Synthesis and structures of (R)-cyclopentadienyl-binaphthoxy titanium(iv) complexes and catalytic properties for olefin polymerization

Abstract

Two new chiral pre-ligands, (R)-3,3′-bis(tetramethylcyclopentadienyl)-2,2′-bismethoxy-1,1′-bisnaphthalene (1) and (R)-3-tetramethylcyclopentadienyl-2,2′-bismethoxy-1,1′-bisnaphthalene (2), were synthesized by reaction of (R)-3,3′-dilithium-2,2′-bismethoxy-1,1′-bisnaphthalene with 2,3,4,5-tetramethyl-2-cyclopentenone at room temperature. Treatment of the pre-ligands 1 and 2 with butyllithium and Me₃SiCl first, and subsequently with TiCl₄ (2 and 1 equiv for 1 and 2, respectively) afforded a binuclear complex (R)-3,3′-bis[(tetramethylcyclopentadienyl)trichlorotitanium]-2,2′-bismethoxy-1,1′-bisnaphthalene (3) and a mononuclear complex (R)-3-(tetramethylcyclopentadienyl)trichlorotitanium-2,2′-bismethoxy-1,1′-bisnaphthalene (4) in moderate yields. Complexes 3 and 4 were further converted into constrained geometry complexes (R)-1,1′-bis{2,2′-naphthoxy-3,3′-bis[(tetramethylcyclopentadienyl)dibromotitanium]} (5) and (R)-1-(2-naphthoxy)-1′-(2′-naphthol)-3-(tetramethylcyclopentadienyl)dibromotitanium (6) by treatment with BBr₃. The pre-ligands 1 and 2 were characterized by ¹H and ¹³C NMR and high resolution mass spectroscopy (HRMS), and the new titanium complexes 3–6 were characterized by ¹H and ¹³C NMR and elemental analyses. Molecular structures of 4, 5, and 6 were determined by single-crystal X-ray diffraction analysis. Complexes 4, 5, and 6 all have a pseudo-octahedral coordination environment and adopt a three-legged piano stool geometry around the titanium atom in their solid state structures. When activated with AlⁱBu₃ and Ph₃CB(C₆F₅)₄, the chiral complexes 5 and 6 show moderate catalytic activities for propylene, 1-hexene, and 5-ethylidene-2-norbornene (ENB) polymerization and ethylene/1-hexene copolymerization. The polymers produced by the chiral 5/ⁱBu₃Al/Ph₃CB(C₆F₅)₄ catalyst system from the 1-hexene, and ENB polymerization and ethylene/1-hexene copolymerization with high comonomer contents exhibit optical activity.