Synthesis, Characterization, and Photocontrolled Ring-Opening Polymerization of Sila[1]ferrocenophanes with Multiple Alkyne Substituents

Abstract

Sila[1]ferrocenophanes with multiple alkyne substituents [Fe(η-C5H4)2Si(C⋮CtBu)2] (2) and [Fe(η-C5H4)2Si(Me)C⋮CC⋮CPh] (5) have been synthesized and structurally characterized. These compounds are prepared by reacting [LiC⋮CtBu] or [LiC⋮CC⋮CPh] 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...