A molecular 'traffic light': highly selective cyanide sensing in aqueous media by a CpFe(indenyl)-functionalized borane.

The CpFe(indenyl)-functionalized borane {η(5)-(4-dimesitylboryl)indenyl}(η(5)-cyclopentadienyl)iron is available in two simple steps from organic precursors (in ca. 50% yield) and binds cyanide in protic media (1:1 thf-H2O) with an accompanying green to red/pink colour change. Extremely high selectivity over fluoride and hydroxide and a detection limit of ca. 10 ppm represent a highly desirable combination among borane derived cyanide receptors.