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

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.