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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