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 (Mn = 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.