Formation of unexpected silicon-and disiloxane-bridged multiferrocenyl derivatives bearing Si-O-CH=CH2 and Si-(CH2)2C(CH3)3 substituents via cleavage of tetrahydrofuran and trapping of its ring fragments

The formation of a family of silicon-and siloxane-bridged multiferrocenyl derivatives carrying different functional groups attached to silicon, including Fc(2)(CH3)(3)C(CH2)(2)SiCH=CH2 (5), Fc(2)(CH2=CH-O) SiCH=CH2 (6), Fc(2)(OH) SiCH=CH2 (7), Fc(2)(CH2=CH-O) Si-O-Si(O-CH=CH2) Fc(2) (8) and Fc(2)(CH2=CH-O) Si-O-SiFc(3) (9) is described. Silyl vinyl ether molecules 6, 8 and 9 and the heteroleptic vinylsilane 5 resulted from the competing metathesis reaction of lithioferrocene (FcLi), CH2=CH-OLi or (CH3)(3)C(CH2)(2)Li with the corresponding multifunctional chlorosilane, Cl3SiCH=CH2 or Cl3Si-O-SiCl3. The last two organolithium species have been likely formed in situ by fragmentation of the tetrahydrofuran solvent. Diferrocenylvinyloxyvinylsilane 6 is noteworthy since it represents a rare example of a redox-active silyl mononomer in which two different C=C polymerisable groups are directly connected to silicon. The molecular structures of the silicon-containing multiferrocenyl species 5, 6, 8 and 9 have been investigated by single-crystal X-ray diffraction studies, demonstrating the capture and storage processes of two ring fragments resulting from the cleavage of cyclic THF in redox-active and stable crystalline organometallic compounds. From electrochemical studies we found that by changing the anion of the supporting electrolyte from [PF6](-) to [B(C6F5)(4)](-), the redox behaviour of tetrametallic disiloxane 8 can be switched from a poorly resolved multistep redox process to four consecutive well-separated one-electron oxidations, corresponding to the sequential oxidation of the four ferrocenyl moieties.