Strained Ferrocenophanes Bridged by Silicon for New Metallopolymers
Esteban Flores, Jose 1993-
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In recent years, the Müller group has developed a route to strained ferrocenophanes (FCPs) with planar chirality. Alkyl groups are usually incorporated into the ferrocene moiety to increase the solubility of the resulting polymers. Unfortunately, thermal ring-opening polymerization (T-ROP) of Sp,Sp-39 (Figure i) equipped with two iPr groups resulted in an insoluble polymer (Sp,Sp-39)n. In order to increase the solubility of the polymers and study the primary structure of the polymers, some alterations have been made either in the monomer or in the ROP process. The iPr groups have been replaced by Et groups, which have a higher conformational freedom. On the other hand, transition-metal-catalyzed ROP (TMC-ROP) of FCPs equipped with iPr groups have been explored. Following the well-known “Ugi’s amine” chemistry, new dibromoferrocene derivatives with planar-chirality were prepared to access new metallopolymers. The syntheses and characterization of C1- and C2-symmetric, new dibromoferrocene derivatives are described. Dibromoferrocene species rac-1,1'-dibromo-2-ethylferrocene (rac-41), and (Sp,Sp)-1,1'-dibromo-2,2'-diethylferrocene (Sp,Sp-42), rac-1,1'-dibromo-2-(hydroxyethyl)ferrocene (rac-46) were prepared and fully characterized (Figure ii). Figure i. Prepared silaferrocenophanes. Salt-metathesis reactions of the dilithio derivatives of rac-41 and Sp,Sp-42 with Me2SiCl2 afforded novel silicon-bridged FCPs rac-36 and Sp,Sp-37, respectively (Figure i). New silaferrocenophane rac-35 and known silaferrocenophanes rac-38 and Sp,Sp-39 were also prepared (Figure i). Figure ii. Prepared dibromoferrocenes. T-ROP of rac-35, rac-36, and Sp,Sp-37 afforded polymers (rac-35)n, (rac-36)n, and (Sp,Sp-37)n, respectively. Polymers (rac‑35)n and (rac-36)n are soluble in thf and benzene. Therefore, they were fully characterized by nuclear magnetic resonance (NMR) and gel-permeation-chromatography (GPC) analysis. Polymer (Sp,Sp-37)n could not be characterized due to its poor solubility. Copolymers 49 and 50, which were obtained from mixtures of rac-38 and Sp,Sp-39 in ratios of 90 : 10 and 70 : 30, respectively, have also been prepared. TMC-ROP of rac-38 and Sp,Sp-39 yielded polymers (rac‑38)n and (Sp,Sp-39)n, respectively. Polymer (rac-38)n is soluble in thf and benzene and was fully characterized by GPC analysis and NMR spectroscopy. However, polymer (Sp,Sp-39)n could not be characterized due to its poor solubility. Polyferrocenylsilane (PFS) (Sp,Sp-37)n was not significantly more soluble in common organic solvents than PFS (Sp,Sp-39)n, which means that replacing iPr groups by Et groups did not increase the solubility of the respective polymer. The decrease of the steric bulkiness in the ferrocene moieties of the polymer (rac-36)n did not affect the weight average molar mass (Mw), whereas the increase of the steric bulkiness on silicon in (rac-35)n resulted in a significant decrease of the Mw. TMC-ROP of rac-38 gave a more regular PFS than that obtained from T-ROP, which means that the addition of new monomers to the propagating chain end occurred with a higher selectivity.
DegreeMaster of Science (M.Sc.)
CommitteeGravel, Michel; Haddadi, Azita; Sanders , David
Copyright DateAugust 2017