Chromium complexes supported by phenanthrene-imine derivative ligands: synthesis, characterization and catalysis on isoprenecis-1,4 polymerization

Abstract

Reactions of CrCl₂(THF)₂ with N-aryl-9,10-iminophenanthraquinone in CH₂Cl₂ give the monoimine chromium complexes ^ArIPQCrCl₂(THF)₂ (1, Ar = 2,6-Me₂C₆H₃; 2, Ar = 2,6-Et₂C₆H₃; 3, Ar = 2,6-ⁱPr₂C₆H₃). Molecular structures of 1 and 3 were revealed to be monomeric with the chromium atoms in distorted octahedral geometries. Similar reactions of CrCl₂(THF)₂ with N,N-bis(arylimino)phenanthrene ligands afford the diimine complexes ^Ar1,Ar2BIPCrCl(μ-Cl)₃Cr(THF)^Ar1,Ar2BIP (4, Ar₁ = Ar₂ = 2,6-Me₂C₆H₃; 5, Ar₁ = Ar₂ = 2,6-Et₂C₆H₃; 6, Ar₁ = Ar₂ = 2,6-ⁱPr₂C₆H₃; 7, Ar₁ = 2,6-Me₂C₆H₃, Ar₂ = 2,6-ⁱPr₂C₆H₃). The X-ray diffraction analysis shows that 4, 5, and 7 are chlorine-bridged dimers with each chromium atom in a distorted octahedral geometry. Upon activation with MAO, all these complexes exhibit good catalytic activities for isoprene polymerization affording polyisoprene with predominantly a cis-1,4 unit.