Functionalization via hydrosilylation of linear and cyclic siloxanes with appendent first generation dendrons containing electronically communicated ferrocenyl units

摘要

The synthesis, structural characterization and redox-properties of a new family of siloxane-based poly(ferrocenyl) dendronized molecules are described. Hydrosilylation reaction of the vinyl-functionalized silicon-bridged biferrocene, CH_2=CHSiMe[Fe(#eta#~5-C_5H_4)(#eta#~5-C_5H_5)]_2 (1) with Si-H-containing poly(siloxane) backbones afforded the novel copolymer 6 and homopolymer 7. To understand the properties of these polymers more thoroughly, we also synthesized the well-defined, closely related tetraferrocenyl-functionalized disiloxane and octaferrocenyl-functionalized cyclotetrasiloxane model compounds 4 and 5. Solution voltammetric studies of the siloxane-based poly(ferrocenyl) derivatives 4-7 showed two reversible redox processes with a wave separation (#DELTA#E) of 190-160 mV, indicating that significant electronic communication exists between the ferrocenyl moieties bridged by a pendant silicon atom. The neutral cyclotetrasiloxane-based octaferrocenyl 5, as well as polymers 6 and 7 become insoluble upon complete oxidation to the corresponding polycationic species, yielding electroactive films onto platinum and glassy-carbon electrode surfaces. The well-defined and persistent redox waves of electrode coated with these films are characteristic of electrochemically stable, surface-confined reversible redox couples. The microstructure of these multimetallic electroactive films has been analyzed by scanning electron microscopy.