A study of the polymerization of ethylene on Ti(III) monocyclopentadienyl compounds by the density functional theory method

Density functional theory was used to study model ethylene reactions with CpTiIIIEt+A− (A− = CH3B(C6F5)3−, or B(C6F5)4−; A− can be absent) compounds. The polymerization of ethylene on an isolated CpTiEt+ cation is hindered because of equilibrium between the CpTi(C2H4)Et+ primary complex and the primary product of CpTiBu+ insertion. At the same time, the polymerization of ethylene on CpTiEt+A− ion pairs (A− = CH3B(C6F5)3− or B(C6F5)4−) is thermodynamically allowed (ΔE from −26.2 to −25.6 kcal/mol and ΔG298 from −10.9 to −10.4 kcal/mol) and is not related to overcoming substantial energy barriers (ΔE# = 8.2−12.3 kcal/mol and ΔG298≠) = 7.8−13.3 kcal/mol). The degree of polymerization can be low because of the effective occurrence of polymer chain termination by hydrogen transfer from the polymer chain to the monomer.