Unique catalytic behavior of chromium complexes having halogenated bis(imino)pyridine ligands for ethylene polymerization

Reactions of CrCl3(thf)3 with bis(imino)pyridines gave a series of {bis(imino)pyridine}chromium(III) trichloride complexes, {2,6‐(RNCMe)2C5H3N}CrCl3 [R = C6H Pr2‐2,6 (1), C6H3Et2‐2,6 (2), C6H3Me2‐2,6 (3), C6H2Me3‐2,4,6 (4), C6H3Me2‐3,5 (5), C6H5 (6), cyclohexyl (7), 2‐methyl‐1‐naphthyl (8), C6H3F2‐2,6 (9), C6H3Br2‐2,6 (10), C6F5 (11)]. Pseudo‐octahedral geometries of 6, 10, and 11 were revealed by X‐ray crystallography. The complexes having bulky substituents such as 1–4 showed high activity for ethylene polymerization in combination with modified methylaluminoxane (MMAO) to give linear polyethylenes. In sharp contrast, the pentafluorophenyl complex 11/modified methylaluminoxane system was found to be moderately active for ethylene homopolymerization to give moderately branched polyethylene with only ethyl branches.