Reactions of CrCl3(thf)(3) with bis(imino)pyridines gave a series of (bis(imino) pyridine}chromium(III) trichloride complexes, {2,6-(RN=CMe)(2)C5H3N)CrCl3 [R = (C6H3Pr2)-Pr-i-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 Xray 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. (c) 2005 Wiley Periodicals, Inc.