Tridentate Cobalt Catalysts for Linear Dimerization and Isomerization of α-Olefins

Upon activation with modified methylalumoxane (MMAO), tridentate pyridine bisimine cobalt catalysts dimerize α-olefins with lower productivity than analagous iron systems, as indicated by comparing the batch dimerization of 1-butene (TON ∼42 000 for Co, ∼147 000 for Fe). The cobalt-produced dimers are extremely linear (>97%) and contain only traces of trimeric species. The cobalt catalysts also have a tendency to isomerize α-olefins, as evidenced by the approximately equal levels of dimerization and isomerization achieved when 1-butene is dimerized. When the cocatalyst is changed to diethylaluminum chloride, isomerization occurs exclusively to give cis - and trans -2-olefins selectively. To mitigate the effects of feed isomerization, dimerization of propylene was also studied. GC analysis of the products reveals a stepwise oligomerization process that makes linear hexenes, nonenes, and dodecenes, with the hexenes comprising up to 70% of the product mix. The hexenes are over 99% linear and may contain over 50% 1-hexene. Catalyst productivity is high, with turnover numbers exceeding 200 000 mol propylene/mol Co (17 000 g oligomers/g Co complex).