Octahedral Chromium(III) Complexes Supported by Bis(2-pyridylmethyl)amines: Ligand Influence on Coordination Geometry and Ethylene Polymerization Activity

This report describes the synthesis, structural characterization, and polymerization behavior of a series of chromium(III) complexes supported by bis(2-pyridylmethyl)alkylamine (BPA) ligands. The compounds are prepared in high yield by room-temperature reaction of the appropriate BPA ligand with CrCl3(THF)3. X-ray crystallographic studies reveal that the complexes' coordination geometries depend on the substituent at the 6-position of the pyridine ring. Unsubstituted ligands yield fac-{N-propyl-N,N-di(2-pyridylmethyl)amine}CrCl3 (6A) and fac-{N-hexyl-N,N-di(2-pyridylmethyl)amine}CrCl3(6B), whereas 6-methyl-substituted ligands produce mer-{N-propyl-N,N-di(6-methyl-2-pyridylmethyl)amine}CrCl3(6C) and mer-{N-hexyl-N,N-di(6-methyl-2-pyridylmethyl)amine}CrCl3 (6D). Moreover, ethylene polymerization studies indicate that, upon activation by methylalumoxane, the fac derivatives are 30−40 times more active than their mer counterparts.