Synthesis of octamethylferrocene derivatives via reaction of (octamethylferrocenyl)methyl carbocation with nucleophiles and application to functionalization of surfaces

Article abstract of DOI:10.1021/ja00177a020

Formylation of octamethylferrocene, Fe(C₅Me₄H)₂, using N,N'-dimethylformamide/OPCI₃ in CHCI₃ solvent at 60-70 °C gives octamethylformylferrocene in high yield (～95%). The aldehyde can be converted to a CN group to give octamethylcyanoferrocene or can be used to prepare ethyl 0-(octamethylferrocenyl)acrylate. Most important, reductionn of octamethylformylferrocene using LiAIH₄ in Et₂O yields the alcohol in ～95% yield. Acid-catalyzed (HBF₄) dehydration of the alcohol. III, leads to formation of (octamethylferrocenyl)methyl carbocation in almost quantitative yield. The carbocation I can be isolated as an orange-red BF₄^- salt in ～ 90% yield from octamethylferrocene. I shows sharp ¹³C and ¹H NMR spectral features consistent with formulation as a diamagnetic Fe(II) species with the positive charge localized on the C having two H's. I slowly dimerizes, even in the solid state, to a C-C coupled product with two Fe(III) centers. The paramagnetic, blue-green dimer can be reduced with cobaltocene or aqueous Na₂S₂O₄ to l,2-bis(octamethylferrocenyl)ethane. Reaction of (octamethylferrocenyl)methyl carbocation with nucleophiles is a convenient synthetic route to octamethylferrocene derivatives, which have proved difficult to obtain by electrophilic substitution of octamethylferrocene. Reaction of the new carbocation I has been used to synthesize octamethylferrocenyl derivatives in good to excellent yields (～60-95%) via reaction with amines, thiols, or CN^- Reaction of (octamethylferrocenyl)methyl carbocation with surface-confined nucleophiles such as NH₂ or SH [surfaces derivatized with (MeO)₃Si(CH₂)₃NH₂ or (MeO)₃Si(CH₂)₃SH] is a convenient way to attach octamethylferrocene derivatives to surfaces including SiO₂, Pt, and indium tin oxide (ITO).