Transition Metal Catalyzed Ring-Opening Polymerization (ROP) of Silicon-Bridged [1]Ferrocenophanes: Facile Molecular Weight Control and the Remarkably Convenient Synthesis of Poly(ferrocenes) with Regioregular, Comb, Star, and Block Architectures

Transition metal (Pt II or Pt 0 ) catalyzed ring-opening polymerization (ROP) of silicon-bridged [1]ferrocenophanes has been found to permit simple and convenient control of the regiostructure, molecular weight, and architecture of poly(ferrocenes). Whereas thermal ROP of the unsymmetrical silicon-bridged [1]ferrocenophane Fe(η-C 5 H 4 )(η-C 5 Me 4 )SiMe 2 ( 3 ) at 150 °C proceeds via a nonselective cleavage of the Si−Cp H and Si−Cp Me bonds (Cp H = η-C 5 H 4, Cp Me = η-C 5 Me 4 ) to yield an amorphous, regioirregular poly(ferrocenylsilane), the Pt-catalyzed ROP of 3 in solution at 25 °C involves selective cleavage of the Si−Cp H bond to afford a crystalline poly(ferrocenylsilane) 5 with a regioregular microstructure. Regioselective ROP of 3 was also detected during the Pt-catalyzed copolymerization of 3 with benzosilacyclobutane ( 7 ). The presence of Et 3 SiH during the Pt-catalyzed ROP of the [1]silaferrocenophane Fe(η-C 5 H 4 ) 2 SiMe 2 ( 1 ) permits molecular weight control and the formation of poly(ferrocenylsilanes) capped by Et 3 Si and Si−H groups, Et 3 Si−[Fe(η-C 5 H 4 ) 2 SiMe 2 ] n −H ( 11 ) with M n = 2000−45 000 and PDIs of 1.1−2.3. The use of siloxane-based materials with Si−H groups such as the random copolymer [MeHSiO-/-Me 2 SiO] n or the cyclotetrasiloxane [MeHSiO] 4 in place of Et 3 SiH allowed the preparation of comb-shaped polysiloxane-poly(ferrocenylsilane) graft copolymers ( 12 ) and star-shaped polymers ( 16 ) with a cyclic siloxane core, respectively. In addition, the use of Si−H terminated poly(dimethylsiloxane)s in place of Et 3 SiH provided facile access to poly(ferrocene)-poly(siloxane)-poly(ferrocene) triblock copolymers ( 18 ).