Synthesis, Characterization, and the Platinum-Catalyzed Ring-Opening Polymerization and Stereoselective Dimerization of Silicon-Bridged [1]Ferrocenophanes with Acetylenic Substituents

Reaction of the lithium acetylides LiC⋮CR (R = Ph, nBu) with the silicon-bridged [1]ferrocenophane Fe(η-C5H4)2Si(Me)Cl (2a) at −78 °C was found to result in selective substitution of Cl, forming sila[1]ferrocenophanes with acetylenic substituents Fe(η-C5H4)2Si(Me)C⋮CR (4, R = Ph; 5, R = nBu). A similar reaction of sila[1]ferrocenophane Fe(η-C5H4)2SiCl2 (2b) with 2 equiv of LiC⋮CPh resulted in the substitution of both Cl atoms, forming Fe(η-C5H4)2Si(C⋮CPh)2 (6). Transition metal-catalyzed ring-opening polymerization of monomers 4, 5, and 6 resulted in the formation of high molecular weight (Mn > 104−105) polyferrocenylsilanes with acetylenic substituents, [Fe(η-C5H4)2Si(Me)C⋮CR]n (7, R = Ph; 8, R = nBu) and [Fe(η-C5H4)2Si(C⋮CPh)2]n (9), respectively. The cyclic dimer [Fe(η-C5H4)2Si(Me)C⋮CPh]2 (10) was isolated from the polymerization mixture derived from 4. The dimer was shown to exist in the cis configuration by single-crystal X-ray diffraction. Detailed studies on the polymerization of 4 have shown that the ratio of high polymer 7 to cyclic dimer 10 formed in the reaction is highly solvent and concentration dependent. Pyrolysis of polymers 7 and 8 during thermogravimetric analysis (TGA) studies have resulted in the formation of black magnetic ceramics in the highest yields found to date for uncrosslinked polyferrocenylsilane homopolymers (2 h, 900 °C; 7, 81%; 8, 61%).