Ligand steric hindrance and electronic effects on β-enaminoketonato half-sandwich chromium(III) olefin polymerization catalysts

A series of new half-sandwich chromium(III) complexes with asymmetric bidentate β-enaminoketonato ligands (3a-f), Cp[PhNC(CF3)CHC(C6H4R(o))O]CrCl (3a, R = H；3b R = CH3; 3c, R = F; 3d, R = CF3; 3e, R = phenyl; 3f, R = naphthyl), have been synthesized by treating CpCrCl2(THF) with 1.0 equiv. of the deprotonated ligands in THF, and the complexes were identified by IR spectra and mass spectra as well as elemental analyses. X-ray structural analysis for 3b and 3e–f revealed that these complexes adopt three-legged piano stool geometry with a pseudo-octahedral coordination environment. Upon treatment with methylaluminoxane, they exhibited moderate to high catalytic activities for ethylene polymerizations. Both the electronic effect and the steric hindrance of the substituents have profound effect on polymerization behaviors. Additionally, these complexes also displayed notable ability to copolymerize ethylene with norbornene, affording the copolymers with high NBE incorporations.

Graphical abstractA series of half-sandwich chromium(III) complexes bearing beta-enaminoketonato ligands have been prepared, characterized, and investigated as the catalyst precursors for ethylene polymerization and ethylene/norbornene copolymerization.Figure optionsDownload full-size imageDownload as PowerPoint slide