Highly Isospecific Polymerization of Methyl Methacrylate with a Bis(pyrrolylaldiminato)samarium Hydrocarbyl Complex
摘要:
New types of samarium alkyl complexes, L-2-SmMe (THF) (2) and L2SmCH2SiMe3(THF) (3), supported by the pyrrolylaldiminato ligand L (L = [2-(2,6-iPr(2)C(6)H(3)N=CH)-5-tBuC(4)H(2)N](-)), were prepared from the corresponding chloride L2SmCl(THF) (1) with the appropriate alkyllithium reagents; the corresponding yttrium alkyl L2YCH2SiMe3 (4) was prepared similarly. The molecular structures of 1 and 3 were determined by X-ray single-crystal analyses. Compound 3 initializes the stereospecific polymerization of MMA to yield highly isotactic PMMA (mm triad 94.8%) with high molecular weight and narrow molecular distribution at room temperature while 2 is inactive. The possible initial step of the polymerization reaction was proposed.