Formation of unexpected silicon- and disiloxane-bridged multiferrocenyl derivatives bearing Si–O–CHCH2 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 Fc2(CH3)3C(CH2)2SiCHCH2 (5), Fc2(CH2CH–O)SiCHCH2 (6), Fc2(OH)SiCHCH2 (7), Fc2(CH2CH–O)Si–O–Si(O–CHCH2)Fc2 (8) and Fc2(CH2CH–O)Si–O–SiFc3 (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), CH2CH–OLi or (CH3)3C(CH2)2Li with the corresponding multifunctional chlorosilane, Cl3SiCHCH2 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 CC 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.