Synthesis of Octamethylferrocene Derivatives via Reaction of (Octamethylferrocenyl)methyl Carbocation with Nucleophiles and Application to Functionalization of Surfaces

Abstract

Formylation of octamethylferrocene, Fe(C5Me4H)2, using N,.N'-dimethylformamide/OPCl3in CHC13solvent 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 β-(octamethylferrocenyl)acrylate. Most important, reductionn of octamethylformylferrocene using LiAlH4in 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. 1 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 Na2S2O4to 1,2-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 NH2or SH [surfaces derivatized with (MeO)3Si(CH2)3NH2or (MeO)3Si(CH2)3SH] is a convenient way to attach octamethylferrocene derivatives to surfaces including Si02, Pt, and indium tin oxide (ITO). © 1990, American Chemical Society. All rights reserved.