bridged biphenolate, MBMPNa2 (MBMP2−=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 SmCl3 with 2 equiv. of MBMPNa2 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.