Rational design of ansa-heterocenes with a long SiOSi bridge as a catalysts for selective dimerization of oct-1-ene

Being activated by methylalumoxane ([Al]/[Zr] = 10), (η⁵-C₅H₅)₂ZrCl₂ (Zr1) and [(η⁵-C₅H₄SiMe₂)₂O]ZrCl₂ (Zr2) catalyze selective dimerization of α-olefins with low productivity (turnover number TON ∼2000). Our previous research of heterocycle-fused ansa-zirconocenes revealed that SiMe₂-bridged complexes catalyze polymerization of α-olefins, whereas CH₂CH₂-bridged complexes are high-performance oligomerization catalysts (TON ∼ 4∙10⁵). We proposed that further elongation of the bridge will allow obtaining dimerization catalysts. New –SiMe₂OSiMe₂– bridged ansa-zirconocenes Zr3–Zr11 were synthesized and studied in oct-1-ene dimerization at 100 °C and [oct-1-ene]/[Zr] ratio of 3∙10⁴. In the absence of H₂ bis(5,6-dihydroindeno[2,1-b]indole) derivatives Zr8 and Zr9 demonstrated high activity and dimerization selectivity up to 94%. In the presence of H₂ symmetrical indenoindole complexes Zr5–Zr9 appeared to be even more active, but up to 24% of hydrogenated oct-1-ene dimer HC16 was formed. Mixed-ligand complexes Zr10 and Zr11 catalyzed oct-1-ene dimerization with up to 99% selectivity without the formation of HC16 even in trace amounts.