Unprecedentedly High Activity and/or High Regio-/Stereoselectivity of Fluorenyl-Based CGC Allyl-Type η³:η¹-tert-Butyl(dimethylfluorenylsilyl)amido Ligated Rare Earth Metal Monoalkyl Complexes in Olefin Polymerization

A series of fluorenyl-based constrained-geometry-configuration (CGC) allyl-type rare earth metal monoalkyl complexes bearing the divalent anionic η³:η¹-tert-butyl(dimethylfluorenylsilyl)amido (η³:η¹-FluSiMe₂N^tBu) ligand (η³:η¹-FluSiMe₂N^tBu)Ln(CH₂SiMe₃)(THF)₂ (1–3) have been synthesized via the alkane elimination reaction between the FluHSiMe₂NH^tBu ligand and rare earth metal tri(trimethylsilylmethyl) complexes Ln(CH₂SiMe₃)₃(THF)_n. Their structures are characterized by means of NMR spectrum, elemental analyses, and X-ray diffraction. These complexes 1–3 are isostructural and isomorphous, and each of them adopts a distorted-trigonal-bipyramidal configuration containing one η³:η¹-FluSiMe₂N^tBu ligand, one CH₂SiMe₃ ligand, and two THF molecules. Unlike traditional CGC allyl-type rare earth metal complexes showing no or low activity and regio-/stereoselectivity in styrene or MMA polymerization, these complexes 1–3 exhibit high catalytic activities and/or high regio-/stereoselectivities in the cis-1,4-polymerization of isoprene and myrcene or in the syndiotactic polymerization of styrene under the aid of different activators (borate or borane) and AlR₃. The in situ ¹H NMR spectra suggest that the exchanges of chelating ligands such as alkyl groups and divalent anionic η³:η¹-FluSiMe₂N^tBu ligands between rare earth metal centers and Al centers result in the formation of a heterobimetallic tetraalkylaluminate complex R₂Al(μ-R)₂Ln(R)(μ-R)₂AlR₂, which is activated by activators to form a divalent cationic species [Ln(μ-R)₂AlR₂]²⁺ as a catalytically active species in the coordination–insertion polymerization of olefins. View Full-Text