Synthesis of rare-earth metal complexes based on quinolinyl-functionalized cyclopenta[b]indoles and their catalytic performance in the polymerization of ortho-methoxystyrene and its derivatives

Abstract

The introduction of polar functionalities into nonpolar polyolefins is highly desirable to enhance their surface properties, adhesion, and compatibility with other polar polymers. In this study, we report the synthesis of novel quinolinyl-functionalized dihydrocyclopenta[b]indole ligands and their corresponding rare-earth metal complexes, where the scandium complexes exhibited high syndiotacticity (>99% rrrr) in the polymerization of ortho-methoxystyrene (oMOS) upon activation with [Ph₃C][B(C₆F₅)₄] and ⁱBu₃Al. A detailed investigation indicated that the polar methoxy group of oMOS promotes monomer activation through σ–π chelation with the central metal, in conjunction with the vinyl group, thereby revealing a notable self-assisted mechanism. Furthermore, the σ–π chelation effect remained unaffected by the presence of other polar groups in the corresponding monomers. When additional polar groups, such as fluoro, bromo or methoxy groups, were incorporated into oMOS, polymerization proceeded efficiently under the scandium-based catalytic system, resulting in polymers with high syndiotacticity (>99% rrrr).