Synthesis of pyrrolidinyl-ethylene fluorenyl rare-earth metal complexes and catalysis for 2-vinylpyridine polymerization

Abstract

The metathesis reaction between pyrrolidinyl-ethylene fluorenyl lithium salts with in situ prepared cationic rare-earth metal dialkyl species [Ln(CH2SiMe3)2(THF)x][BPh4] afford efficiently the corresponding constrained-geometry complexes L1Ln(CH2SiMe3)2 (L1 = FluCH2CH2NC4H8, Ln = Y (1a), Lu (1b), Sc (1c)) and L2Ln(CH2SiMe3)2 (L2 = (2,7-di-tert-butyl)FluCH2CH2NC4H8, Ln = Y (2a), Lu (2b), Sc (2c)) in good yields. All these complexes were characterized by NMR spectroscopy, and the solid-state molecular structure of yttrium complex 1a was defined with single-crystal X-ray diffraction analysis. The catalytic performance of these complexes towards 2-vinylpyridine polymerization was investigated, where these complexes alone can efficiently promote the polymerization of 2-vinylpyridine giving isotactic poly(2-vinylpyridine). Upon the activation with [Ph3C][B(C6F5)4], the yttrium and lutetium complexes also afford isotactic poly(2-vinylpyridine), while the scandium complexes produce syndiotactic poly(2-vinylpyridine).