Ethylene Insertion into Fe–Si Bond Enables the Catalytic Formation of Silyl-Ended Oligo- and Polyethylenes

A family of linear silyl terminated polyethylenes (SiPEs) was prepared via ethylene polymerization catalyzed by a 2,6-bis(imino)pyridine iron complex bearing a bulky 2,6-iPr2C6H3 periphery (1) activated with hydrosilane/B(C6F5)3 (SiHB) systems. Beyond serving as a hydride source for the precatalyst activation, the hydrosilanes acted as chain-transfer agents (CTA), enabling control over both number-average molar mass (Mn) and silicon content of the resulting polymers. Alternatively, SiPEs were obtained using a 1/MMAO/hydrosilane catalytic system, which exhibited activities 2 orders of magnitude higher, albeit with reduced silicon content. In contrast, SiHB activation of a less sterically hindered iron analogue 2 (bearing 2-Me-C6H4 periphery) led to the formation of α,ω-silylalkenes, along with other oligomeric products. The formation of these heterotelechelic oligomers provides strong evidence for an Fe–Si bond as a key catalytic intermediate, in which the silyl functionality is installed prior to ethylene insertion, thereby enabling the catalytic formation of silyl-ended polyethylenes.