The Origin of Living Polymerization with an o ‐Fluorinated Catalyst: NMR Spectroscopic Characterization of Chain‐Carrying Species

To characterize the origin of living polymerization with nonmetallocene titanium‐based catalysts containing o ‐fluoroaryl substituents, ethene polymerization by an o ‐fluorinated bis(enolatoimine) titanium catalyst and its nonfluorinated counterpart has been studied by multinuclear NMR spectroscopy by using methylaluminoxane (MAO) or AlMe 3 /CPh 3 B(C 6 F 5 ) 4 as activators. Formation of ion pairs of the type [TiL 2 Me][MeMAO] and [TiL 2 Me][B(C 6 F 5 ) 4 ] has been observed for both catalysts. These ion pairs react with ethene to afford the chain‐propagating species [TiL 2 P][MeMAO] and [TiL 2 P][B(C 6 F 5 ) 4 ], respectively (P=growing polymeryl chain). For the o ‐F‐substituted catalyst species of the second type, NMR spectroscopy provides evidence that the o ‐F substituents interact with the metal center. This interaction is proposed to keep the polymerization catalysis living by suppressing chain transfer to AlMe 3 and β‐hydrogen transfer processes.