Imido Titanium Ethylene Polymerization Catalysts Containing Triazacyclic Ligands

A comprehensive account of the synthesis, properties, and evaluation of a wide range of ethylene
homopolymerization catalysts derived from imido titanium compounds supported by the triazacyclic ligands
Me3[9]aneN3 and R3[6]aneN3 is described (Me3[9]aneN3 = 1,4,7-trimethyltriazacyclononane; R3[6]aneN3
= 1,3,5-trimethyl- or 1,3,5-tris(n-dodecyl)triazacyclohexane). Conventional preparative-scale reactions
afforded the triazacycle-supported imido titanium compounds Ti(NR)(Me3[9]aneN3)Cl2 (R = tBu (1),
2,6-C6H3Me2, 2,6-C6H3iPr2, Ph, C6F5, or CH2Ph (6)). Solid phase-supported analogues of 1 and 6 (linked
by either the macrocycle or imido ligand to a 1% cross-linked polystyrene support) and representative
Me3[6]aneN3 solution phase systems Ti(NR)(R3[6]aneN3)Cl2 (R = Me or n-dodecyl) were also synthesized.
At ambient temperature, solution phase Me3[9]aneN3 catalyst systems were more active for ethylene
polymerization (methyl aluminoxane (MAO) cocatalyst) than their solid phase-supported or Me3[6]aneN3
analogues. A library of 41 other triazacyclononane-supported catalysts was prepared by the semiautomated,
sequential treatment of Ti(NMe2)2Cl2 with RNH2 and Me3[9]aneN3. The ethylene polymerization capabilities of 46 compounds of the type Ti(NR)(Me3[9]aneN3)Cl2 were evaluated at 100 °C (MAO cocatalyst)
and compared in representative cases to the corresponding productivities at ambient temperature. Whereas
either bulky N-alkyl or N-aryl imido substituents in the compounds Ti(NR)(Me3[9]aneN3)Cl2 were sufficient to give highly active catalysts at ambient temperature, only those with bulky N-alkyl groups excelled
at 100 °C. Polymer end group analysis indicated that polymeryl chain transfer to both AlMe3 and ethylene
monomer is an active mechanism in these systems. The use of MAO pretreated with BHT-H (BHT-H =
2,6-di-tert-butyl-4-methylphenol) led to higher productivites, increased polymer molecular weights, and
more polymer chain unsaturations, but productivity decreased when a large excess of BHT-H was used.
The reactions of the well-defined alkyl species Ti(NtBu)(Me3[9]aneN3)Me2, [Ti(NtBu)(Me3[9]aneN3)(μ-Me)2AlMe2]+, and [Ti(NtBu)(Me3[9]aneN3)Me]+ with BHT-H were examined, and the aryloxide
compound [Ti(NtBu)(Me3[9]aneN3)(BHT)][BArF4] was isolated (ArF = C6F5). The X-ray structures of
Ti(NR)(Me3[9]aneN3)Cl2 (R = tBu, 2,6-C6H3Me2, 2,6-C6H3iPr2, Ph, C6F5) and Ti(NR)(Me3[6]aneN3)Cl2
(R = 2,6-C6H3iPr2, Ph, C6F5) are reported. The perfluorophenyl imido titanium compounds both exhibit
well-defined supramolecular structures based on C···F intermolecular interactions.