Thiophene-NPN Ligand Supported Rare-Earth Metal Bis(alkyl) Complexes. Synthesis and Catalysis toward Highly trans-1,4 Selective Polymerization of Butadiene

Abstract

A series of new rare-earth metal bis(alkyl) complexes [L1−3Ln(CH2SiMe3)2(THF)n] (L1 = MeC4H2SCH2NC6H4(Ph)2P═NC6H2Me3-2,4,6: Ln = Sc, n = 1 (1a); Ln = Lu, n = 1 (1b); L2 = MeC4H2SCH2NC6H4(Ph)2P═NC6H3Et2-2,6: Ln = Sc, n = 1 (2a); Ln = Lu, n = 1 (2b); Ln = Y, n = 1 (2c); L3 = MeC4H2SCH2NC6H4(Ph)2P═NC6H3iPr2-2,6: Ln = Sc, n = 0 (3a)) and L4Sc(CH2SiMe3)2(THF) (4a) (L4 = C6H5CH2NC6H4(Ph)2P═NC6H3Et2-2,6) have been prepared by reaction of rare-earth metal tris(alkyl)s with the corresponding HL1−4 ligands via alkane elimination. Complexes 1a, 1b, 2a−2c, and 4a are monomeric with a coordinating THF molecule. Each metal ion is coordinated by a NPN ligand, two trans-located alkyl groups, and a THF molecule, forming a distorted trigonal-bipyramidal geometry. Complex 3a is THF-free, adopting a distorted tetrahedron geometry. In combination with AlR3 and borate, these complexes have shown medium activity and good trans-1,4 selectivity for the polymerization of butadiene. The resultant polymer has moderate molecular weig...