A competetive way to low-viscosity PAO base stocks via heterocene-catalyzed oligomerization of dec-1-ene
Hydrogenated oligomers of higher α-olefins (primarily, dec-1-ene) represent base stocks for high-quality polyolefin oils (PAOs), transmission fluids, lubricants and greases. Competitive advantages of zirconocene catalysts in oligomerization of α-olefins have been already demonstrated and industrially implemented for higher oligomers. However, the problem of the selective synthesis of α-olefin oligomers that have degree of polymerization (DPn) 3 and 4, remains unresolved. A series of –CH2CH2– bridged ansa-zirconocenes derived from 5,10-dihydroindeno[1,2-b]indole, 'heterocenes' Zr4–Zr6, were synthesized and characterized by NMR spectroscopy and X-ray diffraction (XRD) analysis. New complexes Zr4–Zr6 and known –SiMe2– bridged ansa-heterocenes Zr1–Zr3 were investigated in oligomerization of dec-1-ene using MMAO-12 or [PhNMe2H][B(C6F5)4] activators. In the atmosphere of molecular hydrogen, at [dec-1-ene]/[Zr] ratios up to 4·105, rac-forms Zr4r–Zr6r provided more than 85% yields of dec-1-ene oligomers without skeletal rearrangements. In some experiments, at least 50% yields of lightweight oligomers (DPn=3–4) were achieved. After activation of Zr6r by TIBA and [PhNMe2H][B(C6F5)4] and completion of dec-1-ene oligomerization, we isolated new cationic complex Zr6r-Al containing Zr-(μ-Cl)2-Al fragment, as confirmed by XRD. Zr6r-Al alone was inactive against dec-1-ene, but after addition of TIBA oligomerization started. Due to uniform molecular structure of oligomers, complete catalytic hydrogenation of oligo(dec-1-ene)s was conducted using Ni/Al2O3 catalyst under mild conditions (150°C, 3 h, 20 bar). Hydrogenated dec-1-ene oligomers turned out to be high-quality PAO base stocks far exceeding industrial dec-1-ene PAOs in terms of viscosity characteristics.