Half-sandwich rare-earth metal complexes bearing a C5Me4-C6H4-o-CH2NMe2 ligand: synthesis, characterization and catalytic properties for isoprene, 1-hexene and MMA polymerization

A new ortho-dimethylaminomethylphenyl-tetramethylcyclopentadienyl ligand C5Me4H-C6H4-o-CH2NMe2 (HL) and a series of rare-earth metal complexes bearing this ligand were synthesized. Of these complexes, two binuclear alkyl complexes [(C5Me4-C6H4-o-CH2N(Me)CH2-mu)Ln(CH2SiMe3)](2) (Ln = Sc (1a) and Y (1b)) were obtained from the alkane elimination reaction of the free ligand with Ln(CH2SiMe3)(3)(THF)(2), followed by an intramolecular C-H activation process of a NMe group in the ligand with a CH2SiMe3 group, two binuclear dichloro complexes (C5Me4-C6H4-o-CH2NMe2)(2)Y2Cl4[LiCl(THF)(2)] (2a) and [(C5Me4-C6H4-o-CH2NMe2)LuCl(mu-Cl)](2) (2b) were synthesized by the reaction of anhydrous yttrium or lutetium trichloride with the lithium salt of the ligand LiL, and the binuclear bis(borohydrido) complexes [(C5Me4-C6H4-o-CH2NMe2)Ln(mu-BH4)BH4](2) (Ln = Sm (3a) and Nd (3b)) were synthesized by the reaction of Ln(BH4)(3)(THF)(3) (Ln = Sm and Nd) with the lithium salt of the ligand. The molecular structures of all complexes 1a, 1b, 2a, 2b, 3a and 3b were determined by single-crystal X-ray crystallography. Upon activation with AlR3/Ph3CB(C6F5)(4), MAO or MMAO, the binuclear alkyl complexes 1a and 1b show good catalytic activity for isoprene cis-1,4 enriched regioselective polymerization and moderate catalytic activity for 1-hexene polymerization. Complexes 3a and 3b were studied as catalysts for methyl methacrylate polymerization reaction under different conditions and were found to show moderate to high catalytic activity.