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, n Bu) with the silicon-bridged [1]ferrocenophane Fe( η -C 5 H 4 ) 2 Si(Me)Cl ( 2a ) at −78 °C was found to result in selective substitution of Cl, forming sila[1]ferrocenophanes with acetylenic substituents Fe( η -C 5 H 4 ) 2 Si(Me)C⋮CR ( 4, R = Ph; 5, R = n Bu). A similar reaction of sila[1]ferrocenophane Fe( η -C 5 H 4 ) 2 SiCl 2 ( 2b ) with 2 equiv of LiC⋮CPh resulted in the substitution of both Cl atoms, forming Fe( η -C 5 H 4 ) 2 Si(C⋮CPh) 2 ( 6 ). Transition metal-catalyzed ring-opening polymerization of monomers 4, 5, and 6 resulted in the formation of high molecular weight ( M n > 10 4 −10 5 ) polyferrocenylsilanes with acetylenic substituents, [Fe( η -C 5 H 4 ) 2 Si(Me)C⋮CR] n ( 7, R = Ph; 8, R = n Bu) and [Fe( η -C 5 H 4 ) 2 Si(C⋮CPh) 2 ] n ( 9 ), respectively. The cyclic dimer [Fe( η -C 5 H 4 ) 2 Si(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%).