Rare-Earth Metal Complexes Bearing Pyridyl-Functionalized Amidinate Ligands for Highly trans-1,4-Selective Living (Co)Polymerization of 1,3-Conjugated Dienes

Rare-earth metal complexes bearing pyridyl-functionalized amidinate ligands were synthesized, and upon activation by a borate, all of these complexes exhibited high catalytic activities for the living polymerization of isoprene and myrcene to generate trans-1,4 polymers (≤96.8% for polyisoprene and ≤94.8% for polymyrcene). A metal dependence effect was observed, and the scandium complexes with a smaller central ion afforded polymers with the highest trans-1,4-regularity. Moreover, the 3-Sc/[PhMe2NH][B(C6F5)4] binary system also promoted block copolymerization of isoprene and ε-caprolactone, affording the copolymers that consisted of a nonpolar polyisoprene block possessing trans-1,4-microstructure and a polar poly(ε-caprolactone) block.