Unprecedentedly High Activity and/or High Regio-/Stereoselectivity of Fluorenyl-Based CGC Allyl-Type ?³:?¹-tert-Butyl(dimethylfluorenylsilyl)amido Ligated Rare Earth Metal Monoalkyl Complexes in Olefin Polymerization.

ABSTRACT: A series of fluorenyl-based constrained-geometry-configuration (CGC) allyl-type rare earth metal monoalkyl complexes bearing the divalent anionic ?³:?¹-tert-butyl(dimethylfluorenylsilyl)amido (?³:?¹-FluSiMe₂N^tBu) ligand (?³:?¹-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 ?³:?¹-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 ?³:?¹-FluSiMe₂N^tBu ligands between rare earth metal centers and Al centers result in the formation of a heterobimetallic tetraalkylaluminate complex R₂Al(?-R)₂Ln(R)(?-R)₂AlR₂, which is activated by activators to form a divalent cationic species [Ln(?-R)₂AlR₂]²⁺ as a catalytically active species in the coordination-insertion polymerization of olefins.

SUBMITTER: Guo G 

PROVIDER: S-EPMC6572029 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature