We report the large scale syntheses and 'oxidative purification' of fcI 2 , fcBr 2 and FcBr (fc = ferrocene-1,1'diyl, Fc = ferrocenyl). These valuable starting materials are typically laborious to separate via conventional techniques, but can be readily isolated by taking advantage of their increased E 1/2 relative to FcH/FcX contaminants. Our work extends this methodology towards a generic tool for the separation of redox active mixtures. Scheme 1 Synthesis and oxidative purification of (a) FcI (Goeltz and Kubiak), 21 and fcBr, and (b) fcI 2 and fcBr 2 (this work) (A − = Cl − , [FeCl 3 ] − or [FeCl 4 ] − ).
ABSTRACT:We report the synthesis and full characterization of the entire haloferrocene (FcX) and 1,1'-dihaloferrocene (fcX 2 ) series (X = I, Br, Cl, F; Fc = ferrocenyl, fc = ferrocene-1,1'-diyl). Finalization of this simple, yet intriguing set of compounds has been delayed by synthetic challenges associated with the incorporation of fluorine substituents. Successful preparation of fluoroferrocene (FcF) and 1,1'-difluoroferrocene (fcF 2 ) were ultimately achieved using reactions between the appropriate lithiated ferrocene species and N-fluorobenzenesulfonimide (NFSI). The crude reaction products, in addition to those resulting from analogous preparations of chloroferrocene (FcCl) and 1,1'-dichloroferrocene (fcCl 2 ), were utilized as model systems to probe the limits of a previously reported 'oxidative purification' methodology. From this investigation and careful solution voltammetry studies, we find that the fluorinated derivatives exhibit the lowest redox potentials of each of the FcX and fcX 2 series. This counter-intuitive result is discussed with reference to the spectroscopic, structural and first principles calculations of these and related materials.
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