From tetramerization to oligomerization/polymerization of ethylene by dinuclear pyridyl‐imine Co‐ and Ni‐based catalysts

Abstract

A series of dinuclear pyridyl‐imine Co‐ and Ni‐based complexes (Co: C1 and C2 and Ni: C3 and C4) were prepared in reasonable yields through one‐pot synthesis method. Toward ethylene oligomerization/polymerization, C1 and C2, activated by MMAO, were capable to produce oligomers with moderate activity (up to 5.1 × 105 g mol−1 Co h−1 for C2) which α‐C8 was the major product. In contrast, C3 and C4 polymerized ethylene that the activity of C4 was twofold greater than C2. The high impact of o‐substituent in C2 and C4 was along with dinuclearity effect leading to high productivity and selectivity for ethylene oligomerization and polymerization, respectively. Moreover, polymerization parameters had strong influence on catalytic behavior of C4 and polyethylene samples made. For instance, high sensitivity of the structures led to formation of an oily branched oligoethylene to highly branched, high Mw polyethylene by changing the polymerization conditions. Polymerization of higher α‐olefins such as 1‐hexene and 1‐octene, moreover, emphasized the effect of effective distance between the centers where an oily low Mw oligo‐1‐hexene and a solid poly(1‐octene) having higher Mw were yielded. On the other side, quantum chemistry calculations were performed to investigate the structural properties and reactivity of the Ni‐ and Co‐based species. The obtained results indicated that the Ni atoms have strong molecular orbital interactions with the CC bond which may increase the reactivity of the catalyst in comparison with the Co metals.