Rare-earth metal bis(aminobenzyl) complexes supported by pyrrolyl-functionalized arylamide ligands: synthesis, characterization and styrene polymerization performance

Abstract

An acid–base reaction between the rare-earth tris(o-dimethylaminobenzyl) complexes Ln(CH₂C₆H₄NMe₂-o)₃ and the pyrrolyl-functionalized arylamide ligands 2,5-Me₂C₄H₂NCH₂SiMe₂NHC₆H₄R (R = H, (HL¹); R = Cl-p, (HL²)) was investigated. Treatment of HL¹ and HL² with 1 equiv. of Ln(CH₂C₆H₄NMe₂-o)₃ in toluene at room temperature gave (2,5-Me₂C₄H₂CH₂NSiMe₂NC₆H₅)Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Sc (1), La (2), Lu (3)) and (2,5-Me₂C₄H₂NCH₂SiMe₂NC₆H₄Cl-p)Ln(CH₂C₆H₄NMe₂-o)₂ (Ln = Sc (4), La (5), Lu (6)) in good isolated yields. These complexes were characterized by elemental analysis and NMR spectroscopy. 2, 4 and 5 were structurally authenticated by single crystal X-ray diffraction. NMR and X-ray diffraction show that there are no interactions between the central metal and the pyrrolyl moiety in small sized metal complexes, while in large lanthanum complexes, besides the coordination of the arylamide moiety to La³⁺ in η¹-bonding mode through a N atom, the pyrrolyl ring also has close contact with La³⁺ in 2 and 5. The binary systems of 1–6/[Ph₃C][B(C₆F₅)₄] were employed as catalysts for syndio-specific polymerization of styrene, and the pyrrolyl-ligated lanthanum complexes showed much higher activity than the complexes in which the pyrrolyl moiety had no coordination with the central metal.