Steric and Electronic Tuning of Bis(imino)pyridine Cobalt Catalysts for High 1-Hexene Selectivity in Conversion-Controlled Propylene Oligomerization

This study establishes molecular design principles for bis(imino)pyridine cobalt catalysts to simultaneously enhance activity and 1-hexene selectivity in propylene oligomerization. Systematic substituent engineering revealed: (1) para -Halogenation (e.g., Br in 4d ) boosts activity to high levels (4.68 × 10⁵ g/(mol (Co) ·h)) through electronic effects; (2) ortho -Steric modulation follows a volcano-shaped selectivity trend, with isopropyl groups optimizing 1-hexene formation; (3) Conversion control is critical for suppressing secondary reactions that compromise selectivity. Implementing these insights, catalyst 4L achieves 56.1% 1-hexene selectivity at low conversions (10.4%). These findings provide a blueprint for developing high-performance cobalt oligomerization catalysts through integrated electronic, steric, and process optimization.