Syntheses and structures of bimetallic rare-earth complexes supported by pyrrolyl ligands and their high performance in isoprene polymerization

Abstract

• A series of the pyrrolyl-ligated bimetallic rare earth metal amido complexes were synthesized and characterized. • Complexes used as catalyst for the polymerization of isoprene. • They were to be highly cis-1,4 selective for isoprene polymerization. The reactions of pyrrole with rare-earth metal amides [(Me 3 Si) 2 N] 3 RE( μ -Cl)Li(THF) 3 produced the bimetallic rare earth metal amido complexes (RE = Y( 1 ), Nd( 2 ), Yb( 3 )) in high yields. X-ray diffraction analysis revealed that the pyrrole was deprotonated with the pyrrolyl ring coordinated to one rare-earth metal in an η 5 mode and the nitrogen atom coordinated to another rare-earth metal in an η 1 modes forming the centrosymmetric structures. Complexes 1 – 3 as precatalysts for isoprene polymerization were investigated. Results showed that except for ytterbium system, all other complexes could initiate effectively the polymerization of isoprene to afford polyisoprene with high conversion, high regio- and stereo-selectivity (1,4- cis selectivity up to 95.2%) in the presence of cocatalysts. A types of pyrrolyl-ligated bimetallic rare earth metal amido complexes were constructed, and their coordinated modes and catalytic activity were studied.