Direct one step preparation and 13C-NMR spectroscopic characterization of alpha-ferrocenyl carbocations derived from ferrocene and carbonyl compounds in trifluoroacetic acid medium1a

Abstract

A reação de aldeídos e cetonas com ferroceno, na presença de ácido trifluoroacético, gera uma série de α-ferrocenoalquil carbocátions estáveis por longo tempo que foram caracterizados por espectroscopia de Ressonância Magnética Nuclear de 13 C. De forma inesperada, quando esta reação foi realizada usando tetrafenilciclopentadienona, o correspondente dihidro derivado 3 foi isolado com muito bom rendimento. A formação deste composto pode requerer ferroceno atuando como agente redutor.Reaction of aldehydes and ketones with ferrocene, in the presence of trifluoroacetic acid, afforded a series of stable long lived α-ferrocenylalkyl carbocations which were characterized by 13 C-NMR spectroscopy. When this reaction was attempted using tetraphenylcyclopentadienone, quite unexpectedly the corresponding dihydro derivative 3 was isolated, in very good yield.Formation of this compound may require ferrocene acting as a reducing agent.

Comparison of the bis(ferrocenylethynyl)phenylmethylium cation with bis(ferrocenylethenyl)methylium analogues

“…We attempted to obtain salts of [(FcCC) 2 observe a room temperature 1 H NMR spectrum consistent with the proposed structure in dichloromethane-d 2 on the addition of deuterated trifluoroacetic acid to III (CF 3 CO 2 H has previously been used by others to generate ferrocenyl carbocations [51][52][53]). The UV-Vis-NIR spectrum (vide infra) obtained under similar conditions can, therefore, be identified with that of [2] + .…”

Studies on Long-Lived (Pentafluorosulfanyl)phenyl-Substituted Carbocations

“…The ferrocenyl carbinols derived from addition of the 4-phenylsulfurpentafluoride moiety to ferrocenecarboxaldehyde, acetylferrocene, and benzoylferrocene were also ionized in FSO 3 H–SO 2 ClF. Even though it has been previously shown that α-ferrocenyl carbocations are long-lived even in weaker acids such as trifluoroacetic acid or sulfuric acid, it is still more convenient to use FSO 3 H for 13 C NMR analysis because it does not contain any carbon atoms, and issues of viscosity and concomitant line broadening are avoided. The 13 C resonances (Table ) are highly shielded because of a strong agostic interaction with the iron atom.…”