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.