Ethylene polymerization by PN3-type pincer chromium(III) complexes

• PN3-type pincer type of chromium (III) complexes was prepared.
• Activated by MAO, the complexes showed moderate activity for ethylene polymerization.
• Exclusively linear solid PE without any detectable amount of oligomers was obtained.

Chromium (III) complexes, Cr1, [2,6-(tBu2PNH)2C5H4N]CrCl3; Cr2, [2,6-(Ph2PNH)2C5H4N]CrCl3; Cr3, [2-(tBu2PNH)C5H4N]CrCl3 THF; Cr4, [6-(tBu2PNH)C5H4N-2-CH2NEt2]CrCl3; Cr5, [6-(tBu2PNH)C5H4N-2-C3H2N2]CrCl3; Cr6, [6-(tBu2PNH)C5H4N-2-(3,5-Me2)C3H2N2]CrCl3; Cr7, [6-(tBu2PNH)C5H4N-2-(3,5-iPr2)C3H2N2]CrCl3; Cr8, [6-(tBu2PNH)C5H4N-2-(3,5-Ph2)C3H2N2]CrCl3, bearing a family of neutral PN3-type pincer ligands have been prepared. The molecular structure of Cr2 was further elucidated by the X-ray crystallographic analysis, showing an octahedral geometry. Treatment of these complexes with MAO or alkylaluminum led to catalysts with moderate activities (about 105 g (PE)/Cr(mol) h) for ethylene polymerization, affording exclusively linear low molecular weight solid PE without any detectable oligomers. Among Cr1–Cr8, the highest activity was achieved for Cr1/MAO at room temperature with production of PE with highest molecular weight, indicating that replacement of both tBu groups in Cr1 with Ph groups, or one PtBu2 with the N (imine) arm, resulted in a lower catalytic activity and lower Mw.

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