Abstract
Anilido-imine ligands o-C6H4(NHAr1)(CH=NAr2), in which Ar1 is 2,6-diisopropylbenzyl group and Ar2 contains fluorine (HL1) or methoxyl (HL2) group on ortho-position of phenyl substituent, were synthesized for constructing rare-earth metals based complexes of 1a–1c (HL1 based Sc, Lu, Y) and 2a–2c (HL2 based Sc, Lu, Y). Based on their NMR spectra and X-ray single-crystal structures, the side-arm group of -F and -OMe is identified to chelate to the corresponding central metal. The twisted angles between two planes formed by chelated heteroatoms (N, N, F for HL1 and N, N, O for HL2) are observed, in which the largest dihedral angle (53.3°) for HL1-Y and the smallest dihedral angle (44.32°) for HL2-Sc are detected. After being activated by AliBu3 and [Ph3C][B(C6F5)4], these catalysts showed great activity for isoprene polymerization. Bearing the same ligand HL1, smaller scandium based complex 1a and middle size of lutetium based 1b provided lower cis-1,4-selectivity (57.3% and 64.2%), larger yttrium complex 1c displayed high cis-1,4-selectivity (84%). Chelating by crowded HL2, small size of scandium complex 2a provided impressive trans-1,4-selectivity (93.0%), middle lutetium based 2b displayed non-selectivity and larger yttrium complex 2c showed clear cis-1,4-selectivity (83.3%). Moreover, 2a/AliBu3 system showed the quasi-living chain transfer capability.
Highlights
According to the different regio- and stereo-selective polymerization method, polyisoprene is commonly divided into cis-1,4-polyisoprene, trans-1,4-polyisoprene and 3,4polyisoprene
For complex 2a, O, N1 and N2 all coordinate with the central metal scandium forming a chelating complex
Isoprene was dried over CaH2 with stirring for 48 h and distilled under vacuum before use. [Ph3C][B(C6F5)4] was synthesized following the literature [41]
Summary
According to the different regio- and stereo-selective polymerization method, polyisoprene is commonly divided into cis-1,4-polyisoprene, trans-1,4-polyisoprene and 3,4polyisoprene. Cis-1,4-polyisoprene has similar chemical composition, stereoselectivity and mechanical properties to natural rubber. It is widely used in tires, conveyor belts, adhesives, sports equipment, etc. It is reported that the high-performance rubber can be obtained by mixing a small amount of trans-1,4-polyisoprene with cis-1,4-polyisoprene or natural rubber [2]. Trans-1,4-selective polyisoprene has unique applications in medical materials and shape memory materials, etc. Trans-1,4-polyisoprene is an ideal material for making medical splints, orthopedic components and prosthetics
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