Tuning the Polymerization Behavior of Silicon-Bridged [1]Ferrocenophanes Using Bulky Substituents

Sila­[1]­ferrocenophanes bearing bulky nitrogen- and silicon-based substituents at the ansa bridge have been prepared by nucleophilic substitution of chloride at silicon in Fe­(η⁵-C₅H₄)₂­SiClH (3) by Li­[N­(SiMe₃)₂] and K­[Si­(SiMe₃)₃]. The resulting compounds, Fe­(η⁵-C₅H₄)₂­Si­[N­(SiMe₃)₂]H (4) and Fe­(η⁵-C₅H₄)₂­Si­[Si­(SiMe₃)₃]H (5), have been fully characterized, and their ring-opening polymerization (ROP) chemistry has been explored. Upon heating for 3 h, 4 yields the polymer [(η⁵-C₅H₄)­Fe­(η⁵-C₅H₄)­Si­{N­(SiMe₃)₂}­H]_n (M_n = 38 000 Da, PDI = 7.5), but 5 does not react due to the larger steric bulk of the substituent on silicon. ROP initiated by Na­[C₅H₅] under photolytic conditions involving Fe−Cp bond cleavage occurred for both 4 and 5, to afford (η⁵-C₅H₅)­Fe­(η⁵-C₅H₄)­[SiRH­(η⁵-C₅H₄)­Fe­(η⁵-C₅H₄)]_n−1­SiRH­(η¹-C₅H₅) (R = N­(SiMe₃)₂: n = 20 and 60; R = Si­(SiMe₃)₃: n = 20 and 50), but anionic ROP initiated with nBuLi was unsuccessful, presumably due to the close proximity of the bulky group to the site of nucleophilic attack. The polymeric materials were fully characterized, including the elucidation of atactic microstructures by NMR spectroscopy.