Synthesis, characterization, and photocontrolled ring-opening polymerization of sila[1]ferrocenophanes with multiple alkyne substituents

Sila[1]ferrocenophanes with multiple alkyne substituents [Fe(eta-C5H4)(2)Si((CCBu)-Bu-t)(2)] (2) and [Fe(eta-C5H4)(2)Si(Me)CCCCPh] (5) have been synthesized and structurally characterized. These compounds are prepared by reacting [(LiCCBu)-Bu-t] or [LiCCCCPh] with sila[1]ferrocenophanes containing silicon-chlorine bonds. Ring-opening polymerizations (ROP) of 2 and 5 have been studied using transition metal-catalyzed, thermal, anionic, and photocontrolled routes. Thermal and anionic ROP both failed to give significant amounts of polymer (< 30%). And unlike most other ferrocenophanes, 2 cannot be polymerized by Karstedt's catalyst, possibly due to chelation of the catalyst by the acetylide ligands. Platinum-catalyzed ROP of 5 was also relatively ineffective, giving polymers with bimodal molecular weight distributions in moderate yields. Nevertheless, living polymerization of 2 and 5 was possible using photocontrolled ROP with NaCp as initiator. The key to photocontrolled ROP was the reduced basicity of NaCp compared to BuLi, as the latter reacted with the carbon-carbon triple bonds in the ferrocenophanes. Metal complexation of the triple bonds in 5 was also examined; this species reacted with [Co-2(CO)(8)] to give [Fe(eta-C5H4)(2)Si(Me){Co-2(CO)(6)C2Co2(CO)(6)C2Ph}] (7), a bimetallic ferrocenophane with five metal atoms.