( η5-Cyclopentadienyl)Fe(CO) 2-complexes of sulfonamide anions. Acylation of the amino group in the sulfanilamide complex and its relevance to the protein labelling

Abstract

Illumination with visible light of [CpFe(CO) 2I] (Cp= η 5-C 5H 5) with NH 2SO 2C 6H 4- p-R (R=Me, NO 2, NH 2) in benzene in the presence of diisopropylamine gives [CpFe(CO) 2NHSO 2C 6H 4- p-R] in 62–91% yield. The primary amino group in [CpFe(CO) 2NHSO 2C 6H 4- p-NH 2] was acylated by treatment of this complex with neat carboxylic acid anhydrides (acetic, propionic and isobutyric) or with carboxylic acid (acetic, iodoacetic, β-maleimidopropionic) and 1-[3-(dimethylamino)propyl]-3-ethyl-carbodiimide (EDC) in aqueous solutions at pH 5–6 at room temperature. The latter reaction shows that [CpFe(CO) 2NHSO 2C 6H 4- p-NH 2] can be used as an IR-detectable metallo-carbonyl reagent labelling the COOH groups in proteins and as a parent compound for a new family of reagents labelling the thiol function.