Carbon bridged triphenolate lanthanide complexes: synthesis, characterization, DFT studies and catalytic activities for isoprene polymerization

Abstract

The dinuclear lanthanide complexes [Ln₂(L)₂(THF)_n] (Ln = Nd (1) n = 4, Gd (2) n = 3, Lu (3) n = 2) supported by carbon bridged triphenolate ligands [LH₃ = tris(3,5-di-tert-butyl-2-hydroxyphenyl)methane] were synthesized via a salt metathesis reaction between lanthanide trichlorides and LNa₃ in THF. All complexes were characterized by elemental analysis and X-ray crystallography, and complex 3 was characterized by ¹H and ¹³C NMR spectroscopy. Agostic interactions were found in these complexes and were further substantiated by DFT calculations of complex 3. These lanthanide complexes in combination with aluminum alkyls and [Ph₃C]⁺[B(C₆F₅)₄]⁻ generated efficient homogeneous catalysts for the cis-1,4 polymerization of isoprene, with complex 1 having the best catalytic activity.