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

Abstract

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.

Polyferrocenylsilanes: synthesis, properties, and applications

“…10 The orange crystalline solid isolated after work up has been shown to have the bulk formula of (Z 5 -C 5 H 4 Li) 2 FeÁTMEDA, although single crystal X-ray analysis has shown that other compositions are possible. [13][14][15] Alternatively, chlorine has been introduced as a substituent through the reaction of Fe(Z 5 -C 5 H 4 Li) 2 ÁTMEDA with SiCl 4 or RSiCl 3 , which, via subsequent nucleophilic substitution reactions at the SiCl 2 -or SiClR-bridge, provides a facile route to [1]ferrocenophanes with alkoxy, aryloxy, and amino substituents at silicon. [13][14][15] Alternatively, chlorine has been introduced as a substituent through the reaction of Fe(Z 5 -C 5 H 4 Li) 2 ÁTMEDA with SiCl 4 or RSiCl 3 , which, via subsequent nucleophilic substitution reactions at the SiCl 2 -or SiClR-bridge, provides a facile route to [1]ferrocenophanes with alkoxy, aryloxy, and amino substituents at silicon.…”

Synthesis and Solution Self‐Assembly of Polyisoprene‐block‐poly(ferrocenylmethylsilane): A Diblock Copolymer with an Atactic but Semicrystalline Core‐Forming Metalloblock

“…10,11 Reactions between the dilithioferrocene-TMEDA complex and dichloroorganosilanes give a wide range of sila[1]ferrocenophanes with symmetrically and unsymmetrically substituted silicon atoms bearing alkyl or aryl groups (Scheme 2[A]). [12][13][14] Alternatively, chlorine has been introduced as a substituent through the reaction of Fe(η 5 -C5H4Li)2·TMEDA with SiCl4 or RSiCl3, which, via subsequent nucleophilic substitution reactions at the SiCl2-or SiClRbridge, provides a facile route to [1]ferrocenophanes with alkoxy, aryloxy, and amino substituents at silicon. 15 Hypercoordinate silicon-bridged [1]ferrocenophanes can also be synthesised from chlorosila[1]ferrocenophanes Fe(η 5 -C5H4)2SiRR' (R = R' = Cl or R = Me, R' = Cl) and Li or Fe(η 5 -C5H4)2SiCl(CH2Cl) and N-methyl-N-(trimethylsilyl)acetamide.…”

“…It is noteworthy that even [1]silaferrocenophanes with highly sterically-demanding substituents at silicon such as Si(SiMe3)3 still undergo ROP. 14 Reported synthetic methods to prepare high molecular weight PFSs involve: thermal, transition metal-catalysed, γ-irradiation-induced, cationic, and living anionic and photocontrolled living anionic ROP, and these methods are now discussed.…”

“…Due to its relatively high functional group tolerance, a wide range of strained ferrocenophanes have been used to access alkyl, alkoxy, aryl, aryloxy, amino, and chloro functionalised PFSs (Scheme 3) via this route. 4,7,14,24,25 Interestingly, a cyclic dimer in addition to high molecular weight polymer was isolated from dichlorosila[1]ferrocenophane when attempting thermal ROP. 26,27 The thermal ROP reactions can be performed in either high boiling point solvents or the melt, and although high molecular weight polymers are formed, there is no control over the molecular weight and the molecular weight distributions are broad (PDI > 1.5).…”

“…14 Generally the rate of living anionic ROP decreases as the size of the substituents on silicon increases. 50 Subsequent end functionalisation can occur at the lithiated site on the polymer using a variety of reagents to modify the polymer properties or yield block and graft copolymers.…”