Divergent Synthesis of Thiophene-Bridged Diphosphine Ligands and Their Application in Chromium-Catalyzed Ethylene Tri-/Tetramerization

Chromium complexes supported by tunable thiophene-bridged diphosphine ligands demonstrate exceptional catalytic activity with switchable selectivity in ethylene tri/tetramerization reactions. The catalytic performance was significantly influenced by the synergistic interplay of steric effects from both the P substituents and the thiophene backbone substituents. Complex Cr2, bearing a PCy 2 group, achieved a high activity of 1549 kg/(gCr·h) with excellent total 1-C 6 /1-C 8 selectivity (90.6 wt %) and low PE content (0.34 wt %) at 60 °C. Complex Cr4 having a TMS-substituted backbone and one Cy on the P atom achieved the highest activity of 2139 kg/(gCr·h) at 80 °C, maintained considerable 1-C 8 selectivity (28.1 wt %), and yielded a very low amount of PE (0.24 wt %). However, Cr3 having two steric bulk PCy 2 groups exhibited a decreased activity. The findings underscore the necessity for moderate steric tuning and the significant regulatory role of backbone substituents. Some of the new complexes are among the most efficient ethylene tri/tetramerization catalysts. This work offers a novel family of highly tunable diphosphine ligands, providing valuable insights into the rational ligand design for selective ethylene oligomerization.